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The Organization ofLaboratory of Advanced Science and Technology for Industry
University of Hyogo
The organization
Director

Steering
Committee

Department ofLight and Particle Science and Technology

Department ofLight Application for Advanced Technology⋄Advanced Photon System⋄Beam Physics⋄Nanostructure Science and Technology⋄Guest Chair⋄Nano-science and Technology utilizing
Synchrotron Radiation⋄Nano-Micro System⋄Bio-Medical Technology (to be established)⋄Guest Chair

Research and faculty staff
WATANABE Takeo, Professor, Director
KANDA Kazuhiro, Professor
UTSUMI Yuichi, Professor
SUZUKI Satoru, Professor
NIIBE Masahito, Associate Professor
SHOJI Yoshihiko, Associate Professor
HARUYAMA Yuichi, Associate Professor
YAMAGUCHI Akinobu, Associate Professor
HASHIMOTO Satoshi, Associate Professor
HARADA Tetsuo, Associate Professor
AMANO Sho, Research Associate
FUJII Satoshi, Research Associate
YAMAKAWA Shinji, Research Associate

Administrative staff
HAYASHI Masahiko, General Manager
HIROKAGA Yasuhiro, Manager
KAYAHASHI Hidetoshi, Chief
KUWATA Ayami, NewSUBARU
HASEGAWA Miwa, CASTAKAMATSU Sumiyo, CASTYOSHIDA Mizuho, CAST
KONO Kimi, CAST
MAEDA Yasuhide, CASTSENBA Ayako, CAST
KUSUMOTO Kumi, CAST

Staff (FY 2020)

Coordinator
MIYAMOTO Shuji, NewSUBARUSpecially appointed staff
TERANISHI Nobukazu, Professor
MIYAMOTO Shuji, Professor
NAKANISHI Kouji, Associate Professor

Guest staff
KUDOU Hiroto, Professor
HORIBE Hideo, Professor
BAN Hiroshi, Professor
HARADA Yoshihisa, Professor

Contact address
Advanced Research Building
3-1-2 Kouto, Kamigori-cho, Ako-gun, Hyogo, 678-1205 JAPAN.
T:+81-791-58-0249 F:+81-791-58-0242
NewSUBARU Synchrotron Radiation Facility
1-1-2 Kouto, Kamigori-cho, Ako-gun, Hyogo, 678-1205 JAPAN.
T:+81-791-58-2503 F:+81-791-58-2504
Web URL http://www.lasti.u-hyogo.ac.jp/,
http://www.lasti.u-hyogo.ac.jp/NS/
e-Maillasti@lasti.u-hyogo.ac.jp
Accesshttp://www.lasti.u-hyogo.ac.jp/NS-en/access/

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Part 1. Current Status of NewSUBARUPart 1. Current Status of NewSUBARU
and Other Light Source
and Other Light Source

New Injector Linac
New Injector Linac

Electron storage ring and new injector linac at NewSUBARU
Satoshi Hashimoto
LASTI, University of Hyogo

1. Introduction
NewSUBARU synchrotron light facility
has a 1.5 GeV electron storage ring, whichis the largest accelerator among
universities in Japan. The general layoutof the ring is shown in Figure 1. The ringis consisted with 6 DBA cells with an inverse
bending magnet. There are 6 straight sections
between each cell, and they are used for an
injection septum, an accelerating RF cavity,
three undulators. The main parameters of
the ring are listed in Table I.
The 1.0GeV linear accelerator (linac) ofSPring-8 had been supplying electron beams forover 20 years, but shut down in August 2020.
Therefore, a new 1.0GeV linac dedicated to the
NewSUBARU ring was constructed with thehelp of SPring-8 accelerator staff. Constructionof the new linac was completed at the end of2020 and succeeded in accelerating the beam in
March
2021.
The
construction
andcommissioning of the linac will be reported indetail in Section 5.

GeV user time. Weekday night and weekend canbe used for additional machine study or user
time with the special mode, such as a single
bunch operation or an operation with arbitraryelectron energy. Range of the electron energy isfrom 0.5 GeV up to 1.48 GeV with 1 MeV step.

Fig. 2. Operation time of NewSUBARU in
FY2020.

2. Operation Status of the ring in FY2020
The ring has two operation modes foruser-time, 1.0 GeV top-up mode and 1.5 GeV
current decay mode. The basic operation time is
9:00 - 21:00 of weekdays. Monday is used formachine R&D, Tuesday is for 1.5 GeV user
time, Wednesday and Thursday are for 1.0 GeV
top-up user time, Friday is for 1.0 GeV or 1.5

Due to the injector construction that started inAugust, the user-operation of the ring in
FY2020 was completed in July. The totalmachine time in FY2020 was 1,031 hours, 38%of that of FY2019, excluding the beam downtime and including machine tuning with the new

Fig.1. General layout of the NewSUBARU storage ring. Electron beams are injected from the
newly-constructed 1.0 GeV linac dedicated to the NewSUBARU ring.

14-1. SC3 project (mono-cycle FEL)
Under the collaboration with RIKEN
SPring-8 center, University of Hyogo Graduate
School of Material Science and LASTI, we are
running the SC3 (Slippage-Controlled Coherent
radiation by Chirped micro-bunching) project,
where the generation of the extremely shortradiation pulse corresponding to only a few
wavelengths will be experimentally proved at
NewSUBARU
using
arbitrary
taperedundulators [1], a magnetic chicane and a chirped
seed laser. Main parameters of modulator,
radiator and chicane are shown in Table II.

linac in February and March 2021. Figure 2
shows the breakdown of the ring operating time.
The beam down time includes not only thedown due to machine trouble, but also theoff-beam period after the beam is aborted due tobeam instability or erroneous operation. The
total down time in FY2020 was 2 hours, 0.2 %of the total operation time. The machine's tuning
time is long because all February and March
operations were linac tuning.
Table I Main parameters of the NewSUBARU
storage tingCircumference
118.73 m
Lattice
DBA + inv. Bends
Number of bends
12
Radius of curvature
3.217 mRF frequency
499.955 MHz
Harmonic number
198
Betatron tunes
6.29(H), 2.22 (V)Number of IDs
3
Radiation loss per turn 33.4 keV (@1.0GeV)
Energy acceptance±0.85%
Injection repetition rate 1 Hz

Table II Main parameters of SC3 insertion
device.
[Modulator/Radiator]
magnetpermanent
wavelength
15 cm
Number of periods
24
Total length
7.2 m
Max. field
0.7 T
Max. K parameter
10Gap
280~50 mm(gap can be longitudinally tapered)[Chicane]
MagnetElectromagnet
Number of coils
Main x1, Sub x2
Total length
600 mmMax. field
0.7 T

3. Machine Trouble
Typical troubles for both hardware andsoftware in FY2020 are as follows. The beam
down time was only 2 hours.
3-1. Magnet power supply failure.
Power supplies for quadruple magnet
families often showed “Heat” alarm at startup.
Fluctuations in the current of the sextupole
magnets were observed several times a year.
3-2. Failure of pulsed bump power supply.
At the moment of beam injection, several
reductions in the accumulated current occurred.
This was due to the aging of the thyratron in thebump magnet power supply. Replacing thethyratron solved the problem.
3-3. Failure of cooling fans in the RF klystronpower supply.
After a long period of injector construction,
it turned out that many air-cooling fans inside
the klystron power supply had failed. Until the
repair scheduled for the summer of 2021, it will
be cooled with an external blower and spotcooler as an emergency measure.

Fig. 3. Insertion device for generating
mono-cycle FEL light pulse. Modulator andradiator with high K parameter and a magnetic
chicane between them.
The installation of undulators, a laser system,
and a high-precision timing system werecompleted in FY2019. The first beam
experiment started in April 2020. A single
bunch electron beam could be stored at closest
ID gap of 50 mm. Figure 4 shows the measured
horizontal and vertical tune shifts caused by thestrong magnetic field of the undulator. During
the experiment, this vertical tune shift is

4. Machine StudyIn FY2020, the main theme of the ring R&D
was SC3 project. Another topic was getting thelatest ring parameters in preparation for beam
injection from the new injector into the ring.

25-1. General description of the injector linac
This
sectiondescribes
themainconfigurations of the injector linac [2]. This
injector features a simple and sophisticatedbuncher and accelerator configuration. It
has a C-band high-gradient accelerating
structure and is characterized by being
inexpensive and compact. This injector linac
design is also used at the 3 GeV synchrotron
radiation facility in Sendai [3].

corrected by a real-time tune correction system.
Spontaneous radiation was successfullymeasured at various gaps. Additional tuning for
the FEL experiment, including the overlap ofelectron beams and seed laser pulses in both
space and time, began in April 2021.

Fig. 5. General layout of the new 1.0 GeV linac.
Fig. 4. Horizontal and vertical betatron tune
shifts vs. SC3 radiator gap.

The general layout of the injector linac isshown in Figure 5. The main characteristics of
the injector linac are as follows [3].

4-2. Another studies
Several studies have been done on the ring tosmoothly inject the electron beam into the ringwith the new linac. For example, measuring
lattice functions and circulating beam
parameters, optimizing pulsed magnets forinjection, and readjusting the beam monitor.

50 kV gun using gridded thermionic cathode
A composite RF gun with a gridted thermioniccathode is used for generating stable and low
emittance beam [4]. Stable emission of shortpulse beams is achieved without any special
tuning. Figure 6 and 7 show the electron gun
and 238 MHz RF cavity.

5. Construction and Commissioning of New
Injector Linac
Our storage ring has been supplied withelectron beams from 1.0 GeV electron linac ofSPring-8 as shown in Figure 5. However,
RIKEN SPring-8 center/JASRI decided to
shutdown this linac and to inject electron beams
from 8.0 GeV linac of SACLA to the SPting-8
main ring. Therefore, a new 1.0 GeV injector
is needed, and with the cooperation of RIKEN
SPring-8 center and JASRI, we constructed a
new linac dedicated to NewSUBARU ring.
Fig. 6. 50 kV gridded themionic electron gun
and 238MHz RF cavity.

Fig. 5. Conceptual diagram of beam injection ofSPring-8 and NewSUBARU. Before the
shutdown of 1.0 GeV linac (left) and now(right).

Fig. 7. Gridded themionic electron gun inside
238MHz RF cavity [4].

3238 MHz cavity
The electron gun and focusing magnetic lens
are mounted in a 238MHz cavity as shown in
Figure 7. The 50 keV beam emitted by theelectron gun is accelerated by the cavity up to
500 keV to suppress emittance growth due tospace charge. The cavity is driven by 42 kW
solid state amplifier.
476 MHz cavity
The following 476 MHz cavity provides
velocity bunch compression. It decelerates
beams from 500 KeV to 270~360 keV providing
the energy chirp. Velocity bunch compression
reduces the bunch length from 200 ps (FWHM)
to several ps at S-band first cavity.

Fig. 9. C-band linear accelerating structure of
the new 1.0 GeV linac.

S-band accelerating structure
As shown in Figure 8, one S-band
accelerating structure is used to accelerate theelectron beam up to 50 MeV.

Fig. 10. Beam dump and vertical bending
magnet.
Fig. 8. S-band accelerating structure.
C-band accelerating structure
C-band accelerating structure shown in
Figure 9 is the same type as SACLA. It is wellproven and has a high acceleration gradient of
about 31 MV / m [5]. The length of one
acceleration tube is 2m. One unit (8.6m,
250MeV) consists of four acceleration tubes andis driven by a C-band klystron. Four units areused for 1.0 GeV acceleration.
Fig. 11. Beam envelope functions of the beamtransport line from the exit of the linac to theinjection point of the ring.

Beam dump
A beam dump and a vertical bending magnet are
installed downstream of the C-band accceleration
tubes as shown in Figure 10.

5-2 Construction and commissioning history
Normal user operation in 2020 ended inJuly. Removal of existing equipment in the
beam transport tunnel and construction of
the new linac began in August. Constructionof the new linac was completed by December.
Despite the COVID-19 pandemic, there was no

Beam transport line
Figure 11 shows the designed envelope
functions of the beam transport line from theexit of the linac to the injection point of the ring.
The electron beam from the injector istransported to the ring without loss.

4

beam intensity or injection efficiency. Third,
the beam quality is better than the previous
Linac. As a result, the top-up current
increased from the previous 300 mA to 350
mA. Due to its high long-term stability andreproducibility, the daily accelerator tuning
time is short.

delay in the work process. RF conditioning of
the klystrons and acceleration tubes was
carried out for about a month and a half
until mid-February 2021. The beamcommissioning began in February and the
1.0 GeV electron beam was successfullytransferred to the beam dump on February
17. Beam injection into the ring began on
March 8, and the first synchrotron lightfrom electrons supplied by the new linac
was observed on March 9. A beam
accumulation of 200 mA was achieved on
March 11. User operation restarted on
April 20 with a top-up current of 350 mA.
This is about 3 weeks faster than planned.
Table III summarizes the history of injector
linac construction and commissioning.

SummaryIn FY2020 the new 1.0 GeV injector linac
for NewSUBARU ring was constructed. We
obtained sufficient performance of the beam.
The stability and the reproducibility of thebeam are also good. We re-started user timein April 2021.
The sophistication of accelerators will
enable further contributions to theindustrial use of synchrotron radiation.

Table III Construction and commissioning
history of the new injector linac.
- Feb, 2017
Accelerator design- Mar. 2019
Annex building constructed- Jan. 2020
Install klystron & modulator- July.
Storage ring shut down
Remove beam transport line
- Oct.
Install linac in tunnel- Jan. 2021
RF conditioning- Feb.
Beam commissioning
1 GeV, 100 pC beam
- Mar. 9First light at storage ring
Injection efficiency > 90%- Apr. 20
User run restarted
1-1.5 GeV, 350 mA

Acknowledgements
We would like to express our sincere gratitude to
the accelerator staff at RIKEN SPring-8 center,
JASRI, QST, and SES for their great cooperation in
the construction and operation of the new injector.
We would also like to thank to Mr. Y. Minagawa, Mr.
K. Kajimoto, Mr. H. Hirayama, Mr. S. Nakata of SES,
and Mr. Y. Hamada of JASRI for their efforts inoperating the accelerators.
References[1]“Development of an undulator with a variablemagnetic field profile”, T. Tanaka, Y. Kida, R.
Kinjo, T. Togashi, H. Tomizawa, S. Hashimoto,
S. Miyamoto, S. Okabe, Y. Tanaka, Journal ofsynchrotron radiation 28, ｐ.404-409（2020）[2]"Construction of a Compact Electron Injector
Using A Gridded Rf Thermionic Gun And A
C-Band Accelerator", T. Inagaki†, T. Fukui, T.
Hara, T. Hiraiwa, H. Maesaka, H. Tanaka, T.
Asaka, H. Dewa, N. Hosoda, E. Iwai, C. Kondo,
T. Magome, T. Ohshima, T. Sakurai, K.
Yanagida, S. Inoue, K. Kajimoto, Y. Minagawa,S. Nakata, T. Seno, H. Sumitomo, R. Takesako,
S. Tanaka, R. Yamamoto, M. Yoshioka, S.
Hashimoto, IPAC2021, WEPAB039 (2021)[3]http://www.slitj.tagen.tohoku.ac.jp/oldHP/ab
out.html[4] T. Asaka, et. al., Phys. Rev. Accel. Beams 23,
063401 (2020)[5] T. Inagaki, et. al., PRST-AB 17, 080702(2014)

5-3. Benefits of the new injector linac
Table IV shows the performance required
for the injector and its measurement results.
We obtained sufficient performance of thebeam. Also, linac is working very wellwithout any problems.
Table IV Performance of the new injector linac.
Beam Energy
Bunch charge
Normalized emittance
Energy spread
Energy stability
Bunch length
Injection efficiency

Require1.0 GeV
100 pC<10 mm-mrad<±0.5%
5ps (FWHM)>90%

Measurement
1.0 GeV
100 pC<10 mm-mrad
0.1% (FWHM)
0.4% (STD)<1ps (FWHM)>90%

Having an injector that can be used
exclusively has several advantages. First,
we can schedule the operation of themachines according to the needs of the users
in the facility. Second, we can inject thebeam into the ring at any time and tune theinjector linac at any time to increase the5

Beamlines
Koji Nakanishi
LASTI, University of Hyogo
The arrangement of the beamlines in the
NewSUBARU synchrotron radiation (SR) facility isshown in Fig.1. Total nine beamlines are operating in
the NewSUBARU SR facility.
Four beamlines of BL01, 03, 06 and 11 wereconstructed until 1999. Three beamlines of BL07, 09
and 10 were started the operation from 2000.
BL02 beamline was constructed for the usage of
LIGA in 2003.
BL03B beamline branched from the BL03
beamline propose for the usage of the EUVL (extreme

ultraviolet lithography) microscope for the EUVL
finished mask inspection.
BL05 was built in 2008 to perform industrial
analysis by soft X-ray XAFS and PES. A major
upgrade was started in 2020 for more effective use.
BL09B beamline branched from BL09 beamline
for the usage of the EUV interference lithography toevaluate. And BL09C beamline branched from
BL09B beamline for the usage of the thickness
measurement of the carbon contamination originatedto the resist outgassing during the EUV exposure.

B L0 5 B

B L0 5 A

Fig. 1 Beamline arrangement in NewSUBARU.

6

I. BL01
BL01 is a beamline for research and developing
new light sources. This beamline is one of two longstraight section on NewSUBARU. Optical klystron
was installed at this straight section. Upstream side ofthis beamline (BL01B) is intended to be used forvisible and infrared light generated from free electron
laser (FEL) or synchrotron radiation (SR).
Downstream side of this beamline (BL01A) is used

for laser Compton scattering gamma-rays source.
Gamma-ray beamline hutch just outside of the storage
ring tunnel was constructed in 2004 for gamma-ray
irradiation experiments. Specification of this gammaray sources are listed in Table 1. New gamma-ray
irradiation hutch "GACKO" was installed at BL01A,
collaborating with Konan University. Table 2 shows
the specification of “GACKO”.

Table 1. Specification of BL01 gamma beam
CO2 laser
10.52 µm
5W

Gamma energy : 1.7 - 4 MeV
Gamma flux*: 9 ×106 γ/s: 6×105 γ/s (1.5-1.7 MeV)
(with 3mmφ collimator)

Nd laser1.064 µm / 0.532 µm
5WGamma energy : 17 - 40 MeV
Gamma flux*: 7.5 ×106 γ/s: 3 ×105 γ/s (15-17 MeV)
(with 3 mmφ collimator)*Electron beam energy : 1-1.5 GeV*Electron beam current : 250 mA*Gamma-ray beam divergence : 0.5 mrad

Table 2. Specification of “GACKO”
Maximum gamma-ray power
0.33 mW
Maximum gamma-ray energy
1.7 MeV - 73 MeV
CO2 laser, wavelength/power
10.59 µm / 10W
1-1.7 MeV gamma-ray flux
2×107 γ/sec@10W/300mA
1.064 µm/ 30W,
Nd:YVO4 laser, wavelength/power
0.532 µm/ 20W
10-17 MeV gamma-ray flux
5×107 γ/sec@30W/300mA

II. BL02
The LIGA (abbreviated name of Lithogaphic,
Galvanoformung and Abformung) process which
consists from deep X-ray lithography, electroforming,and molding process is one of the promising
candidates for such 3D micofabrication. More thanhundreds aspect ratio for microstructure can beattained by the usage of the higher energy X-rays (415 keV) from synchrotron radiation (SR) with deeper
penetration depth to the photosensitive resist. In thissystem we have succeeded to enlarge the exposurearea up to A4 size and the fabrication dimension from
submicron to millimeter by varying the energy of the

X-ray source in accordance with the size of desired
microparts. Microstructure with high aspect ratio over
several hundred will be achieved using the X-rays
over 10 keV since high energy X-ray has deep
penetration depth to the photo-sensitive resist
materials. Whereas, in the case of lithography for low
energy X-rays from 1 keV to 2 keV, submicron
structures with high aspect ratio will be achieved
using the X-rays mask with precise line-width andthinner absorber, since low energy X-rays has low
penetration depth. Based on this principle, thebeamline for x-ray exposure have constructed with7

microfabrication process using multi step exposure atvarious configuration between X-ray mask andsubstrates. The relative positions between X-ray mask
and substrates, tilt and rotation angle to the SR
incident direction can be moved simultaneously
during SR exposure using 5 axis stages. The
movement of each axis is controlled by the PC in
terms of the scanning speeds, scanning length, andrepetition number. In order to decrease the heat loadof sample substrate suffered during SR irradiation
helium introduction and substrate cooling mechanism
were also equipped. Specification of spectrometer islisted in Table 3.

continuous selectivity of X-rays from 100 eV to 15
keV by using the X-ray mirrors (plane and cylindricalmirror) and Be film filters. The horizontal angle of theoutgoing SR could be obtained up to 12.5 mrad, whichcorresponds to the horizontal size of 220 mm (A4horizontal size) at the exposure position. The second
characteristic performance of the beamline is the highefficiency differential pumping system. This wasnecessary for maintain the vacuum difference
between the storage ring (<10-9 Pa) and the endstation (<10-9 Pa) at which gasses for substratecooling will be introduced in the exposure apparatus.
The flexibility for the shapes and functions of
microstructure will be enlarged by achieving 3D

Table 3. Specification of the LIGA exposure system
OpticsPlane and cylindrical mirror, Be filters
Exposure energy
0.1 - 2 keV, and 4 – 15 keV
Exposure method
Proximity and multi-step exposure
Wafer size
A4 or 8 inch
Exposure area
230 mm(H) ×300 mm(V)
Exposure environment< 1 atm (He-gas)

III. BL03
reflectometer was UV – VUV reflectometer. At EUV
lithography, out-of-band radiation (100 – 300 nm) of
EUV source degrades image quality. Thus, optics andresist property of out-of-band region was essential toevaluate, for example EUV mask reflectivity, andEUV resist sensitivity. The monochromator
specification was shown in Table 4. The EUV
microscope (3) has Schwarzschild optics, which were
fabricated with collaboration of Dr. Toyoda (Tohoku
Univ.). The spatial resolution was quite high of lessthan 28 nm, which was equal to 7 nm at wafer printing
size.

BL03 is a beamline for the developing the next
generation lithographic technology so called extreme
ultraviolet (EUV) lithography. The extreme
ultraviolet lithography (EUVL) is a promise
technology for fabricating a fine pattern less than 7nm node. There are (1) a EUV resist-sensitivity
evaluation tools, (2) a VUV reflectometer, and (3) an
EUV microscope with Schwarzschild optics. At (1)tool, EUV resist is exposed with SR light of EUV
monochromatized by 7 Mo/Si multilayer mirrors. The
exposure spectrum of this tool was same as the ASML
exposure tools. The monochromator of (2)Table 4. VUV monochromator specification
Mount type
Collimate plane grating monochromator
Grating
Plane Grating (1,000 lines/mm)
Energy range
4 - 120 eV (UV ～ VUV)Resolving power (E/ΔE)～1000

IV. BL05

8

BL05 was constructed in response to a demand in
the industrial world, which is enhancement of theanalysis ability in the soft x-ray region with thedevelopment of nanotechnology. BL05 consists of
two branch lines for use in the wide range from 50 eV
to 4000 eV. BL05A and BL05B are designed to cover
the energy range of 1300-4000 eV and 50-1300 eV,
respectively. The incident beam from the bending
magnet is provided for two branch lines throughdifferent windows of a mask. Therefore, these two
branch lines can be employed simultaneously.
However, both beamlines have not been used asmuch in industrial analysis as expected due to the low
accuracy of obtained spectra and the long acquisitiontime.

