16BU002, 18AG009

BL-09B, BL09A

Multiple Topological States in Iron-Based
Superconductors
Peng Zhanga, Yukiaki Ishidaa, Kazuki Sumidab, Shilong Wub, Koji Miyamotob,
Taichi Okudab and Shik ShinaabInstitute for Solid State Physics, University of Tokyo, Kashiwa, Japan.
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Japan

Keywords: topological states, iron-based superconductor.

Topological materials and unconventional iron-based superconductors are both important areas of study but,to date, relatively little overlap has been identified between these two fields. However, the combination of
topological bands and superconductivity promises the manifestation of exotic superconducting states,
including Majorana fermions, the central component of topological quantum computation. Here, using highresolution spin-resolved ARPES, we have identified topological insulator (TI) and Dirac semimetal (TDS)
states near the Fermi energy in different iron-based superconducting compounds, potentially allowing accessto several different superconducting topological states in the same material. These results reveal the genericcoexistence of superconductivity and multiple topological states in iron-based superconductors, indicatingthat this broad class of materials is a promising platform for high-temperature topological superconductivity.
The topological Dirac semimetal states in Fe(Te,Se).
In the previous papers, we resolved the TI surface states and its related topological superconductivity at thesurface of Fe(Te,Se) [1,2]. Actually, according to the calculations, TI and TDS states should appear in a pair:
the TI states below EF and the TDS states above EF, as shown in Fig. 1a. Since it is difficult to dope Fe(Te,Se)

FIGURE 1. a. Theoretical calculations show that there are two Dirac cones in Fe(Te,Se): One is
the surface band of TI; the other is from the surface component of TDS. b. ARPES intensity plot of
the band structure with a 7eV laser. According to panel a, the band at EF should be partly spinpolarized. c. Spin-resolved EDCs at Cut 3 with a 7eV laser d. Spin polarization along y direction at
Cuts 1 and 3. e. Spin polarization along different directions at Cut 3 measured in HiSOR with 20
eV photons. f. Spin polarization along y direction at Cuts 1 and 3 measured in HiSOR with 25 eV
photons.

- 69 -

with electrons, the TDS cone cannot be resolved by ARPES directly. However, from Fig. 1a we found thatthe surface component of the TDS states extends to below EF and induces spin polarization of the band at
EF, which means that we may obtain indirect evidences of the existence of the TDS bands by measuring spinpolarization. The spin-integrate ARPES intensity plot of the band structure is shown in Fig. 2b. Using spinresolved ARPES, we checked spin polarization of two cuts in Fig. 2b with different photon energies. In Fig.
2c and 2d, we displayed the spin resolved EDCs and the spin polarization curves along y direction measured
with a 7eV laser. Due to the high energy resolution of the laser ARPES, the spin polarization is very clear.
The magnitude of spin polarization is about 50%, indicating coexistence of unpolarized bulk and polarized
surface states.
It is well known that the photoemission process may induce extrinsic spin polarization. However, theextrinsic spin polarization generally depends on the photon polarization, photon energy or sample orientation,
while intrinsic spin polarization of the electronic initial states should show the same result for different
experimental setups. To confirm that the spin polarization from 7eV photons has an intrinsic origin, we
further measured the spin polarization with different photon energies at BL9B endstation in HiSOR. With
20eV photons, we observed spin polarization along y direction only, consistent with calculations and data in
Fig. 2d. With 25eV photons, the result is the same as the one with 7eV photons. These results from different
photon energies confirm that the spin polarization indeed comes from the electronic initial states, and thus
supporting the conclusion that there are TDS states above EF in Fe(Te,Se).
The topological insulator and Dirac semimetal states in Li(Fe,Co)As.
We also studied a series of Li(Fe,Co)As samples with different Co content by using laser ARPES. Form thex = 9% and 12% electron-doped samples, we directly observed both TI and TDS Dirac cones [3]. The two
Dirac cones are consistent with the DFT calculations: the upper cone comes from the the surface componentof the TDS state, while the lower cone comes from the TI surface states. Their surface nature is also
confirmed by the spin-resolved experiments with a 7eV laser. These results provide further support to theexistence of TDS states in Fe(Te,Se).
Our findings of the TI and TDS states in Fe(Te,Se) and Li(Fe,Co)As prove the generic existence of different
types of topological states in iron-based superconductors. Their simple structures, multiple topological states,
and a tunable Fermi level make iron-based superconductors ideal platforms for the study of topologicalsuperconductivity, Majorana bound states, and as such, potentially, topological quantum computation.

REFERENCES
1. Z. Wang et al., Phys. Rev. B 92, 115119 (2015).
2. P. Zhang et al., Science 360, 182 (2018).
3. P. Zhang et al., Nature Phys. 15, 41 (2019).

- 70 -

17BG016

BL-9B

Experimental observation of node-line-like surface states
in LaBi
B. Fenga, J. Caob, M. Yangc, Y. Fenga,d, S. Wu, B. Fub, M. Aritaa, K. Miyamotoa,
S. Hed, K. Shimadaa, Y. Shic, T. Okudaa, and Y. Yaoba

Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Higashi-Hiroshima
739-0046, Japanb
Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Physics,
Beijing Institute of Technology, Beijing 100081, China
cInstitute of Physics, Chinese Academy of Sciences, Beijing 100190, Chinad
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo
315201, Chinae
Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526,
Japan

Keywords: node line, ARPES, surface states, density functional theory

Topological semimetals represent a novel class of quantum materials whose conduction and valencebands touch at discrete points or extended lines [1-4]. Until now, three types of topological semimetals havebeen discovered: Dirac, Weyl, and nodal line. In Dirac/Weyl semimetals, the energy-momentum dispersion
is linear along all momentum directions, forming Dirac/Weyl cones in the proximity of the Fermi level. In
nodal line semimetals, the crossing points form extended lines in the momentum space, i.e., the nodal lines.
While the Dirac cones or nodal lines discovered in topological semimetals typically derive from the bulk
bands, an interesting question is whether they can exist as surface states of three-dimensional crystals. The
nodal line surface states could manifest extraordinary properties that are distinct from other two-dimensional
Dirac materials [5-7]. To date, the surface Dirac cones have already been extensively studied in topologicalinsulators, such as the Bi2Se3 family materials, while theoretical and experimental studies on the surface
nodal lines are still rare.
Recently, rare-earth monopnictide LaBi has been predicted to be a topological insulator based on firstprinciples calculations. Moreover, magnetotransport measurements showed that LaBi hosts extremely large
magnetoresistence (XMR), in analogy to some topological semimetals, such as Cd3As2, TaAs, and ZrSiS.
These results have stimulated great research interest to search for the Dirac bands in LaBi. Recent angleresolved photoemission spectroscopy (ARPES) measurements revealed that there are multiple surface Diraccones on the (001) surface of LaBi. However, the details of the band structures are still controversial. Nayaket al. and Niu et al. reported two surface Dirac cones at the 𝑋̅ point with an energy separation of 75 and
190 meV, respectively. In contrast, Lou et al. reported only one Dirac cone at the 𝑋̅ point. Therefore,clarifying these controversies, which is essential to understand the extraordinary transport properties in LaBi,
calls for further experimental and theoretical efforts.
Here, we present the results of high-resolution ARPES measurements and first-principles calculations on
the electronic structures of LaBi. We find that the surface states near the 𝑋̅ points resemble Dirac nodal
lines. Our calculations show that these node-line-like bands are slightly gapped because of the hybridizationof surface states, but the gap is beyond our experimental resolution. These results may provide
important information to understand the extraordinary physical properties in LaBi and could stimulate further
research interest to search for the exotic physical properties associated with nodal line fermions.

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The photoemission intensity of the Fermi surface of LaBi is shown in Fig. 1(c), which includes several
Fermi pockets at the 𝛤̅ and 𝑋̅ points of the surface BZ. Figure 1(d) shows the measured band structures
along the 𝛤̅-𝑋̅ direction. At the 𝛤̅ point, we observe a Dirac-like band with the crossing point located at
approximately 0.1 eV below the Fermi level, as indicated by the red arrow.
We then focus on the band structures near the 𝑋̅ point. Figure 2 shows the band structures along a seriesof parallel cuts in the proximity of the 𝑋̅ point, as indicated by the red lines in Fig. 1(c). One can see that
there is a linear band crossing along each cut without any detectable gap feature. The Fermi velocity isapproximately 7×105 m·s-1, which is comparable to that in graphene. From cut 1 to cut 12, the crossing point
gradually moves from EB=0.23 eV (cut 1) to EB=0.14 eV (cut 7), and then moves back to higher binding
energies. These results indicate that there is a Dirac nodal line that goes through the 𝑋̅ point. The nodal line
is along the 𝛤̅-𝑋̅ direction and has a weak dispersion. According to the C4 rotational symmetry of the 𝑋̅
point, there must be a perpendicular nodal line crossing the 𝑋̅ point, but its intensity is much weakerbecause of the matrix element effect.
This work has been published in Physical Review B 97, 155153 (2018).

FIGURE 1. Crystal structure of LaBi. Red and blue balls
represent La and Bi atoms, respectively. (b) Bulk Brillouinzone and the (001)-projected surface Brillouin zone. The
calculated band structures along the blue and red lines areshown in Figs. 4(a) and 4(b), respectively. (c) Photoemission
intensity at the Fermi level of LaBi measured with 31-eV
photons. Red lines indicate the momentum cuts along which
the ARPES intensity plots in Fig. 2 were taken. (d) ARPES
intensity plot along the black line in (c). From Ref. 8.

̅ points. The
FIGURE 2: ARPES intensity plots near the 𝑋
data were taken along the red lines in Fig. 1(c). Cut 7
̅ point. Fromcorresponds to the one that goes through the 𝑋
Ref. 8.

- 72 -

REFERENCES
1.
2.
3.
4.

5.

6.
7.
8.

S. M. Young, S. Zaheer, J. C. Y. Teo, C. L. Kane, E. J. Mele, and A. M. Rappe, Phys. Rev. Lett. 108, 140405 (2012).
Z. Wang, Y. Sun, X.-Q. Chen, C. Franchini, G. Xu, H. Weng, X. Dai, and Z. Fang, Phys. Rev. B 85, 195320 (2012).
Z. K. Liu, B. Zhou, Y. Zhang, Z. J. Wang, H. M. Weng, D. Prabhakaran, S.-K. Mo, Z. X. Shen, Z. Fang, X. Dai, Z.
Hussain, and Y. L. Chen, Science 343, 864 (2014).
S. Xu, I. Belopolski, N. Alidoust, M. Neupane, G. Bian, C. Zhang, R. Sankar, G. Chang, Z. Yuan, C.-C. Lee, S.-M. Huang,
H. Zheng, J. Ma, D. S. Sanchez, B. Wang, A. Bansil, F. Chou, P. P. Shibayev, H. Lin, S. Jia, and M. Z. Hasan, Science
349, 613 (2015).
B. Feng, B. Fu, S. Kasamatsu, S. Ito, P. Cheng, C.-C. Liu, Y. Feng, S. Wu, S. K. Mahatha, P. Sheverdyaeva, P. Moras,
M. Arita, O. Sugino, T.-C. Chiang, K. Shimada, K. Miyamoto, T. Okuda, K. Wu, L. Chen, Y. Yao, and I. Matsuda, Nat.
Commun. 8, 1007 (2017).
A. K. Geim and K. S. Novoselov, Nat. Mater. 6, 183 (2007).
A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, Rev. Mod. Phys. 81, 109 (2009).
B. Feng, J. Cao, M. Yang, Y. Feng, S. Wu, B. Fu, M. Arita, K. Miyamoto, S. He, K. Shimada, Y. Shia, T. Okuda, and Y.
Yao, Phys. Rev. B 97, 155153 (2018).

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17BG022

BL-9B

Observation of Bulk and Surface Spin-Orbital Textures inNonsymmorphic NbGeSb
Igor Marković1, O. Clark1, S. Wu2, T. Okuda3, K. Murphy4, J. Alaria4, P. King1
1

SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, KY16 9SS, UK
2
Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Japan
3
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Japan
4
Department of Physics, University of Liverpool, Liverpool L69 7ZE, UK

Keywords: Rashba, nonsymmorphic, NbGeSb, SARPES.

In recent years the interplay of spin-orbit coupling (SOC) and crystalline symmetries has been extensively
explored as a driving mechanism for developing novel electronic band structures in solids. The realisation
by Young and Kane [1] that nonsymmorphic symmetries can stabilise the intersection point of topologicallytrivial and non-trivial states of matter has opened new paradigms for creating and manipulating bulk Diracsystems. Yet experimentally, the role of spin-orbit coupling in those systems has remained elusive. Here, weinvestigate this interplay in NbGeSb, a member of the nonsymmorphic ZrSiS family of Dirac nodal line
semimetals [2-5]. In particular, we use spin- and angle-resolved photoemission spectroscopy (SARPES) to
disentangle the complex bulk and surface electronic structure of this compound. Building on our previous
observation of two sets of surface electronic states in this compound, we sought to uncover their detailed
and strongly intertwined spin-orbital textures.
These surface states disperse within a large bulk-projected band gap along the Brillouin zone edge, while
they become resonant with the bulk states with approaching the Brillouin zone centre (Fig. 1). Similar surface
states have been observed in the structurally equivalent (Zr,Hf)SiS systems [2,4,5], and a detailed
investigation [2] showed that they emerge from the bulk manifold due to the breaking of the nonsymmorphic
symmetry at the cleavage plane of the material. Due to different distribution of valence electrons, we observe
how the surface states move much further away from their parent bulk manifolds in NbGeSb, leading tothem intersecting in the vicinity of EF (Fig. 1b). Using spin-resolved measurements performed at BL-9B, weshowed that these surface states are spin-polarised, exhibiting spin splittings of the Rashba type. The
magnitude of the spin splitting is comparable to the size of atomic SOC energy scales for the relevant orbitals.
Moreover, through systematic measurements of the vectorial spin texture, we have uncovered how the highsymmetry of the surface unit cell leads to a highly structured spin texture of the surface state Fermi surface(Fig.1a). These findings are of key importance for understanding the influence of spin-orbit coupling in thissystem, and the determination of the spin-orbital textures of these states, and their role in shaping the banddegenerices which this system hosts.

FIGURE 1. (a) Brillouin zone and surface state Fermi surface, with spin textures shown schematically. (b) Band dispersions
in the vicinity of X, with spin-resolved EDCs (right) measured along the dotted lines shown.

REFERENCES
1. S. M. Young et al., Phys. Rev. Lett. 115 (2015) 126803
2. A. Topp et al., Phys. Rev. X 7, (2017) 041073
3. C. Chen et al., Phys. Rev. B 95, (2017) 125126

4. L. Schoop et al., Nature Commun. 7, (2016) 11696
5. D. Takane et al., Phys. Rev. B 94, (2016) 121108- 74 -

18AG050

BL-BL9B

Spin-resolved photoemission studies on possible halfmetallic SrRuO3 thin film
Hanyoung Ryua,b , Saikat Dasa,b, Bongju Kima,b, Changyoung Kima,b, and Taichi
OkudacaCenter for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea
Department of Physics and Astronomy, Seoul National University, Seoul, 08826, Koreac
Hiroshima Synchrotron Radiation Center (HSRC), Hiroshima University, Higashi-Hiroshima 7390046, Japanb

Keywords: Spin-resolved photoemission, Half-metal, SrRuO3.

Half-metals with fully spin-polarized conduction electrons are a promising candidate for spintronic
applications. While the ferromagnetic metals are abundant, the half-metallic ferromagnets are limited in
numbers, with examples include CrO2, La0.7Sr0.3MnO3, NiMnSb, and Co2FeSi [1]. It is, therefore, of practicalinterest to explore new materials that are believed to be close to half-metallic (HM) ground states.
SrRuO3 (SRO) is an itinerant ferromagnet (with Tc ~ 165 K), and in bulk is considered to just miss thehalf-metallic ground state due to the lack of strong exchange-correlation [1,2]. Several proposals are put
forward to artificially drive the system to the HM state either by spatially confining the carriers or byheterostructuring in the honeycomb motif [3-5]. A recent attempt following the former route yielded aferromagnetic metallic state with decreased Tc while no information is available on the resulting spinpolarization [6]. On the contrary, the latter approach remains unexplored.

FIGURE 1. (a) The angle integrated spectra of SrRuO3(111) film taken with 21 eV linearly polarized photon. (b) Spinresolved spectra taken with 21 eV photon at Γ point of the Brillouin zone. The red (blue) curve is intensity from plus (minus)
spin. (c) The asymmetry, extracted from the figure (b) exhibiting vanishingly small spin-asymmetry.

Motivated by these considerations, we explored SRO thin films (~ 30 nm thick) grown on the (111)oriented SrTiO3 substrates, which form the basis of the honeycomb motif. Thin films were grown using thepulsed laser deposition (PLD) technique and subsequently capped with Se to prevent direct exposure to theambient. To remove the Se-capping layer, the films were annealed in the preparation chamber at atemperature of about 450o C at a base pressure of 10-8 Torr. Subsequently, the films were transferred to the
ARPES chamber, where we performed spin-resolved photoemission spectroscopy (spin-PES) measurements
at a temperature of 20K with a photon energy of 21 eV. To completely magnetize the films, we cooled down
the films in a magnetic field applied parallel to the surface normal (along the easy axis of the films).
Figure 1 (a) shows the angle-integrated photoemission spectrum taken up to binding energy of 12 eV
below the Fermi energy. Meanwhile, Fig. 1(b) displays the corresponding spin-resolved spectra that are- 75 -

obtained for two opposite polarities of the spin-detector. In Fig. 1(c) we plot the spin-asymmetry extracted
from Fig. 1 (b). Despite being a robust ferromagnet, the spin-PES exhibits no discernable spin-asymmetryaround the Fermi energy level. Such absence of spin-asymmetry might stem from two factors. First, thepresence of a contamination layer in the form of the thin Se capping layer, that reduces the spin polarizationof photo-excited electrons. Second, for the given photon energy (~21 eV), we probed bands with negligible
spin-splitting. More careful studies, with cleaner surface are thus required to elucidate the nature offerromagnetic ground state of (111)-oriented SRO films, and extract the exact spin-polarization value.

REFERENCES
1.
2.
3.
4.
5.
6.

M. I. Katsnelson et al., Rev. Mod. Phys. 80, 315 (2008).
I. I. Mazin and D. J. Singh, Phys. Rev. B 56, 2556 (1997).
Marcos Verissimo-Alves et al., Phys. Rev. Lett. 108, 107003 (2012).
James M. Rondinelli et al., Phys. Rev. B 78, 155107 (2008).
L. Si et al., Phys. Rev. Lett. 119, 026402 (2017).
H. Boschker et al., Physical Review X 9, 011027 (2019).

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18AU017

BL-9B

Spin resolved Dirac cone surface state in trigonal layered
PtBi2
YaFenga , Shaozhu Xiaoa, Kenya Shimadab, Shaolong Heaa

Ningbo Institute of Materials Technology and Engineering,
Chinese Academy of Sciences, Ningbo 315201, China

bHiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan

Keywords:trigonal PtBi2，surfacestate，Diraccone, spin texture

The trigonal PtBi2 has attracted great interest since it has been recently reported as a possible candidate
for triply degenerate pointfermions [1]. Here we measured band structure of PtBi2on BL-9B by spin
resolved ARPES and found a spin polarized surface states at point.

