Present research at Toyota riken
Development of Atomic-resolution Holography Microscope Compact DELMA
for Direct 3D Viewing Atomic Arrangement around Isolated Atoms in Nanoarea
Hiroshi Daimon

1. Atomic-resolution holography
The functionality of many functional materials can be improved by adding small amount of additives.
A typical example is a dopant in Si. Si crystal is widely used for semiconductor electronic devices to realize
computer or mobile phones. However Si itself cannot work as a semiconductor-device materials. It isnecessary to add dopants such as boron or arsenic to realize p-type or n-type semiconductors. Simple
injection of dopant atom is, however, not enough to make the atom active for the desired function. The
doped atom is expected to work as a dopant only when it substitute a bulk Si atom. If the doped atom islocated at an interstitial position, the valence of the doped atom is different from the substituted atom, andcarrier cannot be produced. Hence the local structure around dopant is a key for the atom to work as adopant. Here this local structure around dopant is called "active-site", which is a keyword governing
functions in all inorganic-, organic- and bio- functional materials. The 3D atomic structures around theactive-site atoms, however, cannot be analyzed by a standard structure analysis methods of x-ray or electron
diffraction because this kind of active-site has no translational symmetry.
Recently several techniques have been developed to investigate the 3D atomic arrangement of activesite which has no translational symmetry. Typical methods are atomic-resolution holographies [1, 2] firstly
suggested by Szöke [3]. Atomic-resolution holographies includes “photoelectron holography [4-7]”, “Xray fluorescence holography [8-10]”, and “neutron holography [11, 12]”. In these holographies, the angular
distribution of photoelectrons, fluorescent x-rays, and neutrons are measured, which includes theinterference between the direct wave from (/or to) the emitter atom and the scattered waves fromsurrounding atoms. Because the phase difference information between the direct wave and the scatteredwaves are recorded, the angular distribution pattern is considered as a hologram [3], and the real-spaceatomic arrangement is easily calculated directly. Recently the accuracy of reconstructed atomic positions
improved dramatically by the development of new analysis code [13-15] and a sensitive analyzers anddetectors. A holography to study surface and interface atomic structure was also developed as “CTR
holography [16]”. A new technique of “stereography of atomic arrangement” [17] has also been developed
to study the local non-periodic atomic structure, which is not a holography but more direct method of stereoviewing of 3D atomic structure around specific atoms directly with our eyes without any calculation.
All these techniques have been developed in Japan and received renewed attention recently. Hence a
new project "3D Active-Site Science" of JSPS Grant-in-Aid for Scientific Research on Innovative Areas[18] has been pursued for five years. A lot of results from electronic-device-materials to bio-materials havebeen obtained throughout this project [19]. Some of the revealed structures are very strange and unexpected.
Theoretical works confirmed the function of these strange local structure and even more predict a new local
structure of effective functions. Hence a new field of local functional structure science is growing. Japanese[20] and English [21] text books have already been published. Effective and easy-to-use analysis software
has been opened to public [22], which was downloaded about 1800 times. New notation system of local
active-site has been proposed [2].
As written above atomic-resolution holography is very powerful to study local non-periodic atoms infunctional materials. However, holographic measurement requires synchrotron radiation so far, andanalysis on an industrial site has been impossible. In order to make use of this technique in society widely,
it is necessary to develop an instrument that can measure atomic resolution holography in a laboratory. Inthis study, we develop an atomic-resolution holography microscope, Compact DELMA, which aims to
make it possible to view the local atomic arrangement around isolated atoms stereoscopically anywhere.
The analysis of isolated atoms in micro-samples and micro-areas smaller than 1μm will become possible
for the first time in the world, which will greatly contribute to the elucidation of atomic-level functions in
the functional materials and nano-device industries.