In order to solve these problems, we first started to
improve BL05A. In order to improve the basic
beamline performance of BL05A, most of the opticalelements, measurement system, and control program
were replaced. For example, a Golovchenko-type
double-crystal monochromator capable of high-speed
scanning was newly installed to shorten the XAFS
acquisition time. In addition, newly designed andinstalled masks and slits have made it possible to use
high-intensity X-rays. Two toroidal mirrors as acollimated mirror and a focusing mirror have beenused in the BL05A so far, but the focusing mirror was
temporarily removed. The total electron yield modewith a sample current and the partial fluorescence
yield mode with a silicon drift detector and a digital
X-ray processor can be used for soft X-ray XAFS
measurements. Table 5 shows the specification of
monochromator.

 1) BL05A

Table 5. Monochromator specification
Monochromator
Double crystal monochromator
Monochromator crystals
Beryl(10-10), KTP(011), InSb(111), Ge(111), Si(111)Energy range
1300 - 4000 eV

2) BL05B
The constant-deviation monochromator consistingof a demagnifying spherical mirror and a varied-linespacing plane grating (VLSPG), which can provide
high resolution, simple wavelength scanning with
fixed slits, was mounted on BL05B. The opticalsystem consists of a first mirror (M0), a second mirror(M1), an entrance slit (S1), a pre-mirror (M2), andthree kinds of plane grating (G), an exit slit (S2) anda focusing mirror (M3). The including angle of themonochromator is 175°. Two measurement chambers
Monochromator
Grating
Energy range
Resolution

for XAFS and PES are prepared at the end station of
BL05B. The XAFS spectra in the total electron yieldmode and fluorescence XAFS spectra using SDD(Ourstex) can be measured in a high vacuum chamber.
In addition, the photoelectron spectrum can bemeasured using spherical electron analyzer (VG
Sienta, R3000) in an ultrahigh-vacuum chamber. The
chambers can be replaced by each other within 1 hour.
Table 6 shows the specification of the monochromator.

Table 6. Monochromator specification
Varied-line-spacing plane grating monochromator
100 lines/mm, 300 lines /mm, 800 lines /mm
50 - 1300 eV
E/⊿E=3000

9V. BL06
BL06 has been mainly developed for irradiation
experiments such as photochemical reaction, SRCVD, photo-etching, surface modification. The whiteradiation beam from bending magnet is introduced tothe sample stage using a pair of mirrors, whose
incident angle was 3°. The SR at BL06 sample stage
had a continuous spectrum from IR to soft x-ray,which was lower than 1 keV. A differential pumping
system can be utilized for experiments in a gas
atmosphere, which is difficult in the soft x-ray region.

A sample holder can install four pieces of samples at
a time. By using heater set in the sample holder, thesample can be heated from room temperature to220C. The temperature of sample is monitored usinga Cr-Al thermocouple mounted on the sample holder.
The current BL06 for irradiation experiments was
closed due to plans to build a new beamline for XAFS
in August 2020. Irradiation experiments will be
partially possible at the newly constructed beamline.

VI. BL07
This beamline was designed for the developmentof new materials by SR technology. This beamline
consists of two branch lines, which are provided withan incident beam from a 3-m-long undulator byswitching the first mirror. One of them is a highphoton-flux beamline with a multilayered-mirror
monochromator for the study of SR-process (BL07A)
and another is a high-resolution beamline with avaried line spacing grating monochromator for theevaluation of nano-structure characteristics by SRspectroscopy (BL07B). The useful range of emitted
photons from 50 to 800 eV is covered at bothbeamlines. The light source of BL07 is a 3-m lengthplanar undulator, which consists of 29 sets ofpermanent magnets, a period length of which is 76
mm. The incident beam from the undulator isprovided for two branch lines by translationalswitching of first mirror.

use only first mirror (switching mirror), M0, forfocusing. The MLM monochromator is designed tocover an energy range of up to about 800 eV by
combination of three kinds of mirror pairs with 4
kinds of filter. The flux deliver by this design isestimated to be between a maximum of 1017 photons/s
at 95 eV and a minimum 21014 photons/s at 300 eV
for a 500 mA ring current. Table 7 shows the summaryof BL07A. In addition, X-ray fluorescence (XRF)
apparatus using spherical varied line spacing grating
was mounted at the downstream of irradiationchamber. The poly capillary was used to enhancebeam-condensing efficiency. Measurement energy
range was from 30 eV to 450 eV. This XRF apparatus
was expected to utilize the chemical analysis on thelight metals, Li and Be, and light elements, B, C andN.
Two novel vacuum chambers were installed in2019 for the measurement of inverse Compton
scattering of soft X-rays. One large chamber with asize of W1120×D820×H610 mm3 was set up 16.7 m
downstream of the undulator center. A multi-layer
mirror was placed on high precision auto-stages inside
this chamber with cooling water circulation. The otherchamber was installed 2.6 m upstream of the large
mirror chamber, in order to monitor radiated andreflected X-rays.

1) BL07A
The multilayered-mirror (MLM) monochromator,
which has high reflectivity in the soft X-ray region,
was installed at the BL07A. It consists of a switching
mirror chamber, a slit chamber, a MLM
monochromator, a filter chamber and a reaction
chamber. To obtain a large photon flux, we decided to10Energy range
(eV)
50-60
60-95
90-140140-194
190-400
400-560
550-800

Material

Table 7. Summary of BL07A.
Multilayer mirror
Thickness
NumberSpacingE/E
Ratio
of layers

Mo/Si

20 nm

0.8

20

6.2 %

Mo/B4C

11 nm

0.5

25

3.3 %

Ni/C

5 nm

0.5

60

2.5 %

2) BL07B

FilterMaterial

Thickness

Al

100 nm

None

-

Ag

100 nmCr
Ni

500 nm
500 nmmirrors (M2 and M3). The monochromator isdesigned to cover the energy range 50-800 eV withthree gratings, of which including angle are 168. The
VLSPG has been well known to obtain highresolution in extreme ultraviolet region bydiminishing various kinds of aberration. The total
resolving power about 3000 can be realized in thewhole energy region. Table 8 shows the specificationof the monochromator.

The
constant-deviation
monochromatorconsisting of a demagnifying spherical mirror andvaried line spacing plane grating (VLSPG), which canprovide to high resolution, simple wavelength
scanning with fixed slits, was mounted on BL07B.
The optical system consists of a first mirror (M0), an
entrance slit (S1), a pre-mirror (M1), and three kindsof plane grating (G), an exit slit (S2) and two focusing

Table 8. Monochromator specification
Mount type
Hettrick-Underwood type
Grating G1, G2, G3
Plane VLS (600, 1200, 2400 l/mm)
Energy range
50-150 eV, 150 – 300 eV, 300-800 eVResolving power (E/ΔE)～3000

VII. BL09
A purpose of this beamline is studies on a soft x-ray
interferometry or a holographic exposure
experiment with making use of highly brilliant andcoherent photon beams radiated from 11 m longundulator in NewSUBARU.
BL09 consists of M0 mirror, M1 mirror, G gratingand M2 mirror. M0 mirror is used for horizontal
deflection and beam convergence, M1 is used forvertical beam convergence at the exit slit, and M2 isused for vertical deflection and beam convergence. A
monochromator is constructed by M1 and a planegrating. The maximum acceptance of the undulator
beam is 0.64 mrad in horizontal and 0.27 mrad invertical. The acceptance can be restricted by 4-jaw
slits equipped at upstream of the M0 mirror.

1) BL09A
BL09A beamline is used for material analysis: Xray absorption spectroscopy (XAS) and X-ray
photoelectron spectroscopy (XPS). In 2013, X-ray
emission spectrometer (XES) was introduced at theend-station of the BL-09A. The energy range andresolving power of the XES system was designed to
be about 50-600 eV and 1500, respectively.
2) BL09B
BL09B beamline branched from BL09 beamline
for the usage of the EUV interference lithography for11the evaluation of the exposure characteristics of EUV
resist. Coherence length of 1 mm at the resist exposure
position was achieved using BL09B beamline. And
BL09C beamline branched from BL09B beamline forthe usage of the thickness measurement of the carbon

contamination originated to the resist outgassing
during the EUV exposure. Table 9 shows the
specification of the monochromator.

Table 9. Monochromator specification
Mount typeMonk-Gillieson type
Grating
Plane VLS (300, 900, 1200 l/mm)
Energy range
50 – 750 eVResolving power (E/ΔE)～3000

VIII. BL10
BL10 is for EUV reflectometry and soft X-ray
analysis. M0 mirror is used for horizontal deflection
and beam convergence, M1 is used for vertical beam
convergence at the exit slit, and M2 is used for verticaldeflection and beam convergence. A monochromatoris constructed by M1 and a plane grating. At the
beginning, the multilayer reflectivity measurement
was carried out at this beamline. The characteristics ofthis beamline and the result of the Mo/Si multilayer
measurement are carried out for the development of
the EUV- mask technology.
BL10 utilizes a monochromator of the varied-linespacing plane grating (VLS-PGM). The line density ofthe monochromator in central region of the gratings
were 600, 1800 and 2,400 lines/mm. The reflectometerhas a two-axis vacuum goniometer. One axis carries
the sample, which may be a mirror surface at the centerof the reflectometer vacuum chamber (θ-motion). The
other (φ-motion) carries the detector on a rotating arm.

In addition, there are linear motions to translate thesample in two orthogonal directions (x, y). All motors
are controlled by computer. The reflectivity result
obtained at BL10 has a good agreement with that at
LBNL. Table 10 shows the specification the
monochromator.
The micro-CSM tool was adapted at the mostdownstream of the BL10 beamline for the EUV mask
defect inspection with coherent-diffraction-imaging
method. This too is very effective for the inspection of
the actinic patterned mask with phase imaging.
A large reflectometer was installed in a branch line
for large EUV optical component including EUV
collector mirrors. The reflectometer has a sample stage
with y, z, θ, φ, and Tilt axis, which can hold large
optical elements with a maximum weight of 50 kg, a
diameter of up to 800 mm, and a thickness of 250 mm.
The entire sample surface is able to be measured.

Table 10. Monochromator specification
Mount typeMonk-Gillieson type
Grating
Plane VLS (600, 1800, 2400 l/mm)
Energy range
50 – 1,000 eVResolving power (E/ΔE)～1000

IX. BL11
fabrication of extremely tall three-dimensional (3D)
microstructures with a large aspect ratio. This
process was invented at the Institut Fur
Mikrostrukturtechnik (IMT) of the Karlstuhe
Nuclear Center (KfK) in 1980. Microstructures withheight of over a few hundred µm have been widely

A beam line BL11 is constructed for exposure
Hard X-ray Lithography (DXL) in the LIGA
(Germanacronymfor
Lithographite
Galvanoformung and Abformung) process. LIGA
process, that utilizes a useful industrial application of
SR, is one of the promising technologies for12applied to various fields such as micro-mechanics,
micro-optics, sensor and actuator technology,
chemical, medical and biological engineering, and soon. This beam line was designed by the criteria;
photon energy ranges from 2 keV to 8 keV, and adensity of total irradiated photons ≥ 1011 photons/cm2.
The BL11 can provide the most suitable photon
energy for microfabrication in X-ray lithography,
while the BL2 is equipped for fabricating fine pattern
submicron-scale structure and microstructure withhigh aspect ratio by selectivity of X-rays using
movable mirror system. That is, LIGA process in
NewSUBARU can provide the best 3D
microfabrication because the BL11 and BL2 arecomplementary. The beamline BL11 is consisting ofan absorber chamber, a first-mirror chamber (M1), a
4-way slit chamber, a Be and polyimide windowchamber, and an exposure chamber. The horizontal
angle of the outgoing SR could be obtained up to 17.8

mrad, providing a beam spot size on the exposure
stage ≥ 80 × 10 mm2. The micron-scale structure withhigh aspect ratio will be achieved using the toroidal
typed mirror M1 which can produce a parallel
collimated beam of X-rays. In addition, thehomogeneity of the beam is excellently controlled bya novel adding system. Using the precision stage in the exposure
chamber, the flexibility for the shaped and functionsof microstructure will be enlarged by achieving 3D
microfabrication process using multi step exposure atvarious configuration between x-ray mask andsubstrates. The exposure area of 200 mm × 200 mm
is brought to fruition. In order to decrease the heatload of sample substrate suffered during SR
irradiation, helium introduction and substrate coolingsystem were also equipped. The specification of the
LIGA exposure system is listed in Table 11.

Table 11. Specification of the LIGA exposure system
Exposure method
Proximity exposure
Wafer size
8 inchExposure area
200 mm(H)×200 mm(V)
Exposure environment< 1atm (He-gas)

Establishment of Research Center for Advanced Synchrotron Radiation Analysis
In order to respond to diverse analysis needs fromindustries, it is necessary to advance technologicaldevelopment for analyzing beamlines (BLs) of
NewSUBARU SR facility to advance integrated andstrategic development of analyzing technology. For
this reason, the Research Center for Advanced SR
Analysis was launched in August 2016. As anorganization crossing in university courses, this centeris consulted and administered by all members of the
LASTI related to analysis, and in collaboration with
the SR Nanotechnology Center of Hyogo Prefecture,a wide range of energy from hard X-rays to soft Xrays. We aim to respond to various analysis needs ofthe area on a one-stop basis.

Acknowledgement
We would like to thank all the staff who work at
NewSUBARU synchrotron radiation research facility
for their help to describe the update details of thebeamlines.

13

Part 2. Research Activities

Hydrogen Plasma Emission(BL-9C high-power EUV irradiation tool)Application of Machine Learning Techniques
to Betatron Tune Correction
H. Fujii1, K. Watanabe2, and S. Hashimoto1
1
LASTI, 2University of Hyogo

Abstract
In NewSUBARU synchrotron light facility, a real-time spectrum analysis is performed for betatrontune correction. However, the existing system is a handmade system and its range of application
and accuracy are limited. In this study we developed a new system using logistic regression model,
which is one of the simplest machine learning techniques. As a result, it was found that it ispossible to construct a model with accuracy exceeding the existing system even with a relatively
small amount of teacher datasets.

Introduction
The orbit of the electron beam orbiting thestorage ring is given by the following orbit
equation.
𝑑𝑑2 𝑥𝑥(𝑠𝑠)(1)+ 𝐾𝐾(𝑠𝑠)𝑥𝑥(𝑠𝑠) = 𝐹𝐹(𝑠𝑠).
𝑑𝑑𝑠𝑠2
Where 𝑠𝑠 is the position on the design orbit and𝑥𝑥(𝑠𝑠) is the horizontal deviation from it. Since
the vertical deviation is given in the same form,
only the horizontal direction is considered below.
𝐾𝐾(𝑠𝑠) is a function representing the magnetic
field of each electromagnet and satisfies
𝐾𝐾(𝑠𝑠 + 𝐿𝐿) = 𝐾𝐾(𝑠𝑠). 𝐿𝐿 is the circumference ofthe ring. 𝐹𝐹(𝑠𝑠) mean the strength of the residual
magnetic field on the design orbit. The periodic
solution of Eq. (1) can be written as follows.
</𝛽𝛽(𝑠𝑠)𝜈𝜈 2 𝑓𝑓4 849(:)(2)
𝑒𝑒 ; .
𝑥𝑥(𝑠𝑠) = .
𝜈𝜈 2 − 𝑛𝑛2

As is clear from the denominator of this solution,
when tune value approaches an integer, 𝑥𝑥(𝑠𝑠)becomes large due to resonance with theresidual magnetic field and the electron beam
becomes unstable. In reality, there are various
other resonance conditions. Then, in order toextend the lifetime of the electron beam, it isnecessary to constantly monitor and correct thetune value to keep it away from the resonanceconditions. Figure 2 shows the results of thetune measurement obtained in NewSUBARU
storage ring.

4=><

The aperiodic solutions decay, so it is notconsidered here. 𝛽𝛽(𝑠𝑠) is betafunction andsatisfies𝛽𝛽(𝑠𝑠 + 𝐿𝐿) = 𝛽𝛽(𝑠𝑠). 𝜓𝜓(𝑠𝑠) is a functionthat satisfies 𝜓𝜓(𝑠𝑠 + 𝐿𝐿) = 2𝜋𝜋𝜋𝜋 + 2𝜋𝜋𝜋𝜋 + 𝜓𝜓(𝑠𝑠) ,where 𝑙𝑙 is an integer. 𝜈𝜈 is called betatron tune,
or simply tune, which means the number ofoscillations of the electron beam per round of
the storage ring. 𝑛𝑛 is an integer and 𝑓𝑓4 is theFourier coefficient. Figure 1 shows the betatronoscillation.

Figure 2. Frequency spectrum of voltage
signal from beam positioning monitor on
storage ring. 𝑛𝑛𝑓𝑓BCD is 𝑛𝑛 -th harmonics ofthe revolution frequency of the electron
beam bunch. 𝑓𝑓E and 𝑓𝑓F are the frequencyof horizontal and vertical betatronoscillation, respectively.

The peak around 499 MHz in Fig. 2 is from thehigher harmonics of the revolution frequency ofthe orbiting electron beam bunch. The frequency
of betatron oscillation is observed as its
sideband. The peaks around 500.5 and 500.7
MHz are from the betatron oscillation in thevertical and horizontal directions, respectively.
The tune value is obtained by dividing thesefrequencies by the revolution frequency. (To be

Figure 1. Schematic drawing ofbetatron oscillation of electron beam
bunch. Residual magnetic field is notconsidered in this figure.

17

precise, only the decimal part of the tune is
obtained here.) In the current system, thespectrum in Fig. 2 is smoothed and then peakfitting is performed to obtain the tune. If thetune value is inappropriate, a correction is
performed by changing the current value of theauxiliary
windingofthequadrupoleelectromagnets. The problem here is that thepeak fitting does not always work. Dependingon operating conditions, for example, the peak
may be too small or too large as shown in (a)and (b) of Fig. 3.

reads the spectral data 𝑥𝑥P , 𝑥𝑥N 𝑥𝑥2 , … , 𝑥𝑥V andreturns a value with range from 0 to 1.
∑M>Nand𝑝𝑝(𝑧𝑧I )Obviously,
O=P 𝑝𝑝(𝑧𝑧O ) = 1
represents a probability that the read data
belongs to class 𝑙𝑙 . Logistic regression is amethod classified as supervised learning, and itis necessary to give a correct label in advance.
Compare the estimated value from Eq. (3) withthe correct label and then update the weight(I)
𝑤𝑤U . The update procedure is as follows: first,
the loss function is defined by
M>N

𝐽𝐽 = − . 𝑡𝑡O ln[𝑝𝑝(𝑧𝑧O )] .
O=P

This function means the estimation accuracy ofthe classification model. Here, 𝑡𝑡O is a vector𝑡𝑡⃗ = [𝑡𝑡P , 𝑡𝑡N , 𝑡𝑡2 , … , 𝑡𝑡M>N ] which means the correctlabel expressed by one-hot encoding, i.e., it is avector in which only the element of the correctlabel is one and the other elements are zero. The(I)
derivative of 𝐽𝐽 by 𝑤𝑤U is𝜕𝜕𝜕𝜕(6)= −[𝑡𝑡I − 𝑝𝑝(𝑧𝑧I )]𝑥𝑥U .
(I)
𝜕𝜕𝑤𝑤U
From this derivative, the following gradientdescent method is use to update the weights.
𝜕𝜕𝜕𝜕
(I)
(I)
(7)
𝑤𝑤U = 𝑤𝑤U − 𝜂𝜂 (I) .
𝜕𝜕𝑤𝑤U
In this way, the derivative can eventually reach0 as the learning progresses. 𝜂𝜂 is called thelearning rate (or step size) that determines themagnitude of weight update. Repeat the above
update procedure a specified number of times.

Figure 3. Bad frequency spectrum examples.

In such cases, correct tune value cannot be
obtained and a wrong correction may be
performed. To prevent this, the current systemjudges whether correction should be performed
or not using various criteria such as peak height,
full width at half maximum, and amount ofchange from the previous tune value. However,this method cannot be used to judge complicatedwaveforms. In addition, it is necessary to adjust
the parameters of the criteria every time theoperating status changes. Therefore, weconstruct a new judging system by using themachine learning techniques. In this study, weused logistic regression [1] which is one of thesimplest methods for solving classification
problems. In logistic regression, classification is
performed using the following classification
model,JK

M>N

𝑝𝑝(𝑧𝑧I ) = 𝑒𝑒 Q . 𝑒𝑒 JL ,
V

O=P
(I)

𝑧𝑧I = . 𝑤𝑤U 𝑥𝑥U .
U=P

(5)

Experiments and Results
Figure 4 shows the percentage of correct
answers to the number of teacher datasets usedin the training of the logistic regression model.

(3)

(4)

This is called Softmax function. 𝐾𝐾 is thenumber of classes (0,1,2, … , 𝐾𝐾 − 1). In our case,
𝐾𝐾 = 2. (A correction should be performed: 0, or
not: 1. In this case, the Softmax function isequivalent to the sigmoid function.) 𝑀𝑀 is thenumber of features (or descriptors, explanatory
variables). 𝑥𝑥U is the value of the 𝑗𝑗-th feature. In
our case, feature is spectral intensity at theobservation points in the frequency spectrum.
Here, 𝑥𝑥P ≡ 1 is a bias term (or a constant term).
(I)
𝑤𝑤U is the weight to be learned. Equation (3)Figure 4. Correct answer rate of logistic
regression model as a function of training
datasets.

18

It can be seen from this figure that a model witha correct answer rate of 99.5% or more can beconstructed even with a relatively small numberof teacher datasets of about 140. The judgmentprocessing time of this logistic regression model
is about 0.03 s, which can be sufficiently used
for real-time system. The performance of theconventional system is 99% correct answer rate
and 0.01 s judgment time. Therefore, the logistic
model is a little slower in speed, but higher inaccuracy. Here, in this new system, the spectral
data is integrated, and the data whose integrated
value is too small or too large, such as (a) and(b) in Fig. 2, is excluded in advance to makelearning a little easier. Even with such a simple
machine learning model, it was possible toconstruct a model with high accuracy. In the
future, we will construct a tune correction
system using a more efficient machine learningmodel and use it for actual operation.
Reference[1] C. M. Bishop, “Pattern Recognition andMachine Learning’’, Springer (2006).

19

P e r f o r m a n c e o f B L 0 7 A a t N e wS U B A R U wi t h i n s t a l l a t i o n o f
a new multi-layered-mirror monochromator
Shotaro Tanaka, Shuto Suzuki, Tomohiro Mishima and Kazuhiro Kanda
LASTI, University of Hyogo, 3-1-2 Koto, Kamigori, Hyogo, Japan

Abstract

Soft X-rays excite the inner shells of materials more efficiently than any other form of light. The
investigation of the synchrotron radiation (SR) processes by using inner-shell excitation requires thebeamline to supply a single color and a high-photon-flux light in the soft X-ray region. A new
integrated computing multi-layered mirror (MLM) monochromator was installed at the beamline
07A (BL07A) of NewSUBARU, which has a 3-m undulator as a light source for the irradiation
experiments with high-photon-flux monochromatic light. The MLM monochromator has a highreflectivity index in the soft X-ray region; it eliminates unnecessary harmonic light from theundulator and lowers the temperature of the irradiated sample surfaces. The monochromator can be
operated in a high vacuum, and three different mirror pairs are available for different experimental
energy range; they can be exchanged without exposing the monochromator to the atmosphere.
Measurements of the photon current of a photodiode (PD) on the sample stage indicated that thephoton flux of the monochromatic beam was more than 10 14 photons/s･cm2 in the energy range of
80400 eV and 1013 photons/s･cm2 in the energy range of 400800 eV. Thus, BL07A is capableof performing SR stimulated process experiments.