FIGURE 1.Constant energy contours of trigonal PtBi2, hv=28eV.

The material we measured here is trigonal PtBi2 which is different from former reported hexagonal PtBi2[2-4]. The trigonal PtBi2 belongs to P31m space group while hexgonal PtBi2 belongs to P-3 space goup.
We determined its space group by single crystal analysis using XRD (X-ray diffraction) data which will be
published elsewhere. The most important difference between them is that the hexagonal PtBi2 is inversion
symmetric while the trigonal one isn’t. FIGURE1shows theconstant energy contours of trigonalPtBi2
measured by ARPES with hv=28eV.There is an electron pocket at  point which shrinks to a point at
Eb0.9eV and then becoms to a small circle at Eb=1.1eV. This trend suggests that it should be a cone.

- 77 -FIGURE 2.Band structures of trigonal PtBi2along high symmetricdirections under different photon energies.a,
——

——

——

dispersion along  –M direction，hv=28eV. b, dispersion along  –M direction,
hv=21.2eV. c, dispersion along - Kdirection, hv=28eV.
——

FIGURE 2a and b show dispersions along the same direction–M . FIGURE 2c shows the——dispersion
at point with Eb0.9eV respectively in a , b and c, along -K . There is a crossing pointwhich, associated with FIGURE 1, indicates the presence of a Diraccone at point. Moreover, novariation with different photon energies implies that it’s mainly from surface state.
To further confirm whether it’s a Dirac cone or not, we measured its spin texture.FIGURE 3ashows——the enlarged E-k image along  -Mdirection measured by ARPES. The spin polarized EDCs (energy
distribution curves) along line 1(blue dashed line1 in FIGURE 3a) are shown in FIGURE 3b1 andFIGURE 3c1along different spin directions. The spin polarized EDCs (energy distribution curves) alongline 2(blue dashed line2 in FIGURE 3a) are shown in FIGURE 3b2 and FIGURE 3c2along different
spin directions. The red (blue) lines in FIGURE 3b and FIGURE 3c stand for intensity along positive(negative) direction. Finally, we can get the spin polarization (green lines) along Y axis and Z axis in
FIGURE 3b and FIGURE 3c respectively. Comparing FIGURE 3b1 and FIGURE 3b2, it’s can beconcluded that the spin polarization is opposite at Eb=0.7eV along Y axis while there is no spinpolarization along Z axis. The Y axis is inside the sample surface and perpendicular to the slit of theelectron energy analyzer. The Z axis is normal to the sample surface. So the spin polarization of theband is consistent with that of a Dirac cone surface state.

In summary, we observed a Dirac cone surface state at  point of trigonal PtBi2. We found it’s spinpolarized along Y axis and not spin polarized along Z axis.Moreover, the spin polarization along Y axis
is opposite at opposite k, which means its spin and momentum are locked.

REFERENCES
1.Wenshuai Gao et al,Nat. Comm. 9, 3249 (2018).
2. Yao, Q. et al. Phys. Rev. B 94, 235140 (2016).
3. Thirupathaiah, S. et al. Phys. Rev. B 97, 035133 (2018).
4.Yang, X. et al. Appl. Phys. Lett. 108, 252401(2016).

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18BG003

BL-9B

Electronic and spin structure of Bi-graphene-like system
V.A. Golyashova, A. Kimurab, T. Okudac, O.E. Tereshchenkoa,daInstitute of Semiconductor Physics Siberian Branch, Russian Academy of Sciences, pr.Akademika Lavrent’eva
13, Novosibirsk, 630090 Russian Federationb
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama,
Higashi-Hiroshima 739-0046, Japand
Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japane
Novosibirsk State University, ul.Pirogova2, Novosibirsk, 630090 Russian Federation
Keywords: Bi, InAs, electronic structure, spin- and angle-resolved photoemission

The ultrathin film of group-V semimetal bismuth (Bi) is a promising candidate to investigate the graphenelike properties and surface Rashba effect, since the energy splitting of the bands is fairly large owing to theheavy atomic mass of the Bi atom. For the technological purposes InAs semiconductor is of special interest
because it exhibits downward band bending leading to an accumulation of electrons at the surface, having
characteristic of 2DEG. Such 2DEGs demonstrated many interesting and fundamental phenomena such as theinteger and fractional Hall effect [1], 2D superconductivity [2] as well as technological importance in devices
such as metal–oxide–semiconductor field-effect transistor and high electron mobility transistor.
The aim of this work is to develop the methods of preparation (substrate surface preparation, evaporation
rate, …) and to study the electronic structure of Bi/InAs(111) interfaces using state-of-the-art spin- and angularresolved photoemission spectroscopy (SR ARPES) with synchrotron radiation at BL-9B.

FIGURE 1 Fermi surface mapping of around Г point (a) and EF-Eb=0.35 eV (b) at h=23 eV of the bismuth monolayer on
InAs(111)A surface. (c) LEED pattern on Bi/InAs(111)A-(23x3)Bi surface.

Fig.1 shows the Fermi surface mapping of Bi/InAs(111)A-(23x3)Bi surface. At 1 ML of Bi coverage theInAs(111)A-(23x3)Bi structure is formed which consist of three 60º oriented domains. The electronic structureof InAs(111)A-(23x3)Bi surface is significantly different from those observed on InAs(111)A-(1x1)Bi. The
dispersion contains a small gap, which can be considered in the first approximation as a gap in the primarily
Rashba states.The appearance of a gap is probably induced by the strong spin-orbit interaction in bismuth layer
and reduced structural surface symmetry. The observed dispersion can be interpreted as the graphene-like Diracstate with a gap. Spin-resolved measurements confirmed the spin polarization in upper and bottom branches of
the cones depending on the momentum direction.

REFERENCES
1. K. von Klitzing, et al., Phys. Rev. Lett. 45, 494 (1980).
2. N. Reyren, et al., Science317, 1196 (2007).

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18BG006

BL-9B

Spin Polarized Electronic Structure of Metal Overlayers
on Magneto-Electric Cr2O3
Takashi Komesua, M. Kakokib, T. Okudac, K. Miyamotoc,
Prescott E. Evansa and Peter A. DowbenaaDepartment of Physics and Astronomy, Theodore Jorgensen Hall, 855 N 16th, University of
Nebraska, 880299, Lincoln, NE 68588-0299, U.S.A.
b
Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-6526
c
Hiroshima Synchrotron Radiation Center, Hiroshima University,
Higashi-Hiroshima 739-0046, Japan
Keywords: Spin Polarized Photoemission Spectroscopy, Electronic Structure.

Chromia (Cr2O3) continues to attract much attention as a magneto-electric material [18], with a Néel temperature above room temperature [1]. One interesting feature of thisantiferromagnetic (AFM) is the significant boundary spin polarization at the (0001) surface[1-3,8]. This boundary polarization can be isothermally controlled to provide perpendicularvoltage-controlled exchange-bias in an adjacent ferromagnet [1,4-7]. Previous investigations,on Cr2O3 at HiSOR beam line, successfully acquired evidence of exchange interactions forthin cobalt films with the Cr2O3 substrate [9]. Yet the magnetic coupling at the interface of
Co/Cr2O3(0001) leads to a more complexity magnetic interaction [6,7,9,10]. There is clear
evidence from X-ray magnetic dichroism that the coupling between Co and Cr2O3(0001) is
antiferromagnetic at the interface [10]. Since the magneto-crystalline c-axis anisotropy ofchromia supports a perpendicular magnetization, the interface exchange interaction can be
exploited to add a perpendicular component to the Co magnetization, with antiferromagnetic
coupling at the interface [9,10]. Recently, we investigated palladium (Pd) thin films on Cr2O3
to reveal the influence of the chromia substrate on the Pd overlayer, and the possible
magnetic behavior of Pd that has been realized under some conditions [11].
For the spin polarized photoemission and spin polarized inverse photoemission
studies, the Cr2O3 sample was magneto-electrically field cooled in applied E and B fields
through the chromia Néel temperature (307 K), in order to put Cr2O3 in a single domain stateand enhance the net surface polarization. Figure 1 shows, a) the Spin-Polarized
Photoemission Spectra (SP-PES) for a thin Pd overlayer deposited on top of Cr2O3 at room
temperature performed at HiSOR (BL-9B), using the very low energy electron diffraction(VLEED) spin detector as described elsewhere [12] and a photon energy of 150 eV, and b)
for Spin Polarized Inverse Photoemission Spectroscopy (SPIPES). The blue (red) triangles in
Figure 1 indicate spin up (down) components, respectively, and the green lines indicate thespin integrated spectra. Combining of Figure 1 (a) and (b) reveals substantial Pd spin
projections on perpendicular (SP-PES) and parallel (SPIPES) component to the film plane.
The spin majority dominates the occupied density of states, as expected, but thepresence both a perpendicular (Figure 1a) and in-plane (Figure 1b) component of spinpolarization is a clear indication of a Pd adlayer with canted spin alignment. The canting is
consistent with our previous measurement for Co and micromagnetic simulations andmagnetic force microscopy. This work clarifies the mechanisms by which the anomalous
Hall effect memory cell [13] works and illustrates the value of a combined investigation of
the net spin polarization of both the valence (SP-PES) and conduction (SPIPES) band

- 80 -

electronic structure, and a first in the ongoing investigation Cr2O3 exchange coupling withvarious overlayers.

a)Figure 1.
The
spinpolarized photoemission spectra
for thin Pd layer on top of Cr2O3:(a) the measured out of plane
spin polarization for 5Å Pd and(b) spin polarized invers
photoemission spectroscopy for5Å Pd. The blue (red) triangle
indicate
spinup(down)
components, respectively, andthe green line indicates the spinintegrated spectra. Bottoms arepolarization of spins.

b)

References[1]
X. He, Y. Wang, N. Wu, A. N.
Caruso, E. Vescovo, K. D. Belashchenko,
P. A. Dowben, and C. Binek, Nat. Mater.
9, 579 (2010).
[2]
S. Cao, X. Zhang, N. Wu, A. T.
N’Diaye, G. Chen, A. K. Schmid, X. Chen,
W. Echtenkamp, A. Enders, Ch. Binek, P.
A. Dowben, New J. Physics 16, 073021(2014).
[3]
N. Wu, X. He, A. L. Wysocki, U.
Lanke, T. Komesu, K. D. Belashchenko, C.
Binek, and P. A. Dowben, Phys. Rev. Lett.
106, 087202 (2011).
W. Echtenkamp, and Ch. Binek, Phys. Rev. Lett. 111, 187204 (2013).
K. Toyoki, Y. Shiratsuchi, A. Kobane, S. Harimoto, S. Onoue, H. Nomura, and R. Nakatani, J. Appl. Phys.
117, 17D902 (2015).
[6] T. Ashida, M. Oida, N. Shimomura, T. Nozaki, T. Shibata, and M. Sahashi, Appl. Phys. Lett. 106, 132407(2015).
[7] K. Toyoki, Y. Shiratsuchi,A. Kobane,C. Mitsumata, Y. Kotani, T. Nakamura, and R. Nakatani, Appl. Phys.
Lett. 106, 162404 (2015).
[8] K. D. Belashchenko, Phys. Rev. Lett. 105, 147204 (2010).
[9] R. Choudhary, T. Komesu, P. Kumar, P. Manchanda, K. Taguchi, T. Okuda, K. Miyamoto, P. A. Dowben,
R. Skomski, and A. Kashyap, Europhysics Letters 115, 17003 (2016).
[10] Y. Shiratsuchi, Y. Kotani, S. Yoshida, Y. Yoshikawa, K. Toyoki, A. Kobane, R. Nakatani, and T.
Nakamura, AIMS Materials Science 2, 484-496 (2015).
[11] S. Sakuragi, T. Sakai, S. Urata, S. Aihara, A. Shinto, H. Kageshima, M. Sawada, H. Namatame, M.
Taniguchi, and T. Sato, Phys. Rev. B 90, 054411 (2014).
[12] T. Okuda, K. Miyamaoto, H. Miyahara, K. Kuroda, A. Kimura, H. Namatame, and M. Taniguchi, Rev. Sci.
Instrum. 82, 103302 (2011).
[13] T. Kosub, M. Kopte, R. Hühne, P. Appel, B. Shields, P. Maletinsky, R. Hübner, M.O. Liedke, J.
Fassbender, O.G. Schmidt, D. Makarov, Nature Commun. 8, 13985 (2017).
[4][5]This work was supported in part by the Center for Antiferromagnetic Magnetoelectric Memory and Logic(AMML), one of centers in nCORE as task 2760.001, a Semiconductor Research Corporation (SRC) program
also co-funded by the NSF through ECCS 1740136.

- 81 -

18BG023

BL-9B

Insight Into The Spin-Texture Of Shockley and Dirac
States Handling by Competitive Spin-Orbit and Exchange
Magnetic Interactions in GdRh2Si2, HoRh2Si2, GdIr2Si2
and YbIr2Si2 materials.
Denis Vyalikha, b, Dima Usachovc, Georg Poelhend, Andres Santander-Syroe,
Takehito Imai*, Koji Miyamoto#, and Taichi Okuda#aDIPC, Paseo Manuel Lardizabal 4, Donostia San Sebastian 20018, Basque Country, Spainb
IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Basque Country, SpaincSaint Petersburg State University, Saint Petersburg 198504, RussiadInstitut für Festkörper- und Materialphysik, Technische Universität Dresden, D-01062 Dresden, Germanye
CSNSM, Université Paris-Sud and CNRS/IN2P3, Batiments 104 et 108, 91405 Orsay, France＊
Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526,
Japan#
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Higashi-Hiroshima
739-0046, Japan
Keywords: Spin-Resolved ARPES, rare-earth intermetallics, exchange magnetism, spin-orbit coupling

Our research is focused on the disentangling the properties of 2D electrons in presence of spin-orbit
coupling (SOC) in combination with a lack of inversion symmetry and exchange magnetic interaction (EMI)
as well as Kondo interaction. We have performed SR-ARPES measurements of 2D states for antiferromagnet(AFM) GdRh2Si2 (TN=107 K), AFM-TbRh2Si2 (TN=92 K), and mixed-valent EuIr2Si2 [1-3]. It is known thatfor GdRh2Si2, in the AFM phase the 4f moments lie inclusively in plane, while for TbRh2Si2 they are oriented
along [001] direction, i.e. have out of plane order due to the crystal-electric-field effect. The signature forthe out of plane order is seen in ARPES (fig. 1) as a spin-splitting of the surface states at the M-point (fig.
1b). This property has been discussed for HoRh2Si2 (TN=29.5 K) [1], which exhibits out of plane magnetic
order. We turn to Tb-system, since i) it reveals the similar properties but, ii) it has larger TN, which gives acertain freedom for the experiments. The beauty of EuIr2Si2 [3] is that below the Si-Ir-Si surface block, theEu ions reveal valence 2+, i. e. they have a large and pure spin moment J = S = 7/2. Below 48 K, the Eu 4fs
order ferromagnetically that, together with strong SOC, essentially modifies the properties of 2D states [3].
Our aim was to explore the spin-texture of the surface states when (i) the orientation of 4f moments ischanged from “in plane” (GdRh2Si2) to out of plane (TbRh2Si2), (ii) the SOC remains on the same level or(iii) is enhanced due to substitution of Rh by Ir. Combination of SOC with the EMI of 2D electrons with theordered 4f moments of RE layer underneath the topmost Si-T-Si block opens perspectives to explore howthese electrons are affected and how their properties can be controlled by means of SOC and EMI. We haveobtained the experimental results for all mentioned systems and we are presently working on their evaluation,
DFT calculations, and kp modeling [3, 4]. Here, we present the first curios observation made for Tb system.
In figure 1c, we show how the spin-texture of the surface state at the M-point is seen from DFT calculations.
While the out-of-plane magnetization in the Tb system was thought to be large enough in order to destroy
the original in-plane spin-momentum coupling caused by the SOC, we nevertheless anticipate toexperimentally disclose this in-plane coupling almost unaffected. In the fig. 2 we show the schematic viewof the spin-split surface state as well as the points in k-space, where the SR-ARPES data were taken. The
data reflecting the projection of the spin on X, Y and Z planes are shown together with the DFT modellingof the spectra. Already a first inspection of the experimental data suggests that the expected strong Z-signal
is almost absent. On first sight, this result looks unclear, however, one should keep in mind that we measure
the magnetically ordered system, which should possesses the magnetic-domains structure.

- 82 -FIGURE 1. ARPES data taken from TbRh2Si2 in PM (a) and AFM (b) phases indicating the properties of the surface states at
the M-point. The spin-splitting driven by SOC effect is clearly seen from the inset data for PM phase. The spin-texture of thissurface state derived from ab-initio DFT calculations for both phases is shown in (c).

FIGURE 2. Spin-resolved ARPES data taken from TbRh2Si2 for AFM phase at 18 K for a few k-points of the surface state
derived for X, Y and Z channels that reflects the projection of the spin on the respective axis.

Since the Tb system has the out of plane AFM order, one can reasonably assume that near the Si-surface
within the topmost layer could be domains with the alternating order of 4f moments leading to the very small
net magnetization. This result indeed becomes a big surprise since then, the spin-texture seen by SR-ARPES
is handled via only Rashba effect in the non-centrosymmetric Si-Rh-Si-Tb layer. The results from DFT
support this point. Thus, quenched out of plane net magnetization opens the way to explore the spinpolarization driven solely by the Rashba effect, which is considerably smaller than the exchange interactionin this system (fig. 1c). This is why the respective phenomenon would be hard to explore experimentally for
PM phase, since the spin-split of surface state is very small in the Rh- compounds. In AFM phase with theout-of-plane orientation of the magnetization, the strong exchange interaction strongly splits in energy theband of surface state, while the in-plane spin polarization of the later is exclusively handled via the Rashba
effect. This effect, which is found to be very different from the well-known classical Rashba effect [3, 4], isa subject of our forthcoming paper.

REFERENCES
1.
2.
3.
4.

A. Generalov, et al., Nano Letters 17 811 (2017).
M. Güttler, et al., Scientific Reports 6 24254 (2016).
S.Schulz, et al. npj Quantum Materials 4 26 (2019).
I. A. Nechaev and E. E. Krasovskii, Phys. Rev. B 98, 245415 (2018).

- 83 -

18BG024

BL-9B

Spin structure of the gapped Dirac cone of first
antiferromagnetic topological insulator MnBi2Te4
I.I. Klimovskikh, S. Filnov, D. Estyunin, A.M. ShikinaSaint Petersburg State Univeristy, Russia, 198504

Keywords: Topological insulators, Dirac cone, antiferromagnetism

A number of remarkable experimental observations and theoretical predictions recently made exploiting
the property of antiferromagnetism indicate clearly that antiferromagnetic (AFM) systems can be of greatpractical importance. As opposed to FM materials, antiferromagnets are robust against external magnetic
perturbations and do not produce stray fields.
Moreover, such effects as magnetoresistance, spin torque, and ultrafast dynamics observed in certain
AFM systems promise significant advances in spin transfer electronics, spin-orbitronics and spincaloritronics. At the crossroad of antiferromagnetism and the emerging field of “topotronics”, i.e. electronics
based on the properties of topologically-nontrivial systems, an AFM topological insulator (AFMTI) arises.
The AFMTI surface states are sensitive to the loss of the translational symmetry at surface that can lead tothe gap opening. However, there may also be AFMTIs whose certain surfaces break the S symmetry due tomagnetism which has been predicted to enable exotic physics like quantized magnetoelectric effect or axion
electrodynamics.

