Highlight
FEL

Threshold Photoemission Magnetic Circular Dichroism Using Free Electron
Laser
T. Nakagawa, T. Yokoyama, M. Hosaka, M. Katoh
Institute for Molecular Science (IMS), Okazaki 444-8585, Japan
photoemission threshold, in agreement with theexperimental result.
While the above experiment changes workfunction
to achieve high MCD asymmetry near the threshold,photon energy tuning is another possibility.
Our experiment needs two properties: tunable wave
length and high photon density. As shown in Fig.1, to
obtain high MCD asymmetry we have to tune thephoton energy a little higher than the workfunction.
We have used tunable free electron laser fromUVSOR-II, which can deliver lower energy than hȞ =6.3 eV, close to typical workfunction for transition
metal surfaces without surface modification such asalkali metal adsorption. Second, MCD method inmagnetic field has to be measured by electron draincurrent from the ground to the sample since thetrajectory of emitted electrons strongly depends onthe magnetic field. This prevents the use of electron
multiplier and needs high light intensity to give
sufficient photoelectrons. The FEL in UVSOR candeliver ~100 mW around hȞ = 5 eV [4], which ismuch stronger than usual laser output in thisMagnetic circular dichroism (MCD) in the x-ray
regions (XMCD) has widespread over thesynchrotron radiation facilities all over the world
because of its high sensitivity to the element specificmagnetism. The MCD depends on spin polarizationand spin-orbit coupling.[1,2] Since the spin orbit
coupling is strong in the core shell and the spinpolarization in conduction band is large, x-ray MCD
gives large MCD asymmetry. Now its high sensitivity
combined with electron microscopy, called
XMCD-photoemission
electronmicroscopy(XMCD-PEEM), is used as a very powerful tool forthe nano-scale
magnetic domain imaging.
XMCD-PEEM has been developed into time resolved
imaging by using time structure of synchrotron
radiation. On the other hand, MCD in the regions
from infrared to ultraviolet (UV) is also a useful tool
for the study of ferromagnetic ultrathin films. The
magneto-optical Kerr effect (MOKE) detects therotation and distortion of the polarization of reflected
lights from magnetic materials. The Kerr effect invalence bands in thin films usually rotates thepolarization and changes the ellipticity only by
10-2-10-6 rad. This is because of its weak spin orbit
coupling, although the spin polarization is large in thevalence band. In the valence band photoemission,nevertheless, extensive works have been performed
using circularly polarized synchrotron radiation andangle-resolved measurement, showing high (~10%)
asymmetry [1,2]. The large asymmetry is attributed tothe angle and energy selection of spin orbit split band.
This requirement is not suitable for magnetic
properties such as magnetization hysteresis curves ormagnetic domain imaging because an electron
analyzer is inevitable.
We have investigated the observation of enhanced
MCD near the Fermi level using visible andultraviolet lasers in a total yield mode [3]. Figure 1
shows MCD asymmetry as a function of
workfunction subtracted by photon energy. Here theworkfunction is varied by Cs adsorption and thephoton energy is fixed. More than 10% MCD
asymmetry is achieved on perpendicularly
magnetized 12 ML Ni film on Cu(001), andmagnetization curves are obtained. By changing thework function with the aid of cesium adsorption, thelaser experiments show that the MCD asymmetry isenhanced only near the photoemission threshold, andthat the asymmetry drops to 0.1% for photon energy
larger than the work function by 0.6 eV. A theoretical
calculation also shows enhanced dichroism near the

Fig. 1. (top) MCD asymmetry on Ni(12 ML)/Cu(001)surface as a function of workfunction – photon energy.
Cs is used to change workfunction. The blue line isfor hv = 3.25 eV, while the red 1.95 eV. The inset
shows the inversion of MCD sign at 1 eV. (bottom)
The corresponding theoretical calculation using
Wien2k [6].

47Highlight

Fig. 3. UV-MCD-PEEM image on Cs/Ni(12ML)/Cu(001). The field of view is 25 Pm. The
magnetic domain image is the processed result of theimages by the right and left circular light. The red andblue regions are opposite magnetization directions.
Fig. 2. Magnetization hysteresis curve on
Ni(8ML)/Cu(001) taken by FEL-MCD. The plot
gives 6% asymmetry. Also shown is the data taken by
conventional MOKE.

[1] C. M. Schneider et al., Phys. Rev. B 44 (1991)
R12066.
[2] W. Kuch, C.M. Schneider, Rep. Prog. Phys. 64(2001) 147.
[3] T. Nakagawa, T. Yokoyama, Phys. Rev. Lett. 96(2006) 237402.
[4] M. Hosaka et al., Nucl. Instrum. Methods A 483(2002) 146.
[5] T. Nakagawa et al., Rev. Sci. Instrum. 78 (2007)
023907. 㻌[6] P. Blaha et al., Computer code WIEN2k(Technische Universitat Wien, Vienna, 2002).

wavelength region. Furthermore the light is circularly
polarized inherently. Owing to its tunability and highintensity, FEL at UVSOR-II is a suitable source tothreshold photoemission MCD measurements.
Figure 2 shows a magnetization hysteresis curve on
Ni(8 ML)/Cu(001) using hȞ = 5.37 eV, where thephotoemission threshold for Ni is ~5.3 eV [5]. As
expected from the result shown in Fig. 1, theasymmetry is high, ~6%, near the threshold. This
result evidences that the clean Ni surface also showshigh asymmetry near the photoemission threshold.
The result from conventional magneto-optical Kerr
effect is also shown together in Fig.2, having asimilar hysteresis shape, which confirms the validityof the MCD method.
MCD in the valence band is strong enough formicroscopic measurement. We can measure magnetic
domain imaging using photoemission microscopy,
which needs high brilliance. Figure 3 shows
UVMCD-PEEM result. Unfortunately a FEL-PEEM
measurement is still under construction, and here weshow a result by a laptop laser. The laser used is LD
laser, whose photon energy is 3.06 eV and output
power is 5 mW. The magnetic domains(perpendicular to the surface) are clearly visible,
giving good contrast. This result promises that FEL isbrilliant enough for MCD-PEEM measurements, and
MCD-PEEM with FEL is expected to be used for thereal time imaging of the magnetic domains undersurface modifications.