1. Introduction

Reaction processes originating from theexcitation of inner-shell electrons of atoms aredifferent from those originating from excitation ofvalence electrons, because the inner-shell electrons
are localized within molecules. Specific atoms canbe excited using inner-shell excitation because thebinding energies are particular to each atom andthe chemical bond environment. This ionicdissociation originating from the inner shell
excitation shows contains information on theinitial resonance excitation, namely, the transition
from the inner-shell electron of a particular atom
to an anti-bonding orbital and suggests thepossibility of using inner-shell resonanceexcitation for site-selected chemical-bond cutting.
This reaction process is especially interesting fromthe perspective of cutting specific chemical bonds
through the control of light, i.e. as a "molecular
scalpel". In addition, the soft X-ray region has thelargest reaction cross section in the light spectrum
for such cutting reaction. For these reasons, innershell excitation has attracted attention as a surface
modification
process
atrelativelower
temperatures because it can cause a reaction
without emitting extra energy. To excite innershells of various elements, the energy of the lightsource must be tunable in the soft X-ray region,and synchrotron radiation (SR) is realistically the
only available light source to serve this purpose.
As well, a beam line with a high brightness beam

is necessary to study inner-shell excitation
reactions of a single color by using soft X-rays.
Moreover, the beam line should be able to irradiatea sample’s surface with high-photon-flux
monochromatic light.
In the work reported here, we installed a new
multi-layered mirror (MLM) monochromator at
beamline 07A (BL07A) in NewSUBARU
Synchrotron Radiation Facility for experiments on
inner-shell excitation in which irradiation withhigh-photon-flux monochromatic light produced
by a combination of an undulator source and amultilayer film mirror monochromator.
The BL07A beamline was designed forinvestigating functional surfaces by using highflux soft X-rays. It has a 3-m undulator to supply
soft X-rays in the range of 80800 eV [1]. In theprevious studies, we performed various studies on
surface modification processes by directly
irradiating samples with the undulator light [2].
Many research results were obtained, such as one
showing the crystallization temperature ofpolysilicon is 200 C lower than what waspreviously believed [3]. However, there are two
problems with irradiating a sample directly with
undulator light, which includes multiple higherorder harmonics due to the undulator: (1)harmonics not at the desired energy become a heatsource that needlessly raises the sample’s surface
temperature; (2) the photon flux cannot be20

estimated because the sample is irradiated withmultiple higher-order harmonics with different
energies, and their intensity ratio cannot be
evaluated. Therefore, we could not determine thereaction cross sections of inner-shell excitations at
this beamline. To solve these problems, weinstalled a new MLM monochromator that can be
operated under a high-vacuum, by setting two
differential pumping chambers upstream anddownstream of the monochromator (Fig. 1). Here,
we report the experimentally estimated photon
flux when using the new MLM monochromator
under each irradiation condition at BL07A.
2.

Beamline Overview

Beamline 7 (BL07) at NewSUBARU wasconstructed for researching the creation of new
functional
materials.
For
new-materials
development using SR, two kinds of beamline are
required in the soft X-ray region. One is a highphoton-flux and energy-tunable beamline forstudying SR-stimulated processes, such as innershell excitation leading to selective photochemical
reactions. The other is a high-resolution beamline
for the analysis of the produced materials, such asby photoelectron spectroscopy and X-ray
absorption spectroscopy. BL07 thus consists of
two-branch lines. BL07A is a SR-stimulated
reaction beamline using high photon-flux light; it
has an MLM monochromator. BL07B is a materialanalysis beamline; it has a constant-deviation
monochromator, consisting of a demagnifying
spherical mirror and varied line spacing planegrating (VLSPG). This type of monochromator can
provide high resolution through simple
wavelength scanning with fixed slits.
The light source of BL07 is a 3-m planar
undulator, which consists of 29 sets of permanent
magnets, the period length of which is 76 mm. The
K parameter of the undulator ranges from 0.3 to
5.3, and the radiation wavelength from thisundulator ranges from 66 to 4.4 nm when utilizing
the fundamental and third through seventh higher
harmonics. The brilliance of this undulator, which
was calculated as 100 mA of the ring current(Miyamoto, 2001), is depicted in Fig. 2 (a) for 1.0GeV operation mode and (b) for 1.5-GeV operation
mode. Brilliance steeply decreases at photon
energies more than 400 eV in 1.0-GeV operation
mode. On the other hand, brilliance in 1.5-GeV
operation mode remains high enough out to 800

eV. The incident beam from the undulator isprovided for the two branch lines, BL07A and
BL07B, by translational switching of the firstmirror.

Figure 1 Layout of BL07A showing the position of
beamline components. ABS: absorber; 4Q-S: fourquadrant slit; SM: switching mirror; PW: protective
wall; DPV1: differential pumping vessel 1; MLMM:
multi-layered-mirror monochromator; FC: filter
chamber; DPV2: differential pumping vessel 2; RC:reaction chamber.

Figure 1 shows the overall setup of BL07A
from the front end of the storage ring to thereaction chamber. The optical layout of BL07A
does not change from the design was described inreference [1]. The front end consists of a mask,
absorber and four-quadrant slit. The acceptanceangles are 2.2 mrad horizontally and 2.4 mrad
vertically. The first mirror, the switching mirror, isspherical with a radius of curvature of 312,400 mm.
The center of the first mirror is located 8,174 mm
downstream from the center of the undulator, andits incident angle is 3. The first mirror is made of
Si and its surface is coated with Pt. The induced
undulator light is reflected by this mirror andpropagates outside the protective wall as quasiparallel light.
Undulator light reflected by the first mirror
reaches the MLM monochromator, located 7,100
mm downstream from the center of the first mirror,
through a four-quadrant slit and differential
pumping vessel 1. As described in the introduction,
we installed a new MLM monochromator that canoperate in a high vacuum. This monochromator,
MKZ-7NS (Kohzu Precision Co. Ltd.), is controlledwith integrated computing, in which mechanicallyindependent axes are programmatically controlled
for keeping a fixed exit position. The Bragg angle
can be varied from 9 to 65°. The beam offset of themonochromator is precisely 15 mm. This design
reduces the convolution of mechanical errors, andthe control mechanism is very compact. Threedifferent pairs of mirrors can be selected and they
can be exchanged without exposing themonochromator to the atmosphere. The details of

21

the monochromator were reported by. Okui et al.
[4].
A filter chamber and differential pumping
vessel 2 are downstream of the MLM
monochromator. The undulator light through afilter is introduced into the reaction chamber. A
four-quadrant beam-forming slit is placed in frontof the reaction chamber. The irradiation point of
the sample in the reaction chamber is located at
11,927 mm downstream from the center of the firstmirror. The reaction chamber has a load-locksystem, and samples can be placed at theirradiation position without exposing the chamberto the atmosphere. The plane size of the sample
holder is 70 mm long  25 mm wide, and both sidesof the sample holder can be used. The beam spotat the irradiation point is about 25 mm square. The
intensity of light is made almost homogeneous in
a 20 mm square around the center by checking
with a 3-mm-square photoelectric board.
3. Experimental Setup and Results
The photon flux at the irradiation point wasmeasured with a photodiode (PD), AUXV100(International Radiation Detectors Inc.), whoselight-receiving area was 10 mm square. The PD
was placed about 205 mm downstream from theirradiation point in the reaction chamber. To
confirm the linearity of the photocurrent from the
PD against the photon flux, we measured theoutput current of the PD while varying the currentof the storage ring. The output current of the PD
showed good linearity in the range under 1.7 mA.
The data sheet of the AUXV-100 indicates that its
quantum efficiency has a temperature dependenceof 0.045 %/C. The temperature of the PD can beconsidered to depend on the quantity and energyof the irradiated X-rays. Unfortunately, we could
not measure the surface temperature of the PD
directly, because the reaction chamber does nothave a window port for observing the PD’s surface.
Instead, we measured the surface temperature of
a-Si thin film placed at the irradiation point
through a ZnSe window by using an infrared
radiation thermometer (CPA-T400A, Chino Co.).
Under six energies of X-ray irradiation at thestorage ring current of 300 mA, the surface
temperature of the a-Si thin film varied from 20.5
C to 107.5 C. As a result, the error range of thephoton flux due to temperature was estimated to
be within 2 %.

The photon energy of the monochromatic
light of BL07A cannot be determined precisely,
because the installed M LM monochromator has
low resolving power. Instead, we assessed therelationship of the energies of the undulator
harmonics with the gaps of the 3-m undulator at
BL07B, which has a grating monochromator witha high resolving power, and we set the energy of
the MLM monochromator to the peak positions of
the harmonics estimated from this relationship.
3.1. Multi-layered Mirrors and Energy Resolution
Undulator light includes the fundamental
and multiple higher harmonics. To eliminate
undesired undulator harmonics, undulator light ismonochromatized by a combination of an MLM
monochromator and three different metal foils
prepared as filters. Three different MLMs are used
to cover an energy range from 80 to 800 eV. The
MLMs are composed of multi-layered mirrors
made from Mo and Si, Mo and B4C, and Ni and C.
The filters are made from Ag, Cr, and Ni; the film.
Energy resolution was estimated bymeasuring the PD current against the photon
energy of the MLM monochromator. The electronenergy and current of the storage ring were 1.0
GeV and 300 mA, respectively.
The third
harmonics of the undulator light were used withthe undulator gap of 56.2 mm. The Mo/B4C MLM
and Ag filter were used. The resolution, E/E,
estimated from this figure is 7.9 %, which is about
twice the ideal energy resolution calculated fromthe specifications of the MLM. The resolution is
sufficient for picking out a specific harmonic fromother harmonics of the undulator with a certain
gap.
3.2. Photon flux
Photon fluxes in 1.0-GeV and 1.5-GeV
operation mode were estimated as follows. The
photon flux in 1.0-GeV operation mode wascalculated from the PD current measured when
the ring current was 300 mA. The photon flux in
1.5-GeV operation mode was obtained after the PD
current was normalized by the ring current of 300
mA. After normalization, the photon fluxes wereobtained for each irradiation condition, with thequantum yield corresponding to the photon
energy listed in the data sheet for the AUXV-100.
Figures 2 and 3 show the photon fluxes ofmonochromatic SR at the reaction chamber of22

BL07A measured in 1.0-GeV operation mode and
1.5-GeV operation mode. The colors of the dots
indicate the type of MLM used; red dots, green
dots, and blue dots respectively indicate
measurements made with Mo/Si, Mo/B4C andNi/C MLMs. Moreover, the shapes of the dots
correspond to the harmonics of the undulator;
circular, square, triangular, and diamond-shaped
dots correspond to the fundamental, third, fifth,
and seventh harmonics of the undulator light. An
adequate filter corresponding to the energy aslisted in Table 1 was used for each measurement.
The intensity unit of photon flux was defined as
photons/s･cm2. The error range for the photon fluxin these figures was estimated to be 20-30 %.

normalized by ring current of 300 mA. Red dots, green
dots, and blue dots were measured with Mo/Si, Mo/B4C,
and Ni/C MLM pairs, respectively. Circular, square,
triangular, and diamond–shaped dots represent
fundamental, third, fifth and seventh harmonic ofundulator light, respectively.

In the range of 80-200 eV, the photon flux
ranged up to more than 21014 photons/scm2. The
highest photon flux in the range of 125200 eV
was about 41015 photons/scm2. The photon fluxes
monochromatized by the Mo/Si MLM were higher
than those monochromatized by the Mo/B4C MLM
in the range of 125200 eV. The photon fluxes in
the range of 200400 eV were about 21014
photons/scm2.
The
photonfluxesmonochromatized by the Mo/B4C MLM werehigher than those monochromatized by the Ni/C
MLM in the range of 280360 eV, while they were
almost the same value in the range of 360400 eV.
In the range above 400 eV, photon fluxes measured
in 1.5-GeV operation mode were about 1013
photons/scm2. However, those measured in 1.0GeV operation mode were lower than 10 11
photons/scm2. Therefore, the photon-flux-tosample in 1.5-GeV operation mode was clearlymuch higher than that in 1.0-GeV operation modein the energy range higher than 400 eV. The above
results indicate that BL07A can be used to
Figure 2 Photon flux at irradiation point of sample investigate the SR process for monochromatic soft
stage of BL07A in 1.0-GeV operation mode. Ring current X-rays with photon fluxes higher than 1013
was 300 mA. Red dots, green dots, and blue dots were photons/scm2.
In
particular,
irradiation
measured with Mo/Si, Mo/B4C, and Ni/C MLM pairs,
experiments using high-photon fluxes exceeding
respectively. Circular, square, triangular, and diamond1014 photons/scm2 can be performed in the energy
shaped dots represent fundamental, third, fifth andrange of 80400 eV.
seventh harmonic of undulator light, respectively.

References[1] Kanda, K., Haruyama, Y., Fujisawa, M. &Matsui, S. (2001) Nucl. Inst. Meth. A, 467-468, 500503.
[2] For example, Heya, A., Matsuo, N. & Kanda, K.
(2018) Jpn J. Appl. Phys. 57, 116502 1-6.
[3] Heya, A., Kanda, K., Toko, K., Sadoh, T.,
Amano, S., Matsuo, N., Miyamoto, S., Miyao, M. &Mochizuki, T. (2013) Thin Solid Films, 534, 334-340.

Figure 3 Photon flux at irradiation point of sample
stage of BL07A in 1.5-GeV operation mode. Flux was[4] Okui, M., Yato, N., Watanabe, A., Lim, B.,
Murayama, N., Fukushima & S., Kanda, K. (2016)
AIP Conference Proceedings, 1741, 030033.

23

Photon flux density dependence of graphene synthesis
from pentacene-based molecules on Ni film by soft X-ray
irradiation
Akira Heya1, Yoshiki Yamada1, Kazuhiro Kanda2, Ryo Yamasaki3, and Koji Sumitomo1
1

University of Hyogo, 2 LASTI, University of Hyogo, 3 Tocalo Co., Ltd.,

Abstract
Graphene synthesis from pentacene-based molecules on a Ni film/quartz substrate was investigated. A mixture
film consisting of pentacene, 6,13-dihydropentacene, and pentacene oligomers, prepared by hot mesh deposition,
were irradiated with soft X-rays generated in NewSUBARU. The dependence of photon flux density on
graphene synthesis was evaluated to control the size of nanographene and to clarify the polymerization
mechanism. It was found that the high photon flux density is required to synthesis the graphene. In addition, thepolymerization reaction is considered to be promoted by the photoelectron transfer reaction by soft X-ray
excitation and supply of the excited electrons from the Ni underlayer film. In addition, it was suggested that the
supply of excited electrons also affects the orientation of graphene.

already shown in elsewhere [1]. In this study, toadjust the film property of HMD nanocarbon film,
the deposition of nanocarbon film was performed
the WNi(3%) mesh temperatures (Tmesh) were 1410,
1450, and 1480 C. In this case, the ratio of Pn,
DHP, and PO was slightly different [3].
The irradiation of soft X-rays was carried out
at BL07A of NewSUBARU. Schematic diagram ofsoft X-ray irradiation apparatus is shown in Fig. 1.
The light source of BL07A was a 2.28 m undulator.
The storage-ring energy was 1 GeV during thisexperiment. The undulator gap was 56.4 mm. The
photon energy was 300 eV. The storage-ringcurrent and dose were 300 mA and 100 mA h,respectively. To control the photon flux density,
size of slit in storage ring was varied from 0.8×
0.8 to 8.8 × 8.8 mm2. The saturated sample
temperature during irradiation was 80, 530, and
780 ° C for each slit size. Although the photon flux
density was not measured, the ratios of photon flux
density were expected from the saturated sample
temperature to be 1, 8.5, and 12.7, respectively. To
clarify the effect of soft X-ray irradiation, annealed
samples were prepared at 3 Pa and 780 ° C for 20
min.
The changes in molecular structure by soft
X-ray irradiation was evaluated by Raman
spectroscopy and X-ray diffraction (XRD)
measurements.

Introduction
Nanographenes are attractive two-dimensional
materials consisting of carbon atoms arranged in ahexagonal lattice. The graphene nanoribbons(GNRs) have band gaps that depend on the ribbon
width. Therefore, GNRs are expected to be used in
next-generation semiconductor devices as part oflogical elements, transistors, spin transistors, andgas sensors.
We have investigated the fabrication method of
GNRs using pentacene (Pn), H2 gas, and W mesh.
This method is named as hot mesh deposition(HMD) [1]. By using a nanocarbon film including
PO prepared on a Ni film/quartz substrate using a
WNi(3%) mesh prepared by HMD, graphene wasproduced by soft X-ray irradiation [2]. It was
found that the hydrogen desorption and thecatalytic effect of the Ni film excited by soft X-ray
irradiation assists in pentacene polymerization.
However, to obtain GNRs, the issue of
optimization the conditions for PO formation andsoft X-ray irradiation remained.
In this study, we tried to optimize thenanocarbon precursor film and soft X-ray
irradiation condition.
Experimental
A W mesh (10×55 mm2) with a wire diameterof 0.1 mm and 30 holes/inch was used. Ni particles
were supported on the W mesh surface with anatmospheric plasma spray. A mixture of Ar and H2
was used as the plasma generation gas. The plasma
power was 38.5 kW. The Ni was supported on both
faces. The W mesh with supported Ni area ratios
of 3% (WNi(3%)) was prepared.
The HMD apparatus and typical condition are

Results and discussion
The Raman spectra of the nanocarbon film
prepared by HMD before and after soft X-ray
irradiation are shown in Fig. 2. The broad peaks of
D and G bands were observed in nanocarbon films
prepared at small and medium slit sizes after soft24

References[1] A. Heya, N. Matsuo, Jpn. J. Appl. Phys. 57(2018) 04FL03.
[2] A. Heya, T. Oonuki, R. Utimi, K. Kanda, R.
Yamasaki, K. Sumitomo, Thin Solid Films 713(2020) 138365.
[3] A. Heya, R. Yamasaki, N. Matsuo, Thin Solid
Films 685 (2019) 186.
[4] A. Shiotari, T. Kumagai, M. Wolf, J. Phys.
Chem. C 118 (2014) 11806.

X-ray irradiation. On the other hand, the sharp
peak of D and G bands were observed undercondition of large slit size and thermal treatment. It
is considered that nanographene was obtained
under high photon density and high temperature
heat treatment irradiation conditions andamorphous (or contains fine graphite pieces)carbon film was formed under low photon density(small, medium) conditions.
The XRD patterns of the nanocarbon films
consisting of Pn, DHP, and PO before and after
soft X-ray irradiation are shown in Fig. 3. In thecases of low photon flux densities (small andmedium), the diffraction peak was not observed.
The X-ray diffraction peak due to graphite (002)
was observed in all soft X-ray irradiated sample at26.5. However, in thermal treated sample, the
X-ray diffraction peak due to graphite (002) was
only obtained in the nanocarbon film prepared at a
Tmesh of 1450 C. The effect of soft X-ray
irradiation on graphene orientation was indicated.
Our aim is GNR synthesis. However, from theRaman spectra and XRD patterns, we obtained not
GNR but graphene using soft X-ray irradiation
with high photon flux density. To control
polymerization, the effects of soft X-ray irradiation
on polymerization are discussed. For soft X-ray
irradiation, the film property dependence ofnanocarbon precursor film was not observed in therange of 1410 and 1480 C. On the other hand, inthermal treatment, the crystal orientation wasdepended on nanocarbon precursor film. It implies
that the effects of soft X-ray irradiation such as
electron excitation and enhancement of molecular
movement and photoelectron transfer reaction [4]are useful to obtain high quality GNR.

80 ℃
0.8×0.8 mm2 （Small）
Sample holder
530 ℃
2.0×2.0 mm2 （Medium）
780 ℃
Metal plate
8.8×8.8 mm2 （Large）
Ceramic bond TC
SNSNS
NSNSN
Electron

Soft X-ray
45°

SNSNS
N S N S N Slit
7×7 mm2
76 mm ×29 cycles View port (ZnSe)
Undulator source

Pyrometer

Vacuum chamber

Sample: HMD nanocarbon/Ni/quartz substrate

Fig. 1. Schematic diagram of soft X-ray
irradiation apparatus.
Tmesh=1450℃

Tmesh=1480℃

As-dep.

G

G

D

Medium(530℃)

Large(780℃)

Soft X-ray

D’ Thermal treatment

D’

Small
(80℃)

G

D

Intensity (arb. units)D

Intensity (arb. units)

Intensity (arb. units)

Tmesh=1410℃

D’(780℃)

1000 1200 1400 1600 1800 2000 1000 1200 1400 1600 1800 2000 1000 1200 1400 1600 1800 2000

Raman shift (cm-1)

Raman shift (cm-1)

Raman shift (cm-1)

Fig. 2. Raman spectra of nanocarbon films
consisting of Pn, DHP, and PO before andafter soft X-ray irradiation.

Conclusions
1) Amorphous (or containing fine graphite
pieces) carbon film was produced under low
photon density conditions (Small, Medium), andnanographene was produced under high photon
density conditions (Large) and high temperaturethermal treatment.
2) The structure of the carbon film prepared bysoft X-ray irradiation did not depend on the HMD
precursor film. On the other hand, the orientationof the nanographene film produced by thermal
treatment depended on the HMD precursor film.
3)The polymerization reaction is considered to
be promoted by the photoelectron transfer reaction
by soft X-ray excitation and the supply of excitedelectrons from the Ni film, and it was suggested
that the supply of excited electrons also affects theorientation of graphene.

Tmesh=1410℃

Tmesh=1450℃

Ni (111)Tmesh=1480℃

Intensity (arb. units)

Graphite (002)
Ni (200)

Intensity (arb. units)

Intensity (arb. units)As-dep.

Small（80 ℃）
Medium（530 ℃）
Large（780 ℃）

Soft X-ray
Thermal treatment (780 ℃)

10 20 30 40 50 60
2Θ (degree)

10 20 30 40 50 60
2Θ (degree)

10 20 30 40 50 60
2Θ (degree)

Fig. 3. XRD patterns of nanocarbon films
consisting of Pn, DHP, and PO before andafter soft X-ray irradiation.