Kinetic energy, eVThis project is devoted to spin-resolved photoemission study of the first antiferromagnetic topologicalinsulator, MnBi2Te4[1] and related similar compounds MnBi4Te7 and MnBi6Te10. Theoretical predictions
show the localization of the topologically protected surface states at the natural cleavage plane (0001), which
are gapped due to breaking of the TRS, with the value of the gap of ~90 meV. Our SQUID magnetic
measurements clearly demonstrate the antiferromagnetic phase of MnBi2Te4 with the Neel temperature of
25 K. The ARPES data (see Fig.1) obviously show the Dirac cone formed by surface states, with the gap at
the G point of ~90 meV.

Emission angle, deg
FIGURE 1. ARPES data for MnBi2Te4 taken at G point at a photon energy of 28 eV and temperature of 17 K

- 84 -

By means of spin-resolved ARPES we have studied the spin structure of the Dirac cone of MnBi2Te4,
MnBi4Te7 and MnBi6Te10 compounds. Theory predicts the hedgehog spin structure with out-of-plane
polarization at the G point of opposite sign for upper and lower cones. Fig.2 presents the spin-resolved
ARPES data for the out-of-plane component of spin polarization, taken at G point at the temperature of 17
K. Once can clearly see the spin opposite spin polarization for lower and upper cone, in accordance with themagnetic gap hedgehog spin texture. Our temperature dependent measurements of the spin polarization
exhibit the strong changes under antiferromagnetic transition. Moreover, in order to verify the topologicalcharacter of the formed surface states the in-plane spin polarization components at non-zero wave vector had
been studied testifying its helical behavior.

FIGURE 2. Spin-resolved ARPES data for MnBi2Te4 taken at G point at a photon energy of 28 eV and temperature of 17
K. Spin polarization (Spin-up and spin-down spectra) is presented at left (right) panel.

REFERENCES
1. J. Li et al, https://arxiv.org/abs/1808.08608v1 (2018) and D. Zhang et al., https://arxiv.org/abs/1808.08014 (2018)
M. Otrokov, I.I. Klimovskikh et al., https://arxiv.org/abs/1809.07389 (2019)
2. R. S. K. Mong, et al., Phys. Rev. B 81, 245209 (2010)
3. T. Hirahara, et al., Nano Letters 17, 3493 (2017)
4. I.I. Klimovskikh, et al., Scientific Reports 7, 3353 (2017)
5. M. Otrokov, et al., 2D Materials 4, 025082 (2017).

- 85 -

18BU004

BL-9B

Spin-resolved photoemission spectroscopy study
for half-metal Heusler compounds
K Gotoa, b, Y Sakurabab, M. Kakokic, T. Konoc, T. Okudad and K Honoa, baGraduate school of Pure and Applied Science, University of Tsukuba, 1-1-1 Tennodai Tsukuba 305-0047,
Japanb
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japanc
Departmetn of Physical Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama,
Higashi-hiroshima 739-8526, Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Higashi-hiroshima
739-0046, Japan
Keywords: Half-metal Heusler compounds, Spin-resolved ARPES, Temperature dependence of spin polarization

Co-based Heusler compounds such as Co2MnSi and Co2FeGa0.5Ge0.5 (CFGG) are predicted to have highspin-polarization of the conduction electron at the Fermi level. These materials have been attracting muchattention for spintronics devices of tunneling magnetoresistance (TMR) and current perpendicular to plane
giant magnetoresistive (CPP-GMR) devices [1-4]. However, observed large reduction of MR ratio withtemperature [1, 4] limits a potential of applications using half-metallic Heusler compounds. To understand acause of this problem, the spin-polarized electronic structure of bulk, surface and interface and its
temperature dependence should be observed by spin and angle-resolved photoemission spectroscopy(SARPES) which is the most powerful method for direct measurement of the electronic structure (energy,
moment and spin) in the solids.
the CFGG thin film sample which has L21 structure was prepared by the magnetron sputtering method
equipped at National Institute for Materials Science (NIMS) and it was delivered to beam line 9B of
Hiroshima Synchrotron Radiation Center (HiSOR) with keeping high vacuum (~3.0×10-10 mbar) level by
the suitcase chamber. SARPES experiment was performed with a He lamp (hν = 21.2 eV) at the Efficient
SPin REsolved SpectroScOpy (ESPRESSO) end station with the very-low-energy-electron-diffraction(VLEED)-type spin polarimeter [5]. Before SARPES measurement, CFGG thin film was annealed at 500℃
for 30 min to obtain a clean surface. The measurement temperature was room temperature and 45 K.
Figure 1 shows a spin-integrated ARPES image along the Γ̅ ̅X line of CFGG. A parabolic band whichcrosses Fermi level was clearly observed around 2nd Γ̅ point. This band crosses Fermi level at k || = 0.86
Å−1. To measure the change of the spin polarization with temperature of this band, the SARPES experiment
was carried out. Figure 2(a) and 2(b) show the spin-resolved energy distribution curves (EDC) of CFGG
measured at 45 K and room temperature, respectively. These EDCs were observed at emission angle of -24◦,
where k || value is 0.857 Å−1. The spin polarization P is estimated from the difference of the photoemission
intensity of up spin and down spin. The spin polarization P at Fermi level is 17% at 45 K and it is reduced
to 0.7% at room temperature. However, it is unclear that this band is bulk band or surface band. To clarify
the origin of the reduction of the spin polarization with temperature, SARPES measurement by using- 86 -

synchrotron radiation should be performed.
In conclusion, a parabolic band structure which crosses Fermi level was clearly observed around 2nd Γ̅point for CFGG thin film. SARPES measurement was performed and the reduction of the spin polarization
with temperature at Fermi level was experimentally observed. The spin polarization at Fermi level of theobserved parabolic band is 17% at 45 K and it is reduced to 0.7% a room temperature.

FIGURE 1. Spin integrated ARPES image along the Γ̅ ̅X line of CFGG. The measurement temperature was 40 K.

FIGURE 2. Spin resolved EDCs of CFGG at 40 K (a) and room temperature (b). Circles and squares mean the photoemission
intensity of up spin and down spin, respectively. The dashed line means the spin polarization.

REFERENCES
1.
2.
3.
4.
5.

Y. Sakuraba et al., Appl.Phys. Lett. 88, 192508 (2006)
T. Ishikawa et al., J. Appl. Phys. 103, 07A919 (2008)
S. Li et al., Appl. Phys. Lett. 103, 042405 (2013)
J. W. Jung et al., Appl. Phys. Lett. 108, 102408 (2016)
T. Okuda et al., Rev. Sci. Instrum. 82, 103302 (2011)- 87 -

17BG011

BL-11

Identifying sulfur species adsorbed on particulate mattersin exhaust gas emitted from a container carrier
Satoshi ASAOKAa, Tomoshisa DANb and Shinjiro HAYAKAWAca

Research Center for Inland Seas, Kobe University,
5-1-1 Fukaeminami, Higashinada, Kobe, 658-0022 JAPANb
Graduate School of Maritime Sciences, Kobe University
5-1-1 Fukaeminami, Higashinada, Kobe, 658-0022 JAPANc
Graduate School of Engineering, Hiroshima University
1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527 JAPAN
Keywords: distillate marine fuel, gas oil, ship diesel engine, sulfonate, sulfate

Normalized intensity (a.u.)

Particulate matter (PM) from seagoing ships affect the ocean
environment on various scales. The estimated annual PM
emission from ships is 0.9–1.7 million tons [1]. Because PM
and sulfur emission is closely linked to the sulfur content of
Sulfonate
ship fuels, in 2015 the International Maritime Organization
Sulfate(IMO) introduced regulations that the sulfur content in ship
fuel be less than 3.5% and 0.1% for general and designated sea
areas, respectively. In 2020, the regulation will be further
85% loadstrengthened to reduce sulfur content in ship fuel to 0.5% forgeneral sea areas [2].
50% load
The amount of SOx emitted from seagoing ships hasconventionally been estimated by emission factors based on
2470
2475
2480
2485
2490
X ray energy (eV)sulfur content in fuels. Although sulfur adsorbed on PM in
Fig. 1 Sulfur K edge spectra of PM fromexhaust gases from fuels is considered to be sulfate, the
EMERALD I and sulfate standards
chemical species of sulfur adsorbed on PM in exhaust gases are
Dotted lines are liner combination fit by the two
not well known, which is an impediment to establishingstandards.
appropriate regulations for sulfur emission control from ships.
The purpose of this study is to identify sulfur species adsorbed on PM or soot emitted from various vessels.
Particulate matter and soot samples were collected from a container carrier, EMERALD I. XAFS analysesof the sulfur K-edge spectra were performed using the BL11 at the Hiroshima Synchrotron Research Center(HiSOR). The sample chamber was filled with He gas. The XAFS spectra were measured in two different
modes simultaneously.
The sulfur K-edge spectra of PM collected from the EMERALD I and sulfur and sulfonate standards areshown in Fig. 1 [3]. The sulfur K-edge spectra of the PM fit well with the combination of sulfate andsulfonate by the linear combination fit. The origin of sulfate and sulfonate in PM is considered to be theoxidation of sulfur substances and sulfide in DMX. The concentration of sulfate and sulfonate adsorbed on
PM under 85% load were 19.0 and 1.3 mg m-3, respectively, on the sulfur basis. In the case of 50% load,concentration of sulfate and sulfonate adsorbed on PM were 20.2 and 1.0 mg m-3, respectively, on the sulfur
basis. The sulfur species of PM did not show a statistically significant difference between 85% and 50%
load.

REFERENCES
1.
2.
3.

J. Moldanová, E. Fridell, O. Popovicheva, B. Demirdjian, V. Tishkova, A. Faccinetto, C. Focsa, Atmos. Environ. 43,
2632-2641 (2009)
S. Endres, F. Maes, F. Hopkins, K. Houghton, E.M. Mårtensson, J. Oeffner, B. Quack, P. Singh, D. Turner, Front. Mar.
Sci., 5, 139 (2018)
S. Asaoka, T. Dan., I. Asano, S. Hayakawa, K. Takeda, Chemosphere, 223, 399-405 (2019)- 88 -

18AG032

BL-11

Sulfur K-edge XAFS analysis of aqueous solutions ofsulfur compounds using an in-situ liquid flow cell
Daisuke Nishio, Atsuya Doi, Kenji Komaguchi,
and Shinjiro Hayakawa
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Hiroshima, Japan
Keywords: sulfite, XAFS, in-situ liquid flow cell

[Introduction]
There are limited number of analytical methods that provide information on chemical speciation in asolution. UV spectroscopy is widely used because it is highly sensitive, but absorption bands are generally
broad and interference of coexisting chemical species often occurs. X-ray Absorption Fine Structure(XAFS) spectroscopy is attractive because of its elemental selectivity, wide applicable range in pH andlarge probing depth through a solution. Soft X-rays around 3keV cover K-edges of S, Cl, K and Ca and thechemical states of these elements in a solution receive of great interest, and we have developed a sealed
cell and a flow cell for XAFS measurements in the soft X-ray region. They are applicable to bothtransmission and fluorescence modes.
In this presentation outline of the developed flow cell and its application to sulfite solution will bedemonstrated. Sulfite has two pKa, and there exist several forms of anions including structural isomers anda dimer depending on pH and the concentration [1,2].
[Experimental]
XAFS measurements were performed on the BL-11 at HiSOR. The beamline is equipped with a Si(111)
double crystal monochromator, and K shell spectra from P to Ti are covered. The sample chamber was
filled with He gas for minimizing beam attenuation. Intensities of the incident and transmitted beam weremonitored with an air filled ionization chamber. Energy scans from 2460 to 2490 eV were carried out toobtain K-edge region of sulfur.
The windows of the cell used were commercial silicon nitride of 1.0μm thick (Norcada) and their opening
was 5.0 × 5.0 mm. The effective cell length was about 300 μm. The cell was placed in the He chamber, andthe solution could be circulated from a reserver with a perista pump. A series of measurements werecarried out with the system, and the pH was gradually changed (FIGS 1, 2). The use of the flow cell wasadvantageous to maintain the effective cell length constant during the measurements.

FIGURE1. Sample chamber (top view)

FIGURE2. Schematic layout of flow cell- 89 -

[Result & Discussion]
FIG. 3 shows XAFS spectra of aqueous 0.1 M Na2SO3 solutions as the function of pH. XAFS spectra
obtained at pH 10.5, 4.17, and 1.30 were attributed to SO32, HSO3-, and SO2, respectively. HSO3represented structural isomers of (HO)SO2- and (HS)O3- those have different proton bonding positions
FIG. 4 shows XAFS spectra obtained around pKa2 (7.19) from solutions of lower (0.1 M) concentration.
Isosbestic points appeared, and the solution could be regarded as a binary system within the range of pH.
The isosbestic point indicated that the contribution of S2O52- (dimer) was negligible with this concentrationand that the XAFS spectra of structural isomers of HSO3-could be treated as a single component. The latter
result indicated that the fractions of two components were constant within the range of pH or the XAFS
spectra of these isomers were almost identical for each other.
The isosbestic point disappeared in XAFS spectra obtained from 1.0 M solutions, and the XAFS spectra
were well fitted with the ternary system include contribution of S2O52-. An example of the curve fitting wasshown in FIG. 5. The spectrum was obtained at pH 6.10, and three base spectra were used for fitting. Twoof base spectra were that of HSO3- obtained at pH 4.17, and that of SO32- obtained at pH 9.53, and the restof the component should be that of S2O52- solution. The spectrum from solid of Na2S2O5 was used instead.
The resultant portions of three components were 0.58, 0.37 and 0.05 for HSO3-, SO32- and S2O52-,
respectively.
2.5
10

2.5

pH

pH

2.0
Normalized intensity
Normalized Intensity

Normalized Intensity8

2.0

pH 10.5

6

1.5
1.5

pH 7.20
pH 6.71
pH 6.50

4

10.50

9.53
7.20
7.19
6.71
6.50
6.71
6.21
6.10
5.99
5.79
5.70
5.50
5.39
5.28
4.17
5.18
4.50

1.0
1.0

pH 6.21
pH 5.99
pH 5.70
pH 5.390.5
0.5

2 pH 4.17
pH 1.30

0
2472

2474

2476

2478

2.476
2476

2480

X-ray energy (eV)residual error

Normalized intensity

12
pH 6.10
fitting

108
6

pH 9.53

4

pH 4.172
Na2S2O5(s)
0
2.474

2.480
2480

FIGURE4. S K-edge XAFS spectra of
0.1 M Na2SO3 solutions around pKa2.

FIGURE3. S K-edge XAFS spectra of 0.1
M Na2SO3 solutions as a function of pH.
14

2.477
2.479
2477 2.478
2478
2479
X-ray
X-rayenergy
energy(keV)
(eV)

2.476

2.478

2.480

X-ray energy (keV)

FIGURE5. XAFS spectra obtained at pH 6.10 and the resultof curve fitting with three components[1]D.L. Eldridge et al., Geochimica et Cosmochimica Acta 220, 309–328 (2018)[2]Yaser Beyad et al., Dalton Trans., 43, 2147–2152 (2014)- 90 -

18BG004

BL-11

Polarization dependence of S K-edge XAFS spectrafrom polythiophene thin films
Yuta Hamashimaa, Kohei Fukudaa, Daisuke Kajiyab, Ken-ichi Saitowb,
Atsunori Moric, Kenji Komaguchia, Joji Ohshitaa, Shinjiro Hayakawaaa Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima,
Hiroshima, 739-8527, Japanb Natural Science Center for Basic Research and Development (N-BARD),Hiroshima University, 1-3-1
Kagamiyama, Higashi-hiroshima, Hiroshima, 739-8526, Japanc Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University Rokko,
Nada, Kobe, 657-8501, Japan
Keywords: XAFS, polythiophene, orientation, uniaxial

1. Introduction
Polythiophene is utilized for various organic electronic devices, and the orientation of polymer thin film
affects their performances. Major orientations of planar conjugated backbone are Face-on and Edge-on,
and control of the orientation of the film has been thoroughly investigated as a function of molecularweight and solvent [1]. It has also been reported that a uniaxial orientation of Edge-on film can be preparedby substrate treatment [2].
We have developed a method to evaluate the type and fraction of the orientation of polythiophene thinfilm from the polarization dependence of X-ray absorption fine structure (XAFS).We applied thistechnique to the quantification of orientation parameters of structurally controlled poly(3-hexylthiophene)(P3HT) thin films.
2. Experimental
P3HT of relatively low molecular weight (Mw = 75,000) was dissolved in o-dichlorobenzene and theother P3HT of relatively high molecular weight (Mw=185,000) was dissolved in chloroform. These
solutions were spin-coated on a Si substrate, and they are named as sample A and sample B, respectively.
A chlorobenzene solution of P3HT was also prepared and spin-coated on a special ITO/glass substrate, andthe surface of the substrate was previously brushed with a velvet fabric (Sample C). In sample C, thebackbone of P3HT molecules in Edge-on orientation was aligned along the brushing direction [2].
XAFS measurements were performed at BL-11 of Hiroshima Synchrotron Radiation Center (HiSOR).
X-ray fluorescence yield (XFY) was detected with a silicon drift detector (SDD) in a He filled chamber.
Glancing angle dependence of XFY was compared between sample A and B. Glancing angle θ shown in
Fig. 1(a) was changed from 20° to 80°. Azimuthal angle dependence of XFY was investigated with sample
C. The azimuthal angle was defined as the angle between the electric field vector and the brushingdirection (Fig. 1(b)). The azimuthal angle φ was changed from 0° to 90° by rotating the sample with theglancing angle of 80°.

FIGURE 1. The arrangement for (a) glancing angle dependence and(b) azimuthal angle dependence measurement.

- 91 -

Results and Discussion
FIGURE 2 shows the glancing angle dependence of S K-edge XAFS spectra from sample A and sample
B. The sample A showed decrease of both σ*S-C and π* peaks with the decrease of θ. The result showedthat the transition dipole moments from S 1s to σ*S-C orbital and π* orbital lay in-plane of the substrate. In
sample B, the tendency of π* peak was opposite to that of σ*S-C peak, and the result showed that thetransition dipole moment to σ*S-C orbital lay in-plane while that to π* was perpendicular to the substrate.
These anisotropies suggest that P3HT mainly occupied Edge-on orientation in sample A and Face-on
orientation in sample B. The ratio of Edge-on orientation to Face-on orientation was calculated to 5.2:1 insample A, and 1:2.8 in sample B after separating intensities of σ*S-C peak from π* peak.

FIGURE 2. Glancing angle dependence of S K-edge XAFS spectra from (a) sample A and (b)sample B.