48

BL1A

Performance of CVD Diamond Photon Detectors in the Soft X-Ray Region
Y. Iwakaji, M. Kanasugi, S. Iguchi, O. Maida, T. Ito
Division of Electrical, Electronic and Information Engineering,
Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

Introduction
Since diamond with a bandgap of 5.5 eV has suchvarious excellent properties as high breakdown
electric field, high thermal conductivity and highchemical stability, it is considered as one of theelectronic materials most suitable for high-
performance radiation detectors working under severe
environments. We have so far been investigating
fabrication processes of high-quality single-crystalline
diamond films using a high-power MWPCVD(microwave-plasma chemical vapor deposition)
method [1], and have reported on performances ofphoton detectors fabricated with such high-quality
diamond films for ultraviolet and soft-X-ray photons
with energies below 2 keV [2-4]. In the present study,
the room-temperature performance of such CVD
diamond detectors has been investigated forsoft-X-ray photons of 2.0 – 4.5 keV.

Experimental
Three high-quality homoepitaxial CVD diamondlayers (undoped, boron-doped and undoped ones)
were grown sequentially on a high-temperature /high-pressure-synthesized Ib (100) diamond substratewith a size of 3×3×0.5 mm3. The typical thickness ofthe topmost undoped diamond layers used for thephoton detection was §50 ȝm. After the homoepitaxial growth processes, thin TiN electrodes wereformed for the topmost layer using a standard
photo-lithography technique and a magnetron sputtering method while Ti/Au bi-layer electrodes were
deposited for the buried B-doped layer.
To one of detection areas of the diamond detector
thus fabricated, photons with energies of 2.0 – 4.5
keV were irradiated through an aperture of §1 mm indiameter. Signal currents were measured at various
bias voltages (Vb) of  100 V. The number of theincident photons was calibrated using a Si photon
detector and the temporal storage ring currents.

This means that the diamond detector has animportant function of increasing amplifications with
the increasing Vb, as previously reported [3,4].
On the other hand, at each constant Vb, QE increases
with increasing Eph < §3 keV, above which QE
decreases with increasing Eph. At Vb = 10 V, QE isroughly proportional to Eph below §3 keV, which wellreflects the number of the electron-hole pairs createdin the topmost undoped diamond layer by the incident
photons. The critical Eph (§3 – 3.5 keV) corresponds
roughly to the penetration depth of the photons in
diamond which equals to the thickness of thedetection (topmost undoped diamond) layer. It is also
found that QE increases more strongly with theincreasing Eph at Vb = 100 V than at Vb = 10 V,
indicating that both the location the excited carriers
are created and the number of the excited carriers areimportant factors for the observed signal amplification phenomenon. A possible origin of the amplification is considered to be related to the local high fields
formed near the thin TiN electrodes [3,4].
This work was partly supported by the JSPS,
Grant-in-Aid for Scientific Research (B) (19360018).
6

10

5

Quantum Efficiency

10

10 V
100 V

4

10

3

10

ℕ‒Energy

2

10

1

10

0

10

2000

3000

4000

Energy [V]Results and discussion
Although the number of the incident photons
decreased significantly with the increasing photon
energy (Eph) in the energy region concerned in thisstudy, the signal currents of the diamond detectors
were able to be measured. The quantum efficiency ofthe photon detector (QE) is given by the quotient of
the signal current divided by the product of theelement charge and the number of incident photons.
Figure 1 shows typical plots of QE versus Eph for two
different Vb. On one hand, QE at each Eph is found toincreased greatly (abnormally) with increasing Vb.

Fig. 1. Photon energy dependence of the quantum
efficiency of a diamond detector at the detector bias
voltages of 10 and 100 V.
[1] T. Teraji, T. Ito, J. Cryst. Growth 271 (2004) 409.
[2] T. Teraji et al., Diamond Relat. Mater. 13 (2004)
858.
[3] H. Matsubara et al., Diamond Relat. Mater. 16(2007) 1044.
[4] Y. Iwakaji et al., Appl. Surf. Sci. in press.