２．Efficient energy analyzer
In order to take hologram effectively, the energy analyzer should have high energy-resolution with wide
acceptance angle. The most common concentric hemispherical analyzer (CHA) has high-energy-resolution
capabilities, but it is not efficient for angular distribution measurement because its acceptance angle islimited to ±15°×±0.5° typically, which is about 1/3000 of 2π str. It is necessary to take holograms in awide solid angles of nearly 2π sr. Hence it takes more thanseveral days to take one holograms using CHA. Hence a
display-type analyzer with a wide acceptance angle nearly
1π str is necessary for holography measurement.
Several wide-angle display-type electron analyzers
have been developed so far. An ellipsoidal mirror display
analyzer was developed by Eastman et al. in 1980 [23],which can display ±43° cone (1.8 sr ≈ 0.3π sr) at once. It
has a demerit that the pattern obtained is distorted. A
display-type spherical mirror analyzer (DIANA) (Fig. 1)
was developed by Daimon in 1988 [24], which can display±60° cone (3.4 sr ≈ 1π sr) at once. It has a merit that thepattern obtained is not distorted. The energy resolution of
DIANA is about 1%, which is not enough to measure
Fig. 1 DIANA [10, 11]chemical-shift-resolved hologram. To achieve high energy
resolution a display-type ellipsoidal mesh analyzer(DELMA) (Fig. 2) was developed [2529]. DELMA has microscope function
with high energy resolution in addition to
the feature of DIANA. DELMA consistsof a wide-acceptance-angle electrostaticlens (WAAEL) [30-34], a transfer lenssystem, and CHA (VG Scienta R4000).
WAAEL can accept wide angles of ±50°
cone with reducing spherical aberrations
Fig. 2 DELMA [12-16]
to almost zero. This DELMA system canmeasure high-energy-resolution wide
range 2D angular distribution by a deflector-scanning method. Here the ±50° cone 2D angular distribution
formed at the detector plane of DELMA, which is the input plane of the CHA, is scanned using electrostatic
deflectors, and many 1D (±12.5°×±0.5°) patterns obtained by the CHA are combined to construct the 2D
pattern. These slices then can be combined to reconstruct the 2D real- or k-space images of the sample.
Although, the DELMA solved DIANA’s low-energy-resolution problem, but not used widely due to its
complicated structure, large size, and relative high cost.
Another approach is to use a PEEM technique [35], where a high accelerating voltage around 20 kV isapplied between the sample and an objective lens. A very wide acceptance angle of almost ± 90° cone (2πsr) is achieved for photoelectrons of several tens eV. However, the acceptance angle rapidly decreases withincreasing kinetic energy, and the angular range is not enough to study photoelectron holography at thesuitable kinetic energy of several hundreds eV. Recently another type of retarding-field analyzer (RFA)
was developed [36]. RFA has wide acceptance angle of ±50° cone, and high energy resolution, but works
well only at low binding energy photoelectrons.
In summary of this chapter, there is no ideal analyzer for atomic-resolution holography right now.
Hence the purpose of research in Toyota Riken is to construct an ideal analyzer to take holograms, which
has a capability of high energy-resolution and wide acceptance angle simultaneously.

３．VD-WAAEL Analyzer

Magnified image

2D angular distribution

The idea of the ideal analyzer (we call it Compact DELMA here) was reported in Ref. [37]. This
analyzer is based on the technique of
DELMA but is fundamentally
Diffraction mode
VD-WAAEL
Projection lensdifferent in the objective lens design.
Deceleration ratio 1 / 10
Variable-Deceleration-ratio WideIn DELMA, a wide-acceptanceAcceptance-Angle Electrostatic Lens
angle electrostatic lens (WAAEL) of
einzel type was used. This means
Imaging mode
Deceleration ratio 1 / 10that electrons leave the lens with thesame kinetic energies as those at its
Energy-selecting andentrance. As a result, for electrons
Samplefield-limiting aperture
with kinetic energy of E k = 1 keV,
Magnification 25
high voltages up to around 5 kV
Fig. 3 VD-WAAEL analyzer [39]should be applied to the lens after theobjective lens to focus the electrons. The applied voltages linearly increase with the electron kinetic energy.
This limits the kinetic energy range where
DELMA can be used. A variable-decelerationratio wide-acceptance-angle electrostatic lens
(VD-WAAEL) was proposed in Ref. [37]. VDWAAEL is an improvement of decelerationtype WAAEL in Ref. [38], which cannot change
the deceleration ratio. VD-WAAEL system canchange the deceleration ratio in a wide range
without changing the electron focusing at theexit of the lens. This feature is necessary in themeasurement at high kinetic energies. When we
decelerate the electron kinetic energy, theFig. 4 Instrument of VD-WAAEL Analyzer.
energy resolution become high and the voltages
applied to the lens decreases. The acceptanceangle of VD-WAAEL is the same as that of WAAEL of ± 50° cone.
The simplest analyzer using VD-WAAEL is a “VD-WAAEL analyzer” which is just a combination of
VD-WAAEL, projection lens and a screen, along(b)with an energy-selecting aperture [39] as shown in (a)Fig. 3. VD-WAAEL analyzer has both diffraction
and imaging modes, and it can switch these modes
just by changing voltages of lenses. The imaging
mode is used to display a magnified image of thesample on a screen, and it is useful to see thesample surface. The test of VD-WAAEL analyzer
was done in Nara Institute of Science and(a) Angular distribution pattern and (b)Fig. 5
Technology (NAIST). The angular distribution magnified image of mesh sample taken at Toyota
pattern, energy resolution, and magnified image Riken.