FIGURE 3 shows the azimuthal angle dependence of S K-edge XAFS spectra from sample C. The σ*S-C
peak appeared strongly under the condition of φ = 0 ° because the transition dipole moment to σ*S-C orbital
was mainly parallel to the brushing direction. Plot of the intensities of π* peak as a function of azimuthal
angle is shown in FIGURE 4. They were fitted to the portion similar to sin2φ curve and the other constantportion. The amplitude of the former portion indicated the quantity of uniaxial oriented Edge-on domain.
The rest of the intensity was attributed to those oriented randomly in Edge-on orientation. Approximately
56% of molecules in Edge-on orientation were localized toward brushing direction.
Furthermore, the ratio between uniaxially oriented Edge-on, randomly oriented Edge-on and Face-on
orientation was determined to be 2.5:2.0 :2.0 from the azimuthal angle dependence of the intensity of σ*S-C
peak.

FIGURE 3. Azimuthal angle dependence ofS K-edge XAFS spectra from sample C.

FIGURE 4. Plot of the intensity of π* peak
as a function of azimuthal angle.

References
1. T. Matsumoto, K. Nishi, S. Tamba, M. Kotera, C. Hongo, A. Mori, T. Nishino：Polymer.119,76 (2017).
2. M. Imanishi, D. Kajiya, T. Koganezawa, K. Saitow: Sci.Rep.7,5141 (2017).

- 92 -

A-18BG007

BL-11

Identification of sulfur species in road dust collected fromemerging countries in Asia
Waqar Azeem JADOONa, Satoshi ASAOKAb
Lawrence LIAOc and Shinjiro HAYAKAWAc
a Graduate School of Biosphere Science, Hiroshima University (1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521 Japan)b Research Center for Inland Seas, Kobe University (5-1-1 Fukaeminami Higashinada Kobe 658-0022 Japan)c Graduate School of Biosphere Science, Hiroshima University (1-4-4 Kagamiyama, Higashi-Hiroshima 739-8528 Japan)d Graduate School of Engineering, Hiroshima University (1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527 Japan)

Keywords: road dust, sulfate, sulfonate, XAFSNormalized intensity (a.u.)

In South and East Asia, the rapid development of transportation systems has been linked to the increasing
concentration of air pollutants such as particulate matter and road dust. It is therefore necessary tounderstand sulfur species involved in the temporal and spatial distribution of sulfur-rich particles in order toevaluate human health risks caused by these sulfate-rich particles. The primary goal of this study was to
identify sulfur species of road dust collected from emerging countries in Asia.
Road dust samples were collected from roads in rural, sub-urban and urban areas in Afghanistan andEgypt. Sulfur K edge XAFS spectra (ranges 2460–2490 eV) were measured using the BL11 in the
Hiroshima Synchrotron Research Center (HiSOR). The synchrotron radiation from a bending magnet was
monochromatized with a Si (111) double-crystal monochromator. The sample chamber was filled with Hegas. The XAFS spectra were measured by X-ray fluorescence yield (XFY) mode using a SDD detector.
The CEY mode obtained spectra of CuSO4・5H2O were used to calibrate the incident X-ray energy aroundK edges of sulfur. The K edge main peak of sulfate was set to 2481.6 eV. The road samples were mounted
on a double stick tape (NW-K15; Nichiban)
placed in the central hole (15 mm in diameter)of a copper plate. Incident X-ray angle to thesample surface was adjusted to 20 degrees andKR
the X-ray fluorescence was detected from thedirection normal to the incident beam in theJRplane of electron orbit of the storage ring.
The sulfur K-edge spectra of road and sulfur
AR
references are shown in Fig. 1. The sulfur Kedge spectra of road dust fit well with the
Sulfonate
combination of sulfate, sulfonate and cystein by
the linear combination fit. The composition of
Cysteine
sulfur species ranged 82-88% (Sulfate), 2.85.6% (Sulfonate) and 8.2-15% (Cystein),
Sulfaterespectively. We considered the sulfate to be
2460
2470
2480
2490
derived from the oxidation of sulfur substances
X ray energy (eV)in fuel. These organosulfur compounds such
Figure. 1 Sulfur K edge spectra of road dust
as sulfonate and cysteine which represents C-S
Dotted lines are liner combination fit by the three standards.
bound derived from the incomplete combustion
KR: Kabul in Afghanistanof the carbonaceous components in the fuel.
The sulfonate might have been derived from
JR: Jalalabad in Afghanistan
fuel because sulfonate is one of the major
AR: Alexandria
components in sulfur species in petroleum, orfrom the oxidation of sulfide in fuel.

- 93 -

18BG008

BL-11

Efficient photocatalytic activation of C-H bonds byspatially controlled chlorine and titanium on the silicate
layer
Nao Tsunoji,a Hidechika Nishida,a Kenji Komaguchi, Shinjiro Hayakawa,a Yuya
Yagenji,a Masahiro Sadakane,a and Tsuneji Sanoaa

Department of Applied Chemistry Graduate School of Engineering, Hiroshima University,

Keywords: photocatalysis • tianosilicate • layered silicate • cyclohexane • selective oxidation • C-H activation

The efficient activation and transformation of C(sp3)-H bonds in alkanes to produce higher-value products
remains one of the biggest challenges in modern chemistry. Such bonds are thermodynamically strong andkinetically inert, and molecular oxygen is an unreactive oxidant. Therefore, traditional catalytic strategies
for their conversion require the use of expensive and aggressive reagents and/or severe reaction condition.
Heterogeneous photocatalysis has become regarded as a promising alternative strategy in recent years since
it can be used to activate stable alkanes, even in mild conditions, using solar energy directly. Nonetheless,as the lack of efficient photocatalysts for scale-up production of target organics remains the bottleneck forindustrialization, more precise catalyst design strategies that can efficiently harness photons for organic
transformations are highly desirable.
In the current study, we selected two
inorganic elements (chlorine and titanium) anddeveloped highly efficient photodriven organic
transformations by accurate control of their
spatial distribution.[1] Recently, Yuan et al.
reported that chlorine radicals generated on thesurface of a titanium-oxide-based photocatalyst
can activate primary hydrocarbons andeffectively produce partially oxidized
products.[2] The authors proposed thatchemisorbed chlorine is trapped byphotogenerated holes to produce chlorineradicals. The specific radical generates alkyl
radicals that can subsequently yield partially
oxidized organics through reactions with FIGURE 1. HUS-7 silicate framework viewed along the (a) c-axis,
b-axis, and (c) a-axis. The dotted squares indicate the repeating
molecular oxygen. However, in this system, (b)structural unit containing a silanol and a silanolate group. (d) Ti
over-oxidation can proceed through the grafting and chlorination on the HUS-7silicate layer.
consumption of electron-hole pairs bymolecular oxygen and the hydrocarbon, resulting in low catalytic efficiency for the partially oxidized product.
Therefore, the specific radical mediator (chlorine) should be located at a position neighboring thephotoexcitation center to ensure more efficient electron transfer between them.
Recently, we developed a rational design strategy for realizing isolated metal species on layered silicates.
Layered silicates composed of anionic silicate sheets with interlayer cations are a kind of layered material
whose interlayer surfaces are covered with silanol (SiOH) and silanolate (SiO-) groups withcrystallographically defined arrangements and bond angles.[3-6] We found that isolated titanium species
with uniformly tetrahedral coordination states and high surface densities are provided by the grafting oftitanium(IV) acetylacetonate onto the surface of a Hiroshima University silicate (HUS, Figure 1). As shownin Figure 1, further remarkable features of this material are the specific coordination environment of isolated
species linked by two Ti−O−Si bridges and the presence of exchangeable ligands (acetylacetonate orhydroxyl groups). In this study, we attempted to incorporate chlorine at locations neighboring isolated- 94 -

titanium atoms by ligand exchange, yielding a chlorinated layered silicate catalyst. The C-H activation abilityof the catalyst was evaluated in the photocatalytic oxidation of cyclohexane into its partially oxidized
products cyclohexanone and cyclohexanol, which are important intermediates in the manufacture of nylon
polymers. We also employed a chlorine-incorporating zeolite material (TS-1) and titanium oxide (P25) forcomparison in order to assess the influence of the spatial distribution of the elements on the efficiency of thepartial oxidation reaction.
To investigate the coordination environments in Ti-HUS and TS-1, K-edge X-ray absorption
spectroscopy (XAS) measurement of titanium and chlorine was performed (Figure 2). The titanium K-edge
for TS-1 presents a very sharp pre-edge peak at an energy of approximately 4,968 eV, attributable totransitions from the 1s to the 3d level in isolated titanium atoms surrounded by four oxygen atoms. In contrast,
although the pre-edge peak is broadened in the layered silicate sample, there is hardly any change in the
XANES spectrum upon chlorination. This confirms that chlorination does not affect the coordination
environment of the titanium atoms in either sample. The broad pre-edge for Ti-HUS could possibly result
from the asymmetric coordination environment of titanium, which is composed of organic (acac) andinorganic (SiO) ligands. A similar broadening of the pre-edge peak was also observed in a previous study oftitanium-complex immobilization on layered silicate. For the Cl K-edge, no difference in the spectra of thechlorinated zeolite and layered silicate is observed. The spectra show a very broad second absorption at≈2,840 eV below the broad main absorption at 2,826 eV composed of two partially resolved peaks. A similar
trend in the XANES spectra has been observed for Cl anions in aqueous solution.[6] Considering thedifferences in titanium coordination state between TS-1 and Ti-HUS as well as the loss of organic ligands in
Ti-HUS upon chlorination, it appears that the organic ligands on the silicate-immobilized titanium are firstexchanged for chlorine. Then, hydration occurs due to the low water resistance of Ti-Cl bonds, resulting inchlorine existing as a hydrated HCl in both samples.
The chlorinated layered silicate photocatalyst exhibited a remarkably high production rate (0.7 mmol g-1h-1) and large amount of product formed (0.8 mmol), while the over-oxidation of cyclohexane was inhibited.
This excellent activity and selectivity is explained by the presence of a radical mediator (chlorine) located at
a position neighboring an isolated titanium atom. The high surface density of these active species on thesilicate layer provides efficient electron transfer to form chlorine radicals.

FIGURE 2. (left) Ti and (right) Cl k-edge XANES spectra for TS-1 and Ti-HUS before and after Cl incorporation.

REFERENCES
1. N. Tsunoji, H. Nishida, Y. Ide, K. Komaguchi, S. Hayakawa, Y. Yagenji, M. Sadakane, T. Sano, ACS Catal. 2019, 9,5742-5751.
2. R. Yuan, S. Fan, H. Zhou, Z. Ding, S. Lin, Z. Zhang, C. Xu, L. Wu, X. Wang, X. Fu, Angew. Chem. Int. Ed. 2013, 125,
1069-1073.
3. N. Tsunoji, T. Ikeda, M. Sadakane, T. Sano, J. Mater. Chem. A 2014, 2, 3372-3380.
4. N. Tsunoji, Y. Ide, Y. Yagenji, M. Sadakane, T. Sano, ACS Appl. Mater. Interfaces 2014, 6, 4616-4621.
5. N. Tsunoji, M. Bandyopadhyay, Y. Yagenji, H. Nishida, M. Sadakane, T. Sano, Dalton Trans. 2017, 46, 7441-7450.
6. N. Tsunoji, M. V. Opanasenko, M. Kubu, J. Cejka, H. Nishida, S. Hayakawa, Y. Ide, M. Sadakane, T. Sano, ChemCatChem.
2019, 9, 5742-5751.

- 95 -

16AG008

BL-12

Conformation Analysis of Chitin by Vacuum-Ultraviolet
Circular Dichroism Spectroscopy
Koichi Matsuo
Hiroshima Synchrotron Radiation Center, Hiroshima University,
2-313 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan
Keywords: N-Acetylglucosamine, Chain-length dependence, Conformation, Oligosaccharide

Saccharides has various biological functions such as the molecular recognition between cell and virus and theprotections of biomolecules from cold and dry conditions. However, the characterizations of these conformations
are often difficult because they take a complicated equilibrium state in aqueous solution. Vacuum-ultraviolet
circular dichroism (VUVCD) spectroscopy can extend the CD measurements down to 140 nm and can be used
for detecting the saccharide structures in aqueous solution because the CD spectra sensitively reflect the structuralcharacteristics such as the types of glycosidic linkages of di-saccharides [1, 2]. Previously, we measured the
VUVCD spectra of malto-, isomalto-, cello-, and laminari-oligosaccharides (all of constituent mono-saccharides
are D-glucose) with various chain length, and clearly observed the folding process of the helical structure ofoligomers accompanied with the increment of the chain length [3]. In the present study, the conformation studyof oligosaccharides was extended to chitin (glycosaminoglycans) [4] which is composed of N-acetylglucosamine(NAG) (See the chemical structure shown in Figure 1).
The VUVCD spectra of five types of -(1→4) linked NAG oligomers with the degree of polymerization (DP)from 2 to 6 were measured from 200 to 170 nm at 25oC in aqueous solutions. The VUVCD spectrum of chitin_DP2
showed one negative peak around 210 nm, one positive peak around 190 nm, and negative sign at 170 nm.
Previous study showed that the spectrum of NAG had one negative peak around 210 nm and one positive peakaround 180 nm [4]. From the differences between NAG and chitin_DP2, it is suggested that the effect of -(1→4)glycosidic linkage to CD exhibits below 190 nm. Chitin_DP3 exhibited similar spectrum with that of DP2 but thepositive peak around 190 nm was slightly red-shifted. The chitin_DP3 and DP4 showed mostly same spectral
shape. On the other hand, the spectral shape of chitin_DP5 and DP4 showed slight difference below 200 nm,
although the DP5 and DP6 had similar spectra again. These results suggest that the spectra of chitin changed stepby step with the increment of DP. The CD study of malto- and laminari-oligosaccharides indicated that the spectralchange depending on the chain length between 200 to 180 nm was affected by the formation of regular structureof oligosaccharide [3]. These results mean that the chain-dependence of CD observed in this study might relate to
the formation of unique structure of chitin.

Figure 1. Chemical structure of chitin (DP=2).
References
1.
2.
3.
4.

R. G. Nelson and W. C. Johnson, J. Am. Chem. Soc. 94, 3343-3345 (1972).
K. Matsuo and K. Gekko, Carbohydr. Res. 339, 591-597 (2004).
K. Matsuo, Biomed. Spectrosc. Imaging 6 111-121 (2017).
K. Matsuo, H. Namatame, M. Taniguchi, K. Gekko, Biosci. Biotech. Biochem. 73, 557-561 (2009).

- 96 -

BL-12

18AG008,18BG018

Structural change of DNA repair protein XRCC4
by phosphorylation at c-terminal revealed by VUV-CD
Kai Nishikuboa,b, Maho Hasegawaa, Yudai Izumic, Kentaro Fujiib,
Koichi Matsuoc, Yoshihisa Matsumotod, Akinari YokoyabaGraduate School of Science and Engineering, Ibaraki University, Japan
Quantum Beam Science Research Directorate, National Institutes for Quantum andRadiological Science and Technology (QST), Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University, JapanbdTokyo Institute of Technology

Keywords: XRCC4, vacuum ultraviolet circular dichroism

XRCC4 is activated via phosphorylation of its several sites by DNA-PK in the DNA double strand
break repair pathway (NHEJ) (1). The phosphorylation might cause a change of static electric charge
at the amino acid residues, resulting conformational alteration of the whole protein structure to permit
the protein accessibility to the strand break terminus through the charge re-distribution in the protein.
In order to understand the role of XRCC4 properly, it would be necessary to understand the mutual
relationship between its structural change and activity change. So far, the crystallography of XRCC4
has been performed, but there is no data on the full-length of XRCC4 because it is difficult tocrystallize 130 amino acid residues in the C-terminal which including several targets ofphosphorylation. Instead of crystallography, we have applied circular dichroism (CD) spectral analysis
for XRCC4 in an aqueous solution in a vacuum UV region at HiSOR. When compared the content of
the secondary structures obtained by the CD measurement of the intact XRCC4 (denoted as WT) withthat reported in the previous crystallography, the non-crystalized C-terminal region was revealed tocontain significant turn structures, but not to contain β-strand. A mutated XRCC4, in which the serine320 was substituted to an aspartic acid (denoted as S320D) to mimic phosphorylation, was also
analyzed. The content of β-strand of S320D was slightly less than that of WT. The evidences indicatethat β-strand in the N-terminal region was affected despite the substitution with aspartic acid induced
at the C-terminal region. The phosphorylation of C-terminal region would play a role to regulate theactivity of the protein through altering its whole structure, including the active center in the N-terminal.

- 97 -

Figure 1 shows VUV-CD spectra of full-length XRCC4WT and XRCC4S320D. A positive peakat 190 nm and negative peak at around 208 nm are the characteristic CD peaks of αhelix structures (2).

6

XRCC4WTXRCC4S320D

CD (M-1cm-1)

4
2
0
-2
-4
180

190

200

210

220

230

240

250

260

Wavelength (nm)
FIGURE 1. VUV-CD spectra of full-length XRCC4 in an aqueous solution.
TABLE 1. Secondary structural contents of XRCC4

1FU1(3)WT

S320D

length (residues)

203

342

342

α-helix (%)

38

34.3

37.4

β-strand(%)

26

15.3

13.2

turn (%)

8

22.8

22.4

random (%)

28

27.5

26.9

In table 1, 1FU1 is previously reported from crystallography (3). WT and S320D are theresult of CD measurement at HiSOR.
REFERENCES
1.

Kamdar,R.P. and Matsumoto,Y. Radiation-induced XRCC4 Association with Chromatin
DNA Analyzed by Biochemical Fractionation. J.Radiat.Res 2010; 51, 303-313.

2.

Matsuo.K. Structural analysis of protein using synchrotron radiation vacuumultraviolet circular dichroism. The Journal of Biochemistry 2004 135,3, p. 405-411.

3.

Junop, M.S., Modesti, M., Guarne, A., Ghirlando, R., Gellert, M., Yang, W. Crystal
structure of the Xrcc4 DNA repair protein and implications for end joining. EMBO J
2010. 19: 5962-5970.