49

BL1B, BL7B

Evaluation of New Monochromatic Light Sources for ELEPES

G. Funabashi1, A. Sekiyama1, H. Fujiwara1, M. Hasumoto2, T. Ito2, S. Kimura2,
P. Baltzer3, S. Suga1
1
Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531,
Japan
2
UVSOR-II, Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan
3
MB Scientific AB, Seminariegatan 29B, SE-75228, Uppsala, Sweden
In recent years, the extremely-low-energy (< ~12eV) excitation photoemission study called ELEPES(extremely low energy photoelectron spectroscopy)
has attracted much attentions due to its high potential
for high bulk-sensitivity and high energy-resolution.
However, this technique is not so popular because
there are no conventional light sources at present.
Therefore, we propose the new monochromatic lightsources for ELEPES by means of rare-gas (Ar, Kr,
and Xe) resonance lines and the low-energy-passfilters (LiF, CaF2, and sapphire).
We performed the transmission measurement andthe monochromatization experiment at BL1B and
BL7B of UVSOR-II, respectively.
Ar I resonance lines appear at ~1040 and 1060 Å.
The transmittance limit of LiF is located at ~1040 Å
at room temperature (RT). This value is insufficient
to realize a single monochromatic line. According to
the transmission measurement, the limit wavelengthis ~ 1045 Å at ~50 °C which should be sufficient to
cut the 1040-Å component. Thus, Ar I resonancelines are monochromatized by LiF heated up to~50 °C resulting in 1060-Å (11.7-eV) monochromatic
light. Kr I resonance lines appear at ~1158 and 1230
Å. The transmittance limit of CaF2 is located at~1205 Å at RT and it is sufficient to monochromatize
those lines. Thus, we can get the monochromatic lightof 1230 Å (10.1 eV) from Kr. Finally, Xe I resonancelines appear at ~1464 Å and below 1300 Å (Fig. 1(a)).
The transmittance limit of sapphire is located at~1430 Å at RT and it is sufficient to monochromatize
the lines. We can obtain the monochromatic light of
1464 Å (8.47 eV) from Xe (Fig. 1(b)).
Additionally, we measured the line width of Kr I
and Xe I main lines. The line width of Kr I main line
was measured not with the highest resolution setting.
However, the obtained spectrum can be fitted by aGaussian curve with the width of 1.34 meV.
Considering the resolution, the intrinsic line width isestimated to better than 1 meV. On the other hand, theline width of Xe I main line was measured with thehighest resolution setting (E/'E~20,000) at thesacrifice of the intensity. The obtained spectrum isfitted by a Gaussian with the width of ~600 eV (Fig.
1(c)). The energy resolution at this wavelength (1464Å) is ~423 eV, so the intrinsic line width of Xe I
main line is estimated to be ~426 eV, which is, atleast, much better than 500 eV.
For the transmission efficiency, the transmittance ofIntensity (arb. units)

1-mm-thick LiF heated up to ~50 °C is approximately
40 at 1060 Å (Ar I). Those of 1-mm-thick CaF2 and
2-mm-thick sapphire at RT are approximately 50 and
45 at 1230 (Kr I) and 1464 Å, respectively. The
thinner (0.5-mm-thick) filters are expected to be moretransparent at each line (Ar I: ~55, Kr I and Xe I:~80). Therefore, we can obtain the monochromaticlines with high intensity by using them.
In conclusion, we proposed the new monochromatic
light sources for ELEPES using rare-gas (Ar, Kr, andXe) resonance and the low-energy-pass filters.
Performance test was performed. Thus, it was foundthat they are useful new ultrahigh-resolution
monochromatic light sources for ELEPES.
(a) XeIntensity (arb. units)

1100 1150 1200 1250 1300 1350 1400 1450
Wavelength (Å)(b) Xe through sapphire

1100 1150 1200 1250 1300 1350 1400 1450
Wavelength (Å)

Intensity (arb. units)(c) Xe I mainExp.
fitting
FWHM~ 600 PeV

1464.01464.21464.4
Wavelength (Å)

1464.6

Fig. 1. (a) Xe resonance lines without filter, (b)monochromatized spectrum by using a sapphire filter
at RT. (c) Major resonance line of Xe lamp for thehighest resolution setting of the monochromator(~20,000).

50

BL4B

X-Ray Magnetic Circular Dichroism System Using Superconducting
Magnet and Liquid He Cryostat
T. Nakagawa1, Y. Takagi1, Y. Matsumoto2, T. Yokoyama1
Institute for Molecular Science, Okazaki 444-8585 Japan
2
Japan Atomic Energy Institute, Tokai, Ibaraki 319-1195, Japan1

future magneto-optical Kerr effect (MOKE) and/or
laser-induced photoemission MCD measurements, thechamber possesses several ICF70 viewing ports
accessible to the center of the magnet. These ports
enable the MOKE measurements with the polar andtransverse configurations. The chamber is pumped
with a turbo molecular pump, which can be shut
down during liquid He insertion. The base pressure is
below 2×10í10 Torr at the ionization gauge positionand should be much lower at the sample position.
The XMCD system was installed at Beamline 4B
of UVOSR-II in IMS. The beamline is a bending-magnet soft X-ray station equipped with a variedline spacing grating monochromator, which covers
the photon energies of 25–1000 eV. The circularly
polarized X-rays were obtained by adjusting the vertical aperture upstream of the first mirror. The
circularly polarization factor of Pc=0.70–0.85 can beobtained with a reasonable photon intensity.
The examples of measured spectra can be referred
to in this booklet.

Introduction
The X-ray magnetic circular dichroism (XMCD)
technique has become matured as a valuable element-specific tool for the determination of microscopic spin- and orbital magnetic moments method.
The measurement under high magnetic field and low
temperature is substantially important when one
wants to investigate, for instance, magnetic anisotropy. This is because saturation magnetization isessential to estimate precisely the spin and orbital
magnetic moments along a magnetically hard axis.
Since the XMCD system with a superconducting
magnet and a liquid He cryostat [1] is not populararound the world especially for public use, we have
exploited a new system in this work [2].