25

Effect of soft X-ray irradiation on film properties of ahydrogenated Si containing DLC film
Kazuhiro Kanda 1, Ryo Imai 1, Shotaro Tanaka 1, Shuto Suzuki 1, Masahito Niibe 1, Takayuki Hasegawa 1,
Tsuneo Suzuki 2, and Hiroki Akasaka 3
1 LASTI, University of Hyogo, 3-1-2 Koto, Kamigori, Hyogo, Japan
2 Energy-Density Research Institute, Nagaoka University of Technology, 1603-1 Kamitomioka-machi,
Nagaoka, Niigata, Japan
3 School of Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, Japan

Abstract

The effect of soft X-ray irradiation on hydrogenated silicon-containing diamond-like carbon (SiDLC) films intended for outer-space applications was investigated by using synchrotron radiation(SR). We found that the decrease in film thickness was about 60 nm after 1600-mAh SR exposure,
whereas there was little change in their elemental composition. The decrease in volume wasattributable to photoetching caused by SR, unlike desorption of hydrogen in the case of exposure ofhydrogenated DLC (H-DLC) film to soft X-rays. The sp2/(sp2+sp3) ratio of the C atoms in thehydrogenated Si-DLC films increased rapidly from 0.2 to 0.5 for SR doses less than 20 mAh. SR
exposure significantly changed the local structure of carbon atoms near the surface of thehydrogenated Si-DLC film. The rate of volume reduction in the irradiated hydrogenated Si-DLC
film was 80 times less than that of the H-DLC film. Doping DLC film with Si thus suppresses thevolume reduction caused by exposure to soft X-rays.

1. In
ntroduction
To investigate the effects of the soft X-ray
irradiation inside and on the surface of thehydrogenated Si-DLC films and the influenceof Si atoms on these effects, we exposedhydrogenated Si-DLC films to SR in the soft
X-ray region in a dose region from 0 to 3000mAh and discussed on the local structure ofcarbon and silicon atoms on the basis of the C
K-edge, Si K-edge, and Si L-edge near-edge Xray absorption fine structure (NEXAFS)
spectra. In addition, we measured various
film properties depending on the SR dose as
follows. 1) Film thickness, from which thedecrease in film volume can be estimated,
was measured with a stylus profiler, SEM
and XRR. 2) Film density was estimated bymakingX-rayreflection-measurements(XRR). 3) Elemental composition of thehydrogenated Si-DLC film was evaluated by
a combination of elastic recoil detection
analysis(ERDA)
andRutherford
backscattering spectrometry (RBS). 4)
Surface composition of the hydrogenated SiDLC film was observed by X-ray
photoelectron spectroscopy (XPS).

chemical vapor deposition method (Nippon
ITF Co.). The observed thickness of the asdeposited hydrogenated Si-DLC film was 522
nm using a scanning electron microscope(SEM).
The irradiation of the hydrogenated SiDLC films by soft X-rays was carried out at
BL06. The SR at the irradiation point had acontinuous spectrum from the infrared to soft
X-ray region (less than 1 keV). During theexposure of the hydrogenated Si-DLC films to
the soft X-rays, the sample holder was
confirmed to be room temperature. In addition,
the temperature of the sample holder could beraised to 150 degrees Celsius by using a heater.
To discuss the variations in the local
structure of the hydrogenated Si-DLC film
due to exposure to SR, the C-K edge, Si-K
edge, and Si-L edge NEXAFS spectra were
measured. The C K edge and Si L edgemeasurements were performed at BL09A,
which has grating monochromator. The
NEXAFS measurement of the Si K absorption
was performed at BL05A, which has a double
crystal monochromator. In the measurement
at both beamlines, the irradiation angle atthe sample was the “magic angle” of 54.7°
with respect to the surface. The electrons
coming from the sample were detected in total
electron yield (TEY) mode.

2. Materials and Methods
Hydrogenated Si-DLC film was deposited
on a Si wafer by using an amplitudemodulated radio-frequency plasma-enhanced26

irradiation were classified as type 3. That is,the σ* peak was narrower than that of typical
DLC film and shifted to the lower energy of5 eV, due to the influence of the peak at 289
eV derived from the 1sσ*(C-Si) transition.
In addition, the peak intensity of the 1sπ*transition at 285.4 eV was weak.

3. Results
The C-K edge NEXAFS spectra of thehydrogenated Si-DLC film before and after
SR irradiation are depicted in Figure 1
together with that of -SiC powder andtypical commercial DLC film.

The features of the C K-edge NEXAFS
spectra of hydrogenated Si-DLC film greatly
varied between before and after irradiation
by soft X-rays. The peak intensity of the1sπ* transition at 285.4 eV increased withan SR dose of 15 mAh and it increased gently
with an SR dose more than 15 mAh. The σ*peak became broader and the intensity peakshifted to a higher energy. In other words, theC K-edge NEXAFS spectra of thehydrogenated Si-DLC films changed fromtype 3 to type 1 or 2. As a result, the spectralfeatures of the hydrogenated Si-DLC film
after SR exposure of more than 320 mAhresembled that of typical DLC film consisting
only of carbon and hydrogen without silicon.
The C atoms in the DLC films consist of
hybridization
carbonandsp3
sp2
hybridization carbon. The sp2/sp3 ratio haveis considered to be a structural parameterthat characterizes DLC film properties. The
absolute sp2/(sp2+sp3) ratio of carbon atoms in
the DLC film can be accurately determinedfrom the C K-edge NEXAFS spectra, as
described in Ref. 2. The SR-dose dependenceof the sp2/(sp2+sp3) ratio in the hydrogenated
Si-DLC film is plotted in Figure 2. The
amount of sp2 bonded carbon atoms can be
determined by normalizing the area of theresonance corresponding to the 1sπ*transitions at 285.4 eV with a large section of
the spectrum. The absolute sp2/(sp2+sp3) ratio
was determined by comparing the normalized1sπ* area from the sample with that fromthe NEXAFS spectrum of highly orderedpyrolytic graphite (HOPG) as a standard
sample. The sp2/(sp2+sp3) ratio of thehydrogenated Si-DLC film before irradiation(open circle) was 0.23, which indicated thatsp3 hybridized carbon was a major componentof the hydrogenated Si-DLC film. The
sp2/(sp2+sp3) ratio increased rapidly to 0.5
for SR doses less than 20 mAh. At doses morethan 20 mAh, the sp2/(sp2+sp3) ratio
remained approximately constant at 0.5.

Figure 1. Dependence of C K-edge
NEXAFS spectra of hydrogenated Si-DLC
films on SR dose, together with those of -SiC
powder, and IP-DLC film.
The sharp π* peak observed at 285.4 eV
is ascribed to the C 1sπ* resonancetransition originating from the carbon-carbon
double bond. The broad σ* peak observed atabout 285-310 eV is ascribed to the C1sσ*resonance transition. The C K-edge NEXAFS
spectra of the Si-DLC films were classified
into four types according to silicon content [1].
The C K-edge NEXAFS spectra of thehydrogenated Si-DLC films before SR

27

deoxidization of SiO2. These results meanthat an oxidized Si layer was generated at thesurface of the hydrogenated Si-DLC film byoxidation of surface Si atoms with residual
oxygen in the vacuum chamber due to SR
irradiation. The oxidized Si layer was
deoxidized by additional exposure to soft Xrays. On the other hand, the SR exposure did
not change the positions of the absorption
edge and the white line. Therefore, thechemical environment around the Si atoms in
the hydrogenated Si-DLC film was notchanged by the SR irradiation.

Figure 2. Dependence of sp2 / (sp2 + sp3) ratio
in hydrogenated Si-DLC film on SR dose. The
open circle indicates sp2 / (sp2 + sp3) ratio ofhydrogenated Si-DLC film before SR
irradiation.
The Si K-edge NEXAFS spectra of thehydrogenated Si-DLC film before after
irradiation are depicted in Figure 3 together
those of reference materials, SiO2 powder, Siwafer, -SiC powder and amorphoushydrogenated silicon (a-Si:H) film. In the
spectra of the Si wafer and a-Si:H film, peaks
from SiO2 due to native oxidation wereobserved at 1846.8 eV. Si atoms in thehydrogenated Si-DLC film can be expected tohave Si, C, H, and/or O as neighboring atoms.
The chemical environment around theabsorbing atom can be evaluated from thepositions of the absorption edge and the whiteline in the NEXAFS spectrum. The Si K-edge
shifts towards the higher energy side withincreasing positive charge on the Si atom. Theedge from the hydrogenated Si-DLC film
before irradiation was at 1840 eV, i.e., nearthose of the Si wafer and a-Si:H film. The
white line was observed about 3 eV above theabsorption edge, which resembled those of the
Si wafer and a-Si:H film. These results
indicate that the chemical environment of Si
atoms in the hydrogenated Si-DLC film issimilar to that in the Si wafer and a-Si:H film.
After SR irradiation, a peak at 1846.8 eV,
which was derived from SiO2, appeared in the
NEXAFS spectra of the Si-DLC films. The
intensity reached a maximum at 800 mAhand decreased beyond 1000 mAh. On theother hand, the intensity increased in theenergy range about 1843-1846 eV. The peakin this energy range was reported to be due to

Figure 3. Dependence of Si K-edge NEXAFS
spectra of hydrogenated Si-DLC films on SR
dose, together with those of SiO2 powder, Siwafer, -SiC powder and a-Si:H film.

28

Development of a new -beam source by X-ray Compton
scattering
Norihito Muramatsu1, Shinsuke Suzuki2, Haruo Ohkuma3, Schin Daté3, Kazuhiro Kanda4, Shuji Miyamoto4,
Tetsuo Harada4, Takeo Watanabe4, Hajime Shimizu1, Manabu Miyabe1, Atsushi Tokiyasu1, Masahiro Okabe1
1
ELPH, Tohoku University, 2 JASRI/SPring-8, 3 RCNP, Osaka University, 4 LASTI, University of Hyogo

Abstract

We are developing new techniques to produce a high energy -beam via Compton scattering of soft
X-rays from 1 or 1.5 GeV electrons at NewSUBARU. The X-rays of 92 eV are obtained from theshort undulator at BL07A and reflected backwardly into the storage ring by using a Mo/Si
multi-layer mirror. We performed basic tests of the X-ray mirror in terms of surface condition, heatload, and reflection.

Introduction
We aim to develop and demonstrate a
new method to produce a high energy
-beam via Compton scattering of X-rays
at an electron storage ring. In our project[1], soft X-rays of 92eV are obtained froma short undulator (total length: 2.28 m,
period length: 7.6cm) installed to BL07 at
NewSUBARU, and backwardly reflected
into the storage ring by using a Mo/Si
multi-layer mirror. This method increases
the maximum energy of a produced -beam
up to 0.58 and 1.02 GeV for the electron
beam energy of 1 and 1.5 GeV, respectively.
These maximum energies are much higher
than that of laser Compton scattering,which is usually adopted all over theworld.
We have set up a large mirror chamberat BL07A [2] to place the Mo/Si multi-layer
mirror with automatic stepping-motor
stages in a vacuum of 10−6 Pa. An initial
version of the mirror is put on an
oxygen-free copper holder with watercooling. In addition, we have installed an
X-ray wire scanner and gamma detectors[3]. The wire scanner measures profiles
and intensities of both radiated andreflected X-ray beams, while the gamma
detectors are used to get a rate, profile,and energy spectrum of the -beam. This
report describes results of basic tests forthe installed multi-layer mirror in terms of
surface condition, heat load, and X-ray
reflection.
Examination of surface condition
A substrate of the Mo/Si multi-layer

mirror is made of a low thermal expansion
glass ceramic (Zerodur) with an area of 50
×50 mm2 and a thickness of 5 mm. Its
reflective surface is cylindrically polishedto make a focus on the electron beam at
the 16.7-m upstream straight section of
the storage ring. This cylindrical surface
was made by bending the substrate withapplication of stress at two edges, thenpolishing a surface flatly, and finallyreleasing the stress [4]. A curvature radiusof the cylindrical surface, corresponding to
the focal length of 16.7 m, was confirmedby measuring a depth of the mirror centerand alternatively counting the number of
Newton fringes. The reflective surface wascoated by Mo/Si multi-layers with 50
periodic repetitions.
We examined the surface condition of amirror substrate after polishing. The
measurement was done at National
Metrology Institute of Japan, which is a
research center of AIST. Figure 1(a) showsa result of surface roughness obtained fora region of 2×2 m2 by using an atomic
force microscope (AFM). The RMS value of
surface roughness was measured to be
0.990.46 nm without anisotropy. It was
confirmed that the surface roughness of
our multi-layer mirror is moderately goodfor the reflection of 92-eV X-rays (=13.5nm). Simultaneously, we measured surface
accuracy in the central region of 40 ×40
mm2 by using an ultrahigh accurate 3D
profilometer. As shown in Fig.1(b), a
cylindrical surface is clearly formed evenby using the unique method mentioned29

4. Discussion
The effect of soft X-rays irradiatinghydrogenated Si-DLC films was investigatedfor dose ranges up to 3000 mAh. The
thickness (film volume) of hydrogenated SiDLC film decreased after the exposure tocontinuous soft X-rays up to 1000 eV.
However, the rate of decrease in film
thickness of the hydrogenated Si-DLC film
was much smaller than that of the H-DLC
film. The density of the hydrogenated Si-DLC
film rose a little as a result of the exposure tosoft X-rays. The elemental composition (H, C,
and Si) of the hydrogenated Si-DLC film,
which was estimated from the ERDA/RBS
study, did not significantly change as a resultof the exposure. In addition, no significant
change occurred in the surface elemental
composition (C, Si, and O) in the XPS
measurement. On the other hand, C K-edge
NEXAFS measurements showed that soft Xray exposure significantly changed the local
structure of the C atoms, while the Si K-edge
and Si L-edge NEXAFS measurements
showed no significant.
From these experimental results, thereason why the rate of decrease in film
thickness of hydrogenated Si-DLC film ismuch smaller than that of H-DLC film is
ascribable to the process of the decrease infilm thickness. The dominant process in the
exposure of H-DLC film to the soft X-rays isshrinkage of the film by desorption ofhydrogen from inside the film. These changes
in the C-K edge NEXAFS spectra are believed
to correspond to hydrogen desorption fromthe film. As described in ref. 3, hydrogencontent in H-DLC films decreases from 50 to30% due to 200-mAh SR exposure. On theother hand, in the exposure of thehydrogenated Si-DLC film to soft X-rays,
hydrogen does not desorb from the interior of
the film. In this case, the dominant process ofthe decrease in thickness is photoetching,which is much slower than the shrinkage due
to desorption of hydrogen. This photoetchingprocess is not one in which the activationenergy determines the reaction rate, because
the rate of decrease in film thickness does notchange when the substrate temperature rises.
In other words, this photoetching does notproceed through a temperature rise in a local
area due to exposure to SR, but rather

30

through direct inner shell excitation of the C
and Si atoms in the hydrogenated Si-DLC
film by the soft X-rays.
Soft X-rays caused reactions several nm
from the surface of the hydrogenated Si-DLC
film. In the C K-edge NEXAFS spectra, theintensity of the 1sπ* transitions at 285.4 eV
increased and the peak of the 1s*transition shifted with increasing SR dose to
the high energy side in the dose range lessthan 20 mAh. The shift of the peak of 1s*transition was ascribable to the decrease in C
atoms coupling with Si and H atoms. The
sp2/(sp2+sp3) ratio of the C atoms increased
from 0.23 to 0.5 the dose range up to 20 mAh.
An increase in the sp2/(sp2+sp3) ratio due toirradiation by soft X-rays was also observedin the irradiated H-DLC film, and thisincrease was concluded to occur throughformation of C-C double bonds induced by the
coupling between C atoms through desorptionof hydrogen [4].
As described above, it was found that thevolume change of the hydrogenated DLC film
due to soft X-ray irradiation was suppressedby silicon doping into film. This is attributed
to the suppression of hydrogen desorption
from the film. We think that the mechanismof the suppression of hydrogen desorption bysilicon doping may be as follows: (1) Si atoms
on the surface of the hydrogenated Si-DLC
film are spontaneously oxidized to siliconoxide, which suppresses hydrogen desorption
from inside the film. (2) Soft X-ray irradiation
desorbs hydrogen from the film near thesurface, increasing the concentration of Si
atoms in the surface vicinity, which oxidizes
in the same way as (1), and the silicon oxide
layer suppresses hydrogen desorption. (3)Soft X-ray irradiation desorbs hydrogen fromthe film near the surface, forming the C-Si
network in the surface vicinity, which
suppresses hydrogen desorption.
Reference
1) K. Kanda et al., Jpn. J. Appl. Phys. 2013,
52, 095504.
2) K. Kanda et al., Jpn. J. Appl. Phys. 2002,
41, 4295–4298.
3) K. Kanda et al., Jpn. J. Appl. Phys. 2011,
50, 055801.
4) K. Kanda et al., Sensor Mater. 2017, 29,817-826.

Figure 1 (a) Mirror surface roughness measured by an atomic force microscope in an area of
2×2 m2. (b) Mirror surface accuracy measured by an ultrahigh accurate 3D profilometer inan area of 40 ×40 mm2.
above. A mean curvature radius wasmeasured to be 14.380.06 m, which was
shorter than the design value.

BL07A.
Figure 2 shows a result of temperaturechange when X-rays are incident on the
mirror in a region of 10 ×10 mm2 with theHeat load test with X-ray irradiation
undulator setting where a component of 92
The heat resistant temperature of aeV is peaked as the third harmonics of
Mo/Si multi-layer mirror is known to beradiation. The mirror temperature wasobtained by using a radiation thermometer
300C. In addition, high heat load may
result in the distortion of a mirror surface,thorough a ZnSe window, which was newly
although we adopted a low thermal
attached to the mirror chamber for
expansion glass ceramic as a mirror
infrared transmission. In Fig.2, X-rays
were irradiated for the first 70 minutes. A
substrate. Therefore, we seriously tested
temperature of the whole mirror increased
heat load by X-ray irradiation on themulti-layer mirror that was installed at
by about 100C in two minutes andreached 190C at maximum.
After stopping the irradiation of
X-rays, the mirror temperature
gradually dropped over 100
minutes by thermal radiation.
We have also confirmed thatwater cooling of the mirror
holder was not effective becauseof bad heat conductance.
Expected heat load wasestimated to be a few Watt by
taking into account higher
harmonic radiation that was notreflected. Nevertheless, bad heatcontact of the multi-layer mirror
in a vacuum causes a rapid
increase of its temperature. We
confirmed that the maximum
Figure 2 Temperature change of the Mo/Si multi- temperature was lower than thelayer mirror with the irradiation of X-rays in an area of heat resistant temperature of
10 ×10 mm2. The irradiation was stopped after 70 Mo/Si multi-layer coating.
minutes.

31

X-ray reflection test at BL07A
We further tested the performanceof the installed Mo/Si multi-layer
mirror. As described above, profiles
and intensities of radiated andreflected X-rays can be monitored byusing the wire scanner where micro
current due to a photoelectric effect is
detected with wire position shift.
Figure 3 shows a result of verticalscanning with a horizontal wire. The
profile of reflected X-rays is clearlyseen beside a large peak of undulatorradiated X-rays, which contains highharmonic radiation other than a 92 eVcomponent. In this measurement, anelevation angle of the Mo/Si multilayer mirror was upwardly shifted sothat the reflected X-ray profile should Figure 3 Vertical profiles of radiated and reflected
not overlap with the incident X-rays. X-rays, obtained by the wire scanner that measures a
A position of the reflected profile micro current with the shift of wire position.
moves depending on the mirror angles,
layer mirror by introducing a silicon
and adjustment of the reflected X-ray axis
substrate and a thermal contact sheet for
can be done based on the relation between
better heat conductance to the waterthe profile position and the angle setting.
cooled mirror holder. We also expect an
improvement of surface distortion, caused
Prospect of our project
We are going to demonstrate theby heat load. We are simultaneously
considering fluid polishing to achieve
production of a high energy -beam via
better surface roughness and accuracy. We
Compton scattering of soft X-rays fromaim for the surface roughness of 0.5 nm inelectrons in the storage ring, for the first
RMS. Our development of a new -beamtime. At an initial stage of production tests,
we will use the installed cylindrical mirror
source will be helpful for next-generation
whose substrate is made of a low thermal
researches of hadron photoproduction
expansion glass ceramic. In addition, we
experiments.
will continue the development of a multiAcknowledgments
This research was supported in part by Grant-in-Aid for Challenging Research(Pioneering) No. 18H05325/20K20344.
References[1]. http://www.rcnp.osaka-u.ac.jp/~mura/kaitaku/[2]. “Performance of BL07A at NewSUBARU with installation of a new multi-layeredmirror monochromator”, Shotaro Tanaka, Shuto Suzuki, Tomohiro Mishima andKazuhiro Kanda, J. Synchrotron Rad. 28, 618, 2021.
[3]. “Experimental studies to produce a high energy photon beam by inverse Compton
scattering of soft X-rays”, Norihito Muramatsu et al., LASTI Annual Report Vol.21 (2019),
39, 2020.
[4]. “Development of a High Energy Gamma-ray Beam via Inverse Compton Scattering ofSoft X-rays”, Norihito Muramatsu et al., J. Particle Accelerator Society of Japan Vol.16
No.3, 154, 2019.

32

In-situ Evaluation of Surface Cleaning Methodwith Atomic Hydrogen

Masahito Niibe1,2, Akira Heya2 and Seigo Ito2
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
2
Department of Materials and Synchrotron Radiation Engineering, University of Hyogo
1

Abstract
An atomic hydrogen (AH) irradiation device was introduced at the beamline BL-09A of the
NewSUBARU synchrotron radiation facility for the purpose of cleaning the surface of monoatomic
layer films and reducing surface oxidation of samples. In order to evaluate its performance, themonatomic layer carbon film and the native metal oxide films were irradiated with AH, and thechange in surface state was evaluated with in-situ soft X-ray absorption spectroscopy. Hydrocarbonbased contaminants and oxides could be removed to some extent by irradiation with AH. However,even with long-term AH irradiation, the contaminants could not be completely removed. In the future,
it will be necessary to study under conditions where the sample temperature is raised and the reaction
rate is increased.
Introduction
Since the existence of Dirac fermions ingraphene was pointed out by A. Geim and K.
Novoselov [1], many studies have been conducted
on various Van der Waals two-dimensional (2D)
layered materials in terms of both basic physicalproperties and applications [2]. In the longundulator beamline, BL-09A, of NewSUBARU
synchrotron radiation (SR) facility, we have been
evaluating those substances of 2D layeredmaterials mainly composed of light elements, suchas monoatomic layer h-BN thin film [3],monoatomic layer graphene [4], monoatomic layerboron
hydride[5],
several-atomlayermolybdenum disulfide, and graphene film
synthesized from pentacene [6], etc., with X-ray
absorption spectroscopy (XAS) and X-ray
emission spectroscopy (XES) in the soft X-ray
region.
These 2D layered materials may sometimes be
synthesized in an ultra-high vacuum and evaluatedfor their physical properties as they are, without
exposing it to the atmosphere. In another case, they
may be synthesized and evaluated in different
devices. In the latter case, there is a common
phenomenon that the surface is oxidized orcontaminants are deposited due to atmosphericexposure of the sample or long-term storage in the
air. However, since the 2D layered material is amonoatomic layer or a few atomic layers, its
physical properties are greatly affected by thecontaminations. An Ar ion beam etching or the likehas often been used as a method for cleaning
contaminants on the surface. But this method
causes great damage (crystal structuraldeformation) to 2D substances, so it is not
appropriate to use the ion etching method as in thecase of bulk materials.