- 98 -

18AG014

BL-12

Circular Dichroism Analysis of Optical Activity
Emergence in Amino-acid Thin Films Irradiated by
Vacuum-ultraviolet Circularly-polarized Light
Jun-ichi Takahashia, Toshiki Sakamatoa, Yudai Izumib, Koichi Matsuob
Masaki Fujimotoc, Masahiro Katohc, Yoko Kebukawaa, Kensei KobayashiaaFaculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku,
Yokohama 240-8501, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama,
Higashi-Hiroshima 739-0046, Japanc
UVSOR Facility, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji,
Okazaki 444-8585, Japan

Keywords: Homochirality, Amino Acid, Optical Activity, Circularly-polarized Light, Circular Dichroism

The origin of homochirality in terrestrial bioorganic compounds (L-amino acid and D-sugar dominant)remains one of the most mysterious problems in the research for the origins of life. Rational explanations
for the chiral asymmetry introduction of into bioorganic compounds are required because organic
compounds synthesized in abiotic environments are intrinsically racemic mixtures (equal amounts of Land D-bodies). One of the most attractive hypotheses in the context of astrobiology is “Cosmic Scenario”
as below;(1) Asymmetric reactions of prebiotic molecules adsorbed on interstellar dust surfaces in molecular
cloud circumstances were introduced by asymmetric radiation sources in space, that is “chiral radiations”.
(2) The chiral products were transformed into the complex organic materials including amino-acidprecursors as “chiral seeds”. (3) The complex organic materials as “chiral seeds” were transported withmeteorites or asteroids to primitive Earth resulting in terrestrial biological homochirality [1].
Eventually, wide radiation regions of circularly-polarized light (CPL) in space originated by lightscattering from interstellar dusts in star formation regions have been observed by telescopic infrared
polarization analysis. These observations have indicated that CPL is one of the potential candidates for“chiral radiations” sustaining the credibility of Cosmic Scenario [2].
In addition to observations, several ground experiments to validate the scenario have been investigatedasymmetric photochemical reactions in simple biochemical molecules using CPL radiation fromhigh-energy particle accelerators. We have reported optical activity emergence in solid-phase films ofracemic amino acids by left- or right-handed CPL (L- or R-CPL) irradiation of 215 nm in wavelength fromfree electron laser (FEL) of UVSOR-II [3]. By analysis using conventional circular dichroism (CD)
spectrometer, preferential structural changes between the two enantiomers in racemic amino-acid mixtures
have been introduced by L- or R-CPL irradiation.
As mentioned above, CD spectroscopy can detect optical activity emergence with a high accuracy
because CD spectra sensitively reflects the steric structures of chiral molecules. The theoretical calculationof CD spectrum of L-alanine molecule has revealed that the chromophores such as carboxyl and aminogroups are derived from characteristic electronic transitions (n-π*, π-π*, and n-σ*) corresponding todifferent wavelengths below 230 nm [4], suggesting that optical activity emergence by asymmetricphotochemical reactions depends on the irradiation wavelength.
In present, we are carrying out irradiation experiments of different CPL wavelengths at an undulator
beam line BL1U of UVSOR-III. As for the sample, we formed thin solid films of racemic mixture ofalanine on quartz substrates from crystal powders of DL-alanine (L/D = 50/50) as a sublimation source byusing a thermal-crucible vacuum-evaporation system in Hiroshima Synchrotron Radiation Center (HiSOR).
Sublimation temperature was controlled in the range of 150~200°C and pressure of the vacuum chamber
was approximately 5x10-2 Pa throughout the evaporation process. The CD spectra of thin solid films just- 99 -

after the deposition were measured from 260 to 160 nm in wavelength using a vacuum-ultraviolet (VUV)
CD instrument at beam line BL-12 of HiSOR and confirmed to be mostly zero CD before the irradiation,
showing that the spurious CD due to the contamination of film surface were negligible.
The thin solid films of racemic mixture of alanine were irradiated of L- or R-CPL in different wavelengths
using the undulator beam line BL1U of UVSOR-III [5]. In case of CPL irradiation in shorter wavelengths than
200 nm, the samples were set in a vacuum sample chamber preventing attenuation by air absorption [6]. On the
beam entrance side of the vacuum sample chamber, a gate valve with a vacuum-sealed MgF2 or LiF window
was mounted. The irradiated CPL wavelengths were 180 and 155 nm corresponding to photon absorption bandsof alanine molecule [7]. The irradiated photon energy dose was measured with photoelectron current of a silicon
photodiode (International Radiation Detectors, Inc.) settled at the sample position. The typical energy dose
calibrated by using quantum efficiency data of the silicon photodiode was approximately 30~60 mWhour.
CD spectra of the CPL irradiated films were measured at beam line BL-12 of HiSOR to clarify the opticalactivity emergence by CPL irradiation. In order to delete the effects of linear dichroism (LD) and/or linear
birefringence (LB) components, dependence on sample rotation angle (0, 45, 90, and 135 degrees) of the CD
spectra was measured. The observed spectral profile strongly depends on the irradiated CPL wavelength and thepolarization (L- or R-CPL). In Fig.1, CD spectra of DL-alanine films irradiated by L- or R-CPL at 180 or 155
nm in wavelength are shown. Detailed analysis of CD spectra are in progress to clarify full mechanism of
the optical activity emergence, which potentially has relevance to the origin of terrestrial bioorganic
homochirality stimulated by “chiral radiation”.
(a)

(b)

FIGURE 1. CD spectra of the L- or R-CPL irradiated DL-alanine film measured at BL-12 of HiSOR.
The CPL irradiation wavelengths were (a) 180 nm and (b) 155 nm at BL1U of UVSOR-III.

REFERENCES
1. W. A. Bonner, Orig. Life Evol. Biosph. 21, 407 (1991).
2. T. Fukue et al., Orig. Life Evol. Biosph. 40, 335 (2010).
3. J. Takahashi et al., Int. J. Mol. Sci. 10, 3044 (2009).
4. T. Fukuyama et al., J Phys. Chem. A109, 6928 (2005).
5. K. Matsuo et al., UVSOR Activity Report 2016 44, 157 (2017).
6. J. Takahashi et al., HiSOR Activity Report 2017, 126 (2018).
7. F.Kaneko et al., J. Phys. Soc. Jpn. 78 013001 (2009).

- 100 -

18AG021

BL-12

VUVCD Measurement of Lysine-36 Trimethylated
Histone H3 protein (H3K36me3)
Yudai Izumi and Koichi MatsuoaHiroshima Synchrotron Radiation Center, Hiroshima University, Japan

Keywords: Post-translational modification, epigenetics

Post-translational methylation and demethylation of histone H3 proteins have been reported to play
substantial roles in cellular functions. For example, it is known that trimethylation of H3 on the lysine-36(K36) residue links to DNA damage repair [1]. The conformation of protein closely relates to its biological
function, and hence the structures of (un)methylated H3 proteins would be important factors forunderstanding the roles in the cellular functions. In this work, the CD spectrum of K36 trimethylated H3(H3K36me3), which is recognized as one of the important methylated H3 proteins, was measured in orderto predict the positions of α-helix and β-strand structures of the protein [2].
Recombinant Xenopus laevis H3K36me3 protein was purchased from Active Motif. The reagent wasdissolved with 25 mM sodium phosphate buffer supplemented with 250 mM sodium fluoride (pH 8.6 at25°C). Final concentration of H3K36me3 was 1 mg/ml. CD spectroscopy was carried out in the BL12
beamline at the Hiroshima Synchrotron Radiation Center in Japan. The secondary-structure sequence waspredicted using neural-network method based on CD spectroscopic results [3].
Figure 1 shows the CD spectra of H3K36me3 and unmethylated H3. The CD spectrum of unmethylated
H3 was reproduced from Ref. [4]. Both spectra show a positive peak around 190 nm and negative peaks
around 200-230 nm. However, the spectral shapes differed from each other. CD spectral shapes reflect thesecondary structure contents of proteins, which means that trimethylation of K36 residue induced thestructural alterations of H3.

Fig. 1. CD spectra of H3K36me3 (thick line) and unmethylated H3 (thin line) [4].

Figure 2 shows predicted secondary structure sequence of H3K36me3 and unmethylated H3. It waspredicted that the structural alterations were not limited to the regions around methylation site. For example,
α-helix formations induced by K36 trimethylation were predicted at the 14th–17th, 77th–82nd, and 85th–
86th residues. Similarly, β-strand formation was also predicted at 36th–42nd residues. On the other hand,the α-helix and β-strand structures at the 122nd–130th residues changed to other structures, namely turn
and/or unordered structures.
The structural alteration induced by K36 trimethylation differed from those induced by mono-, di-, or- 101 -

trimethylation of lysine-4 or -9 residues [4, 5]. These results suggest that the structural changes induced bypost-translational methylation are not uniform, but are rich in variation depending on the sites of methylationand methylation degree. The various structural alterations may be strongly related to the regulation of cellularfunctions, such as DNA repair pathway.

Fig. 2. Sequence-based secondary structures of H3K36me3 and unmethylated H3. The positions predicted formation of αhelix, β-strand, and other structures are colored in gray, light gray, and white, respectively. The mark ★ in the rectangle
represents methylated site. The data of unmethylated H3 was reproduced from Ref. [4]. The 110th residue of unmethylated H3reagent is cysteine (C) which is different from that of the H3K36me3 reagent.

References[1] T. Clouaire and G. Legube, Nucleus 6, 107-113 (2015).
[2] Y. Izumi and K. Matsuo, Molecules 23, 2865 (2018).
[3] K. Matsuo et al., Proteins 73, 104-112 (2008).
[4] Y. Izumi et al., J. Radiat. Res. 59, 108-115 (2018).
[5] Y. Izumi et al., Chirality 30, 536-540 (2018).

- 102 -

18AU006

BL-12

Study on Structural Changes of Histone Core Proteins in
Arabidopsis after Gamma Irradiation
Jin-Hong Kima,*, Tae Ho Ryua, and Yudai IzumibaAdvanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 29 Geumgu-gil,Jeongeup-si, Jeollabuk-do 56212, Republic of Koreab
Hiroshima Synchrotron Radiation Center, Hiroshima University,2-313 Kagamiyama, Higashi-Hiroshima,
Hiroshima 739-0046, Japan
Keywords: histone modification, chromatin remodeling, DNA damage response, Arabidopsis thaliana, circular dichroism.

SWITCH/SUCROSE NONFERMENTING (SWI/SNF) chromatin remodeling proteins play essential
roles in diverse biological processes including DNA repair and apoptosis [1]. The DECREASE IN DNA
METHYLATION1 (DDM1), a plant-specific SWI2/SNF2-like chromatin remodeler, is necessary for DNA
methylation and heterochromatin maintenance in Arabidopsis thaliana [2, 3]. We found that the ddm1-2
mutant, which has a defect in the helicase domain of DDM1, is more sensitive than the wild type (WT) in
response to gamma irradiation. However, the radiation-sensitive phenotype was complemented byoverexpressing the intact DDM1 in the ddm1 mutant. Therefore, the comparative analysis of chromatin
structure in the ddm1-2 and DDM1-OE/ddm1-2 lines is important in elucidating the mechanism of
DDM1-mediated chromatin remodeling in response to gamma irradiation. This study aimed to elucidate
the structural changes of core histone proteins in chromatin after gamma irradiation, which can beassociated with the differential DNA damage responses in the WT, ddm1-2 and DDM1-OE/ddm1-2 lines.
The sterilized A. thaliana seeds were stratified at 4℃ for 2 days and germinated in 1/2 MS medium
supplied with 1% sucrose and 0.65% agar. The 14-day-old seedlings were exposed to gamma radiation
with a dose of 200 Gy (50 Gy/hr) using a 60Co source (42.6 TBq, AECL, Canada) at Korea Atomic Energy
Research Institute) at room temperature. Core histone proteins were extracted using the Histone
Purification Kit (Active Motif Inc., Carlsbad, CA) as described by Izumi et al. [4] with some modifications.
The extracted proteins were lyophilized using a freeze dryer (FreezeMobile 25EL, SP Scientific,
Warminster, PA) and stored at room temperature until use. For VUVCD analysis, the lyophilized samples
were dissolved with 10 mM Tris-HCl and 250 mM NaF to induce higher-order structures of histone
proteins.
The circular dichroism (CD) intensities obtained as ellipticity θ in millidegrees were converted to molar
CD Δε (M-1 cm-1) to compare them. Molar CD is approximately described as ,32980  
where MRW, c, and L are residue weight, concentration of the sample (mg/ml), and path length (0.0050cm), respectively. In this analysis, we defined MRW as follows.
∆ε 

MRW 

2 ∗ 14000  13900  15400  11400
 111.4.
2 ∗ 129  125  135  102In the CD spectra analysis, the WT, ddm1-2 and DDM1-OE/ddm1-2 showed substantially different CD
spectra of core histone proteins before and after gamma irradiation (Fig. 1). However, the difference in CD
spectra between the CT and GR samples was much more conspicuous in the ddm1-2 than in the WT and
DDM1-OE/ddm1-2.

- 103 -FIGURE 1. CD spectra of core histone proteins in WT, ddm1-2, and DDM1-OE/ddm1-2 plants. CT, control; and GR,
gamma ray. All values are average ± S.D. (n = 2 or 3).

Secondary structure contents of core histone proteins were calculated using the SELCON3 programfrom the CD spectra, based on the reference data measured at HiSOR [4]. The content of α-helix wasnoticeably increased in the ddm1-2 but decreased in the DDM1-OE/ddm1-2, whilst that of β-strand showed
the reverse trend between the two lines. The unordered secondary structures were commonly increased.
These results suggest that DDM1 may function in chromatin remodeling required for DDR in plants.
TABLE 1. Secondary structure contents of core histone proteins in WT, ddm1-2, DDM1-OE/ddm1-2 plants. CT, control;and GR, gamma-irradiated. All values are average ± S.D. (n = 2 or 3). Unit: %.
WT CT

α-Helix
11.9 ± 2.1

β-Strand31.3 ± 1.7

Turn21.2 ± 0.5

Unordered
35.6 ± 1.2

WT GR

11.5 ± 2.1

25.6 ± 2.3

21.2 ± 1.0

41.7 ± 0.9

ddm1-2 CT

10.3 ± 0.6

30.0 ± 1.4

23.2 ± 0.3

36.7 ± 1.0

ddm1-2 GR

14.7 ± 0.6

21.3 ± 1.0

21.5 ± 0.3

42.5 ± 1.4

DDM1-OE/ddm1-2 CT

14.1 ± 1.6

22.7 ± 3.2

22.3 ± 1.1

41.0 ± 1.4

DDM1-OE/ddm1-2 GR

7.8 ± 1.1

24.3 ± 2.0

21.5 ± 1.1

46.5 ± 0.8

In conclusion, this study demonstrates that DDM1, a SWI/SNF chromatin remodeling protein, isinvolved in radiation sensitivity of plants by affecting the structural changes of core histone proteins andchromatin remodeling in response to gamma radiation. In the further study, the functional roles ofIR-induced structural changes of core histone proteins will be explored in association with DNA damage
responses.

REFERENCES
1. J-H. Park, E-J. Park, S-K. Hur, S. Kim and J. Kwon, Mammalian SWI/SNF chromatin remodeling complexes are
required to prevent apoptosis after DNA damage, DNA Repair 8, 29-39 (2009).
2. T. Kanno, W. Aufsatz, E. Jaligot, M. F. Mette, M. Matzke and A. J. Matzke, A SNF2-like protein facilitates dynamic
control of DNA methylation, EMBO Rep. 6, 649-655 (2005).
3. A. Zemach, M.Y. Kim, P.-H. Hsieh, D. Coleman-Derr, L. Eshed-Williams, K. Thao, S.L. Harmer and D. Zilberman, The
Arabidopsis nucleosome remodeler DDM1 allows DNA methyltransferases to access H1-containing heterochromatin,
Cell 153, 193-205 (2016).
4. Y. Izumi, K. Fujii, F. Wien, C. Houéé-Lévin, S. Lacombe, D. Salado-Leza, E. Porcel, R. Masoud, S. Yamamoto, M,
Réfrégiers, M-A. H. du Penhoat and A. Yokoya, Structure change from β-strand and turn to α-helix in histone H2A–H2B
induced by DNA damage response, Biophy. J. 111, 69-78 (2016).

- 104 -

18BG042

BL-12

Effects of mono-saccharides on structural stability of apomyoglobin investigated by VUVCD spectroscopy
Takeru Shimizua, Munehiro Kumashiroa, Yudai Izumib, and Koichi MatsuobaGraduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima
739-8526, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama, Higashi-Hiroshima,
Hiroshima 739-0046, Japan
Keywords: apo-myoglobin, circular dichroism, acid-denaturation, mono-saccharide, structural stability

Helical Content / %Protein structure closely relates to the biological function. Hence the denaturation of structure due to theheat, cold, and acid (pH) induces the depression of the functions. To protect the denaturation or enhance thestability of protein structure, saccharides are often used as a stabilizer as well as polyols. Considerable efforts
have disclosed that the addition of saccharides largely affects the amount of hydrations (or the numbers ofwater molecules) around proteins, enhancing the structural stability of proteins [1]. However, thestabilization mechanism at molecular level remains unclear. As well as proteins, saccharides are also
hydrated by water molecules [2]. The numbers of water molecules depend on the structural characteristics
of saccharides such as the numbers and orientations of hydroxy groups, and also it is reported that the
methylation of mono-saccharides contributed to the increment of the amount of hydrations [2]. In this study,
to reveal the contributions of the saccharide hydrations to the structural stability of protein, we measured thevacuum-ultraviolet circular-dichroism (VUVCD) spectra of apo-myoglobin (apoMb) at the acid-unfolded(AU) state in the presence of four types of mono-saccharides (D-Glucose (glc), methyl β-D-glucose (β-glc),
D-xylose (xyl), and methyl β-D-xylose (β-xyl)).
The VUVCD spectra of apoMb were100
measured in the presence or absence of monosaccharides. In the case of the absence of mono80
76saccharides, the helical content of apoMb at the60
native state (pH 6) was 76%, but that at the AU
54.5
state (pH 2) decreased to only 7.7% owing to the40acid denaturation (Fig. 1). Adding glc, β-glc, xyl,20
and β-xyl, the helical content increased to 17.8,
17.8
20
10.4
7.7
20.0, 10.4, and 54.5%, respectively (Fig. 1),
0
showing that the folded structure of the nativeNAU+glc +-glc +xyl +-xyl
state was recovered from the acid denaturation.
Figure 1. Helical contents of ApoMb at pH 2 (AU) in theConsidering the free energy of acid-denaturation
presence of glc, β-glc, xyl, and β-xyl. The results of native (pHof apoMb, it was indicated that the correlations
6; N) and AU states are also described for comparisons.
between the amount of hydration of monosaccharide and the structural stability of proteinswould be positive.

REFERENCES
1.
2.

S. N. Timasheff, “Preferential interaction of water and cosolvents with proteins,” in Protein-Solvent Interactions, editedby R. B. Gregory: Marcel Dekker, pp. 445-482 (1995)
S. A. Galema, H. Hoeiland, “Stereochemical aspects of hydration of carbohydrates in aqueous solutions. 3. Density andultrasound measurements”. J. Phys. Chem. 95, 5321-5326 (1991).

- 105 -

18BG049, 18BG052

BL-12

Vacuum-Ultraviolet Circular Dichroism of Sucralose
Yasuyuki Makia and Koichi Matsuob
ab

Kyushu University, Fukuoka 819-0395

Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-8526

Keywords: Saccharide, Artificial sweetener, Vacuum-ultraviolet circular dichroism.