Design and Performance
We have designed and fabricated a new XMCD
measurement system with a 7 T UHV-compatible
superconducting magnet. The system consists of two
separated UHV chambers for XMCD measurement
and sample preparation. The schematic view and image of the system are depicted in Fig. 1. The sample
preparation chamber is equipped with metal evaporators, reflection high-energy electron diffraction(RHEED) or low-energy electron diffraction and Auger electron spectroscopy (LEED/AES) optics, an ion
gun, a sample heating system, and so forth. The
chamber is evacuated with a turbo molecular pump, a
non-evaporation getter pump and a Ti sublimation
pump. The base pressure is around 8×10í11 Torr.
The measurement chamber was constructed by
JANIS Research Company. The system (model
7THM-ST-UHV) consists of a superconducting magnet and a variable temperature insert. The magnet is a
7 T (horizontal field) split multifilamentary NbTi
superconducting magnet with a homogeneity of±0.5% over a 1 cm diameter sphere. The sweep
speeds are 1 T/min up to 5 T and 0.25 T/min from 5
to 7 T. A liquid helium reservoir with a 25 l capacity
and a minimum of 12 h static hold time (24 h holdtime without applying magnetic field) was used.
The sample cryostat has a built in heater and two
calibrated Cernox thermometers plus a two-section
high-efficiency continuous-flow-type liquid heliumtransfer line. This offers the lowest sample temperatures of ~4.8 K for accumulated He and ~3.8 K for
pumped He.
The sample cryostat can be rotated 360q, allowing
us to measure angle-dependent XMCD spectra. A
sample holder is a hexagonal Mo with a screw. For

Fig. 1. Schematic rear view and image of XMCD
measurement system. The X-rays come from the backsurface with a configuration parallel to a magnetic
field. The liquid He reservoir with a 25 l capacity issurrounded by a liquid nitrogen reservoir with anominal 10 l capacity.
[1] T. Koide, T. Shidara, H. Fukutani, Rev. Sci.
Instrum. 63 (1992) 1462.
[2] T. Nakagawa, Y. Takagi, Y. Matsumoto, T.
Yokoyama, Jpn. J. Appl. Phys., in press.

51

BL4B

Sensitivity Calibration of a Compact Flat-Field EUV Spectrometer for theDevelopment of Extreme Ultraviolet Light Sources
H. Tanuma1, H. Ohashi1, S. Suda1, S. Fujioka2, H. Nishimura2, K. Nishihara2, T. Kaneyasu3
1
Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan
2
Laser Engineering, Osaka University, Osaka 565-0871, Japan
3
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan

Extreme ultraviolet lithography (EUVL) is expected
to be used as one of the key technologies in the next
generation semiconductor device production. Notingthat a Mo/Si multi-layer mirror has the highest
reflectivity of about 70% at 13.5 nm of wavelength, alight source peaking of emission around 13.5 nm
should be selected for the EUVL technology. For thispurpose, a laser-produced plasma (LPP) of tin andxenon is an extremely attractive light source due to its
compactness and high efficiency, and it has been
investigated both experimentally and theoretically allover the world in this decade [1].
For the understanding of plasmas, spectroscopic dataon ions composing the plasmas is definitely required
as necessary information. The available spectroscopic
data on tin and xenon ions, however, is fairly limited
at this moment in time. Publishing works on xenon
ions through December 2002 have been compiled by
Saloman [2]. Even in this most detailed article about
the energy levels and spectral lines of xenon ions, thenumbers of levels and lines are not so many and notnearly as good as complete for the multiply charged
states. On the other hand, the spectroscopic data of tinions has not be compiled since the historical work by
Moore [3] and is extremely scanty in particular for
highly charged states.
In order to provide the fundamental spectroscopic
data on tin and xenon ions, we have performed themeasurement of various emission spectra frommultiply charged tin and xenon ions with charge
exchange spectroscopy in Tokyo Metropolitan
University [4-6]. In a series of these experiments, wehave used a compact flat-field grazing-incident
spectrometer, which is equipped with a toroidal-type
conversing mirror and a varied line spacing groove
grating blazed at 100 nm, and a liquid nitrogen cooled
CCD camera as a detector. Efficiencies of thespectrometer and the detector depend on the
wavelength. To discuss not only absolute emission
intensities also relative intensity distribution, theefficiency should be investigated by experimental
measurements.
Absolute efficiency of a similar grating has beenstudied using bremsstrahlung continuum from LHD(Large Helical Devise) plasmas in NIFS [7], and thesensitivity of a similar CCD has been measured in thesynchrotron radiation facility BESSY [8]. However,
we wish to know the efficiency of the overall system.
Figure 1 shows a typical spectrum measured in thisexperiment. This spectrum was observed with
injection of 14 nm as the first order light fromUVSOR at BL4B with the grating G3 into thecompact EUV spectrometer. As can be seen, theprominent peak is at 7 nm. This finding indicates thatthe second order of the diffraction at the G3 issignificant. Not only the higher order light from theG3 but also higher order light from the grating GC in
the compact spectrometer can be observed in thisfigure. For example, the weak peak at 8 nm can be
assigned as the 4th order of the GC and the 7th orderof the G3.
Because of the very complicated contribution of thehigher order lights, the analysis of the obtained data
has not be finished at all. We, however, wish tocontinue the analysis to obtain some results on thehigher order diffraction of the gratings and thedetection efficiency of the spectrometer.

Fig. 1. Observed emission spectrum with injection of
14 nm into a compact EUV spectrometer.
[1] V. Bakshi, “EUV Light Sources for Lithography”(SPIE Press, Washington, 2005).
[2] E. B. Saloman, J. Phys. Chem. Ref. Data 33(2004) 765.
[3] C. E. Moore, NSRDS-NBS 35 (1971).
[4] H. Tanuma et al., Nucl. Instrum. Meth. B 235(2005) 331.
[5] H. Tanuma et al., J. Phys. Conf. 58 (2007) 231.
[6] H. Ohashi et al., J. Phys. Conf. 58 (2007) 235.
[7] M. B. Chowdlhuri et al., Rev. Sci. Instrum. 78(2007) 023501.
[8] G. Schriever et al., Rev. Sci. Instrum. 68 (1997)
3301.