On the other hand, we have been using atomic
hydrogen (AH) generated when hydrogen gas isbrought into contact with a high temperature metal(W, etc.) heated to about 1700 °C or higher toremove contaminants deposited on mirrors for SR
beamline [7,8]. Since AH is a radical itself, it ischemically active, and the momentum of theparticles is small. Therefore, it is expected that the
problem of crystal structural deformation can begreatly reduced. In this study, in order toinvestigate the surface cleaning effect of AH froma more microscopic point of view, the AH
generator was directly attached to the SR analysis
chamber, and the surface changes before and after
AH irradiation were observed in-situ using XAS
technique.
Experimental Apparatus and Methods
The AH generator is a commercially available
device called "H-flux" (tectra, Germany), whichheats a W-made capillary with an electron
bombardment and passes H2 gas through thecapillary to obtain AH [9]. The overview
photograph is shown in Fig.1. Since the hightemperature AH source is surrounded by a watercooled Cu plate, heat is less dissipated to thesurroundings. The connection to the processing
chamber is made with an ICF-70 flange. This
device was attached to the BL-09A analysis
chamber of the NewSUBARU SR facility at the
University of Hyogo to enable AH irradiation ofsamples and evaluating with in-situ soft X-ray
absorption spectroscopy. Evaluation samples
include HOPG, single-layer and multi-layer
graphene stored in the air for a long time, diamondpowder, contaminated Au plates, various metaloxide films, and the like.

33

The generation of AH was confirmed byirradiating the tungsten oxide powder, WO3, forseveral minutes. An electron bombardment with
1000 V, 40 mA was applied to the heating
mechanism of the H-flex device to heat thetungsten capillary. Although the capillarytemperature was not calibrated, but it wasestimated to be around 1800 °C under standard
operating conditions. Hydrogen gas was flowed
inside the capillary at the gas pressure of 0.013 Pa,
and the generated atomic hydrogen was irradiatedon the WO3 powder. The results are shown in Fig.
2. As can be seen in the figure, the color of the WO3
powder not irradiated with AH was yellowish
green, whereas the powder after AH irradiation
changed to black. This is because the metal W is
produced by the reduction reaction. In this AH
irradiation experiment, the sample temperature is
not particularly controlled, and it is considered thatthe temperature rise due to the radiant heat fromthe H-flux device is small.

Fig. 2 Confirmation of atomic hydrogengeneration by AH irradiation on WO3 powder.
Left: before AH irradiation and right: after AH
irradiation.

Monolayer graphene_AH-irrad_2~5min_35deg.
1.2

before AH irrad.

1

Normalized absorption [a.u.]

Fig. 1
Photograph of the atomic
hydrogen generation equipment (H-flux).

AH irradiation to samples and results ofevaluation with AXS measurement
Figure 3 shows the soft X-ray absorption
spectra at the C-K edge before and after AH
treatment of single-layer graphene stored in theatmosphere. The spectra show two peaks
overlapping at the photon energy of 287.7 eV and
288.5 eV, in addition to the π* peak at 285.4 eV
and the broad σ* peak above 292 eV as seen ingraphite samples. These are identified as chemical
species with a double bond with oxygen, theformer being considered to be an oxide with acarbonyl group C=O and the latter being an oxidewith a carboxyl group COOH [10]. When thesample is irradiated with AH, the oxide peakdecreases and the π* peak increases slightly after 2
min of irradiation. However, even if the irradiation
time was further extended to 5 min, the spectral
shape did not change much. This is common toother carbon films, and it is thought that physicallyadsorbed contaminants can be easily removed by
AH irradiation, but strongly chemically adsorbed
oxides may be difficult to remove. Further
optimization of processing conditions is requiredin the future.

0.8

0.6

0.4

after AH 5minafter AH 2min

0.2

0

-0.2

280

290

300

310

Photon energy [eV]Fig. 3 Soft X-ray absorption spectra ofmono-layer graphene at C K-edge before
and after AH irradiation.

Figure 4 shows the CK absorption edge spectra
before and after AH irradiation of the hydrocarbon
contaminants deposited on an Au plate. In this caseas well, the peak of 288.8 eV decreased by AH
irradiation, but the π* peak of 285.2 eV increased.
Moreover, the contaminants containing C could
not be completely removed by AH irradiation for
10 min.

34

18706 (2014).
[11] M. Yamamoto et al., Jpn. J. Appl. Phys. 48,
026503 (2009).

Au-plate surface_AH_10min_35deg.
1.4

before AH irrad.
Oxidized Al film _before-after H-flux_1000V_40mA_10min

1
1.4

0.8

Absorption intensity (arb. units)

Absorption intensity [a.u.]

1.2

after AH irrad.
0.6

0.4

0.2

0

280

290

300

310

Photon energy [eV]Fig. 4 Soft X-ray absorption spectra ofcontamination on Au-plate at C K-edge
before and after AH irradiation.

1.2

1

0.8

0.6

before AH irrad.

0.4

after AH irrad.
0.2

0

520

530

540

550

560

570

Photon energy (eV)Oxidized Ni film_before-after H-flux 1100V_45mA_10min

Figure 5 shows the absorption spectra of thenative oxide films of Al and Ni metals before andafter AH irradiation (displayed withoutnormalized). After AH irradiation, the intensity of
OK absorption decreased, and it is presumed thatoxide reduction occurred. Aluminum is considered
to have a strong bond with oxygen, and it was
found that the metal oxide can be reduced to someextent even in such a case. It has been reported thatthe sample temperature is also related to the AH
treatment [11]. In the future, we will compare andexamine the changes with AH irradiation when thesample temperature is further raised and thereaction rate is increased.

1

Absorption intensity [a.u.]

0.8

0.6

before AH irrad.
0.4

after AH irrad.
0.2

0

520

530

540

550

560

570

Photon energy [eV]Fig. 5 Soft X-ray absorption spectra of
Al (upper) and Ni (lower) native oxide
film at O K-edge before and after AH
irradiation.

References[1] K. S. Novoselov et al., Nature, 438, 197 (2005).
[2] Monatomic Two-Dimensional Layers: Modern
Experimental Approaches for Structure, Properties,
and Industrial Use, edited by I. Matsuda (Elsevier,2018).
[3] S. Suzuki, Y. Haruyama, M. Niibe et al., Mater.
Res. Express, 6, 016304 (2019).
[4] M. Niibe, S. Suzuki, S. Honda, The 66th JSAP
Spring Meeting 2019, 9p-W521-1.
[5] I. Tateishi, M. Niibe, I. Matsuda et al., Phys.
Rev. Materials, 3, 024004 (2019).
[6] A. Heya, M. Niibe, K. Kanda et al., Jpn. J. Appl.
Phys., 60, 045506 (2021).
[7] M. Niibe et al., AIP Conf. Proc., 2054, 060010(2019).
[8] A. Heya et al. J. Photopolymer Sci. Technol. 33,
419 (2020).
[9] C. Eibl, et al., J. Vac. Sci. Technol. A 16, 2979
(1998).
[10] R. P. Gandhiraman et al., J. Phys. Chem. C 118,

35

Valence Band Analysis of RuOx using Soft X-Ray
Photoemission Spectroscopy for Oxygen Evolution Reactionat Water Electrolysis
Taku Yoshimura,1 Ryuki Tsuji,1 Yuichi Haruyama,1,2 and Seigo Ito1*
Department of Materials and Synchrotron Radiation Engineering, Graduate School of Engineering, Universityof Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan.
2
Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 3-1-2 Kouto, Ako, Hyogo
678-1205, Japan.
1

Abstract

For research and development of water electrolysis, a famous catalyst (RuO2) for oxygen evolution
reaction in water electrolyzing has been studied using X-ray photoemission spectroscopy (XPES),
which revealed the energy diagrams of catalyst surface. It was confirmed that RuO2 has higher
energy potential than the substrate (SUS304).

Introduction
Constructionofhydrogen-energy
society is quite important for mankind in
the future due to global energy andenvironmental issues. The technology of
producing high purity hydrogen by waterelectrolysis using electric power obtained
from natural energy is the most attractive
method of converting natural energy into
chemical energy, because it does not emit
any CO2. In order to reach a practicalenergy conversion efficiency, it isnecessary to lower the overpotential of theoxygen evolution reaction (OER) at theanodic side using effective catalysts.
In this work, we have prepared RuOx
catalysts deposited on stainless steel rod(SUS304) by a coating of the precursor
solution and applying flame-annealing,which is a very easy method to fabricate
electrocatalysts
inashort time.
Specially, the performance of waterelectrolysis RuOx catalyst deposited on
SUS304byflame-annealing
were
analyzed
andevaluatedbyelectrochemical cyclic voltammetry (CV)and X-ray photoemission spectroscopy(XPES).

a catalyst precursor solution of RuOx,
ruthenium (Ⅲ) nitrosyl nitrate solution(Ru 1.5 %, Solvent content: water 95.0 %)(Ru(NO)(NO3)3, Strem Chemicals, Inc.)was used as purchased. The precursor
solution was transferred into an elongatedtest tube to a depth of 4 cm or more, whichis to deposit the catalyst on the SUS304
rod over the range of 4 cm. The SUS304
rod were immersed in the catalyst
precursor solution and annealed in gas
flame. The immersion and annealing
were
repeated
10
times
to
be
RuOx/SUS304.
Figure 1 shows theschematic illustration of the fabrication
procedure of RuOx catalysts deposited ona stainless-steel rod by flame-annealing.

Experiments
In this study, a stainless-steel rod(SUS304), which is low cost and useful asa base material for the catalyst depositedelectrode, was used as a base material forcatalysts for water electrolysis. The
stainless-steel electrodes with RuOx
catalysts were named RuOx/SUS304. For

Figure 1. Procedure of flame annealing
deposition of RuOx on stainless steel rods.
The electrochemical performance of the
RuOx/SUS304 were characterized byelectrochemical cyclic voltammetry (CV)36

in 0.5 M H2SO4, 0.5 M K2SO4, and 1 M
KOH using a reference electrode(reversible hydrogen electrode: RHE).
The energy profile of valence band of
RuOx/SUS304 was obtained by a soft X-ray
photoemission
spectroscopy(XPES)
system installed at a beamline 07B end
station of NewSUBARU synchrotron
radiation facility.

(c)

Results and Discussions
Figure 2 shows the current-voltage curves byelectrochemical cyclic voltammetry using a
SUS304 rod (without RuOx) and RuOx/
SUS304. It was confirmed that, by depositing
ruthenium oxide (RuOx) on stainless steel(SUS304), the current-onset potential foroxygen evolution decreases in the acidic (0.5 M
H2SO4) and the neutral (0.5 M K2SO4)
electrolyte. However, the improvement was
obscure using alkaline (1 M KOH) electrolyte. It
can be judged that, when the current-onset
potential for oxygen evolution is close to thetheoretical value (1.23 V) for water electrolysis,
the material has effectively active as the oxygen
evolution catalyst. From this result, it isconsidered that ruthenium oxide has good waterelectrolysis activity on the oxygen evolutionside, as is generally known.

Figure 2.
Electrochemical cyclic
voltammetry (CV) in 0.5 M H2SO4 (a),0.5 M K2SO4 (b), and 1 M KOH (c)using a reference electrode (reversiblehydrogen electrode: RHE).
Figure 3 shows XPES results using rods of
SUS304 and RuOx/SUS304. In this case, it
was confirmed that the onset energy of RuOx
has close to zero binding energy against Fermi
energy level in material and that the energy levelof RuOx was higher than the substrate(SUS304).
In this work, it was confirmed that
RuOx/SUS304 has high activity on oxygen
evolution reaction for water electrolysis and thatthe conduction band of RuOx/SUS304 has
higher energy than that of SUS304. The
relationship between the OER activity andenergy level is under discussion for the
improvement of catalytic materials.

(a)

(b)

Figure 3.
X-ray photoemission
spectroscopy (XPES) of SUS304 andRuOx/SUS304.

37

Sample heating system installed in XAS chamber at BL10
Kae Hiramatsu, Kyoka Maee, Toshiyuki Tanaka, Runa Maruyama, Takuya Motokawa, and Yasuji
Muramatsu
Graduate School of Engineering, University of Hyogo
Abstract
To achieve X-ray absorption spectroscopy (XAS) measurements under sample heating conditions, anewly-developed sample heating system was installed in the XAS chamber at BL10. The system
can heat a sample plate up to 250 oC. Prior to XAS measurements, off-line heating experiments usingsugar samples were performed to clarify the relationship between the heating temperature andvacuum in the XAS chamber. During heating of the sugar samples up to 210 oC, vacuum pressureof the XAS chamber increased to 2 × 10-5 Pa due to degas from melted sugar. Critical vacuum for
XAS measurements in BL10 is set to 2 x 10-4 Pa on the interlock system. It is therefore confirmedthat in-situ or operand XAS measurements of heated sugar samples would be safely performed in
the XAS chamber at BL10.
1. Introduction
Soft X-ray spectroscopic measurements
should be performed under high vacuum pressure,because soft X-rays are intensively absorbed byoxygen and nitrogen in atmosphere. Hence, volatileor outgassing materials are generally prohibited to be
directly put in a vacuum chamber for themeasurements. However, soft X-ray spectroscopic
measurements of them have recently been requiredfor industrial chemical analysis. To perform such theanalysis, we have developed the X-ray absorption
spectroscopy (XAS) chamber which has a powerful
vacuum pumping system, and installed it at BL10 [1,2].
XAS measurements during sample heating
have recently been required. For example, sugar isan interesting material for the XAS measurements.
Commercially available sugar consisting of sucrose
crystals is generally highly purified material.
However, the melting point (mp) of them often
differs in 140 - 190 oC range, depending on the sugar
manufacturing process. X-ray diffraction (XRD)
studies on sugar have not explain the mp-fluctuation.
This suggests that the mp-fluctuation does not arise
from crystal structure difference. On the other hand,
we have recently found the spectral profile
differences in X-ray absorption near-edge structure(XANES) spectra of sugar samples [3], which
depends on the sugar mp. From the theoreticalanalysis of C K- and O K-XANES of sugar samples,
it is suggested that the spectral profile differences isdependent on hydrogen bonds among sucrose
molecules. To confirm the effect of hydrogen bonds
for the mp-fluctuation, we have planned to perform
in-situ XANES measurements of sugar melted byheating in vacuum.
Hydrogen bonds in liquid samples such as
water and alcohol have been measured by soft X-ray
emission spectroscopy or fluorescence-yield (FY)XAS measurements [4,5]. In these measurements,

liquid samples are separated from vacuum by thin
SiN windows. On the other hand, our XAS
measurements of sugar samples were achieved insolid states by using a total-electron-yield (TEY)method [3]. This suggests that hydrogen bonds insolid would be directly observed by the TEYXANES.
Furthermore,
in-situTEY-XASmeasurements of solid samples heated to be melt
would explore a new XAS technique. We havetherefore developed a sample heating system andinstalled it in the XAS chamber [6] at BL10.
Prior to in-situ TEY-XAS measurements
under sample heating, we have conducted off-line
experiments. The present paper describes the sample
heating system and the off-line experiments
performed to measure the vacuum pressure
evolution during sample heating.
2. Sample heating system
Figure 1 shows the sample heating system. A
heating base is a cupper (Cu) block having theelectrically heating wires and thermocouple. The
heating block is attached behind the sample holder
in the XAS chamber. Volume of the XAS chamber isapproximately 15 L, and it is pumped by a 350-L/s
turbo molecular pump (Leybold, TURBO-VAC 361).
The large pumping speed for the chamber volume
achieves the high vacuum pressure of 10-7 Pa.
Heating and monitoring temperature are controlled
by a heating controller put outside the chamber.
Sample heating up to 250 oC can be performed by
the system.
For the sample heating, sample holding should
be carefully performed. Conductive carbon tapes andindium (In) substrates, which are used for sample
holding in usual TEY-XAS measurements underroom temperature, cannot be used in the sample
heating measurements. Hence, sample holder should
be assembled in all-metal. Figure 2 shows theschematic drawing and photo of the sample plate.

38

The sample plate is made from Cu. Gold (Au) plateand Au mesh are put on the Cu plate by using screws.
Sugar samples are hold between the Au plate andmesh, and then incident X-ray beams irradiate thesamples through the Au mesh. Sample current canflow through the Au mesh/plate and Cu plate, and be
detected by a galvanometer put outside the XAS
chamber. In the present off-line experiments,
granulated sugar and zarame sugar (mp: 158 - 180oC) are put on the holder.

3. Off-line heating experiments
Off-line experiments were proceeded in two
steps; 1st step is heating of sample holder without
sugar samples for degassing from the Cu sample
plate, and 2nd is heating of sample holder with sugar
samples held on the degassed Cu plate.
1st step: Back pressure of the XAS chamber was
1.26×10-6 Pa. Preset temperature was varied from 40
oC to 200 oC. Vacuum pressures were monitored at
individual preset temperature for 500 s. Figure 3(a)shows the evolution of vacuum pressure during
heating of the Cu plate in the 40 - 200 oC range.
Heating at 40 - 100 oC, vacuum pressure gradually
increased up to 2 × 10-5 Pa. Heating at 120 - 200 oC,
pressure rapidly increased and peaks can beobserved near 100 s heating at individual preset
temperature. The vacuum pressure reached to the
maximum of 5 × 10-5 Pa at 200 oC heating. Such the
behavior means degases of water and/or volatileorganic compounds incorporated in Cu plate. After
heating at 200 oC for 500 s, vacuum pressure reached
to 3 × 10-5 Pa, which is lower than the limit vacuumfor XAS measurements. It is therefore confirmedthat heating of the Cu plate at 200 oC for 500 s is asufficient degassing condition.
2nd step: Granulated sugar powders (mp: 158 - 180oC) and zarame sugar particles (mp: 158 - 178 oC)
were held on the baked Cu plate, and then heated up
to 220 oC. Figure 3(b) shows the evolution of
vacuum pressure during the heating.
At the beginning of heating, the temperature wasFig. 1 Photos of a heating base (a), heating baseattached to the sample holder in the XAS
chamber (b), and a heating system installed in
BL10 (c).

Fig. 3 Left panel (a) shows the vacuum pressureof XAS chamber during heating the sample platein the 40 - 200 oC range. Right (b) shows thevacuum pressure during heating the heatedsample plate with sugar samples in the 100 - 220oC range. Inset shows the enlarged graph in the
100 - 180 oC range.

Fig. 2 Schematic drawings of Cu sample plate(left panel) and photo of the plate on which sugar
samples are held between the Au plate and mesh(right).

39

100 oC and the vacuum pressure was 3.0×10-6 Pa.
There was little change in pressure during heatingfrom 100 oC to 150 oC. This suggests little degassing
from Cu plate and sugar samples under 150 oC
heating. Vacuum pressure gradually increased to
5×10-6 Pa heating at 160 - 180 oC, in which sugars
may be melting. When the temperature reached to
190 - 210 oC, the vacuum pressure rapidly increased
to 1.5×10-5 Pa, because of the sugar melting.
Actually, melting of sugar samples can be visuallyobserved at the temperature. Further heating to 220
oC exhibited a drastic increase of vacuum pressure
reaching to 8×10-5 Pa. Boiling of melted sugar
samples can be visually observed at 220 oC. Such themelting state and vacuum pressure should be thelimit of heating condition in the XAS vacuum
chamber. Hence, off-line heating experiments were
terminated at 220 oC.

Report, 21, 57-59 (2019).
[4] J. Guo and Y. Luo, J. Electron Spectrosc. Relat.
Phenom., 177, 181-191 (2010).
[5] T. Tokushima, Y. Harada, Y. Horikawa, O.
Takahashi, Y. Senba, H. Ohashi, L.G.M.
Pettersson, A. Nilsson, S. Shin, J. Electron
Spectrosc. Relat. Phenom., 177, 192-205(2010).
[6] T. Uemura, Y. Muramatsu, K. Nambu, D.
Fukuyama, M. Kuki, T. Harada, T. Watanabe,and H. Kinoshita, Adv. X-Ray Chem. Anal.
Japan, 46, 317-325 (2015).

4. Conclusion
To perform in-situ TEY-XAS measurements
during sample heating, we have developed a new
sample heating system and installed it in the XAS
chamber at BL-10. Prior to the XAS measurements,
we have performed off-line experiments to clarify
the vacuum pressure evolution during sample
heating. Followings can be clarified;(1) Before sample heating, all-metal sample plates
should be baked up to 200 oC for 500 s.
(2) For sugar samples (mp: 140 - 190 oC), they canbe surely melted around 200 oC with the vacuum
pressure of 1.5×10-5 Pa. Such heating conditionis sufficiently lower than the interlock vacuum
limit of 2.0×10-4 Pa. Hence, in-situ TEY-XAS
measurements of sugar sample would be
performed under this heating condition.
(3) High temperature heating up to 220 oC of sugar
samples should be prohibited, because sugars
are boiled.
Acknowledgements
We would like to express thanks to Professor
Kaoru Sakamoto of University of Hyogo forfinancial support (Grants-in-Aid from the Ministryof Education, Culture, Sports, Science, andTechnology of Japan under contract No.17K00823)
and preparation of the sugar samples.
References[1] T. Uemura, Y. Muramatsu, K. Nambu, D.
Fukuyama, M. Kuki, T. Harada, T. Watanabe,and H. Kinoshita, Adv. X-Ray Chem. Anal.
Japan, 46, 317-325 (2015).
[2] Y. Muramatsu, A. Tsueda, T. Uemura, K. Nambu,
T. Ouchi, T. Harada, T. Watanabe, and H.
Kinoshita, LASTI Annual Report, 17, 27-28(2015).
[3] K. Maee and Y. Muramatsu, LASTI Annual40

C K-XANES simulations of n-alkanes and cis-4-alkenes
Runa Maruyama, Toshiyuki Tanaka, and Yasuji Muramatsu
Graduate School of Engineering, University of Hyogo

Abstract

To clarify the fine structures around σ* peak in C K-XANES of carbon materials, C K-XANES
spectra of various n-alkanes and cis-4-alkenes were simulated by the first-principles calculations.
For n-alkanes, double peak structure can be obtained as σ* peak. The peaks exhibit thelower-energy shifts as the alkyl chain length becomes longer. The peak intensity ratio of the double
peaks is also dependent on the alkyl chain length. C K-XANES spectra of cis-4-alkenes also show
the similar double peak structure which dependent on the alkyl chain length. It is therefore
confirmed that C K-XANES spectra of carbon materials containing alkane structures will exhibit
broad σ* peak profile composed of double peaks which will exhibit energy-shifts.

