P1323AG019

BL-5

Current Activities of Research and Education on BL-5(FY2023)
T. Yokoyaa,b, T. Wakitaa and Y. Muraokaa,bab

Research Institute for Interdisciplinary Science, Okayama University
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan

Keywords: Photoemission spectroscopy, photoelectron emission microscopy

We present an overview of our resent research and educational activities on beamline 5 (BL5) in the fiscal
year 2023. Our beamline has two experimental stations in a tandem way. The first station is equipped withan angle-resolved photoemission spectrometer (ARPES), a low energy electron diffraction (LEED)
apparatus and an X-ray source. The hemispherical analyzer of ARPES spectrometer (HA54, VSW) has amean radius of 50 mm and is mounted on a twin axis goniometer in ultra-high vacuum chamber. Using thisgoniometer, one can perform ARPES and photoelectron diffraction (PED) measurements. It is also possible
to perform resonant photoemission spectroscopy (RPES) measurements by using photon energy tunabilityof synchrotron radiation with X-ray absorption spectroscopy (XAS) measurement. With the X-ray source(XR2E2, FISONS), we can perform an X-ray photoelectron spectroscopy (XPS) measurement for thechemical state analysis and the PED. At the second station, we have installed a photoelectron emission
microscope (PEEM, ‘PEEM III’, Elmitec). PEEM provides a magnified image of lateral intensity
distribution of photo-emitted electrons from a sample surface. The spatial resolutions are several ten
nanometers with Hg lamp and a few micrometers with synchrotron radiation. The sample is transferred
between the ARPES and the PEEM chamber in-situ, and one can perform measurements at both stations forthe same sample.
In the recent researches on BL-5, we have studied the electronic structure of potassium doped aromatic
molecule (Kx picene) [1], iron-based superconductor (FeSexTe1-x) [2], transition metal di-oxide films such as
VO2 thin films which exhibits a first-order metal-to-insulator transition at 340 K [3], CrO2 thin films which
are known as a half-metallic material [4], TaO2 film which is stabilized with a new technique developed inour group [5], and phase-separated TiO2-VO2 films on mica substrates. We have also studied the electronic
structures of a high-quality boron-doped diamond film which shows a signature of the highest
superconducting transition temperature of 25 K [6] and a high quality single crystal of YbFe2O4 which isone of multiferroic materials [7], by utilizing RPES at B K- and Fe M2,3- edges, respectively. In addition, we
have studied the sp3 content in diamond-like carbon films by using photoemission spectroscopy in order tooptimize the conditions to produce Q-carbon (quenched carbon) which is a newly discovered amorphousphase of carbon with several exotic properties [8]. In the last few years, we have performed PEEM and TEY
measurements at BL5 in HiSOR for (1) a B-doped carbon nano wall film on a Si substrate, (2) a micro-droplet ofsolidified L-boronophenylalanine (L-BPA) on a Si substrate and (3) cancer cells dosed with L-BPA in order toinvestigate microscopic chemical states of trace B atoms in them from fine structures in local- and wide-areaXAS spectra near B K-edge and to visualize B distributions on their surfaces. For this kind of measurementswith PEEM, we have developed a new auto-measurement system where we can obtain a serial PEEM images
with excitation x-ray energies for a certain energy range with a fixed energy step.
Recently, we have prepared an auto-measurement system and an X-ray focusing capillary lens forphotoemission holography (PEH) measurements. PEH is a method that has been greatly developed in Japanin recent years as a measurement method for elucidating the local structure of materials with an atomicresolution [9]. In particular, various results have been reported in the study of the three-dimensional atomic
configurational structure around the dopants in crystals [10]. However, the opportunity to use state-of-theart apparatuses (for example, DA30 analyzer and RFA of BL25SU at SPring-8) are limited. Although our
photoelectron energy analyzer is an old model and it is difficult to separate and observe small shifts in corelevels because of the energy resolution of 1-2 eV of the system, we expect that our apparatus will be used
for preliminary experiments on undoped materials prior to experiments for doped samples using state-of-the-art systems. It can also be used for educational purposes such as experiencing photoelectron holography
experiments and learning the analysis methods.
We have used the BL-5 for education activity as well, for example, practical education for undergraduate
students of Okayama University. The students have an opportunity to study the synchrotron radiation
mechanism and to experience XPS measurement which is very useful for the surface science research. We
accepted more than 100 students from 2006 to 2012. From 2014, we have started to join the practical lecture
for experiments using the beamline end stations in HiSOR for both graduate school students of Hiroshima
and Okayama Universities. In 2018, we have had a new project for education under a Japan-Asia youth
exchange program in science supported by Japan Science and Technology Agency (JST), “Sakura Exchange
Program in Science”. We have accepted six students from Changchun University of Science and Technologyin China.

REFERENCES
1. H. Okazaki et al., Phys. Rev 82, pp. 195114 (5 pages) (2010).
2. Y. Yoshida et al., J. Phys. Soc. Jpn 78, pp. 034708 (4 pages) (2009).
3. K. Saeki et al., Phys. Rev 80, pp. 125406 (5 pages) (2009).
4. Y. Muraoka et al., MRS Proceedings 1406 (2012).
5. Y. Muraoka et al., Thin Solid Films 599, pp. 125-132 (2016).
6. H. Okazaki et al., Appl. Phys. Lett 106, pp. 052601 (5 pages) (2015).
7. K. Fujiwara et al., Trans. Mater. Res. Soc. Jpn. 41, pp. 139-142 (2016).
8. H. Yoshinaka et al., Carbon.167, pp. 504-511 (2020).
9. T. Matsushita et al. Europhys. Lett. 71, 597 (2005). Phys. Status Solidi B 255, 1800091 (6 pages) (2018).
10. K. Hayashi, T. Matsushita, SPring-8 Research Frontiers 2020, pp. 12 -15 (2021).