52

BL5B

Design and Fabrication of Wide-Band Multilayer for 40 – 30 nm Region
T. Goto1, T. Ejima1, S. Kimura2
1
Institute for Multidisciplinary Research for Advanced Materials, Tohoku University,
Sendai 980-8577 Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan

Monochromators used in the vacuum ultraviolet
region (O200nm) are normal-incidence one in longer
wavelength region (O!50nm) and grazing-incidence
one in shorter wavelength region (O50nm) [1],because normal-incident reflectances of conventional
mirrors decrease in the shorter wavelength region.
Merit of the normal-incidence monochromators ishigh wavelength-resolution if both types ofmonochromators can be applied in a same wavelength
region. Recently, some reflection multilayers weredeveloped in 50 – 30 nm wavelength region, therefore
possibility that normal incidence monochromators
will be applied in this wavelength region was
suggested [2, 3]. In this study, it were made thatdesign and fabrication of wide-band reflection
multilayer
mirrors
andapplying
developed-multilayers to the M1 mirror of BL7U at
UVSOR-II [4].
Multilayers for normal incidence (I 7.5q) were
designed to increase the bandwidth while maintaining
the reflectivity in 40 – 30 nm wavelength region. The
first step of the design was to select material pairsthat show high reflectance in the wavelength region.
Among the selected pairs, the pairs to show wide
bandwidth of reflectance were chosen. Finally,
Mg/SiC pair was remained, because reflection
multilayers using this material pair show both highreflectivity and wide band-width. Obtained design
parameters are listed in Table 1, and the calculated
reflectances using these parameters are shown as
solid curves in Figure 1.
The multilayers were deposited on Si substrates(L25.4uW25.4uH10mm) for the M1 mirrors of BL7U
beamline using a conventional magnetron sputteringsystem (ANELVE SPL-500). For evaluation of
fabricated multilayer mirrors, the multilayers were
deposited simultaneously on Si wafers. Deposition
rates were controlled to keep periodic lengths of themultilayers constant in the mirror area. Obtained
deposition rate of the Mg deposition was 5.8 nm/min,and of the SiC deposition, 0.87 nm/min in average.
The error of the periodic lengths of fabricatedmultilayers estimated from XRD measurements was
r2% in the mirror area.
Reflectance measurements were made using theG3M4 combination of BL5B beamline. Wavelength
resolution O/'O was about 200. Obtained results areshown as squares and triangles in Fig. 1. Squares
represent the reflectance of the center of the mirrors,
and triangles, of the edge of the mirrors. The peakreflectances of the multilayers are about 0.3, and its
values between the center and the edge of the mirrors

are nearly equal to each other. Fabricated 4 multilayer
mirrors cover 43 – 28 nm wavelength region with that
their reflectances are 0.2 or more. These multilayer
mirrors were installed in the M1 mirror of BL7U
beamline. Throughput of this beamline in thiswavelength region was about 10 times or more
greater than the previous one, which usedconventional Au mirror as the M1 mirror [4].
Table 1.
Design parameters for wide-band
multilayers in 40 – 30 nm wavelength region.
Multilayer
Periodic
Periodic
ThicknessNo.
numberlength D
ratio(nm)
J=dSiC/D
1
7
16.6
0.42
2
7
18.0
0.41
3
6
19.8
0.40
4
6
22.2
0.40

Fig. 1. Calculated and measured reflectances ofwide-band multilayer mirrors. Numbers at the peaks
represent the multilayer number in Table 1.
[1] Vacuum Ultraviolet Spectroscopy II, edited by J.
A. Samson, D. L. Ederer (Academic Press, San Diego,CA, 2000), Chap. 1 & 2.
[2] Y. A. Uspenskii et al., Optics Letters 23 (1998)
771.
[3] T. Ejima et al., Jpn. J. Appl. Phys. 40 (2001) 376.
[4] S. Kimura et al., UVSOR activity report 2006
(2007) 50.

53

BL5B

Evaluation of Higher Order Diffraction Light Contaminations at EUV
Region by Using Transmission-Grating Spectrometer
F. Suzuki1, T. Ito1, K. Fukui1, T. Hatsui2, N. Kosugi2
1
Dept. Elec. Elec. Engi., Univ. of Fukui, Fukui 910-8507, Japan
2
Institute for Molecular Science, Okazaki 444-8585, Japan