1. Introduction
X-ray absorption near-edge structure(XANES) using synchrotron radiation (SR) has
been utilized for electronic/chemical-state
analysis of carbon materials. Advantages of
XANES measurements to characterize carbon
materials are briefly summarized as follows. (1)Element/orbital-selective information of theelectronic structure can be obtained. (2) Highenergy-resolution
spectroscopy
canbeperformed due to the highly resolved
monochromatized SR beams. (3) The orientationof the carbon structure can be evaluated using
the polarized SR beams. Additionally,
theoretical XANES analysis has recently been
performed using first-principles calculations.
Hence, a combination of XANES measurements
and theoretical analysis provides an advanced
characterization method for carbon materials.
Graphitic carbons composed mainly of
sp2-carbon (C) atoms generally exhibit
characteristic π* and σ* peaks in C K-XANES.
On the other hand, sp3-C atoms exhibit only σ*
peak. From the viewpoint of peak profiles, σ*peaks are generally broader than π* peaks, andσ* peaks overlap continuous conduction band
structures. For sp3-C compounds, althoughdiamond takes rigid crystal structure, alkane
molecules take flexible structures because of thenumerous conformation caused by rotations
around single C-C bonds. This suggests thatalkane structure exhibits characteristic σ* peak
profile dependent on their conformation and/or
alkyl chain length. Hence, the present study
aims to clarify the σ* peak structure of alkanes
in C K-XANES. Prior to C K-XANES
measurements, we have simulated C K-XANESof various n-alkanes and cis-4-alkenes using thefirst-principles calculations.

calculated by the DFT calculation code of CASTEP
on the Material Studio platform. Calculation
models were n-alkanes and cis-4-alkenes. Details of
the models will be explained later. Each model wasplaced in a sufficiently larger super cell to suppress
the intermolecular effects. In the super cell,distance between cell walls and calculation model
edge was set longer than 0.5 nm which is
sufficiently longer than usual chemical bonds.
Hence, such the super cell condition can performthe calculations for isolated models without
intermolecular effects. After structure optimizationby the Material Studio, DFT calculations in the
ground state (initial state) were achieved in
CASTEP. Then calculations in an excited state(final state) with a C1s-1 core hole were performed
for each carbon atom to determine the transition
probability, because XANES can mainly reflect theelectronic structure in the final state. The transitionenergy of the calculated XANES was corrected byconsidering the energy differences at the valence
and core levels in the ground (initial) and excited(final) states. The calculated XANES spectra were
finally obtained from the transition probability as afunction of the transition energy.
Density of state (DOS) was partiallycalculated using the discrete variational (DV) -Xα
method.
3. Results and Discussion
3.1 n-Alkanes
Table 1 shows the target n-alkanes (CnH2n+2).
Considering C K-XANES measurements undervacuum, models of n = 9 ~ 50 are chosen. Figure 1
shows an example of the calculated C K-XANES
and C1s-DOS of n-Nonane (C9H20). In themolecular structure, C atoms are labelled as 1C 9C, where 1C and 9C are methyl carbons andothers are methylene carbons. In the calculated
XANES, methyl 1C and 9C exhibit a single peak
profile (marked with + in the figure), while
methylene 2C - 8C exhibit a double peak profile

2. XANES Calculation
C K-XANES spectra were theoretically41

(marked with *). The peaks also show energy shifts.
From the edge (1C, 9C) to center (5C), they exhibit
the higher-energy shift as shown by dotted line in
the figure. Such energy shift can be explained by
the C1s core energy shifts. Figure 1(b) shows the
C1s-DOS of 1C - 9C. All C atoms exhibit the single
peak profile, showing the lower-energy shift fromedge to center carbons. Such the lower-energy
shifts on C1s-orbital reflect the higher-energy shifts
on the C1s - σ* transitions. Reflecting the energy
shifts on XANES of individual 1C - 9C, total
XANES which is obtained by summing up theindividual XANES of 1C - 9C exhibits a broad
double peak profile.

Figure 2 shows the calculated C K-XANES ofthe n-alkanes. All compounds exhibit a double peak
profile (denoted by a and b in the figure). The
peaks exhibit the lower-energy shift of 4 eV from
C9H20 to C35H72, keeping the energy gap of 2.5 eV
between peaks a and b. Peak height of a and b isalso dependent on the alkyl chain length. Relative
peak height of b/a increases as the alkyl chain
length becomes longer. Hence, such thealkyl-chain-length-dependence on the peak energy
shifts and relative peak height will exhibit a broader
σ* profile on C K-XANES of sp3-C containing
carbon materials.

Table 1 Calculated compounds of n-alkanes.

Fig. 2 Calculated C K-XANES of n-alkanes.
3.2 cis-4-Alkenes
Table 2 shows the target cis-4-alkenes(R1-CH=CH-R2), in which R1 is propyl -C3H7 andR2 are alkyl substituents of -CnH2n+1 (n = 3 - 10).
Hence, calculated C K-XANES of them will show
the R2 dependence.
Figure 3-1 and 3-2 show the calculated C
K-XANES of the cis-4-alkenes with their model
structures. In the models, C atoms of R1 are labelled
as C1 - C3, and sp2-C atoms are as C4 and C5.
Hence, C1 is a methyl carbon, and C2 and C3 are
methylene carbons. For R2, C atoms are labelled

Fig. 1 Calculated C K-XANE (a) and C1s-DOS(b) of n-Nonane.

42

from C6 to C8 (cis-4-Octene), to C9 (cis-4-Nonene),
to C12 (cis-4-Dodecene), and to C15(cis-4-Pentadecene).
Table
2 Calculated
cis-4-alkenes.

compoundsof

6C to the terminated methyl carbon. Hence,calculated C K-XANES summed up the total C
atoms exhibit broader and complicated structures
between the π* - σ* region. It is also found that C K
XANES of R1 and R2 are isolated by the doublebond formed by sp2-C atoms.

Fig. 3-2 Calculated C K-XANES ofcis-4-Dodecene (c) and cis-4-Pentadecene (d).

Fig. 3-1 Calculated C K-XANES
cis-4-Octene (a) and cis-4-Nonene (b).

ofIn the calculated C K-XANES, XANES ofindividual C atoms and the total XANES summed
up them are described. In all models, sp2-C atoms(C4 and C5) exhibit π* peak at the lowest energy
position. The methyl 1C (marked with + in the
figure) exhibits a single peak, and methylene 2C
and 3C atoms (marked with *) exhibit double peaks.
These peaks show the higher-energy shifts from 1C
to 3C. Such the peak profiles and energy shifts are
as same as the above-mentioned n-alkanes.
Methylene carbons and terminated methyl carbons
in R2 also show the double peak and single peak
profiles, respectively. Energy position of 6C is assame as that of 3C in all compounds, and other C
atoms in R2 show gradual lower-energy shifts from43

4. Conclusion
To clarify the σ* peak profiles in C
K-XANES of alkanes, calculated C K-XANESof various n-alkanes and cis-4-alkenes were
calculated by using the first-principles
calculations. The following findings wereobtained;(1) Terminated methyl C atoms exhibit a single
peak, while methylene C atoms exhibit adouble-peak profile.
(2) Comparing to the terminated methyl C atoms,
peaks of methylene C atoms exhibit the gradualhigher-energy shifts as the longer alkyl chain
length.
(3) Alkyl substituents isolated by double bonds
behave independently as alkanes on C
K-XANES.
(4) Such the energy shifts dependent on thealkyl chain length will make the broader σ*peak profiles.

Coating Uniformity Effect of EUV Resist
for Resonant Soft X-ray Scattering
Tetsuo Harada, Shinji Yamakawa, Takeo Watanabe
LASTI, University of Hyogo

Abstract

Resonant soft X-ray scattering (RSoXS) method is applied to evaluate the chemical contents
spatial distribution. Around the carbon absorption edge, the resonant absorption peaks are specificto the chemical contents of carbon. In RSoXS method, the soft X-ray scattering intensity from theresist is recorded by a CCD camera, which the incident photon energy irradiate to the resist sample
is varied around the carbon absorption K-edge of 284 eV. If these chemical contents have large
dispersion, the stochastic becomes worth. In this report, we reported the scattering from samples
that were coated with uniform and not-uniform distribution.

Introduction
Resist material has large absorption in thesoft X-ray energy region, especially aroundthe carbon K absorption edge. There areresonant absorption peaks which corresponds
to chemical structures. For examples, resonant
absorption peaks of 286 eV, 289 eV and 296
eV correspond to the π* bond structure ofbenzene group, acrylate group, and σ bondstructure of carbon, respectively. Therefore,
the scattering measurement in soft X-ray
region could evaluate the chemical structure
distribution. In the resonant soft X-ray
scattering (RSoXS) method [1,2], the incident
soft X-ray irradiates to the sample, and thescattering light from the sample is recorded by
a CCD camera which is installed in a vacuum
chamber. The incident photon energy wasvaried around the carbon absorption edge of
284 eV. The spatial resolution in this method
is approximately 12 nm, and this spatial
frequency is enough high to analyze the resist
uniformity of the chemical structure
distribution, which might be affected with the
LWR and stochastic.
However, the sample should be coatedwith good uniformity to analyze the chemical
structure
distribution.
The
coating
non-uniformity would cause large scatteringfrom the sample, which would hide thescattering from the chemical distribution.

reflectometry to measure the reflectanceof EUV optics and the X-ray absorption
spectroscopy (XAS) for the chemical
reaction analysis of EUV resist
materials. The photon energy range
exposing on a sample is from 60 to 1100
eV. The number of photons estimated by
the photodiode current at the focal point
was 4 × 109 photons/s at the photon
energy of 280 eV.

Fig.1 Schematic drawing of
measurement of the sample resist.

RSoXSAs shown in Fig.1, the incident soft X-ray
was irradiated from the right side to the left
side, which formulated almost in parallel
beam. The focusing point of the incident beam
was located at 2.1 m upstream from thesample. A pinhole with 200 µm in diameter
employed as an incident aperture to limit theincident beam size to 200 µm. A pinhole with
400 µm in diameter employed as a scattering
cut was located just before the sample to cut
the direct-back-scattering light from theincident aperture. And then the sample was
exposed by the soft X-ray beam and scattered
light was led to the in-vacuum CCD camera(MTE-2048B, Roper Scientific) to measure
the scattered image from the resist sample.

Experiments and Results
Figure 1 shows a schematic drawing
the RSoXS system at BL-10 beamline of
NewSUBARU. This beamline provides
monochromatized energy of the soft
X-ray region from 80 to 1000 eV. This
beamline has been used for the EUV

44

The center-stop plate with 1 mm in width was
located just before the CCD camera, which
cut the strong direct beam from the sample
Around the carbon absorption edge, theresonant absorption peaks are specific to thechemical contents. Then, the scattering at theabsorption peaks related to the chemical contents
in the resist film. Therefore, the resist samples
were measure by XAS with the total electron
yield (TEY) method around carbon K edge. After
that, the probe photon energies could bedetermined as the incident photon energy for thesmall angle scattering. In the XAS measurement,
the resist on a Si wafer was measured.
Figure 2 shows the XAS result of thepolymer sample. The vertical axis shows theabsorption amount of the polymer. The
horizontal axis shows photon energy of theincident soft x-ray beam. The strong
absorption peak at 286 eV was observed,
which corresponded to the π* bond structureof benzene group. Absorption peak at 289 eV
was corresponded to the bonding structure ofacrylate group. The broad absorption peaks
around 296 eV correspond to σ bond structureof carbon.

from the base line, the chemical dispersion
might be large.
In sample fabrication process, Si3N4
membrane was attached on a Si wafer bypolyimide tape. The liquid was dripped on themembrane using a dropper. The polymer was
spin coated and prebaked. The spin-coating
speed were 500 rpm or 1500 rpm in 30 s. The
prebake condition was at the temperature of
130 °C in 60 s. Thickness of the polymer
would be approximately 280 nm and 170 nm
when the spin-coating speed of 500 rpm and1500 rpm, respectively.

Fig.2 XAS result around CK region of resist
which was coated on a Si wafer.

(b)Fig. 3. The optical microscope images of theresist coated on the Si3N4 membrane at the
spin coating speed of (a) 500 rpm and (b)1500 rpm.

(a)

The RSoXS was performed at the photon
energies of 280, 286, 289, and 296 eV. The
photon energy of 280 eV had just lower thanthat of the carbon absorption edge. The
scattering profile at 280 eV was the base lineof the small polymer absorption. Thus, if thespectrum of scattering vector has a similar
profile in comparison of that from the baseline, the chemical dispersion might be small.
Otherwise, if the spectrum of scattering vector
has a different profile in comparison of that

Figures 3(a) and (b) show the optical
microscope image of the coated membrane withthe spin coating speed of 500 rpm and 1500 rpm,
respectively. In Fig. 3(a), the resist film thickness
was not uniform. In Fig. 3(b), the resist film
thickness was coated with good uniformity.
Figure 4 shows the RSoXS result of thesample with the spin coating speed of (a) 500
rpm and (b) 1500 rpm. Scattering images at 445

The dispersion of these scattering signal shows
the cluster size and aggregation of the functionalgroup. For the coating condition at 500 rpm,
there was large amount of clusters in in the resist
films, which was also observed the optical
microscope image as shown in Fig. 4(a).
The coating condition affected the cluster sizeof the polymer, which was detected to the RSoXS
result. The coating on the small membrane was
hard to obtain uniform coating. To evaluate
chemical structure uniformity of the resist, resist
should be coated on the Si wafer, and measured
by the RSoXS in the reflection mode. Therefore,
we are now developing this reflection-mode
RSoXS.

photon energies were measured. The horizontal
axis shows the scattering vector q. The verticalaxis shows scattering signal from the sample,
which was normalized at the lowest scatteringvector around 0.17 nm-1. For the non-uniform
sample, the scattering of each photon energy wasquite different with each other in q > 0.022 nm-1
region which corresponds to the spatial size of
300 nm.

References
1. Y. Nakatani, T. Harada, A. Takano, M.
Yamada, and T. Watanabe, J. Photopolym.
Sci. Technol., 30 (2017) 77.
2. J. Tanaka, T. Ishiguro, T. Harada, and T.
Watanabe, J. Photopolym. Sci. Technol., 32(2019) 327.
(a)(b)
Fig. 4. RSoXS result of the sample on themembrane with the spin coating speed of (a) 500
rpm and (b) 1500 rpm.
The polymer would have large cluster of 300
nm. At 280 eV, the polymer had lower absorption
because that is just below the carbon absorption
peak of 284 eV. The scattering signal of 280 eV
was lower than the scatterings of other photon
energies at high frequency region. If the cluster
has uniform chemical structure, the four
scatterings would have same profile. Thus, thecluster would have the chemical structure
aggregation, which could be caused byhydrophilicity of functional group in the polymer.

46

Elimination of Charging Effect in Photoemission
Spectroscopy by Gas Introduction
Kento Takenaka1, Kenta Adachi1, Koji Takahara2, Hirosuke Sumida3, Satoru Suzuki2
Graduate School of Science, University of Hyogo, 2LASTI, University of Hyogo, 3Mazda Motor Corp.

1

Abstract
One major problem in photoelectron spectroscopy is the charging effect in measuring bulk insulator
samples. We succeeded in eliminating the charging effect of a glass slide and a LiNbO3 byintroducing nitrogen gas in the near-ambient-pressure hard X-ray photoemission spectroscopy
apparatus. The charging effect was eliminated at 2500 Pa when the distance d between the sample
surface and the front-cone of the electron analyzer was 0.3 mm. The elimination of the charging
effect is considered to be because secondary electrons created by electron scattering in the gas
neutralize the charge on the sample surface. Moreover, the pressure required to eliminate thecharging effect was found to strongly depends on d. The charging effect was eliminated at only 250
Pa at d=2.1 mm. Two possible reasons are considered for the strong d dependence. One is pressure
decrease near the sample surface induced by the differential pumping through the cone. The otherone is the interference of the electron scattering caused by the presence of the corn near the sample
surface.

Introduction
Photoelectron Spectroscopy (PES) is a powerfultool for studying the elemental composition,
chemical bonding, and electronic structure ofmaterials. However, one of the problems of PES
is charging effect in measuring bulk insulator
samples. To eliminate charging effect, various
methods have been tried [1][2]. The commonlyused methods are the simultaneous irradiation of
low-energy electrons and ions [3], and thecoating of the sample surface with a highly
conductive material [4][5]. In the former, it isdifficult to control the irradiation conditions. And
there is a possibility of sample degradation due toion irradiation. In the latter case, the coating
decreases the photoelectron intensity byscattering. Also, in the measurement with the gas
introduced, the coating covers the surface of thesample, making it impossible to observe thereaction between the gas and the sample. Thus,
both methods have disadvantages, and it is major
challenge to accurately measure bulk insulator
samples in photoelectron spectroscopy.
Recently, light sources become more luminous
for sensitivity improvement, making it moredifficult to control charging effect. It has beenreported that measurement under a gas
atmosphere reduce the charging effect [6][7][8].
In the previous report, it was shown that the
charge relaxation progressed as the gas pressure
was increased, but the charge was not completely
eliminated even at the maximum pressure in theexperiment (~500 Pa). In this study, we attempted
to almost completely eliminate the charging
effect of an insulator sample by introducing

higher pressure gas using the Near-AmbientPressure Hard X-ray Photoelectron Spectroscopy(NAP-HAXPES) apparatus.
Experiments
A glass slide (thickness: 1 mm) and a LiNbO3
wafer (0.5 mm) were used as typical insulating
samples. The measurements were carried out at
near-ambient-pressure hard X-ray photoemission
spectroscopy (NAP-HAXPES) station at
BL24XU of SPring-8. The excitation light was
set at 8 keV using a channel-cut monochromator.
The energy analyzer is HiPP-2 from Scienta
Omicron. In this system, H2, N2 and O2 gases canbe introduced at present. In this experiment, weused N2 gas, which is relatively stable and has
low reactivity, to perform the measurement
without chemical change of the sample.

47

(a)

(b)

Fig. 1 (a) Schematic diagram of HiPP-2 [9].
(b) Picture of the sample and front cone of theprelens part.

(b)

(c)

(d)

Fig. 2 (a) Nb 3d HAXPES of a LiNbO3 plate
under various nitrogen pressures. (b) Pressure
dependence of the Nb 3d5/2 binding energies
and the FWHM. (c) Si 1s HAXPES of a glass
plate under various nitrogen pressures. (d)Pressure dependence of the Si 1s binding
energies and the FWHM.

Fig. 1a shows the schematic diagram of HiPP2. The photoelectrons emitted from the sample
enter the hemispherical electron energy analyzer
through the prelens, and draw a semicircle toreach the detector. Fig. 1b shows the sample andfront cone of the prelens part. There is a small
orifice at the tip of the cone through which thephotoelectrons enter. If sample-to-cone distanced is too short, the gases flow into the electron
spectrometer causes pressure decrease on thesample surface [10]. Simulation results reportthat when d is larger than or equal to the holediameter Φ, the pressure at the sample surface isalmost equal to the environmental one [11]. SinceΦ = 0.3 mm for this apparatus, we set d = 0.3 mm
as the normal position and introduced gas to see
if the charging would be eliminated. After that,
we performed similar measurements withincreasing d.
Results and discussion
Fig. 2a shows the Nb 3d spectra of the LiNbO3
sample obtained under various nitrogen gas
pressures, and Fig. 2b shows the pressure
dependence of the binding energy and FWHM of
the Nb 3d5/2 peak obtained from Fig. 2a. At
nitrogen gas pressures above 2500 Pa, the Nb
3d5/2 binding energy and FWHM values become
mostly constant. The Nb 3d5/2 binding energy at
2500 Pa is 207.28 eV, which is close to theliterature value of 208 eV [12]. From these results,
it is considered that the charging effect of the
LiNbO3 was eliminated at a nitrogen gas pressureof 2500 Pa.
Fig. 2c shows the Si 1s spectra of the glass slide
sample obtained under various nitrogen gas
pressures, and Fig. 2d shows the pressure
dependence of the binding energy and FWHM of

(a)

(a)

(b)

(c)

(d)

Fig. 3 (a) Pressure dependence of Nb 3d5/2 binding
energy by sample-to-cone distance d. (b) Pressure
to eliminate Nb 3d charge at each distance d. (c)Pressure dependence of Si 1s binding energy bysample-to-cone distance d. (d) Pressure toeliminate Si 1s charge at each distance d.

the Si 1s peak obtained from Fig. 2c. At nitrogengas pressures above 2500 Pa, the Si 1s binding
energy and FWHM values become mostly
constant. The Si1s binding energy at 2500 Pa is1843.3 eV, which is close to the literature valueof 18844.2 eV [13]. From these results, it isconsidered that the charging effect of the glass
slide was eliminated at a nitrogen gas pressure of2500 Pa.
Fig. 3a shows the change in Nb 3d5/2 binding
energy as the pressure is changed at different
distance d. At any distance d, as the pressure is48

charging effect. The other one is that the presenceof the corn interferes with the electron scattering.
Fig. 5 shows the scattering of 100 electrons withkinetic energy of 8 keV emitted vertically fromthe sample in nitrogen gas at 2500 Pa by Monte
Carlo simulation. According to the simulation, atclose distances from the sample, many electrons
travel straight ahead with little loss of energy andare expected to enter the cone without being
scattered in the actual measurement. The smaller
the distance d is, the higher the probability thatphotoelectrons will enter the front cone without
being scattered, thus suppressing the emission of
secondary and Auger electrons necessary forcharge elimination, and thus the gas pressure
required to eliminate the charging effect becomes
higher.

Fig. 4 Schematic diagram of the mechanism of
charge elimination.

100 mmincreased, the binding energy becomes almost thesame value, indicating that the charging effect iseliminated. Fig. 3b shows the variation ofpressure required for charge elimination of the
LiNbO3 sample with distance d, based on Fig. 3a.
The smaller the distance d, the higher thepressure required to eliminate the charging effect.
Fig. 3c shows the change in Si 1s binding energy
as the pressure is changed at different distance d.
Fig. 3d shows the variation of pressure requiredfor charge elimination of the glass slide sample
with distance d, based on Fig. 3c. The results here
are similar to those of LiNbO3, but the pressure
required to eliminate the charging effect tends tobe larger than that of LiNbO3. This indicates thatthe degree of charging effect varies from sample
to sample.
Fig. 4 shows a possible mechanism of charge
elimination by gas introduction. First, thephotoelectrons emitted from the sample or gas
molecules by X-ray irradiation are scattered by
the surrounding gas molecules. Then, secondary
electrons and Auger electrons are emitted by thescattering, and these electrons are repeatedly
scattered. Finally, the electrons that lose energy
through scattering reach the positively charged
area of the sample by Coulomb attraction, and thecharging effect is eliminated. Based on thismechanism, the charge elimination would
depend on how much of the electrons arescattered by the gas molecules. The higher thegas pressure, the higher the probability ofelectrons colliding with gas molecules, and thus
the greater the chance of scattering, and the more
the process of charge elimination goes on.

Fig. 5 Monte Carlo simulation of the scattering of 100
electrons of energy 8 keV vertically emitted from asample in nitrogen gas at 2500 Pa.

Acknowledgments
HAXPES measurements were performed at thebeamline BL24XU at SPring-8 (proposal no.
2020A3231 and 2020B3231).

References[1] H. Iwai, J. Surf. Anal. 7(1), 37-48 (2000).
[2] T. Oyama et al., Surf. Sci. 20(8), 530-534(1999).
[3] L. Edwards, P. Mack, and D. J. Morgan, Surf.
Interface Anal. 51(9), 925–933 (2019).
[4] Y. Mori, J. Surf. Anal. 12(2), 113–117 (2005).
[5] S. Suzuki et al., J. Appl. Phys. 128, 015304(2020).
https://www.specs[6]EnviroTM,
group.com/nc/enviro/products/detail/enviroesca/[7] X.R. Yu and H. Hantsche, J. Electron Spectrosc.
Relat. Phenom. 50,19 (1990).
[8] S. Matsumoto, T. Nanba, Y. Miura, Surf. Sci.
18(7), 466-472 (1997).
[9]
Scienta
Omicron,

There are two possible reasons why the smaller
the distance d, the higher the pressure required toeliminate the charging effect. The first one is thatdifferential pumping causes a pressure drop on
the sample surface. In this case, the smaller the
distance d is, the larger the pressure drop is, andthe larger the deviation from the pressure
indicated by the pressure gauge is, the larger “theindicated gas pressure” required to eliminate the49https://premium.ipros.jp/omicron/catalog/detail/557
590/[10] Y. Takagi, T. Uruga, M. Tada, Y. Iwasawa and T.
Yokoyama, Acc. Chem. Res. 51, 719-727 (2018).
[11] J. Kahk et al., J. Electron Spectrosc. Relat.
Phenom. 205, 57 (2015).
[12] Y. Yun et al., Surf. Sci. 601, 4636 (2007).
[13] M. Yoshiki, K. Fujii. SPring-8/SACLA
Research Report. 8, 2 (2020).