were obtained successfully [39].
The instrument of VD-WAAEL analyzer was moved from NAIST to Toyota Riken and many
improvement was done as shown in Fig. 4. The electron gun was remodeled to produce fine electron beam.
The reproducibility of the angular distribution pattern and magnified image were confirmed successfully
as shown in Fig. 5.
This simple analyzer has good energy resolution only at large angles more than 20°, because theprinciple of energy selection is focus-defocus type. Even though large angular range can be used to takehologram, the central area of 0° – 20° cannot be used. Hence we are developing the final analyzer CompactDELMA.

４．Atomic-resolution Holography Microscope Compact DELMA
A diagram of Compact DELMA system is shown in Fig. 6. As seen in Fig. 6 an energy analyzer wasinserted between VD-WAAEL and projectionlens in VD-WAAEL analyzer. A highEDS is not
SEMenergy-resolved electron hologram will benecessary
displayed on the screen of Compact
ScreenDELMA in a wide angular range of ± 50°
cone.
Deceleration-

type WAAEL
Because Compact DELMA is to be
Energyused in a laboratory without synchrotron
SampleAnalyzerradiation, the excitation source is anelectron beam. Hence a combination ofCompact
Compact DELMA and SEM (Scanning
DELMA
Electron Microscope) as shown in Fig. 6
is preferable. The hologram can bemeasured using Auger electrons orenergy-loss electrons emitted from thenano-area irradiated by SEM electron
EELS system isbeam. Hence nano-sized electron beam is
not necessary
important to take hologram from nanoEELS spectrum
area. A small SEM from APCO Ltd. has
Fig. 6 Compact DELMA systembeen installed in this system. When thesize of electron beam is small, the energy
resolution becomes high. The sample surface is characterized by SEM image. Hence a highenergy-resolved hologram of local isolated atom from selected nano-area can be obtained using
this Compact DELMA system.

References[1] H. Daimon, J. Phys. Soc. Jpn., 87, 061001 (2018). https://doi.org/10.7566/JPSJ.87.061001[2] H. Daimon, Jpn. J. Appl. Phys. 59, 010504 (2020).
[3] A. Szöke: AIP Conference Proceedings, No.147, AIP New York (1986).
[4] C.S. Fadley, Y. Chen, R.E. Couch, H. Daimon, R. Denecke, H. Galloway, Z. Hussain, A.P. Kaduwela,
Y.J. Kim, P.M. Len, J. Liesegang, J. Menchero, J. Morais, J. Palomares, S.D. Ruebush, S. Ryce, M.B.
Salmeron, W. Schattke, S. Thevuthasan, E.D. Tober, M.A. Van Hove, Z. Wang, R.X. Ynzunza, andJ. J. Zaninovich, Journal of Surface Analysis, 3, 334 (1997).
[5] J. J. Barton, Phys. Rev. Lett. 61, 1356 (1988).
[6] T. Matsushita, T. Muro, F. Matsui, N. Happo, S. Hosokawa, K. Ohoyama, A. Sato-Tomita, Y. C. Sasaki,