Absolute measurement of physical properties
generally requires quantitative information on theunwanted higher diffraction-order intensity in lightsources. However, there are many difficulties toevaluate the higher diffraction-order intensity in EUV
region. The energy analysis of the photoelectron
emitted from the appropriate material which isirradiated by the target monochromatized light is one
way to realize the evaluation of the higher-ordercontaminations, but the composition of the photoelectron spectrometer is complicated and theoperation is not so easy. Another way to realize theevaluation is using the second monochromator. It
means that the target monochromatized lights by the
first monochromator are monochromatized again by
the second monochromator. In EUV region, however,this method also has the difficulties, because thediffraction efficiency of the reflectance grating under
the grazing incidence condition is quite sensitive tothe incidence angle. On the other hand, the diffraction
efficiency under the normal incidence is not sensitive.
However, the normal incidence condition in EUV
region is only achieved by the use of transmission
grating which is very difficult to fabricate. In thisexperiment, our object is to present a simple but
precise method for the evaluation by using thecompact transmission grating spectrometer (CTGS).
A CTGS is equipped with a quasi-free-standingtransmission grating with groove density of 5882
l/mm made by electron-beam lithography and a nickel
electroplating method. The collimated monochromatized light by both the 100 um aperture and a
100 um entrance slit is re-monochromatized by thetransmission grating which is located just behind theentrance slit. The re-monochromatized light isdetected by the silicon photodiode (SPD) which ismounted on the linear motion stage. This stage isapart 196.5 mm from the grating and is able to movealong to the dispersion direction of the grating.
The present method has been first applied to theplane-grating monochromator beamline (BL5B).
Figure 1 shows the typical spectrum observed by the
CTGS. The incident light is monochromatized 17.8
nm by the G2-M22 configuration of BL5B. The peakat 17.8 nm is basically denoted as (1 - 1) peak, where
the label is denoted as (diffraction order of themonochromatized light by PGM – diffraction order ofthe re-monochromatized light by CTGS). The peaks
at 8.9 nm and 5.9 nm are labeled as (2 – 1) and (3 – 1)
peaks, respectively. Fig. 1 also suggests that (4 – 1)
peak is negligible small. In other word, 17.8 nm lightunder G2-M22 configuration has up to 3rd ordercontaminations. Then, 17.8 nm peak is definitely
labeled as (1 – 1)+(2 – 2)+(3 – 3) peak, and 26.7 nm
peak as (2 – 3) peak. By measuring spectral profile of
EUV light from G2-M22 configuration at eachwavelength using CTGS, higher diffraction- order
light intensity in EUV light source, and dependenceof CTGS efficiencies on wavelength, are determined
self-consistently. The results assume only thedetection efficiency of SPD (IRD Inc., AXUV-100).
Figure 2 shows number of the photon ratio rn of then-th diffracted contamination to the 1st order light at
the G2-M22 configuration of BL5B. Fig. 2 represents
the purity of the monochromatized light underG2-M22 configuration is good at shorter wavelengthside and is consistent with the optical design of
BL5B.
.
㻌
㻔㻜㻙㻜㻕

㻝㻱㻙㻥

㻔㻝㻙㻝㻕
㻔㻞㻙㻞㻕
㻔㻟㻙㻟㻕

㻝㻱㻙㻝㻜
㻔㻟㻙㻝㻕

㻔㻞㻙㻟㻕

㻝㻱㻙㻝㻝

㻌

㻸㼛㼓㻌㻵㼚㼠㼑㼚㼟㼕㼠㼥

㻔㻞㻙㻝㻕

㻝㻱㻙㻝㻞
㻝㻱㻙㻝㻟
㻜

㻝㻜

㻞㻜

㻟㻜

㼃㼍㼢㼑㼘㼑㼚㼓㼠㼔㻔㼚㼙㻕

Fig. 1. Typical spectrum of the CTGS at 17.8 nm.
㻌㼞㻞㻌
㻌㼞㻟
㻌㼞㻠

㻝㻜

㻝

㻌

㻺㻔㼚㻙㼠㼔㻌㼛㼞㼐㼑㼞㻕㻛㻺㻔㻝㼟㼠㻌㼛㼞㼐㼑㼞㻕

㻌

㻜㻚㻝

㻜㻚㻜㻝

㻝㻜

㻝㻡

㻞㻜

㻞㻡

㼃㼍㼢㼑㼘㼑㼚㼓㼠㼔㻔㼚㼙㻕

Fig. 2. Number of the photon ratio rn of the n-thdiffracted contamination to the 1st order light at theG2-M22 configuration of BL5B.

54

BL5B

Measurement of Absolute Efficiency for Micro Channel Plates by Using
Pure-Calibrated EUV BeamK. Yoshioka1, G. Murakami1, T. Toyota1, G. Ogawa1, A. Yamazaki2, I. Yoshikawa1
1
Department of Earth and Planetary Science, Graduate School of Science,
The University of Tokyo, Tokyo 113-0033 Japan
2
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency,
Sagamihara, Kanagawa 229-8510 Japanthe MCPs is 11.9±1.4% at 58.4nm line.
As the next step, in addition to the 58.4nm line, weplan to measure the quantum efficiency at the 73.4nm
and 83.4nm lines, which are other observational
objects of PHEBUS (73.4nm is the emission line of
Neon and 83.4nm is that of the ionic oxygen). Thenthe purities of 73.4nm and 83.4nm lines are essential,
and must be investigated for the next machine time.

Introduction
We study the tenuous atmosphere of the planet
Mercury thorough the optical observations. One of
the main components of the atmosphere is helium.
The atom has resonance scattering emission lines inthe extreme ultraviolet (EUV) region, at 58.4nm. The
intensity of the emission is proportional to column
density of the scattered particle under the assumptionof the optically thin condition. The information of theamount and the distribution of helium are crucial for
discussing about the current environment and theevolution of the planet.
The Mercury Planetary Orbiter (MPO) in the
BepiColombo mission will be launched in 2013 andput into the orbit around the Mercury after
6.5-year-long cruise. An ultraviolet Spectrometer,
PHEBUS (Probing of Hermean Exosphere by
Ultraviolet Spectroscopy) that is loaded onto the
MPO will observe the atmosphere of Mercury in the
EUV and FUV (far ultraviolet) region from the
Mercury orbit. In our experiment, in order to calibrate
the sensitivity of the PHEBUS, we measure thequantum efficiency of the micro channel plates(MCPs) which we use as the standard detector, at
58.4nm line.

Fig. 1. The transmittances of a Sn (173nm) filter. The
red dot shows the results of the measurements at the
EUV facility of ISAS (the error is smaller than the
dot size) and the solid line with dots shows that at
UVSOR.