50

In-situ Formation of Micro- and Nanobubbles in a
Scanning Electron Microscope
Koji Takahara, Satoru Suzuki
LASTI, University of Hyogo

Abstract
The formation of nanobubbles by water radiolysis has been observed by transmission electron
microscopy using a very high electron dose ratio. Here, we used a conventional scanning electron
microscope to generate nanobubbles in situ at a relatively low magnification of ~1000x. Among theobserved bubbles, the one with the lowest dose ratio was 1.3×1011 electrons/cm2s, which is 5-7 ordersof magnitude smaller than previously reported TEM studies. Furthermore, these bubbles survived formore than three days, contrary to the high Laplace pressure contained within them.
Introduction
Today, micro- and nano-bubbles are being
used not only in industrial fields but also in daily
necessities such as showers. However,fundamental issues such as the detailed
mechanism of stabilization remain unexplored.
As an example, nanobubbles do not diffuse andremain in the liquid even though they arecovered by a large Laplace pressure.
Several studies have reported thatnanobubbles are formed by the radiolysis ofwater by electron beam irradiation. In thesestudies, transmission electron microscopy wasused to form and observe the nanobubbles.
Scanning electron microscopy (SEM) is asimilar method of observation using electron
irradiation, but there have been no reports of
nanobubble formation using SEM, and the firstobservation using a flow cell has only recently
been reported.
In this study, we used SEM to irradiate purewater with electrons and succeeded ingenerating microbubbles and nanobubbles insitu [1]. In addition, we used much lower
radiation doses than those reported in TEM
studies [2].

electron microscope (JEOL, JSM-6700F).
mainly, beam of accelerating voltage is 5kv.
Result and Discussion
The SEM images of the process of
microbubble formation by electron irradiation
are shown in Fig 1. In (a), a bubble formed by
mistake during sample preparation is observedin the upper right corner. In (b-e), many
microbubbles newly appeared and the firstobserved bubble became larger. After further
irradiation (f-m), the size of each bubble
increased while the density of the bubbles
remained constant. In (n-r), the grown bubbles
collided with each other to form large bubbles of~20 μm. These bubbles were formed byirradiating the cell with a 5 keV electron beam
(beam current 26 pA) at a dose ratio of 9.6 × 1011
electrons/cm2s. In our present study, the lowest
dose ratio at which bubble formation wasobserved was 1.3×1011 electrons/cm2s, which is
5-7orders of magnitude smaller than previous
TEM studies[2][3].
The bubble is observed to be white in thisexperiment, which means that the bubble isemitting more secondary electrons than theliquid in the cell. Since the density of the gas
inside the bubble is much smaller than that of theliquid, it is inferred that these secondary
electrons originate from the bubble interface. In
the experiment using the liquid flow cell, whichis the only example of SEM observation so far,the bubble was observed to be black, but this isprobably because the detection method wasbased on reflected electrons [4].
These tiny bubbles have a very large Laplacepressure due to their small radius of curvature.

Experiments
Liquid cells using Si chips with SiN or Si
membranes (EMJapan Co., Ltd., Tokyo) as
electron-transparent
windows
wereconstructed. The thickness and dimensions of
the membrane were typically 15 nm and 100µm × 100 µm, respectively. Electron
irradiation of the water and in situ observation
were performed at room temperature in a
vacuum using a conventional scanning51

microbubbles and nanobubbles will be a futurechallenge.
As a factor in the formation of bubbles, weconsidered the possibility that boiling was

However, the lifetime of the bubbles generated
in this study reached at least three days.
Elucidation of the stabilization mechanism of

Fig 1. SEM images showing the formation process of large microbubbles by merging of small
microbubbles. The electron energy was 5 keV and the irradiation dose ratio was 9.6 × 1011
electrons/cm2⋅s. (a) Initial state of the liquid cell with a SiN membrane. The microbubbles observed in
the upper right of the image were formed during a previous observation. SEM images after irradiationfor (b) 44 s, (c) 120 s, (d) 162 s, (e) 204 s, (f) 247 s, (g) 289 s, (h) 329 s, (i) 374 s, (j) 414 s, (k) 491 s,(l) 601 s, (m) 678 s, (n) 789 s, (o) 967 s, (p) 1111 s, (q) 1188 s, and (r) 1367 s. The numbers correspondto those in Fig. 3.

Fig 2. (a) SEM images of micro- and nano-bubbles immediately after formation. (b) SEM images
obtained 3 days after bubble formation. The relatively low image quality is due to the effect ofcharging. Si was used as the film material.

52

Footprint length (μm)

10
8
6
4

1
2
3
4
5
6
7
8
9
10
11
12

2

200

400
Time (s)600

Fig 3. Relationship between footprint lengths and irradiation time of 12 microbubbles observed inFig. 1. The broken lines are fitting results with linear functions. The numbers correspond to thosein Fig. 1.
the thickness of the liquid cell is usually chosen
to be close to the inelastic mean free path (188nm at 200 keV for water). The thickness of theliquid cell was chosen to be close to the inelastic
mean free path (188 nm at 200 keV for water [6]).
Therefore, the liquid cell is very transparent toincident electrons. On the other hand, in thepresent SEM, the thickness of the cell (100-200µm) is much larger than the maximum
transmission depth (~8 µm at 20 keV and ~0.8µm at 5 keV [5]), so the incident electrons cantransfer almost all of their energy to the confinedwater. In addition, the supersaturation required
for the formation and stabilization of bubbles
was considered to have been achieved in thisexperiment. The small volume of the liquid cell
(1-2 nl) and the low pressure in the cell (themaximum pressure that the membrane canwithstand is 2 atm) contributed to thesupersaturation state.

caused by the temperature rise of water due toelectron irradiation. However, the irradiationinduced temperature was estimated by referringto the previous report [5] and the value forboiling was negligibly small (~1 mK). Therefore,
the bubble formation is considered to be causedby the radiolysis of water.
Fig 3 shows the time dependence of the
footprint length (before coalescence) of the 12
microbubbles observed in Fig 2. The footprint
lengths increase almost linearly with irradiation
time, indicating that the growth rate is almost
constant regardless of the change in size. theclose slope of the 12 bubbles means that thegrowth rate of all bubbles is close. Assumingthat the three-dimensional shape of the bubbles
is invariant, the linear dependence means thatthe bubble volume (V) increases rapidly withincreasing irradiation time t, i.e., V ∝ t3. dV/dt ∝t2 ∝ S (surface area), we tentatively propose thefollowing bubble growth model. Uniform
electron beam irradiation produces gas species
uniformly in the liquid cell. When bubbles areformed by the agglomeration of gas species, theygrow by taking in gas species (or invisible
nanobubbles) uniformly dispersed near thesurface from the surface.
The reason for the formation of bubbles atmuch lower dose ratios in the present
experiment than in previous TEM studies isthought to be the difference in the permeabilityof the sample to electrons: in TEM observations,

Conclusion
The formation of surface micro- and nanobubbles by electron irradiation was observed
using a conventional scanning electron
microscope with a liquid cell confined with purewater. Bubbles were formed at an irradiationdose ratio 5~7 orders of magnitude lower thanprevious TEM studies. The results show thatmicro- and nano-bubbles can be formed in SEM
and observed stably for a long time, suggesting53

that SEM may become an important analytical
tool in the study of micro- and nano-bubbles.
References[1] K.Takahara and S.Suzuki, J. Appl. Phys.
(accepted).
[2] J. M. Grogan et al., Nano Letters 14, 359(2014).
[3] Q.Kim et al, Applied Nanoscience (2018).
[4] T. Ishida, Electronics and Communicationsin Japan 102 (9), 55-60 (2019).
[5] H. Takahashi, J. Surf. Sci. Soc. Jpn 25 (4),224-231 (2004).
[6] Q. Kim, D. Shin, J. Park, D. A. Weitz and W.
Jhe, Applied Nanoscience (2018).

54

Cross-sectional Observation of Micro- andNanobubbles Formed In-situ in a Scanning Electron
Microscope
Koji Takahara, Satoru Suzuki
LASTI, University of Hyogo

Abstract

Cross-sectional observation of micro- and nano-bubbles formed by water radiolysis was successfully
carried out, and the average value of contact angle of 69 bubbles was 69°. The average value of the contact
angle of 69 bubbles was 69°. In previous AFM studies, microbubbles were observed in a flat shape, and thepresent results are contrary to these studies. In addition, the lifetime of the bubbles reached more than threedays even though they contained a large Laplace pressure from these large contact angles.

Introduction
In recent years, microbubbles andnanobubbles have been utilized in a variety offields ranging from industrial fields such as
agriculture and fisheries to daily necessities suchas washing machines. However, it is difficult toanalyze these microbubbles individually, andtheir basic physical properties, such asstabilization mechanisms, remain unresolved.
Several studies measuring the shape of surface
microbubbles and nanobubbles have beenreported using AFM at present. However, thepresent study using scanning electron
microscopy (SEM) showed different resultsfrom the previous studies. In this study, we
directly observed the cross-section of surface
bubbles formed by SEM radiolysis [1].
This study is also a companion to "In-situ
Formation of Micro- and Nanobubbles in a
Scanning Electron Microscope" presented in thisannual report.

micro- and nanobubbles formed by electron
irradiation at the edge of the electrontransmission window. These bubbles touchedboth the SiN film and the Si wall, as shown
schematically in Fig. 2. In Fig. 2 (top), the top
cross-sectional view of the SEM observed
bubbles is shown. Fig 2. (bottom) shows the sidecross section which cannot be observed by SEM.
Edge bubbles, such as the one observed at theedge of the window in this study, are assumed tobe part of a sphere with a radius of curvature R.
To identify the contact angle of the bubble, wemeasured the wettability of the SiN film and thatof the Si wall. Since the wettability of each wasvery close, we assumed that the contact anglesof the SiN film and the Si wall were the same.
From these considerations, the radius ofcurvature R is determined as a simple surface
bubble by the following equation
𝑅𝑅𝑅𝑅 = 𝐿𝐿𝐿𝐿/(2 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 )(1)
From the SEM image of the cross-section, thecontact angle θ′ and footprint length L′ can bemeasured. As shown in Figure 2, θ ′, L′, and R′
are slightly different from θ, L, and R can be
determined from geometric considerations by
the following equation.

Experiments
Liquid cells using Si chips with SiN or Si
membranes (EMJapan Co., Ltd., Tokyo) as
electron-transparent windows were constructed.
The thickness and dimensions of the membrane
were typically 15 nm and 100 µm × 100 µm,
respectively. Electron irradiation of the waterand in situ observation were performed at room
temperature in a vacuum using a conventionalscanning electron microscope (JEOL, JSM6700F). mainly, beam of accelerating voltage is
5kv.

𝑅𝑅𝑅𝑅 = 𝑅𝑅𝑅𝑅𝑅𝑅1 + cos2 𝑠𝑠𝑠𝑠′(2)

θ = cos−1(cos 𝑠𝑠𝑠𝑠′/√1 + 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑠𝑠𝑠𝑠 2 𝑠𝑠𝑠𝑠′)(4)

𝐿𝐿𝐿𝐿 = 2𝑅𝑅𝑅𝑅𝑅 = 𝐿𝐿𝐿𝐿𝐿/sin𝑠𝑠𝑠𝑠′(3)

The real radius of curvature R, which is related

Result and Discussion
Fig. 1. is a cross-sectional SEM image of the

55

(a)

(b)

(c)

(d)

(e)

1 µm

1 µm

2 µm

10 µm

10 µm

Fig 1.

(a)-(e) Cross-sectional SEM images of nano- and microbubbles of various sizes.

Fig 2. Schematic of a bubble formed at an edge and definition of L, L′, θ, θ′, R, and R′. Side
view (bottom) and top view (top).
hemispherical surface bubbles similar to our
results [4]. The simple average of θ′ for the 69
edge bubbles we observed in this study was 69.
Fig 3 shows the smallest bubble that we wereable to observe in this study.If we apply thepreviously shown θ′ to the smallest bubble asshown in Fig 3 (L′ =100 nm), we were able tocalculate the Laplace pressure to be about 25 atm.
Furthermore, it is worth noting here that the
bubble with such a high Laplace pressure
continued to exist for more than three days.

to the Laplace pressure and other physicalproperties of the edge bubble, is determined by
L and L′, but they differ little when θ′ isrelatively large. Since the difference between R
and R′ is small and L′ and θ′ could be measured
directly, L′ and θ′ are used for the bubble formedat the edge in the following discussion. This
does not qualitatively affect the discussion.
An important result from Fig. 1 is that theshape of the bubble is close to a hemisphere,
regardless of its size. This is in contrast to
previous AFM studies, where the bubbles werereferred to as micropancakes due to their shape[2][3]. TEM studies have also shown

Conclusion
Direct cross-sectional observation of bubbles

56

Fig3. (a)–(c) SEM images of nanobubbles. During formation and observation of the
nanobubbles, the irradiation dose ratio was 1–15 × 1015 electrons/cm2⋅s and the electron kinetic
energy was 5 keV. The membrane material was SiN.
formed in situ by electron beam irradiation. The
shape of the bubble was similar to a hemisphereregardless of its size. This result is contrary to
the results of the AFM study, but is very close to
the TEM study. The bubbles also had highLaplace pressure due to this shape, but their
lifetime reached at least three days.

References[1] K.Takahara and S.Suzuki, J. Appl. Phys.
(accepted).
[2] J. R. T. Seddon and D. Lohse, Journal of
Physics: Condensed Matter 23 (13), 133001(2011).
[3] T. Nishiyama, Y. Yamada, T. Ikuta, K.
Takahashi and Y. Takata, Langmuir 31 (3), 982986 (2015).
[4] D. Shin, J. B. Park, Y.-J. Kim, S. J. Kim, J.
H. Kang, B. Lee, S.-P. Cho, B. H. Hong and K.
S. Novoselov, Nature Communications 6 (1),6068 (2015).

57

Irradiation Effect of Atomic Hydrogen on Si Surface
D. Morimoto1, A. Heya2, K. Sumitomo2, S. Ito2, S. Suzuki1, and Y. Haruyama1
Laboratory of Advanced Science and Technology for Industry, University of Hyogo
2
Graduate School of Engineering, University of Hyogo

1

Abstract
The irradiation effect of atomic H on Si surface was investigated by X-ray photoelectron spectroscopy.
After the atomic H irradiation at RT, C atoms on the Si surface were removed but O atoms were notremoved. To control the sample temperature during atomic H irradiation, a heater was installed behind thesample holder. After atomic H irradiation below 660 °C, no spectral change was observed. With increasing
the sample temperature during atomic H irradiation at 830 °C, the peak of the O 1s level disappeared but
a peak of the C 1s level appeared. This indicates that the surface oxide layer on Si surface was removed
and Si carbide was generated during atomic H irradiation at 830 °C.
Introduction
Since the atomic H, which is generated onheated W under ambient H2 gas, is very reactive,
it has been used for a wide range of applications
such as the low-temperature crystallization of aSi [1], the dry etching of crystalline Si [2],vacuum chamber cleaning and photoresist
removal [3]. One of the authors has developed
as the atomic H annealing treatment [1, 4] andhas demonstrated that the Si-rich SiOx film was
reduced and was etched [5]. However, it isconsidered that the atomic H treatment is difficult
to reduce and etch the SiO2 film [6].
In this study, we attempt to remove the nativeoxide on Si surface by irradiating the atomic H.

and H2(5 %) mixture gas was filled at the pressureof 10 Pa and at the flow rate of 100 sccm during
the atomic H irradiation. The distance between W
mesh and the sample was 150 mm in the case of
the atomic H irradiation at RT. To control thesample temperature during atomic H irradiation,a heater made from a rolled W wire with adiameter of 0.4 mm was installed behind thesample holder. In addition, the distance between
W mesh and the sample was approached at 50mm in the case of the atomic H irradiation at
higher sample temperature. The sample
temperature during heating was recorded at a
Cr/Al thermocouple attached to the sample
holder.
X-ray photoelectron spectroscopy (XPS)
experiments were performed by using theconventional
photoelectron
spectroscopy
apparatus, which was mounted with a R3000(VG scienta) hemispherical electron energy
analyzer. The Mg Kα line (hν = 1253.6 eV)
was used as an X-ray source and was incident at
45° with respect to the surface normal. XPS
spectra were measured at the emission angle of
45° to the surface normal. The total energy
resolution was ~0.7 eV. The base pressure in
the photoelectron analysis chamber was 4×10-8
Pa. The typical size of the Si (001) sample for
the XPS measurements was 10×10×1 mm3.

Experiments
The atomic H irradiation apparatus wasconstructed at the BL-07B end station of the
NewSUBARU synchrotron radiation facility, theUniversity of Hyogo. This apparatus is directly
connected to a vacuum chamber of the end station

through a gate valve. In Figs. 1 and 2, a picture
and a schematic diagram of the atomic H
irradiation apparatus are shown, respectively. Asa filament, W mesh composed of 0.03 mmφwire at
the density of 30 wires per inch was used and heatedat the temperature of about 1700 °C. Ar(95 %)

H
Ar＋H₂

Ｗmesh

Heatersamplesample holder

Fig. 2 Schematic diagram of the atomic H
irradiation apparatus.

Fig. 1 Picture of the atomic H irradiation
apparatus.

58

Fig. 5 XPS spectra of a Si 2p level after
atomic H irradiation at RT and at 830 °C.
minutes, the peak intensity of the C 1s level was
decreased considerably. Further, the C 1s level
was not observed after atomic H irradiation for
30 minutes. This indicates that the C atoms on the
Si surface were removed by the atomic H
irradiation.
Figure 4 shows the wide range of XPS spectraof a Si sample as a function of the temperatureduring atomic H irradiation. The atomic H
irradiation time was an hour. After atomic H
irradiation at less than 660 °C, the spectralfeatures were not changed. After atomic H
irradiation at 700-750 °C, the peak intensity of
the O 1s level was decreased and that of the C 1s
level appeared. The origin of the C atoms isprobably due to the reaction with the residual gas
because a base pressure of the atomic H
irradiation apparatus was ~10-6 Pa. After atomic
H irradiation at 830 °C, the peak intensity of theO 1s level was completely eliminated while thethat of the C 1s level was increased. This
indicates that the surface oxide layer was
removed at 830 °C during atomic H irradiation.
In Fig. 5, the XPS spectrum of the Si 2p level
after atomic H irradiation at 830 °C wascompared with that after atomic H irradiation at
RT. After atomic H irradiation at RT, two peaks
were observed at ~104 and ~100 eV. Thesepeaks at ~104 and ~100 eV were assigned tosurface SiO2 and bulk Si components,
respectively.
After atomic H irradiation at
830 °C, the peak at ~104 eV disappeared and a
new peak appeared at ~101.5 eV. From thebinding energy, the peak at ~101.5 eV was
assigned to SiC component [8]. Therefore, it
was found that the Si carbide is generated on thesurface.
In this study, it was found that the surface
oxide layer on Si was removed and Si carbide is
generated at 830 °C during atomic H irradiation.

Fig. 3 Wide range of XPS spectra of a Si sample
at RT as a function of the atomic H irradiation
time.
Results and discussion
Figure 3 shows the wide range of XPS spectraof a Si sample at RT as a function of the atomic
H irradiation time. Before atomic H irradiation,
several peaks originating from the C, O, and Si
atoms were observed in the photoelectron
spectrum. The peaks at ~1000, ~750, ~530,~290, ~150 and ~100 eV were assigned to Augerlevels by C KVV and O KLL decay process, theO 1s level, C 1s, Si 2s and Si Si 2p levels,
respectively [7]. These peak assignments aredenoted beside the top spectrum. It is clear that
there are C and O atoms on the surface of the Si
sample before atomic H irradiation. The O atoms
are derived from the native oxide layer and the C
atoms are from the contamination on the nativeoxide layer. After atomic H irradiation for 10

References[1] A. Heya, A. Masuda, and H. Matsumura: Appl.
Phys. Lett. 74, 2143, (1999).

Fig. 4 Wide range of XPS spectra of a Si
sample as a function of the sample temperatureduring atomic H irradiation.

59

[2] K. Uchida, S. Hashioka, A. Izumi, and H.
Matsumura: 2000 Dry Process Symp., 2000, p.
231.
[3] A. Izumi and H. Matsumura: Jpn. J. Appl.
Phys. 41, 4639, (2002).
[4] A. Heya and N. Matsuo: Jpn. J. Appl. Phys.
46, 3545, (2007).
[5] A. Heya: Proceeding of 26th International
Workshop on Active-Matrix Flatpanel Displays
and Devices (AM-FPD) 2019.
[6] S. Veprek, C. Wang, M. G. J. VepprekHeijman, J. Vac. Sci. Technol. A, 26, 313, (2008).
[7] C. D. Wagner, W. M. Riggs, L. E. Davis, J. F.
Moulder and G. E. Muilenberg: Handbook of Xray photoelectron spectroscopy, ed. G. E.
Muilenberg (Perkin-Elmer, Eden Prairie,
Minnesota, 1978).
[8] Jiahao Guo Kaiyue Song Bingbing Wu Xiang
Zhu Beilin Zhang and Yantao Shi: RSC advances.
7, 22875, (2017).

60

Part 3. List of Publications

New Injector Linac
Papers
1.

"Development of a convenient positron annihilation lifetime and Doppler broadening
measurement system for bulk materials using the 17 MeV gamma beam at the NewSUBARU
synchrotron radiation facility"
Kento Sugitaa, Shuji Miyamotob, Mititaka Terasawab,Sho Amanob, Satoshi Hashimotob, Kenji
Umezawaa, Fuminobu Hori
Nuclear Instruments and Methods in Physics Research Section A, Accepted for publication

2.

"Development of an undulator with a variable magnetic field profile"
T. Tanaka, Y. Kida, R. Kinjo, T. Togashi, H. Tomizawa, S. Hashimoto, S.Miyamoto, S. Okabe, Y.
TanakaJournal of synchrotron radiation 28, pp.404-409 (2020)

3.

"Neutron emission spectrum from gold excited with 16.6 MeV linearly polarized monoenergetic
photons"
Y. Kirihara, H. Nakashima, T. Sanami, Y. Namito, T. Itoga, S. Miyamoto, A. Takemoto, M. Yamaguchi,
Y. Asano
Journal of Nucl. Sci. Technol., vol. 57, no. 4, pp. 444-456 (2020)

4.

"Real-time in vivo dosimetry system based on an optical fiber-coupled micro-sized
photostimulable phosphor for stereotactic body radiation therapy"
R. Yada, K. Maenaka, S. Miyamoto, G. Okada, A. Sasakura, M. Ashida, M. Adachi, T. Sato, T. Wang,
H. Akasaka, N. Mukumoto, Y. Shimizu, and R. Sasaki
Medical Physic, Vo.47, Issue10, pp.5235-5249 (2020)

5.

"Energy and angular distribution of photo-neutrons for 16.6 MeV polarizedphoton on medium–heavy targets"
T. K. Tuyet, T. Sanami, H. Yamazaki, T. Itoga, A. Takeuchi, Y. Namito, S. Miyamoto, Y. Asano
Nuclear Instrum. Methods in Phys. Res. A 989, 164965 (2021). (Available online 17 December 2020)

6.