Sucralose (1,6-dichloro-1,6-dideoxy-β-D-fructofuranosyl-4-chloro-4-deoxy-α-D-galactopyranoside) is
one of artificial sweeteners and has emerged as one of the most commercially useful compounds in the fieldof sucrochemistry [1]. It is a trichlorinated derivative of sucrose synthesized by selective chlorination of
sucrose at three of the primary hydroxyl groups. Its biological functions have been intensively studied but
its conformations in aqueous solution are poorly understood, although they could be related to its functions.
Vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy is an effective tool for analyzingsaccharide structure in aqueous solution because they contain high-energy chromophores such as hydroxyl
groups and acetal bonds whose electronic transitions are only detectable in the vacuum-ultraviolet (VUV)
region below 190 nm [2-4]. VUVCD data accumulated for various types of saccharides still have not been
fully assigned [4], but in the case of a substituted saccharide such as sucralose, comparison of the spectrumwith that of the unsubstituted one may be informative for the assignment. In this study, a VUVCD spectrumof sucralose in aqueous solution was measured using a VUVCD spectrophotometer with a synchrotron
radiation (SR) light source and was compared with that of sucrose.
Sucrose (FUJIFILM Wako Pure Chemical Corp.) and sucralose (Sigma-Aldrich) were used without
further purification. The sample solutions were prepared by dissolving them in de-ionized water atconcentrations of 10 wt%. The VUVCD spectra were measured from 262 to 172 nm at 25 oC under a nitrogen
atmosphere using the SR-VUVCD spectrophotometer of Hiroshima Synchrotron Radiation Center (BL-12)[5,6]. The CaF2 optical cell with 50 µm path length or the SiO2 optical cell with 10 µm path length was used.
Figure 1 shows the VUVCD spectrum of the aqueous sucralose solution. The CD spectrum of sucralose
was observed only below 192 nm. It would have a positive peak below 180 nm, of which the position cannot
be specified because of the limited wavelength range. In Figure 1, the VUVCD spectrum of the aqueous
sucrose solution was also shown. The CD spectrum of sucrose was observed only below 200 nm. The peak
was not observed in the present wavelength range, but there should be a positive peak below 172 nm. The
molar ellipticity values of sucralose was much smaller than those of sucrose. It is not obvious if thisdifference is attributed to the effect of the substituent or the different molecular conformation between
sucralose and sucrose, which will be the subject of the future work.

FIGURE 1. VUVCD spectra of sucralose (solid blue line) and sucrose (dotted red line) in aqueous solutions at 25 oC.

- 106 -

REFERENCES
1.
2.
3.
4.
5.
6.

H. Zhang, S. Sun, Y. Wang and J. Cao, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 187, 92-97 (2017).
K. Matsuo, Biomed. Spectrosc. Imaging 6, 111-121 (2017).
K. Matsuo, H. Namatame, M. Taniguchi and K. Gekko, J. Phys. Chem. A 116, 9996-10003 (2012).
K. Matsuo and K. Gekko, Carbohydr. Res. 339, 591-597 (2004).
K. Matsuo, K. Sakai, Y. Matsushima, T. Fukuyama and K. Gekko, Anal. Sci. 19, 129-132 (2003).
N. Ojima, K. Sakai, K. Matsuo, T. Matsui, T. Fukazawa, H. Namatame, M. Taniguchi and K. Gekko, Chem. Lett. 30, 522523 (2001).

- 107 -

18BU001

BL-12

Secondary-Structure Analysis of DNA Gyrase Inhibitor
Derived from Staphylococcus aureus by VacuumUltraviolet Circular-Dichroism Spectroscopy
Fuminori Katoa and Koichi MatsuobaGraduate School of Biomedical and Health Sciences, Hiroshima University,
1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University,
2-313 Kagamiyama, Higashi-Hiroshima 739-0046, Japan

Keywords: VUVCD spectroscopy, protein secondary structure, Staphylococcus aureus

Staphylococcus aureus is a Gram-positive pathogenic bacterium causing various diseases including minor
skin infections to life-threatening diseases. Multidrug-resistant strains, including methicillin-resistant S.
aureus (MRSA), make therapy against S. aureus infections increasingly difficult. There is an urgent need todevelop new therapeutic approaches and identify novel targets for drugs against this pathogen [1].
Until now, we have found and revealed the function of novel DNA gyrase inhibitor encoding a 50-residue
peptide in the Staphylococcus aureus genome. Bacteria have four DNA topoisomerases that are coordinatedto maintain DNA topology for replication, transcription, and recombination. DNA gyrase is an essential
topoisomerase and is unique to bacterial cells [2]. Therefore, DNA gyrase inhibitors cause a growth arrest
and cell death in bacteria. DNA gyrase is also the target of quinolone and aminocoumarin antibiotics.
Recently, we demonstrated that amino acid substitution at the 27th Glu or the 37th Asp residues of the
DNA gyrase inhibitor caused a reduction of its biological activity in E. coli cell (Fig. 1). However, we lackinformation about the protein structure and the role of these amino acid residues in its biological activity. In
this study, we aimed to determine the secondary structure of DNA gyrase inhibitor by comparing ProS2tagged DNA gyrase inhibitor with a soluble tag protein ProS2 [3], thus providing important insight into
structure-function relationship for this DNA gyrase inhibitor.
Vacuum-ultraviolet circular-dichroism (VUVCD) measurements were carried out on the ProS2-tagged
DNA gyrase inhibitor and ProS2-tag protein at the BL12 beamline of the Hiroshima Synchrotron Radiation
Center. The secondary structure contents of ProS2-tagged DNA gyrase inhibitor and ProS2-tag protein were
estimated using SELCON3 program [4]. The DNA gyrase inhibitor contained 22.9% α-helix, 6.7% β-strand,
27.5% turn, and 42.7% unordered structures (Table 1). To determine the position of the α-helical and βstrand segments, the sequence-based prediction of the secondary structure segments was performed by
combining the VUVCD spectral data with the Neural Network algorithm (VUVCD-NN method) [5]. The
22nd-33rd residues and the 18th-20th residues of the DNA gyrase inhibitor formed an α-helix and a β-strand
structure, respectively (Fig. 2). Interestingly, the 27th Glu residue, critical for the biological activity, waslocated at the center of the α-helix structure. Further, the DNA gyrase inhibitor derivatives containing E27D
or D37Q amino acid substitution have folded its secondary structure correctly in comparison to the native
DNA gyrase inhibitor. These results give insight into the role of the 27th Glu and the 37th Asp residues inthe DNA gyrase inhibitor required for its biological activity.

- 108 -

O.D660
4

Negative control(without protein induction)

3

Proteininduction

2

E27D substitution
D37Q substitution
Native protein

1

0
0

1

2

3

4

5

6

7

8

9

10 (hr)

FIGURE 1. The effect of DNA gyrase inhibitor, its derivatives (E27D, and D37Q) on E. coli cells. E. coli BL21(DE3) strains
were cultured in M9 GLY medium. Arabinose was added to a final concentration of 0.2% after 2.5 h (OD660 0.3-0.4). The
arrows indicate the time point of protein induction. DNA gyrase is an essential enzyme for a bacterial cell, therefore DNA
gyrase inhibitors show a reduction in bacterial cell growth.

TABLE 1. Contents of secondary structures of ProS2 tag protein and ProS2-tagged DNA gyrase inhibitor obtained using
SELCON3 program.
Structure content (%)α-helix
β-strand
Turn
Unordered
ProS2 tag
8.53
46.56
20.66
24.25
ProS2-tagged DNA
11.45
38.50
22.06
27.99
gyrase inhibitor
DNA gyrase inhibitor
No. of amino acids

1

22.94 (%)
11.7 (A.a)

10

6.75 (%)
3.4 (A.a)

20



30

27.59 (%)
12.0 (A.a)



40

42.72 (%)
21.7 (A.a)

50

MSKDKDPKLN YHEEENSMVT DFEDLKELGK EMEQISDQND QEKNSEEDSQ
CCCCCCCCCC CCCCCCCEEE CHHHHHHHHH HHHCCCCCCC CCCCCCCCCC

FIGURE 2. Sequence-based secondary structure of DNA gyrase inhibitor obtained by the VUVCD-NN method. The α-helix(H), β-strand (E), and coil (C) structures are shown by cylinder, arrow, and line, respectively. Asterisks represent the 27th Glu
and the 37th Asp residues.

REFERENCES
1. Tacconelli E, Magrini N. “Global priority list of antibiotic-resistant bacteria to guide research, discovery, and developmentof new antibiotics.” World Health Organization, Geneva, Switzerland. 2017 Feb 27.
2. Champoux JJ. “DNA topoisomerases: structure, function, and mechanism”, Annu Rev Biochem. 70, pp. 369-413 (2001).
3. Kobayashi H, Swapna GV, Wu KP, Afinogenova Y, Conover K, Mao B, Montelione GT, Inouye M. “Segmental isotope
labeling of proteins for NMR structural study using a protein S tag for higher expression and solubility”, J Biomol NMR,
52, pp. 303-13 (2012).
4. Sreerama N and Woody RW, “Estimation of protein secondary structure from circular dichroism spectra: comparison of
CONTIN, SELCON, and CDSSTR methods with an expanded reference set”, Anal Biochem, 287, pp. 252–260 (2000)
5. Matsuo K, Watanabe H, Gekko K, “Improved sequence-based prediction of protein secondary structures by combining
vacuum-ultraviolet circular dichroism spectroscopy with neural network”, Proteins: Struct Funct Bioinf. 73, pp. 104–112(2008).

- 109 -

18BU010

BL-12

Spectrum Measurement of Human De Novo Evolved Gene
Product NCYM Using Vacuum-Ultraviolet Circular
Dichroism
Tatsuhito Matsuoa, Yusuke Suenagab, Koichi Matsuoc, and Taro TamadaaaInstitute for Quantum Life Science, National Institutes for Quantum and Radiological Science andTechnology, Ibaraki, Japanb
Department of Molecular Carcinogenesis, Chiba Cancer Center Research Institute, Chiba, Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University, Hiroshima, Japan

Keywords: de novo proteins, secondary structure, perdeuteration

Non-genic regions in eukaryotic genomes produce noncoding RNAs, and mutations in these regions
during evolution generate new lineage-specific coding genes, called de novo genes [1]. We previously foundthat NCYM, a cis-antisense gene of the MYCN oncogene that was believed to be a long noncoding RNA, isa human de novo gene that encodes a homininae-specific protein that promotes metastases in humanneuroblastomas [2]. To understand the molecular basis underlying this function, structural characterizationof NCYM is needed. NCYM is expected to show high molecular flexibility, and its character is unsuitableto determine its structure by high-resolution methods such as protein crystallography. Therefore, we
employed the vacuum-ultraviolet circular dichroism (VUV-CD) to study the secondary structure of NCYM.
Furthermore, we also measured the perdeuterated-NCYM to see isotopic effects on its structure.
In this beamtime, the measurements were conducted on the following samples in addition to the solvents:(1) Hydrogenated NCYM (Tagged), 1.1 mg/ml(2) Perdeuterated NCYM (Tagged), 1.4 mg/ml(3) Hydrogenated Tag, 0.6 mg/ml(4) Perdeuterated Tag, 1.4 mg/ml
The chemical composition of the solvents was 20 mM
phosphate buffer (pH or pD 8.0), 3 mM DTT.
The measured VUV-CD spectra are shown in Figure 1.
Significant differences in the spectra are seen in the
wavelength range of 190–240 nm between the tagged
proteins and the tags. These differences should arise fromthe spectra of NCYM.
Secondary structure contents of these samples wereanalyzed using these CD spectra and SELCON3 program [3,
FIGURE 1. VUV-CD spectra of H-NCYM(blue), D-NCYM (red), H-Tag (green), and D4]. As a result, it was found that the hydrogenated tag (129
Tag (orange). The CD spectra were measured
residues) contains ~14% of α-helices and ~29% of β-sheets,
over the wavelength range of 175–260 nm withwhich are in good agreement with those calculated from thea resolution of 1 nm.
atomic structure of the tag. The tagged hydrogenated NCYM
(238 residues) was found to contain ~17% of α-helices and ~27% β-sheets, indicating that NCYM without
the tag also contains secondary structures. The isotopic effects appear to be marginal, but the detailed
analysis is currently underway.

REFERENCES
1. McLysaght, A. and Guerzoni, D., Phil. Trans. R. Soc. B 370, 20140332 (2015).
2. Suenaga, Y. et al., PLoS Genetics 10,
e1003996 (2014).
3. Sreerama, N. and Woody, R.W., Anal. Biochem., 287, 252-260 (2000).
4. Matsuo, K. et al., J.
Biochem., 138, 79-88 (2005).

- 110 -

18AG046, 18BG012

BL-13

Ultrafast Charge Transfer Dynamics on
Partially Fluorine-Substituted Aromatic Monolayers
Analyzed by Auger Electron Spectroscopy
Shin-ichi Wadaa,b, Yoshiki Iyobea, and Atsunari Hirayaa,baDepartment of Physical Science, Hiroshima University
Hiroshima Synchrotron Radiation Center, Hiroshima Universityb

Keywords: Self-assembled monolayers (SAMs), Resonant Auger electron spectroscopy (RAES), Core-hole-clock (CHC)
method, Molecular conductivity

Charge transfer dynamics at organic interfaces has attractive potential for future applications based onorganic molecular devices. We consider that such dynamics can be evaluated by resonant core-excitations.
Especially, core-hole clock (CHC) method is a powerful technique to measure ultrafast charge transfer
dynamics. Generally, resonant Auger decay only occur after a resonant core-excitation below ionizationthreshold, and normal Auger decay takes place after direct core-ionization. But normal Auger electron canbe also observed in resonantly excited solid surfaces. This is caused by fast dissipation of the excited electron
to conductive band of the substrate before core-hole decay. So, we can get information about such chargetransfer dynamics from branching ratio between resonant Auger and normal Auger yields in comparison withthe core-hole lifetime [1,2]. Actually, we have successfully measured the ultrafast charge transfer for wellordered, self-assembled monolayers (SAMs) with aromatic molecular chains as strong reduction of resonant(spectator) Auger components in comparing with absorption intensity (total Auger yields). We haveconfirmed that there is the critical relationship between site-selective ion desorption and ultrafast chargetransfer dynamics [3]. Such charge transfer takes place along molecular chains via molecular orbitals of
excited resonant states. So, substitution of aromatic skeleton, especially fluorine-substitution which makes
localization of delocalized π electrons, affects charge transfer dynamics. In this study, we studied ultrafast
charge transfer dynamics on partially fluorine-substituted aromatic monolayers by measuring resonant Auger
electron spectra.
Measurements of near edge X-ray absorption fine structure (NEXAFS) and Auger electron spectra were
performed at the beamline BL-13 of HiSOR. During measurements, the experimental chamber had a basepressure of about 5×10-9 Torr. NEXAFS spectra around the O K-edge were recorded in total electron yield(TEY) mode by measuring a sample drain current. Resonant Auger electron spectra were measured using a
concentric hemispherical analyzer (Omicron EA125U5) by changing photon energy of irradiation light in
the O K-edge region.
Fig. 1 shows the schematic drawings of SAMs used in this study.
SAMs were prepared by immersing Au substrates into 1.0 mM
ethanol solutions of MFB (HSC6H4C6F4COOCH3) and MBF(HSC6F4C6H4COOCH3) as well as previously studied SAMs of M2P(HSC6H4C6H4COOCH3) and MHDA (HS(CH2)15COOCH3) [3]. All
samples have –COOCH3 at head groups, and MFB, MBF, and M2Phave conductive phenyl rings (–C6H4C6H4–) at the molecular chain,
while MHDA has an insulating aliphatic methylene chain.
Fig. 2 shows the typical result measured for partially fluorinesubstituted MFB SAM as well as that for non-substituted M2P as areference. Both SAMs have oxygen atoms only on their head group–COOCH3, so the TEY spectra in the O K-edge show quite similar
structure each other. Total Auger yields are also similar to each other- 111 -

MF B

MB F

M2 P

MH D AFIGURE 1. Molecular structure of
SAMs used in this study, MFB, MBF,
and M2P (conductive), and MHDA
(insulating) SAMs.

and proportional to NEXAFS spectra. On the other hand, spectator Auger yields are strongly reduced above
533 eV. Oxygen core-electrons are resonantly excited to the unoccupied molecular orbitals around–COOCH3 moieties in all SAM samples studied here. It indicates that ultrafast charge transfer from the headgroups to Au substrates occurs in this energy region. The ratios of spectator Auger components of MFB (23%
at 534 eV) and MBF (25%) are not so much reduced than that of M2P (18%). This result shows that the
charge transfer at MFB (estimated charge transfer time 6.6 fs) and MBF (8.8 fs) is slower than M2P (3.8 fs),
indicating that substitution of electron-accepting fluorine atoms cut off π conjugation of unoccupied
molecular orbitals and intercept ultrafast charge transfer from their head groups to Au substrates.

REFERENCES
1. J. Schnadt, P. A. Bruhwiler, L. Patthey, J. N. O’Sea, S. Sodergren, M. Odelius, R. Ahuja, O. Karis, M. Bassler, P. Persson,
H. Siegbahn, S. Lunell, and N. Martensson, Nature 418, 620-623 (2002).
2. A. Fohlische, P. Feulner, F. Hennies, A. Fink, D. Menzel, D. Sanchez-Portal, P.M. Echenique, and W. Wurth, Nature 436,373-376 (2005).
3. S. Wada, M. Ogawa, S. Hosoda, R. Koga and A. Hiraya, HiSOR Activity Report 2016, 111-112 (2016).

4

4

MFB
3

Intensity / arb.units

Intensity / arb.units

3

Spectator Auger yeield
Total Auger yield
TEY

2

1

M2P

2

1

0

0
528 530 532 534 536 538 540 542 544 546 548
Photon Energy / eV
1.0
Ratio of spectator component
スペクテーター収量の割合
0.8
0.6
0.4
0.2
0.0
528 530 532 534 536 538 540 542 544 546 548
Photon Energy / eV

530 532 534 536 538 540 542 544 546 548
Photon Energy / eV

Ratio

Ratio

Spectator Auger yeield
Total Auger yield
TEY

1.0
0.8
0.6
0.4
0.2
0.0

Ratio of spectator component
スペクテーター収量の割合

530 532 534 536 538 540 542 544 546 548
Photon Energy / eV

FIGURE 2. NEXAFS and Auger electron yield spectra measured for MFB (left) and M2P (right)
SAMs. Gray lines show NEXAFS, and gray and black circle plots are total and spectator Auger yields,
respectively. The lower bar graphs indicate the ratio of spectator components to the total Auger yields
at each excitation energy.