Measurement and Result
We install a Sn (354.5nm) filter on the entrance of
the SOR beam to eliminate the multi-order lines fromthe 58.4nm line with PGM35. At first, we investigate
the purity of the 58.4nm line through the Sn filter. We
judge the purity from the consistency between the
wavelength characteristics of an Sn (173nm) filter forthe particular lines at the EUV facilities of Institute ofSpace and Astronautical Science (ISAS) and those forthe continuous lines at UVSOR. The former ismeasured for the emission lines of the helium gas
with the discharge light source. Fig. 1 shows thetransmittances of the filter measured at ISAS andUVSOR. It is clear that transmittances of the filter are
consistent around the wavelength 58.4nm. We
interpret from the result that the pure 58.4nm can be
introduced through the Sn filter by using PGM35.
With the available pure 58.4nm line, then wemeasure the quantum efficiency of the MCPs. The
quantum efficiency is calculated by the rate of the
MCPs count to the electron yield of the photo diodewhich is absolutely calibrated. The result of themeasurement shows that the quantum efficiency of

55

BL6U

Design of a New Monochromator for BL6U

E. Shigemasa1, Y. Hikosaka1, E. Nakamura1, N. Kondo1, T. Horigome1, K. Amemiya2
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan2
Photon Factory, Institute of Materials Structure Science, Tsukuba 305-0801 Japan
Various types of monochromators for synchrotron
radiation have been proposed and constructed torealize vibrational spectroscopy in the soft x-ray
range (100 ~ 1000 eV), which contains the K-shellthresholds of chemically important elements like C, N,
and O, since the first successful observation for thevibrational structures of the S* resonance in the
K-shell photoabsorption spectrum of nitrogenmolecules [1]. Thanks to the high brilliance offeredby undulator radiation, both high-resolution andhigh-flux are achievable simultaneously at aconsiderable high level. At the UVSOR, there is
only one soft X-ray undulator beamline for highresolution spectroscopy, BL3U, in the photon energy
region of interest.
Concerning the utilization of the first in-vacuum
type undulator, which has been relocated from thelong straight section U7 to the short one between B05
and B06, a new project for constructing the undulator
beamline BL6U has been initiated. We have decided
to choose the entrance slit-less configuration for the
monochromator. A varied-line-spacing (VLS) planegrating monochromator (PGM) seems to be one of
the most trustworthy ones to realizing high resolution
in the soft x-ray range. In order to cover a wide
photon energy region (30-500 eV) with one single
grating, a variable-included-angle Monk-Gillieson
mounting VLS-PGM [2], in which the grating is
illuminated by converging soft X-rays, has been
selected. Design study for the monochromator at
BL6U has been completed, with the collaboration of
KEK-PF. The monochromator designed will cover
the photon energy ranging from 30 to 500 eV, withthe resolving power higher than 10000 and the photon
flux more than 1010 photons/sec.
Figure 1 shows a schematic layout of the opticalelements of the present VLS-PGM. In front of all
optical elements, there is an aperture S0, located 5.0
m from the source position. The usual setting of thisaperture is 2.0 mmV u 2.0 mmH, which limits the half
acceptance angle to 0.4 mradV u 0.4 mradH. The
radiation is deflected horizontally by a toroidal mirror
M0 located 1.5 m downstream of the aperture. M0 is
one of the most important optical elements torealizing high resolution, which essentially focuses
the radiation onto an exit slit S1, and converging soft
X-rays illuminate the VLS grating indicated by G. A
plane mirror M1 is located 1.5 m behind M0. M0, M1,
and G (Si substrates) are cooled from both sides bywater-cooled copper alloy blocks. One laminar
profile plane grating, which is ruled holographically,
with the varied-line-spacing, is designed to cover theenergy range from 30 eV to 700 eV. The groove
density of the grating is 500 l/mm at its center
position. The included angle of the grating should bechanged from 167Û to 176Û in order to minimize theaberrations. A refocusing mirror M2 has a toroidal
shape, which focuses the monochromatized radiation
at the sample position. All the grating and mirrors arecoated with Au.
The resolution of the present monochromator wasstudied by ray-tracing simulation as well as analyticalestimation. As a result, it is found that a resolving
power E/'E of more than 10000 is achievable overthe energy range from 30 to 500 eV with one single
grating having the groove density of 500 l/mm. The
throughput photon flux estimated ranges from 1010 to1012 photons/sec for the ring current of 350 mA, witha resolving power of 10000. The practicalconstruction of BL6U is expected to start from thesummer of 2008.
[1] C. T. Chen, Y. Ma, F. Sette, Phys. Rev. A 40
(1989) 6737.
[2] K. Amemiya. T. Ohta, J. Synchrotron Rad., 11(2004) 171.

Top view
D=88.0rr=r'=6500
R=186249.1
U=219.0

167r<DE <176r
N=N0࣭(1+ a1࣭x+ a2࣭x2 +a3࣭x3)
N0=500 l/mm

Side viewFig. 1. Schematic layout of the monochromator designed for BL6U.