and K. Hayashi, J. Phys. Soc. Jpn 87, 061002 (2018).
[7] F. Matsui, T. Matsushita, and H. Daimon, J. Phys. Soc. Jpn. 87, 061004 (2018).
[8] G. Faigel, G. Bortel, C. S. Fadley, A. S. Simionovici, and M. Tegze, X-ray Spectrom. 36, 3 (2007).
[9] K. Hayashi, N. Happo, S. Hosokawa, W. Hu, and T. Matsushita, J. Phys.: Condens. Matter 24, 093201(2012).
[10] K. Hayashi and P. Korecki, J. Phys. Soc. Jpn. 87, 061003 (2018).
[11] L. Cser, G. Krexner and Gy. Török, Europhys. Lett., 54, 747 (2001).
[12] K. Hayashi, K. Ohoyama, N. Happo, T. Matsushita, S. Hosokawa, M. Harada, Y. Inamura, H. Nitani,
T. Shishido, and K. Yubuta, Science Advances, 3, e1700294 (2017).
[13] T. Matsushita, F. Z. Guo, M. Suzuki, F. Matsui , H. Daimon, and K. Hayashi, Phys. Rev. B 78,
144111 (2008).
[14] T. Matsushita and F. Matsui, J. Electron. Spectrosc. Relat. Phenom., 195, 365 (2014).
[15] T. Matsushita, e-J. Surf. Sci. Nanotech., 14, 158 (2016).
[16] T. Takahashi, K. Sumitani, S. Kusano, Surf. Sci. 493, 36 (2001).
[17] H. Daimon, Phys. Rev. Lett. 86, 2034 (2001).
[18] [http://en.3d-activesite.jp/],[https://kaken.nii.ac.jp/ja/grant/KAKENHI-AREA-2604/][19] Jpn. J. Appl. Phys. Selected Topics in Applied Physics “Frontier of active site science: new insights
on material functions”, Edited by Hiroshi Daimon, Koichi Hayashi, Toyohiko Kinoshita, and Kazuo
Tsutsui[20] H. Daimon and Y. C. Sasaki, (Eds.) Kinou kouzou kagaku nyu-mon, (Maruzen 2016).
[21] H. Daimon and Y. C. Sasaki, (Eds.) 3D local Structure and Functionality Design of Materials,(Maruzen and World Scientific 2019).
[22] https://ja.osdn.net/projects/tmcoca/releases/p14436[23] D. E. Eastman, J. J. Donelon, N. C. Hien, F. J. Himpsel, Nuclear Instruments and Methods, 172, (1–2) 327 (1980).
[24] H. Daimon, Rev. Sci. Instrum. 59, 545 (1988). https://doi.org/10.1063/1.1139884[25] K. Goto, H. Matsuda, M. Hashimoto, H. Nojiri, C. Sakai, F. Matsui, H. Daimon, L. Tóth, and T.
Matsushita, e-J. Surf. Sci. Nanotech. 9, 311 (2011). https://doi.org/ 10.1380/ejssnt.2011.311[26] E. Ikenaga, M. Kobata, H. Matsuda, T. Sugiyama, H. Daimon, and K. Kobayashi, J. Electron
Spectrosc. Relat. Phenom. 190, 180 (2013). https://doi.org/ 10.1016/j.elspec.2013.04.004[27] H. Matsuda, K. Goto, L. Tóth, M. Morita, S. Kitagawa, F. Matsui, M. Hashimoto, C. Sakai, T.
Matsushita, and H. Daimon, J. Electron Spectrosc. Relat. Phenom. 195, 382 (2014). https://doi.org/
10.1380/ejssnt.2011.311[28] Y. Hashimoto, M. Taguchi, S. Fukami, H. Momono, T. Matsushita, H. Matsuda, F. Matsui, and H.
Daimon, Appl. Phys. Express 51, 115 (2019). https://doi.org/ 10.1002/sia.6568[29] M. Taguchi, F. Matsui, N. Maejima, H. Matsui, and H. Daimon, Surf. Sci. 683, 53 (2019).
https://doi.org/ 10.1016/j.susc.2019.02.001[30] H. Matsuda, H. Daimon, M. Kato, and M. Kudo, Phys. Rev. E 71, 066503 (2005). https://doi.org/
10.1103/PhysRevE.71.066503[31]
H.
MatsudaandH.
Daimon,
Phys.
Rev.
E
74,
036501(2006).
https://doi.org/10.1103/PhysRevE.74.036501[32] H. Matsuda, H. Daimon, L. Tóth, and F. Matsui, Phys. Rev. E 75, 046402 (2007).
https://doi.org/10.1103/PhysRevE.75.046402[33] L. Tóth, H. Matsuda, T. Shimizu, F. Matsui, and H. Daimon, J. Vac. Soc. Jpn. 51, 135 (2008).
https://doi.org/10.3131/jvsj2.51.135[34] L. Tóth, H. Matsuda, F. Matsui, K. Goto, and H. Daimon, Nucl. Instrum. Methods Phys. Res. 661, 98

(2012). https://doi.org/10.1016/j.nima.2011.09.018[35] E. Bauer, J. Electron Spectrosc. Relat. Phenom. 185, 314 (2012). https://doi.org/
10.1016/j.elspec.2012.08.001[36] T. Muro, T. Ohkochi, Y. Kato, Y. Izumi, S. Fukami, H. Fujiwara, and T. Matsushita, Rev. Sci. Instrum.
88, 123106 (2017). https://doi.org/ 10.1063/1.4990769[37] H. Matsuda, L. Tóth, and H. Daimon, Rev. Sci. Instrum. 89, 123105 (2018). https://doi.org/
10.1063/1.5043317[38] H. Matsuda, H. Daimon, Phys. Rev. E 74, (3) 036501-1-9 (2006).
[39] H. Momono, H. Matsuda, L. Tóth, H. Daimon, e-Journal of Surface Science and Nanotechnology 18,
1−5 (2020).