- 112 -

18AG047, 18BG013

BL-13

Ion Desorption Measurements Using Pulsed HVTime-of-Flight Mass Spectrometer at HiSOR
Kamon Yamamotoa, Atsunari Hirayaa,b, and Shin-ichi Wadaa,baDepartment of Physical Science, Hiroshima University
Hiroshima Synchrotron Radiation Center, Hiroshima Universityb

Keywords: Resonant core-electron excitation, Site-selective bond breaking, Ion desorption, Organic thin films

Core-excitation takes place within quite local area, so a specific atom in a molecule can be excitedresonantly. Using tunable synchrotron radiation, site-selective core excitation can be achieved and siteselective bond breaking is expected in the vicinity of the atom where the primary core excitation takes place.
This suggests the possibility that the resonant excitation by soft x-ray can control chemical bond scission
selectively. Recently, it was found that site-selective ion desorption takes place at resonant core excitationsof C1s,O1s(OCH3) → σ*(O-CH3) and O1s(OCH3) → σ*(C-OCH3) on surface molecules of methyl ester
compounds like poly-methylmethacrylate (PMMA) thin films and self-assembled monolayers (SAMs) [1,2].
The investigation points out an importance of the primary excitation to the anti-bonding orbital localized ona specific bonding to trigger off ion desorption selectively.
Experiment using a time-of-flight mass spectrometer (TOF-MS) is a powerful approach to investigate
photon stimulated ion desorption. TOF-MS combined with the pulsed synchrotron radiation from single
bunch operation at KEK-PF (single bunch interval: 624 ns) has been used to measure the desorbed ion. Thision spectrometer, however, needs sufficient long SR pulse interval. In this study, to measure the desorbing
ion for compact storage ring such as HiSOR (pulse interval: 73 ns), we have adapted a pulsed HV TOF-MS
to the end station of BL-13 and investigated optimized measurement conditions.
BL-13 is a soft X-ray beamline in HiSOR with a Dragon-type spherical grating monochromator [3]. The
beamline has been developed to investigate soft X-ray surface photochemistry and has kept a potential tomeasure X-ray absorption and photoelectron spectra especially for organic materials. X-ray absorption
spectroscopy (XAS) as well as X-ray photoelectron spectroscopy (XPS) is a great tool to investigate elementspecific electronic states of samples. So far, XAS measurements at the end station of BL-13 has been
provided with the total electron yield (TEY) and total ion yield (TIY) modes. Last year, a newly built partial
yield detector was installed in order to measure XAS with partial electron yield (PEY) and total fluorescence
yield (TFY) modes. And this study makes partial ion yield (PIY) measurement possible in BL-13 to study
spectroscopic dynamics of x-ray irradiated organic materials from various aspects.
Fig. 1 shows a schematic drawing of the pulsed HV TOF-MS adopted to the end station of BL-13. Pulsed
HV was supplied to the first acceleration grid in front of sample surface to introduce desorbing ions into thedrift tube and detector (from left side to right side in the figure). Typical HV was -0.5 kV and its pulse
First
SecondDrift tube
acceleration unit acceleration unit

lens

Drift tube

Detector

FIGURE 1. Schematic sketch of pulsed HV TOF-MS adopted to the end station of BL-13.

- 113 -

duration and repetition rate were several hundreds of ns and a few kHz in this study. During off-time of HV
pulses, retardation voltage (typically +20 V) was also supplied to the first grid in order to store ions between
the sample and first grid (Fig. 2). Although this retardation voltage helps to detect much more ion signal, we
must pay attention to adjust the voltage because the voltage can also cause broadening of flight time of eachion due to various direction and magnitude of initial velocities of stored ions as shown in Fig. 2.
The other optimization of experimental setup was pulse width of HV. Typical results are summarized inFig. 3. In supplying HV with 700 ns pulse width, we can measure CHn+, OCH+, and COCH3+ ions fromPMMA thin films by C1s → σ*(O-CH3) resonant core-excitation. In reducing the pulse width to 300 ns, thesignal of CH2+ and CH3+ ions were well discriminated from CHn+ signal, while heavier ions like OCH+ and
COCH3+ were quenched. In supplying 200 ns pulse, most of ions were not detected. The result indicates theimportance of suitable experimental conditions, which are still needed to adjust in order to efficiently detect
desorbing ions by using pulsed HV TOF-MS.

REFERENCES
1. S. Wada, H. Kizaki, Y. Matsumoto, R. Sumii and K. Tanaka, J. Phys.: Condens. Matter 18, S1629-S1653 (2006).
2. S. Wada, “Site-selective bond breaking induced by resonant core-excitations” in Encyclopedia of Interfacial Chemistry 1st
Edition - Surface Science and Electrochemistry, edited by K. Wandelt, Amsterdam: Elsevier, 2018, pp. 621-628.
3. Homepage of Hiroshima Synchrotron Radiation Center, http://www.hsrc.hiroshima-u.ac.jp/english/storagering_
beamlines/ beamlines.html.

FIGURE 2. Illustration of ions stored
between the sample and first grid of TOF
by supplying retardation voltage. Arrows
suggest velocities of each desorbing ion.

FIGURE 3. TOF spectra measured for coreexcited PMMA thin films by changing pulse
width of supplied HV with (a) 700 ns, (b) 300 ns,
and (c) 200 ns.

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18AU007&18BG009

BL-13

Study toward Time-of-Flight Mass Spectrometry of Ion
Desorption Following Inner-shell Excitation of Molecules
Adsorbed on a Surface
Yasumasa Hikosaka,a Hiroyuki Shimadab and Shin-ichi Wadaca

University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japanb
KEK-IMSS-PF, 1-1 Oho, Tsukuba,305-0801, Japanc
Hiroshima University, 1-3-2 Kagamiyama, Higashi-Hiroshima, 739-8511 Japan
Keywords: Ion desorption; Inner-shell excitation; Mass spectrometry; UMP

Ion desorption following inner-shell excitation of molecules adsorbed on a surface has attracted muchattention from the viewpoint of chemical reaction control. The idea of site-selective scission of chemicalbond arises from the fact that inner-shell excitation of a molecule and the subsequent Auger decay occur inthe vicinity of a specific site in the molecule. One of the most conspicuous examples of the site-selective
chemical bond scission induced by inner-shell excitation is observed in ester compounds adsorbed on
surfaces [1]. In practice, ion desorption is not a simple result from mono-molecular reaction dynamics atAuger final states, but the energy transfer from/to surrounding molecules and the substrate also can be an
important role in leading the site-selective scission.
Mass spectrometry is common tool to study ion desorption from molecules adsorbed on surfaces.
Particularly, the method on the time-of-flight basis is useful for its high ion detection efficiency. The
time-of-flight measurement of ions requires a pulsed light source. Wada’s group has conducted
time-of-flight mass spectrometry of desorbed ions using the single-bunch operation of the Photon Factoryin Tsukuba [1]. The 624-ns pulse period is, however, much shorter than ion times-of-flight typically in
microsecond time range, and the superimposition of peak structures resulting from different light pulses
constitutes an ambiguity in spectral interpretation. Furthermore, the Photon Factory abandoned its single
bunch operation several years ago, and such ion time-of-flight measurements cannot be performed now at
the Photon Factory. The objective of our project which started in FY2018 is to develop a time-of-flightmass spectrometer which can operate with the continuous light from HiSOR in Hiroshima. A time-of-flightmass spectrometer in this sort was already constructed at HiSOR long ago [2], and the main components
are utilized in the current project. We have carried out in FY2018 the maintenance and the preparation of apulsed power supply and electronics circuits for applying pulsed electric field to the spectrometerelectrodes. Ion time-of-flight measurements will be ready soon in the early stage of next fiscal year.
One of the target samples in our mass spectrometric study is uridine 5′-monophosphate (UMP)
adsorbed on a surface. Understanding of the ion desorption following inner-shell excitation of such kind of
nucleotides is important in its close connection with DNA lesions induced by ionizing radiation. A single
UMP molecule contains two nitrogen atoms which locate at different chemical environments in themolecule. It is known that in the aqueous solution the chemical shift of the nitrogen 1s binding energies
shows dependence on pH, due to the deprotonation of N3 atom in UMP at high pH [3]. One of ourconcerns is whether the deprotonation links to ion desorption following inner-shell excitation. A sample
deposited on a metal or Si surface, instead of aqueous solution, is adequate to the investigation with ourtime-of-flight mass spectrometer. We attempted a simple method for preparing UMP sample deposited on ametal: a drop of UMP aqueous solution (~0.01 mM) of pH 11 was dried on the Au substrate during several
hours. This sample preparation has a risk of contamination by manipulation in the atmosphere. To examine
if the deprotonation of N3 atom keeps in the condensed UMP sample prepared by this simple method, we
have measured the XANES and XPS spectra in the N-K edge range, prior to a mass-spectrometricinvestigation to the ion desorption. Figure 1 shows N1s photoelectron spectra measured at two different
photon energies. The N 1s photoelectron structure in the spectrum measured at a photon energy of 472 eV
exhibits a shoulder at the high kinetic energy side. The energy difference between the peak top and the- 115 -

shoulder is about 3 eV, which is reasonable as the energy splitting for the chemical shift of the nitrogen 1s
binding energies [3]. However, the observed intensity ratio of the splitting components is around 2:1, muchdifferent from the expected 1:1 peak ratio. Similar intensity ratio is observed in the photoelectron structure
measured at a photon energy of 522 eV, indicating that the intensity ratio does not result from resonanceeffect at a particular photon energy range. While the observed peak ratio suggests a deformation of themolecular structure and the deprotonation of UMP located at the outermost surface of the condensed
sample, the peak splitting implies that the deprotonation of the UMP sample keeps in the condensed
sample prepared by the present method. We plans to perform mass spectrometry using this sample
preparation, to give insight into ion desorption following inner-shell excitation of the condensed UMP
molecules.

FIGURE 1. N1s photoelectron spectra measured at two different photon energies for uridine 5′-monophosphate adsorbed onan Au surface.

REFERENCES
1. S. Wada, H. Kizaki, Y. Matsumoto, R. Sumii and K. Tanaka, J. Phys: Cond. Matt., 18, S1629-S1653 (2006).
2. K. Fujii, D. Taga, Y. Nakashima, S. Waki, S. A. Sardar, Y. Yasui, S. Wada, T. Sekitani and K. Tanaka, Nucl. Instrum
Meth. Phys. Res A 467-468, 1509-1513 (2001).
3. H. Shimada, H. Minami, N. Okuizumi, I. Sakuma, M. Ukai, K. Fujii, A. Yokoya, Y. Fukuda and Y. Saitoh, J. Chem.
Phys. 142, 175102 (2015).

- 116 -

18AU020, 18BG018

BL-13

Soft X-ray Spectroscopies for Br-incorporated DNA
Nucleotide
Misaki Hiratoa,b and Kentaro Fujiib,Akinari Yokoyab,c, Shin-ichi Wadad,YujiBabaea

Ibaraki University, Mito, Japan
Tokai Quantum Beam Science Center, QST, Tokai, Japanc
Graduate School of Science and Engineering, Ibaraki University, Mito, Japand
Graduate School of Science, Hiroshima University, Higashihiroshima, Japane
Fukushima research and development department, JAEA, Fukushima, Japanb

Keywords: bromouracil, BrdUMP, TMP, DNA damage, XPS, XANESThe aim of the present study is to clarify the electronic states of DNA related molecules
incorporating a bromine atom. Since cells with DNA incorporating 5-bromouracil (BrU) as athymine analogue have been known to be highly sensitive to ionizing irradiation, BrU is
expected to be pharmacological agents as sensitizers in radiation therapy. Previously, aradiation-track simulation study proposed a mechanism that hydrated electrons produced bywater radiolysis could react with DNA incorporating bromine atoms (hereafter denoted as BrDNA) to form damage [1]. A recent EPR study reported that the bromine atom changes theyield of unpaired electrons in the uracil moiety [2].
In order to understand the physicochemical nature of Br-DNA, we investigated the binding
energies of inner shell electrons of particular atoms in the DNA molecule using X-ray
photoelectron spectroscopy (XPS) and X-ray Absorption Near Edge Structure (XANES)
around the energies of C, N, O and Br K-absorption edges. Thin film samples of BrU, 5-bromo2’-deoxyuridine-5’-monophosphate (BrdUMP) and thymidine-5’-monophosphate (TMP) wereused for the spectroscopies at the Photon Factory BL-27 and HiSOR BL-13.
Obtained results indicate that the photoelectron binding energies, as well as the absorption
edge energies, were similar for those sample molecules regardless of binding of a bromine
atom to them. Contrary to the initial expectation, it is concluded that a bromine atom does not
significantly contribute to the inner shell or unoccupied states in these molecules. Effect ofbromine atom on the valence electronic states should be addressed in future studies.
[1] Watanabe and Nikjoo Int. J. Radiat. Biol. 78, 953-66 (2002).
[2] Oka et al. Appl. Phys. Lett. 113, 243701 (2018).

- 117 -

18AG003

BL-14

X-ray absorption spectroscopy of YbCux
at Cu-L3 absorption edge
Hitoshi Yamaokaa Naohitio Tsujiib, Masahiro Sawadac, and Kenya Shimadaca

RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo 679-5148, JapanbInternational Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science,c

1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 7390046, Japan

Keywords: x-ray absorption spectroscopy, YbCux, Cu L absorption edge

Recently, some Yb compounds were found to show anomalous decrease of the Yb valence at low pressures.
In YbCu4.5 a first-order valence transition to the divalent Yb state was found around 0.6-2.7 GPa [1]. Thisvalence transition is accompanied by the structural transition at the same pressure range. In the cubic YbCu5based compounds the Yb valence was found to decrease with increasing pressure without structural phasetransition at low pressures less than 10 GPa. It indicates a pressure-induced crossover from a localized 4f13
state to the valence fluctuation regime, which was not expected for Yb systems with the conventional c-f
hybridization [2]. High-pressure study for the Yb-Cu binary alloy systems, YbCu, YbCu2, YbCu4.5, YbCu5,
and YbCu6.5 has been performed at SPring-8. Here, complementary to the high-pressure experiments for the
Yb site, we study the electronic structures for the Cu sites of the Yb-Cu binary alloy systems by x-ray
absorption spectroscopy (XAS) at ambient pressure.
Figure 1(a) show high-resolution XAS spectra at the Cu-L3 absorption edge for YbCu, YbCu2, YbCu4.5,
and YbCu6.5, being comapred with XAS spectra for YbInCu4 and Cu2O. Spectra for YbCu and YbCu2 aresimilar each other. The spectrum of Cu2O is in agreemwnt with the previous results [3]. The single peakaround 933 eV in Cu2O was assigned to a 2p53d10 final state coming from a 2p63d9 initial state [4]. The
spectra of YbCux are very different from that of Cu2O, where Cu atoms are covalently bonded to the O atoms[2,5,6], and are similar to that of Cu metal [3] except YbCu6.5. This suggests the metallic bond of the YbCux
systems. Theoretical calculations for fcc and bcc Cu metal suggested that the peak P2 at 935 eV and the peakP3 at 939 eV correspond to the transitions of 2p-3d and 2p-3s, respectively [5]. From the analogy to the XAS
spectra of the Cu2FeS4 compounds, the peaks P1, P2, and P3 could be assigned to the final states cd10Ls2,
cd10s, and cd9s2, respectively, where L denotes the ligand hole [7]. The energy of the absorption edge shifts
to higher energy in the following order: YbCu < YbCu2 < YbCu4.5.
In YbInCu4 a slight shift of the peak P2 to higher energy was observed with increasing the intensity of thepeak P1 below the temperature of the valence transition, where the weak shoulder peak P1 was considered
to be derived from the Cu 3d states [8]. It was suggested that across the valence transition the electron transferfrom the Cu 3d sites to the Yb 4f sites occurred at low temperature, resulting in the increase of the DOS of
the Yb2+ states near the Fermi level. The peak intensity of YbCu and YbCu2 corresponding the peak P1 of
YbInCu4 is relatively stronger than that of YbCu4.5. This suggests that the empty states of Cu 4d of the former
compounds are larger than those of the latter. This explains the Yb valence of YbCu and YbCu2 are smaller
than that of YbCu4.5.
The electronic structure of YbCu6.5 is very different from others and rather similar to that of K2NaCuF6[9]. YbCu6.5 has a sharp and strong peak at 931 eV, which is not observed in YbCu, YbCu2, and YbCu4.5.
Two peaks around 931 eV and 934 eV could be assigned to be Cu2+ and Cu3+ states and described as theelectronic configurations of 2p53d10 and a mixing of 3d8 and 3d9L, respectively [9]. A weak shoulder peakon the right of the 934 eV peak in YbCu6.5 is due to the multiplet effect [9]. In K2NaCuF6 the charge transfer
energy (∆) was considered to be negative, where ∆ is equivalent to the energy difference between 3d8 and3d9L for the ground state [9], suggesting the negative charge transfer also in YbCu6.5. In this case, the 3d9L
states are more preferred than the 3d8 states because the energy level of the former is lower than the latter.

- 118 -

Figure 1(b) shows the temperature dependence of the XAS spectra of YbCu4.5 below 80 K. No temperaturedependence was observed. In YbCu4.5 the Yb valence decreased with decreasing the temperature from 2.94
at 100 K to 2.92 at 16 K [1]. The result in Figure 1(b) indicates that the temperature-induced change in theelectronic structure of the Cu sites is too small to observe in the present resolution.
The electronic structure of the Cu sites of YbCu6.5 is different from that of YbCu4.5. While the Yb valencedrastically decreased with pressure at low pressures in both compounds in the similar way. YbCu4.5 is known
to have a complex crystal structure and has more than two Yb sites. Present XAS spectra in Fig. 1(a) suggestthat YbCu6.5 has two kinds of Yb sites. The role of the each Yb sites in YbCu4.5 and YbCu6.5 under pressureis unknown and remains as an interesting study in the future because both compounds show the pressureinduced anomaly and have the multi-Yb sites in common.

(a)
(b)

FIGURE 1. (a) XAS spectra of YbCu, YbCu2, YbCu4.5, YbCu6.5, and YbInCu4 at 10 K with that of Cu2O at 300 K. (b)Temperature dependence of the XAS spectra of YbCu4.5.

REFERENCES
1. H. Yamaoka, N. Tsujii, Y. Yamamoto, Y. Michiue, J.- F. Lin, N. Hiraoka, H. Ishii, K.-D. Tsuei, and J. Mizuki, Reentrant
valence transition in YbCu4.5 under pressure, Phys. Rev. B 97, 085106 (2018).
2. H. Yamaoka, N. Tsujii, M.-T. Suzuki, Y. Yamamoto, I. Jarrige, H. Sato, J.-F. Lin, T. Mito, J. Mizuki, H. Saku- rai, O. Sakai,
N. Hiraoka, H. Ishii, K.-D. Tsuei, M. Gio- vannini, and E. Bauer, Pressure-induced anomalous valence crossover in cubic
YbCu5-based compounds, Sci. Rep. 7, 5846 (2017).
3. M. Finazzi, G. Ghiringhelli, O. Tjernberg, Ph. Ohresser, and N. B. Brookes, Radiationless Raman versus Auger behavior at
the Cu L3 resonance of CuO and Cu2O, Phys. Rev. B 61, 4629 (2000).
4. M.-J. Huang, G. Deng, Y. Y. Chin, Z. Hu, J.-G. Cheng, F. C. Chou, K. Conder, J.-S. Zhou, T.-W. Pi, J. B. Good- enough,
H.-J. Lin, and C. T. Chen, Determination of hole distribution in Sr 14-xCaxCu24O41 using soft x-ray absorption spectroscopy at
the Cu L3 edge, Phys. Rev. B 88, 014520 (2013).
5. H. Ebert, J.Stöhr,S. S. P. Parkin, M. Samant, and A. Nilsson, L-edge x-ray absorption in fcc and bcc Cu metal: Comparisonof experimental and first-principles theoretical results, Phys. Rev. B 53, 16067 (1996).
6. P. Jiang, D. Prendergast, F. Borondics, S. Porsgaard, L. Giovanetti, E. Pach, J. Newberg, H. Bluhm, F. Besenbacher, and
M. Salmeron, Experimental and theoretical investigation of the electronic structure of Cu 2O and CuO thin films on Cu(110)using x-ray photoelectron and absorption spectroscopy, J. Chem. Phys. 138, 024704 (2013).
7. R. A. D. Pattrick, G. Van Der Laan, J. M. Charnock, and B. A. Grguric, Cu L3 x-ray absorption spectroscopy and theelectronic structure of minerals: Spectral variations in non-stoichiometric bornites, Cu5FeS4, American Mineralogist 89, 451(2004).
8. Y. Utsumi, H. Sato, H. Kurihara, H. Maso, K. Hiraoka, K. Kojima, K. Tobimatsu, T. Ohkochi, S.-I. Fujimori, Y. Takeda,
Y. Saitoh, K. Mimura, S. Ueda, Y. Yamashita, H. Yoshikawa, K. Kobayashi, T. Oguchi, K. Shimada, H. Namatame, and M.
Taniguchi, Conduction-band electronic states of YbInCu4 studied by photoemission and soft x-ray absorption spectroscopies,
Phys. Rev. B 84, 115143 (2011).
9. C. De Nadaï. Demourgues, and J. Grannec, L2,3 x-ray absorption spectroscopy and multiplet calculations for KMF3 andK2NaMF6 (M = Ni, Cu), Phys. Rev. B 63, 125123 (2001).