56

D=88.0rr=r'=1500
R=42980.6
U=52.3

BL7U

Performance Test of High-Throughput Three-Dimensional Angle-Resolved
Photoemission Spectroscopy at BL7U
T. Ito1,2, S. Kimura1,2, M. Sakai1
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
2
School of Physical Sciences, the Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, JapanIn FY2006, we have constructed a new VUVbeamline BL7U equipped with a three-dimensional
angle-resolved photoemission (3D-ARPES) apparatus[1]. The aim of this beamline is to investigate theanisotropic interaction at the Fermi surface (FS) ofinter-metallic compounds [1], namely ”Fermiology”,
which is one of the most facilitated research fields inrecent days, since the interactions among carriers,
local spins, and lattice vibrations play a dominant rolein the functionality of materials. After adjustment of
the beamline and ARPES apparatus, we realize
high-throughput 3D-ARPES beamline for thebulk-sensitive Fermiology of strongly correlated
electron systems (SCES).
The BL7U equips an APPLE-II-type undulator for
the VUV light source, a Wadsworth-type VUVmonochromator, a multi-channel electron energy
analyzer (MBScientific AB; ‘Peter’ A-1) and aliquid-helium flow-type cryostat with a 6-axis
manipulation system (R-dec Co. Ltd.; i-Gonio). The
light source and monochromator provide high-energy
resolution (E/E  104) with high photon flux ( 1012ph/s). The definition of the 6-axis of the manipulator
are illustrated in Fig. 1.
Figure 2 shows a 3D-ARPES result on a strongly
correlated 4f electron compound CeSb. With tuning
sample tilting (y) as well as photon energy (h), we
have successfully mapped out the 3D FS topology ofcigar-shaped hole-like FS at the X point (image plot
in Fig. 2), which is well reproduced by the bandcalculation (3D illustration in Fig. 2). It should be
noted that the acquisition time of the present three
dimensional (3D) FS image together with the 3Dband structure is within 6 hours. The present
high-throughput measurement can be realized by thewealth of the high-photon flux at BL7U as well as the
6-axis sample manipulation systems.
The present result clearly indicates that the VUV
3D-ARPES gives us a detective information of bulk
3D electronic structure which can be compared withband calculations. Furthermore, this method makes it
possible to elucidate the origin of various
functionalities through the direct observation ofanisotropic interactions as quasi-particle band
dispersions. In turn, it also derives a key for opening
a new research field of functionality design byunderstanding the essential origin of various
functionalities in the future.

Fig. 1. The definition of 6-axis of the manipulator
with respect to a sample (yellow square) together
with the experimental layout of 3D-ARPES.

Fig. 2. 3D-FS image of CeSb obtained by mappedout the 3D-ARPES intensity at the Fermi level. 3D
illustration of calculated FS is also depicted.
[1] S. Kimura et al., AIP Conf. Proc. 879 (2007) 527.

57

BL8B1

1

Characterization of Mo/Si Multilayer Mirror for Time-Resolved
Spectroscopy with Laser High Order Harmonic Pulses

M. Fushitani1,2, A. Matsuda1, A. Hishikawa1,2,3Dept. of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
2
Dept. of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
3
PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan

Recent advances in laser technology have allowed
us to generate laser high-order harmonics (HH) in thesoft X-ray region by focusing intense femtosecond
infrared (IR) laser pulses to gaseous nonlinear media[1]. The laser HH pulses have characteristic featuresas 1) high photon energies extending up to the keV
region, 2) ultrashort pulse duration on an attosecond
timescale, 3) high photon flux comparable tosynchrotron radiation, and 4) simple and precise
synchronization of other laser light sources. Becauseof these aspects, the laser HH pulses are of greatinterest as a potential light source for time-resolved
spectroscopy of ultrafast dynamics of electrons andnuclei that could not be elucidated in real time byconventional techniques.
To fully utilize the characteristics of laser high-orderharmonics, appropriate optical components need to be
employed. The laser HH pulses consist of odd orderharmonics with different photon energies below the“cut-off” [1]. The harmonic-order (or wavelength)
selection could be achieved by using a grating withlarge incident angles. In this case, however, the time
resolution will be significantly reduced because of thepulse stretching due to large optical path differences.
To keep pulse duration as short as possible,
multi-layer coated mirrors are preferable. Amongthem, the molybdem/silicon (Mo/Si) multilayer has
been widely used as a reflective coating for opticalmirrors in the 13 nm (95 eV) region. In order to use
one of the harmonics, Mo/Si multilayer mirrors witha narrow band width can be fabricated in such a waythat only the selected harmonic pulse is reflected. In
the present study, we characterize reflectance of
Mo/Si multilayer mirrors at small incident angles.
The reflectance measurements of Mo/Si multilayer
mirrors (NTT-AT Inc.) were performed at BL8B1.
The synchrotron radiation, which was dispersed by
the G3 grating (360 l/mm), was measured as
reference light simultaneously by using gold (Au)mesh and Si photodiode (AXUV100, IRD Inc.)
detectors in an energy range of 30~140 eV. Theenergy scale was calibrated with a sharp absorption
edge of an aluminium (Al) filter (a thickness of 120
nm, Luxel Inc.) at 72.7 eV as well as that at 36.3 eV
due to the second order light from the grating. From
the transmission of the Al filter around the 90 eV
region, the higher order light contribution was
estimated to be less than 4 % of the total current of
the Au and Si detectors. The light reflected by the

Mo/Si multilayer mirror was detected at various
incident angles of 5~27.5 degree by using the Si
photodiode. The light before reflection was also
monitored by the Au mesh, by which the intensity ofincident light with respect to that of the originalreference light is normalized at each wavelength.
Figure 1 shows reflectance of a Mo/Si multilayer
mirror as a function of photon energy. The incident
angle (T) was varied from 5 to 27.5 degree with a stepof 2.5 degree. The reflectance was determined to be
60 %, irrespective of the incident angle except for T =27.5Û. The reflectance peak shifts toward the higher
energy side while the band width becomes narrower
as the incident angle increases. For T = 5Û, the peak
position and the full width at half maximum of thereflectance were determined to be 89.6 eV and 2.8 eV,
respectively. In this arrangement, the Mo/Si mirror
selectively reflects the 59th harmonic (89.7eV) of an
IR laser pulse at 815 nm (1.52 eV).
We are very grateful to the staff of the UVSOR
facility.

Reflectance

0.8

Incident angle
5¼
7.5¼
10¼
12.5¼
15¼
17.5¼
20¼
22.5¼
25¼
27.5¼

0.6
0.4
0.2
0.0
85

90
95
100 105
Photon energy (eV)Fig. 1. Reflectance of Mo/Si multilayer mirror atincident angles between 5 and 27.5 degree.
[1] T. Brabec, F. Krausz, Rev. Mod. Phys. 72 (2000)
545.

58