"Low-lying electric and magnetic dipole strengths in 207Pb"
T. Shizuma, F. Minato, M. Omer, T. Hayakawa, H. Ohgaki, and S. Miyamoto
Phys. Rev. C 103, 024309 (2021). (Published 5 February 2021)

7.

"Local Structure Analysis on Si-Containing DLC Films based on the Measurement of C K-edge
and Si K-edge X-ray Absorption Spectra"
Kazuhiro Kanda, Shuto Suzuki, Masahito Niibe, Takayuki Hasegawa, Tsuneo Suzuki and Hedetoshi
SaitohCoatings, 10 (2020) 330; doi:10.3390/coatings10040330

8.

"Graphene synthesis from pentacene by soft X-ray irradiation"
Akira Heya, Tomohiro Oonuki, Ryuichi Utimi, Kazuhiro Kanda, Ryo Yamasaki and Koji SumitomoThin Solid Films, 713 (2020) 138365; doi:10.1016/j.tsf.2020.138365

9.

"DLC 膜の構造分析法と ISO20523"
神田一浩
表面技術, 71, 543-546 (2020)

10. "Effect of Soft X-ray Irradiation on Film Properties of a Hydrogenated Si-Containing DLC
Film"
Kazuhiro Kanda, Ryo Imai, Shotaro Tanaka, Shuto Suzuki, Masahito Niibe, Takayuki Hasegawa,
Tsuneo Suzuki, and Hiroki Akasaka
Materials, 14, 14924 (2021)

6311. "Control of Molecular Orientation of Spiro-OMeTAD on Substrates"
Naoyuki Shibayama, Hiroyuki Maekawa, Yuiga Nakamura, Yuichi Haruyama, Masahito Niibe, Seigo
Ito
ACS Appl. Mater. Interfaces 12, 50187-50191 (2020). doi: 10.1021/acsami.Oc15509
12. "Effect of nonequilibrium atmospheric pressure O2 plasma-assiated annealing on anatase TiO2
nanoparticls"
Retsuo Kawakami, Yuki Yoshitani, Akihiro Shirai, Shin-ichiro Tanagiya, Hirofumi Koide, Yuki
Mimoto, Kosuke Kajikawa, Masahito Niibe, Yoshitaka Nakano, Chisato Azuma, Takashi Mukai
Appl. Surf. Sci. 526, 146684 (2020). doi: 10.1016/j.apsusc.2020.146684
13. "Electronic structure of a 3x3-ordered silicon layer on Al(111)"
Yusuke Sato, Yuki Fukaya, Mathis Cameau, Asish K. Kundu, Daisuke Shiga, Ryu Yukawa, Koji
Horiba, Chin-Hsuan Chen, Angus Huang, Horng-Tay Jeng, Taisuke Ozaki, Hiroshi Kumigashira,
Masahito Niibe, and Iwao Matsuda
Phys. Rev. Mater., 4, 064005 (2020). DOI: 10.1103/PhysRevMaterials.4.06405.
14. "X-ray absorption and photoemission spectroscopy of bulk insulating materials usinggraphene"
Satoru Suzuki, Yuichi Haruyama, Akinobu Yamaguchi, Tomoki Yamamoto, Takuya Yoshizumi, Ayaka
Fujii, Seiji Nakashima, Yakumo Fuchiwaki, Hironori Fujisawa, Takuo Ohkochi, Mari Ishihara,
Hirosuke Sumida
J. Appl. Phys. 128, 015304-1-8 (2020)15. "Water electrolysis using thin Pt and RuOx catalysts deposited by a flame-annealing method on
pencil-lead graphite-rod electrodes"
R. Tsuji, Y. Koshino, H. Matsutani, Y. Haruyama, M. Niibe, S. Suzuki, S. Nakashima, H. Fujisawa, S.
Ito
ACS Omega 5, 6090-6099 (2020)16. "Immobilizing a π-Conjugated Catecholato Framework on Surfaces of SiO2 Insulator Films via
a One-Atom Anchor of a Platinum Metal Center to Modulate Organic Transistor Performance"
Keishiro Tahara, Yuya Ashihara, Takashi Ikeda, Tomofumi Kadoya, Jun-ichi, Fujisawa, Yoshiki Ozawa,
Hiroyuki Tajima, Noriaki Toyoda, Yuichi Haruyama, and Masaaki Abe
Inorganic Chemistry, 59, 17945–17957 (2020). doi.org/10.1021/acs.inorgchem.0c02163
17. "A Global Shutter Wide Dynamic Range Soft X-Ray CMOS Image Sensor with BacksideIlluminated Pinned Photodiode, Two-Stage Lateral Overflow Integration Capacitor, and Voltage
Domain Memory Bank"
H. Shike, R. Kuroda, R. Kobayashi, M. Murata, Y. Fujihara, M. Suzuki, S. Harada, T. Shibaguchi, N.
Kuriyama, T. Hatsui, J. Miyawaki, T. Harada, Y. Yamasaki, T. Watanabe, Y. Harada
IEEE Trans. Electron Devices 68, 2056-2063 (2021)
18. "A Global Shutter Wide Dynamic Range Soft X-ray CMOS Image Sensor with BSI Pinned
Photodiode, Two-stage LOFIC and Voltage Domain Memory Bank"
H. Shike, R. Kuroda, R. Kobayashi, M. Murata, Y. Fujihara, M. Suzuki, T. Shibaguchi, N. Kuriyama, J.
Miyawaki, T. Harada, Y. Yamasaki, T. Watanabe, Y. Harada and S. Sugawa
IEEE IEDM 2020, 16.4, pp. 339-342 (2020)19. "Analysis of Chemical Contents Spatial Distribution in EUV Resist Using Resonant Soft X-ray
Scattering Method"
Jun Tanaka, Takuma Ishiguro, Tetsuo Harada, Takeo Watanabe
J. Photopolym. Sci. Technol. 33, pp. 491-498 (2020)64

20. "Higher Sensitive Extreme Ultraviolet (EUV) Resist Materials DerivedFrom
p-t-Butylcalix[n]arenes (n = 4 and 8) " (Invited)
Hiroyuki Maekawa, Hiroto Kudo, Takeo Watanabe, Hiroki Yamamoto, Kazumasa Okamoto, Takahiro
KozawaPhotopolym. Sci. Technol., 33, 45-51 (2020)21. "Removal of Surface Contamination by Atomic Hydrogen Annealing"
A. Heya, T. Harada, M. Niibe, K. Sumitomo, and T. Watanabe
J. Photopolym. Sci. Technol. 33, 419-426 (2020)22. "Molecular Structure Evaluation of Bulk Polytetrafluoroethylene Modified by X-ray
Irradiation"
Masaya Takeuchi, Atsushi Kinoshita, Akinobu Yamaguchi, Yuichi Utsumi
Journal of Photopolymer Science and Technology, 33, 3, 295-299 (2020)23. "Design and Fabrication of PTFE Substrate Integrated Waveguide Coupler by SR Direct
Etching"
M. Kishihara, M. Takeuchi, A. Yamaguchi, Y. Utsumi, and I. Ota
IEICE Trans. Electron. Volume and Number: Vol.E104-C, No.9 (2021)
24. "Anisotropic pyrochemical dry etching of fluorinated ethylene propylene induced by
pre-irradiation with synchrotron radiation"
Kaito Fujitani, Masaya Takeuchi, Yuichi Haruyama, Akinobu Yamaguchi, and Yuichi Utsumi
AIP Advances 11, 025104 (2021)
25. "Non-Destructive Imaging on Synthesised Nanoparticles"
Kelvin Elphick, Akinobu Yamaguchi, Akira Otsuki, Neil Lonio Hayagan, and Atsufumi Hirohata
Materials, 14, 613 (2021)
26. "Direct observation of a magnetic domain change in Ni wire and film on a LiNbO3 substrateusing X-ray magnetic circular dichroic photoemission electron microscopy"
Ryo Nakamura, Shunya Saegusa, Naoya Akamatsu, Keisuke Yamada, Takeshi Ogasawara, Masaki
Oura, Takuo Ohkochi, Akinobu Yamaguchi
Japanese Journal of Applied Physics 60, SBBC01-1-5 (2021)
27. "A Lab in Bento Box: Autonomous centrifugal microfluidic system for an enzyme-linked
immunosorbent assay"
Takaaki Abe, Shunya Okamoto, Akinobu Taniguchi, Michiyasu Fukui, Akinobu Yamaguchi, Yuichi
Utsumi, Yoshiaki Ukita
Analytical Methods, 12, 4858-4866 (2020)28. "Highly Stable and Reproducible Au Nanorod Arrays for Near-Infrared Optofluidic SERS
sensor"Samir Kumar, Takao Fukuoka, Ryo Takahashi, Mitsuhiro Yoshida, Yuchi Utsumi, Akinobu Yamaguchi,
Kyoko Namura, Motofumi Suzuki
Materials Letters 286, 129106 (2021)
29. "Visualization of elemental distributions and local analysis of element-specific chemical-states ofArachnoidiscus sp. frustule using soft x-ray spectromicroscopy"
Tomoko Ishihara, Takuo Ohkochi, Akinobu Yamaguchi, Yoshinori Kotani, Masaki Oura
PLOS ONE 15(12), e0243874 (2020)30. "Gold nanoparticles enhance EGFR inhibition and irradiation effects in head and neck65

squamous carcinoma cells"
Masahiko Kashin, Yasumasa Kakei, Shun Teraoka, Takumi Hasegawa, Akinobu Yamaguchi, Takao
Fukuoka, Ryohei Sasaki, Masaya Akashi
BioMed Research International Article ID 1281645 (2020)31. "Application of microprobe soft x-ray fluorescence analyses to characterize the multi-layeredburied micro-structure"
M. Oura, T. Ishihara, A. Yamaguchi
Jpn. J. Appl. Phys., 59, 060902 (2020)32. "Dependence of Gilbert damping constant on microstructure in nanocrystalline YIG thin films
chemically prepared by co-precipitation and spin-coating on a Si substrate"
K. Yamada, K. Kogiso, Y. Shiota, A. Yamaguchi, T. Moriyama, T. Ono, and M. Shima
Journal of Magnetism and Magnetic Materials 513, 167253 (2020)33. "Enhancement of the rectifying voltage and Gilbert damping of a Ni wire fabricated on LiNbO3
substrate"
A. Yamaguchi, R. Nakamura, S. Saegusa, N. Akamatsu, K. -J. Kim, T. Lee, A. Nakao, T. Ohkochi, K.
YamadaJapanese Journal of Applied Physics 59, 083001 (2020)34. "Solid/Liquid-interface-dependent synthesis and immobilization of copper-based particles
nucleated by the X-ray-radiolysis-induced photochemical reaction"
Akinobu Yamaguchi, Ikuya Sakurai, Ikuo Okada, Hirokazu Izumi, Mari Ishihara, Takao Fukuoka,
Satoru Suzuki, and Yuichi Utsumi
Journal of Synchrotron Radiation 27, 1008-1014 (2020)35. "ママイクロ波加熱によるオンチップ金ナノ粒子合成"
竹内雅耶，岸原充佳，福岡隆夫，山口明啓，内海裕一
電気学会論文誌 C Vol. 140, pp. 471-475 (2020)"On Chip Synthesis of Au Nanoparticles by Microwave Heating"
Masaya Takeuchi, Mitsuyoshi Kishihara, Takao Fukuoka, Akinobu Yamaguchi, Yucihi Utsumi
IEEJ Transactions on C Vol. 140, pp. 471-475 (2020)36. "Lab-on-a-disc におけるオイラー力を用いた異密度液体の混合"
竹内雅耶，藤谷海斗，三枝峻也，石本睦，山口明啓，内海裕一
電気学会論文誌 C Vol. 140, pp. 465-470 (2020)"Mixing of difference density liquids by Euler-force on Lab-on-a-disc"
Masaya Takeuichi, Kaito Fujitani, Atsushi Ishimoto, Akinobu Yamaguchi, Yuichi Utsumi
IEEJ Transactions on C Vol. 140, pp. 465-470 (2020)37. "Observing the Delamination Interface in Multi Layered Thin Films with a MgAg Alloy Top
Layer and Organic Semiconductor under Layers on a Flexible Substrate"
KOBAYASHI Toshiro, FURUMOTO Hideaki, YAMAGUCHI Akinobu, KANEMATSU Hideyuki,
GRUESCU Ion Cosmin
Advanced Experimental Mechanics, Vol.5, pp.151-156 (2020)
Books
1.

"Characterization of Hydrogen-Free and Hydrogenated DLC Films"
Toru Harigai, Takahiro Imai, Hirofumi Takikawa, Satoru Kaneko, Shinsuke Kunitsugu, Masahito
Niibe, Kazuhiro Kanda and Masao Kamiya
in "Carbon Related Materials", Springer, 2020, pp. 55-69 (ISBN 978-981-15-7610-2)

66

Proceedings
1.

"Resist pattern inspection for defect reduction in sub-15 nm templates"
T. Motokawa, M. Suenaga, K. Hagihara, N. Iida nee Sakurai, R. Komatsu, H. Sakurai, S. Kanamitsu,
K. Tsuda, T. Harada, T. Watanabe
Proc. SPIE 11518 (2020) 115180H.

2.

"Showcase of the Fundamental Research to Resolve the Technical Issues in EUV Lithography at
NewSUBARU Synchrotron Light Facility of University of Hyogo" (Invited)
Takeo Watanabe, Tetsuo Harada, Shinji Yamakawa
Proceedings of EUVL International Workshop 2020.

3.

"Reflectance Measurement of EUV Mask under OoB-Irradiation, and Hydrogen and Water
Vapor Environments under the High Power EUV Irradiation" (Invited)
Takeo Watanabe and Tetsuo Harada
Proceedings of EUVL International Workshop 2020.

4.

"Showcase of the Fundamental EUVL Research" (Invited)
Takeo Watanabe, Tetsuo Harada, and Shinji Yamakawa
Proceedings of 2020 EUVL Supplier Showcase.

5.

"Fundamental Research Activities of EUV Lithography at NewSUBARU Synchrotron Light
Facility" (Invited)
Takeo Watanabe and Tetsuo Harada
Proceedings of High-brightness Sources and Light-driven Interactions Congress, OSA, Nov. 16-20,
2020.

6.

"Fundamental Research Activities of EUV Lithography at NewSUBARU Synchrotron Light
Facility" (Invited)
Takeo Watanabe and Tetsuo Harada,
Proceedings of 5th EUV-FEL Workshop 2021, Jan. 22, 2021

7.

"Real-time optical monitoring of cell culture in centrifugal microfluidics"
Edwin En-Te Hwu, Lina Gruzinskyte, Atsushi Ishimoto, Laura Serioli, Sriam Thoppe Rajendran,Akinobu Yamaguchi, Kinga Zór, and Anja Boisen
The 24th International Conference on Miniaturized Systems for Chemistry and Life Science (mTAS
2020), pp. 1039 - 1040 (2020)

Articles1.

"Synchrotron radiation extreme ultraviolet lithography technology that opens up the world ofinnovative IoT and AI" (Invited paper)
Takeo Watanabe
Clean Technology, 2, pp.1-5 (2020). (in japanese)

67International Meetings
1.

"GDR cross sections updated in the IAEA-CRP"
H. Utsunomiya, I. Gheorghe, D. M. Filipescu, K. Stopani, S. Belyshev, H. Wang, G. Fan, T.i Ariizumi,
Y.-W. Lui, D. Symochko, M. Krzysiek, S. Miyamoto, S. Goriely, and T. Kawano
EPJ Web of Conferences 239, 01002 (2020)
https://doi.org/10.1051/epjconf/202023901002

2.

"NEXAFS evaluation for the lumen of DLC coated small diameter long-sized medical objective
tube by using AC high-voltage burst plasma CVD method"
Yuichi Imai, Kazuhiro Kanda, Yasuhiro Fujii, Susumu Ouzawa, Daiki Ousaka and Tatsuyuki Nakatani
12th International Symposium on Advanced Plasma Science and its Applications for Nitrides andNanomaterials / 13th International Conference on Plasma-Nano Technology & Science(ISPlasma2020/IC-PLANTS2020) [10P2-52], 2020.3.8-11, Nagoya University

3.

"Stability of Amino Acid Precursors in Space: Verification by Ground Simulations and Space
Experiments"
Kensei Kobayashi, Tomohito Sato, Takuya Yokoo, Soushi Kuramoto, Yoko Kebukawa, Hajime Mita,
Miki Nakayama, Kazumichi Nakagawa, Hiromi Shibata, Hitoshi Fukuda, Yoshiyuki Oguri, Isao Yoda,
Satoshi Yoshida, Kazuhiro Kanda, Itsuki Sakon, Hajime Yano, Hirofumi Hashimoto, Shin-ichi Yokobori
and Akihiko Yamagishi
European Astrobiology Network Association 2020 (EANA2020) 2020.8.27-28 virtual meeting

4.

"A Global Shutter Wide Dynamic Range Soft X-ray CMOS Image Sensor with BSI Pinned
Photodiode, Two-stage LOFIC and Voltage Domain Memory Bank"
H. Shike, R. Kuroda, R. Kobayashi, M. Murata, Y. Fujihara, M. Suzuki, T. Shibaguchi, N. Kuriyama, J.
Miyawaki, T. Harada, Y. Yamasaki, T.Watanabe, Y. Harada and S. Sugawa
IEEE IEDM 2020, Online, 2020/12.

5.

"Resist pattern inspection for defect reduction in sub-15 nm templates "T. Motokawa, M. Suenaga, K. Hagihara, N. Iida nee Sakurai, R. Komatsu, H. Sakurai, S. Kanamitsu, K.
Tsuda, T. Harada, T. Watanabe
SPIE Photomask technology 2020, Online, 2020/9.

6.

"Removal of Surface Contamination by Atomic Hydrogen Aneealing"
A. Heya, T. Harada, M. Niibe, K. Sumitomo, and T. Watanabe
ICPST37, Japan, 2020/6.

7.

"Analysis of Chemical Contents Spatial Distribution in EUV Resist Using Resonant Soft X-ray
Scattering Method"
Jun Tanaka, Takuma Ishiguro, Tetsuo Harada, Takeo Watanabe
ICPST37, Japan, 2020/6.

8.

"Showcase of the Fundamental Research to Resolve the Technical Issues in EUV Lithography at
NewSUBARU Synchrotron Light Facility of University of Hyogo" (Web online) (Invited)
Takeo Watanabe, Tetsuo Harada, Shinji Yamakawa
EUVL International Workshop, Jun. 2020, Berkeley, CA, USA, Jun. 7-11, 2020.

9.

"Reflectance Measurement of EUV Mask under OoB-Irradiation, and Hydrogen and Water
Vapor Environments under the High Power EUV Irradiation"
Takeo Watanabe and Tetsuo Harada

68

EUVL International Workshop (Web online), Jun. 2020, Jun. 7-11, 2020.
10. "Higher Sensitive Extreme Ultraviolet (EUV) Resist Materials Derived From
p-t-Butylcalix[n]arenes (n=4 and 8) "Hiroyuki Maekawa, Hiroto Kudo, Takeo Watanabe, Hiroki Yamamoto, Kazumasa Okamoto, Takahiro
KozawaICPST-37, Japan, May. 18-21, 2020.
11. "Showcase of the Fundamental EUVL Research" (Web online) (Invited)
Takeo Watanabe, Tetsuo Harada, and Shinji Yamakawa
2020 EUVL Supplier Showcase, Web conference by ZOOM, 2020.Sep. 14-15, 2020.
12. "Fundamental Research Activities of EUV Lithography at NewSUBARU Synchrotron Light
Facility" (web online) (Invited)
Takeo Watanabe and Tetsuo Harada
High-brightness Sources and Light-driven Interactions Congress, OSA, Nov. 16-20, 2020.
13. "Fundamental Research Activities of EUV Lithography at NewSUBARU Synchrotron Light
Facility" (Web online) (Invited)
Takeo Watanabe and Tetsuo Harada
5th EUV-FEL Workshop 2021, Jan. 22, 2021.
14. "Aqueous-soluble Ink including Nano Beacon"
Akinobu Yamaguchi, Yuichi Utsumi, Kyoko Namura, Motofumi Suzuki, and Takao Fukuoka
L51-03, Pittcon 2021, March 11, 2021. Oral.
15. "Real-time optical monitoring of cell culture in centrifugal microfluidics"
Edwin En-Te Hwu, Lina Gruzinskyte, Atsushi Ishimoto, Laura Serioli, Sriram Thoppe Rajendran,Akinobu Yamaguchi, Kinga Zór, and Anja Boisen
M1-180.e, The 24th International Conference on Miniatuarized Systems for chemistry and life sciences(µTAS 2020), October 5, Monday, 2020.
16. "Study on magnetic properties of artificial magnets induced by ferromagnetic/ferroelectric
heterojunction"
Akinobu Yamaguchi, Ryo Nakamura, Shunya Saegusa, Naoya Akamatsu, Aiko Nakao, Yuichi Utsumi,
Masaki Oura, Takeshi Ogasawara, Keisuke Yamada, Takuo Ohkochi
IEEE-NEMS 2020 (The 15th IEEE International Conference on Nano/Micro Engineered & Molecular
Systems,” TS9-3, September 29, 2020, Oral
17. "Study on solid/solid- and solid/liquid-interface-dependent material properties for an artificial
multiferroic system and additive manufacturing process"Akinobu Yamaguchi, Shunya Saegusa, Ryo Nakamura, Naoya Akamatsu, Aiko Nakao, Ikuya Sakurai,
Ikuo Okada, Yuichi Utsumi, Takeshi Ogasawara, Keisuke Yamada, Masaki Oura, Takuo Ohkochi2020 International Conference on Solid State Deives and Materials (SSDM 2020), C-2-04, September 28,
2020, Oral

69

Academic Degrees
Master of Engineering
Takuma Ishiguro (University of Hyogo)"Resonant Soft X-ray Reflectivity for the Chemical Analysis in Thickness Direction of EUV Resist"
Ayato Ohgata (University of Hyogo)"Hydrogen Damage Evaluation of Mo/Si Multilayer using High-Power EUV Irradiation Tool"
Jun Tanaka (University of Hyogo)"Analysis of Chemical Contents Spatial Distribution in EUV Resist Using Resonant Soft X-ray Scattering
Method"Keisuke Tsuda (University of Hyogo)"Development of Grazing-Angle Coherent EUV Scatterometry Microscope for Resist Pattern Observation"
Atsushi Ishimoto (University of Hyogo)"Study on implementation of mixing system in microfluidic devices"
Shunya Saegusa (University of Hyogo)"Particle agglutination control by microsystem and its application to molecular sensor"
Ryo Nakamura (University of Hyogo)"Creation of novel artificial materials consisting of heterojunction and study on their physical properties"

70

LASTI Annual Report Vol. 22 (2020)                             
October 2021, Published byLaboratory of Advanced Science and Technology for Industry
University of Hyogo
3-1-2 Kouto, Kamigori-Cho, Ako-gun, Hyogo 678-1205, JAPAN
Phone: +81-791-58-0249 / FAX: +81-791-58-0242

Editorial board
Tetsuo Harada (Editor in Chief)
Kouji Nakanishi
Yoshihiko Shoji
Yuichi Haruyama
Akinobu Yamaguchi                             