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BL-14Development of a Soft X Ray Reflectometer in a Low
Vacuum environment at HiSOR-BL14
Tatsuya Mayumia, Yuka Ohashib, Norikazu Ichikawab, Masahiro SawadacaDepartment of Physical Sciences, Faculty of Science, Hiroshima University
Department of Physical Science, Graduate School of Science, Hiroshima Universityc
Hiroshima Synchrotron Radiation Center, Hiroshima Universityb

Keywords: apparatus development, soft X-ray, reflectometry

Soft X-ray reflectometry is one of useful methods for investigation of a valence electron structure,
which is probed through a resonant scattering process in the vicinity of an absorption edge. Since amagneto-optical effect appears in a reflectance profile of polarized SR light, the reflectometry method canalso be utilized to analysis of a magnetic state and a magnetic structure for many kind of magnetic
materials including insulators. Insensitivity to sample surface of the photon-in-photon-out technique is anadvantage to investigate practical materials like an electronic/spintronic device, whose region of interestare deep inside of the layered structures. Measurements under low vacuum or atmospheric pressure in
helium-pass expands the capability of soft X-ray reflectometry into ambient/operando spectroscopy, whose
vacuum environment can be easily established by vacuum separation technique with X-ray transmission
membrane.
In this development project, we have constructed an experimental system of X-ray reflectometer
connected to HiSOR-BL14, in order to realize soft X-ray reflectometry in a low vacuum environment. A
device unit of reflectometer was assembled as stand-alone instrument, which was finally installed into a
low vacuum chamber. The reflectometer unit consists of two motorized rotation stages for θ/2θ scanningwhich are so fixed on an aluminum main flame that the rotation axes are coaxially aligned. A sample stage
and a X-ray detector component are mounted on the θ and 2θ rotation stage with support arms, respectively.
In the sample stage component, two-axes adjustment mechanism is installed so that a sample surface and ascattering plane can coincide with the rotation center and the θ/2θ scanning plane, respectively. Figure 1
shows schematic views of the reflectometer unit. Mechanical alignment and evaluation of geometrictolerance were carried out using laser and a transit telescope. After our confirmation for the reflectometerto achieve good tolerance in θ/2θ scanning, the whole instrument was completely build up including
electrical and vacuum system, and it was successfully installed to a SR beamline of BL14. Practicaladjustments and a first test measurement were carried out for a gold foil sample using synchrotron
radiation. Figure 1 shows

sample sample holder

samplepivot point axis of te rorarion stageθ
2θ
detector rotation stage

sample rotation stage
sample level z stage

X ray detector

ZE
Y
! E
XE

Z
XE E
!
YE

X ray detector
motor controller

ammeter- 120 -FIGURE 1. schematic view of the measurement unit

schematic views of the reflectometer unit. Mechanical alignment and evaluation of geometric tolerance
were carried out using laser and a transit telescope. After our confirmation for the reflectometer to achieve
good tolerance in θ/2θ scanning, the whole instrument was completely build up including electrical andvacuum system, and it was successfully installed to a SR beamline of BL14. Practical adjustments and afirst test measurement were carried out for a gold foil sample using synchrotron radiation.

REFERENCES
1. K. Sakurai, Introduction to X-ray Reflectivity,2009.
2. K. Ishii, M. Sawada, Development of a soft X-ray reflectometer in an ambient pressure or a low vacuum environment at
HiSOR-BL14, 2018. (Japanese)- 121 -

BL-14Magnetic properties of Co ultrathin films intercalated
underneath monolayer h-BN grown on Ni(111)probed by soft X-ray magnetic circular dichroism
Yuka Ohashia, Norikazu Ichikawaa, Tatsuya Mayumib, Masahiro SawadacaDepartment of Physical Sciences, Graduate School of Science, Hiroshima Universityb
Department of Physical Sciences, Faculty of Science, Hiroshima Universityc
Hiroshima Synchrotron Radiation Center, Hiroshima University

Keywords: cobalt, h-BN, nickel ; soft X-ray magnetic circular dichroism

A magnetic tunnel junction (MTJ) is a trilayer structure that consists of two ferromagnetic metallic
layers and a nonmagnetic insulating layer sandwiched with them. Tunnel magnetic resistance (TMR) effectis observed in the MTJ structures, whose electrical conductivity is well known to depend on relative
direction of magnetization between the two ferromagnetic layers. TMR effect is widely applied tomagnetic devices such as a magnetic random access memory and a magnetic head in hard disk drive [1].
MR ratio is one of important performance indices of the TMR devices, and it is crucially affected byatomic arrangement at an interface between the ferromagnetic layer and the insulating barrier layer.
Recently, MTJ structures with an insulating monolayer of hexagonal boron nitride (h-BN) is paid attention
to [2], because it provides ideal flat interfaces without pinholes to be expected for improvement of the MR
ratio. Since spin polarization at the interface is also important for the MR ratio, investigation of interface
magnetism is essentially required for the ferromagnetic layers contacts to the h-BN monolayer.
In this research, we fabricated h-BN/Co ideal interfaces by intercalation of 0.5-7.2 ML Co ultrathin
films underneath a h-BN monolayer grown on Ni (111) under ultra-high vacuum condition at HiSOR
BL-14. The magnetic properties of Co ultrathin films were probed by soft X-ray magnetic circulardichroism.
Intensities of XMCD spectra at Co L2,3 edges were observed as a function of the Co thickness. At 1 ML,
antiferromagnetic spin alignment was observed, whose spin direction is opposite to the external magnetic
field and magnetization of Ni substrate. This spin alignment was changed gradually into ferromagnetic
spin alignment as the Co thickness was increased. The corresponding spin magnetic moment was
ferromagnetically saturated near 5 ML and the estimated value was larger than bulk Co [3].
The antiferromagnetic spin alignment at 1 ML Co was disappeared by momentary exposure of oxygenon the top of h-BN monolayer. However, neither residual atoms of oxygen nor Co oxide in the ultrathin
films was observed after the oxygen exposure. From this result, we can indicate the possibility that atomic
structure and magnetic properties of Co ultrathin films are changed by oxygen collision on the monolayerh-BN surface.

REFERENCES
1. R. Jansen, Appl. Phys. 36, R289 (2003).
2. M. Piquemal-Banci, et al. Appl. Phys. Lett., 108, 102404 (2016).
3. C. T. Chen, et al. Phys. Rev. Lett., 75, 152 (1995).

- 122 -

BL-14

Antiferromagnetic coupling at the interface of
Co/h-BN/Ni(111) studied by soft X-ray magnetic circulardichroism
Norikazu Ichikawaa, Yuka Ohashia, Tatsuya Mayumib,
Masahiro Sawadac, Akio KimuraaaDepartment of Physical Sciences, Graduate School of Science, Hiroshima University,
1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526, Japanb
Department of Physical Sciences, Faculty of Science, Hiroshima University,
1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526, Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University,
2-313 Kagamiyama, Higashi-Hiroshima, 739-0046, Japan

Keywords: boron nitride, cobalt, nickel; X-ray magnetic circular dichroism

Tunnel magnetoresistance (TMR) effect is one of key phenomena for developing of spintronic devices.
Monolayer hexagonal boron nitride is an insulating layered material with stable honeycomb structure. It is
expected to provide an ideal barrier layer in magnetic tunnel junction (MTJ), where a pinhole-less ultrathin
barrier layer ensures large MR ratio and low power consumption. Spin-dependent transport studies with
the MTJ incorporating a monolayer h-BN have shown the MR ratio up to 150% at room temperature [1, 2].
So far, magnetic state at the interface between a magnetic layer and a monolayer h-BN has not been
sufficiently clarified, although it takes an essential role in a mechanism of TMR. To clarify magnetic stateat the interface between a magnetic layer and monolayer h-BN, we have investigated magnetic properties
of Co layers in Co/h-BN/Ni(111) structure by means of soft X-ray magnetic circular dichroism (XMCD)
spectroscopy.
We fabricated Co wedge films on h-BN/Ni(111) films for this purpose. High-quality h-BN monolayer
was prepared on a Ni(111) surface by cracking of vaporized borazine (B3N3H6) [3]. The samples of
Co/h-BN/Ni(111) are obtained by MBE evaporation of Co at room temperature. The XMCD experiments
were in-situ performed at HiSOR-BL14 [4, 5]. Figure 1 shows the XMCD spectrum measured at room
temperature at Co and Ni L2,3 edges in normal incidence geometry under the external magnetic field of 1.1
T along sample normal direction. The Co magnetic moment is antiferromagnetically saturated below 2.3
ML whose direction- 123 -FIGURE 1. XMCD spectrum at Co L2,3 edge and Ni L2,3 edge in normal incidence geometry with magnetic fieldof 1.1 T along sample normal direction

is opposite to Ni spin and external magnetic field. As the Co film thickness is increased, theantiferromagnetic coupling (AFC) is gradually released by increasing energy gain of ferromagneticalignment parallel to the field. This indicates that only a Co monolayer at the interface isantiferromagnetically coupled. We estimated a quantitative value of AFC energy between Ni and a Co
monolayer at the interface by analyzing Co thickness dependence of M-H curves derived from fielddependent XMCD signals. As a result, we have found the AFC energy is about 25 meV/atom. A previous
study has suggested hybridization between h-BN π and Ni 3d orbitals leading to spin polarized gap statesat the nitrogen site [6]. Considering charge transfer effect from the spin polarized π-orbital of nitrogen to
dz2 -orbitals of cobalt, we calculated the AFC energy based on second-order perturbation in an electron
hopping process between their orbitals. From good agreement between the estimated AFC energy and theexperimental value, we have concluded the AFC between Co and Ni at the interface results fromsuperexchange interaction via h-BN.

REFERENCES
1. A. Dankert, M. V. Kamalakar, A. Wajid, R. S. Patel, and S. P. Dash, Nano. Res. 8, 1357 (2015).
2. M. Piquemal-Banci, R. Galceran, S. Caneva, M. -B. Martin, R. S. Weatherup, P. R. Kidambi, K. Bouzehouane, S. Xavier,A. Anane, F. Petroff, A. Fert, J. Robertson, S. Hofmann, B. Dlubak, and P. Seneor, Appl. Phys. Lett. 108, 102404(2016).
3. C. Oshima and A. Nagashima, J. Phys.: Condens. Matter 9, 1 (1997).
4. M. Sawada, K. Yaji, M. Nagira, A. Kimura, H. Namatame, M. Taniguchi, AIP Conf. Proc. 879, 551 (2007).
5. M. Sawada, T. Ueno, T. Tagashira, H. Namatame, M. Taniguchi, AIP Conf. Proc. 1234, 939 (2010).
6. A. B. Preobrajenski, S. A. Krasnikov, A. S. Vinogradov, May Ling Ng, T. Kä ä mbre, A. A. Cafolla, and N. Mȧ rtensson,
Phys. Rev. B 77, 085421 (2008).

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18BG048

BL-14

Cation Distribution and Magnetic Properties of NiFe2O4
Nanofilms on MgO andSrTiO3 substrates: XAS and XMCD Soft X-ray Studies
Andrey K. Kaveev,a Alexander G.Banshchikova, Nikolay S. Sokolova andMasahiro SawadabaIoffe Institute, 194021, 26 Polytechnicheskaya str., Saint-Petersburg, Russiab
Hiroshima University, 739-8527, Higashi Hiroshima, Japan

Keywords: Spinel ferrite, NiFe2O4, cation distribution.

+

12

Fe

L3

8

A
A

L2

-

2

XMCD, (A -A )

4

+

4

+

-

XMCD, (A -A )Absorption (a.u.)16

Absorption (a.u.)

Among spinel-type materials nickel ferrite (NiFe2O4, NFO) represents a known insulating material. It is
attractive properties demanded in RF and microwave applications are a reason of intensive studies of thismaterial since the middle of 20th century. The necessity of modern spintronic and magnonic devices require
NFO films with thickness in the nanometer range. However, such films usually exhibit magnetic properties
that are inferior to those of the bulk crystals. Studies of ultrathin (2-10 nm) films attractive for spin
filtering have been carried out in Ref. [1]. Lately excellent magnon transport properties of 40 and 450 nm
thick NFO films on MgGa2O4 substrates has been demonstrated in Ref. [2]. In this work, 10-250 nm thick
NFO films were grown on SrTiO3 (STO) and MgO(001) substrates by laser molecular beam epitaxy in awide range of growth conditions. XMCD spectra of the films were studied depending on the growthparameters.

0
-2
-4
700

710

720

730

6
5

A
A

L3

4

L2

3
2
2
1
0
840

740

+

Ni

850

860

870

880

890

Photon energy (eV)Photon energy (eV)

(a)

(b)

FIGURE 1. Characteristic XAS and XMCD spectra for L2,3 edges of Fe (a) and Ni (b) for the NFO/STO(001) film grown at
1000С with the subsequent annealing in the air.

Thin NFO films (1-100 nm) were grown with the use of laser molecular beam Epitaxy on MgO andSrTiO3 substrates at the different growth conditions. XRD and RHEED measurements showed high crystal
quality of the films.
It was found that NFO films grown on STO(001) at elevated temperatures (1000C) with post-growthannealing at 1100C have strong XMCD signal as for Fe, so for Ni (see Fig. 1). In the first case large
signal is related to main absorption L3 peak shift at 0.6 eV after an applied field direction inversion. In the- 125 -

second case large XMCD signal exceeds that observed in Refs. [3-5]. According to Ref. [6], magnetic
moments of metals in octahedral (Oh) and tetrahedral (Td) environments in spinels are antiparallel. The
largest of these moments is oriented parallel to the applied external magnetic field direction. The magnetic
moment of atoms situated in Oh environment is higher, because of twice larger amount of octahedral sites
than amount of tetrahedral sites (in the case of inverted spinel the moment is defined by two types ofatoms, in contrast to the case of normal spinel with only one type of atoms), and taking into accountcharacteristic values of the moments: 5 μB for Fe3+, 4 μB for Co3+, 2.3 μB for Ni2+. This means that themagnetic moment in the Oh environment is oriented parallel to the external magnetic field direction, themagnetic moment in the Td environment is oriented antiparallel. Moreover, the XRD signal sign at the L3
absorption edge, and, hence, the sign of the Ni magnetic moment, corresponds to that of clear metallic Ni
measured at the same conditions (not shown there). Therefore, all Ni magnetic moments in NFO films
measured in the experiment, are collinear to the external magnetic field direction. This means that the NFO
spinel in our case is completely inverted, i.e. there are no Ni atoms in the Td environment. It is inagreement with the simulation results. This circumstance distinguishes our results from the obtained inRefs. [3-6], where the value of the Ni magnetic moment is smaller. The samples prepared in this way are
the most promising from the point of view of the spin wave propagation in the NFO films. In case the NFO
growth on MgO(001) the situation is not so straightforward, because of possible intermixed the materials
at the interface during the growth and annealing at elevated temperatures.
This work was partly supported by the Russian Science Foundation (Project No 17-12-01508).

REFERENCES
1. V.G.Harris et al., J.Magn.Magn.Mater.321, 2035–2047 (2009).
2. J.Shan et al., Appl.Phys.Lett., 113, 162403 (2018).
3. M.C. Richter, J.-M. Mariot, et al, Eur. Phys. J. Spec. Topics,169, 175–180 (2009).
4. V. K. Verma,V. R. Singh et al., Phys. Rev. B, 89, 115128 (2014).
5. C. Klewe, M. Meinert at al., J. Appl. Phys., 115, 123903 (2014).
6. L. Néel, Ann. Physique, 3, 137, (1948).

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18BU013

BL-14

Investigation of multi-mode spin–phonon coupling andlocal B-site disorder in Pr2CoFeO6 by Raman spectroscopy
and correlation with its electronic structure by XPS and
XAS studies
Arkadeb Pala, Surajit Ghosha, Amish G Joshib, Shiv Kumarc, Swapnil Patila,
Prince K Guptaa, Prajyoti Singha, V K Gangwara, P Prakashd, Ranjan K Singhe,
Eike F Schwierc, M Sawadac, K Shimadac, A K Ghoshe, Amitabh Dasd,f andSandip ChatterjeeaaDepartment of Physics, Indian Institute of Technology (BHU) Varanasi 221005
CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, Indiac
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima City, 739-0046 Japand
Solid State Physics Division, Bhaba Atomic Research Centre, Mumbai 400085, Indiae
Department of Physics, Banaras Hindu University, Varanasi 221005, Indiaf
Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, Indiab

Keywords: X-ray photoemission spectroscopy and X-ray photo-absorption spectroscopy

Electronic structure of Pr2CoFeO6 (at 300 K) was investigated by x-ray photoemission spectroscopy (XPS)
and x-ray absorption spectroscopy techniques. All three cations, i.e. Pr, Co and Fe were found to be trivalent
in nature. XPS valance band analysis suggested the system to be insulating in nature. The analysis suggested
that Co3+ ions exist in low spin state in the system. Moreover, Raman spectroscopy study indicated therandom distribution of the B-site ions (Co/Fe) triggered by same charge states. In temperature-dependent
Raman study, the relative heights of the two observed phonon modes exhibited anomalous behaviour nearmagnetic transition temperature TN ~ 270 K, thus indicating towards interplay between spin and phonon
degrees of freedom in the system. Furthermore, clear anomalous softening was observed below TN which
confirmed the existence of strong spin–phonon coupling occurring for at least two phonon modes of thesystem. The line width analysis of the phonon modes essentially ruled out the role of magnetostriction effectin the observed phonon anomaly. The investigation of the lattice parameter variation across TN (obtained
from the temperature dependent neutron diffraction measurements) further confirmed the existence of thespin–phonon coupling.

REFERENCES
1. S. W. Cheong and M. Mostovoy, Nat. Mater. 6, 13 (2007).
2. Y. Kitagawa et al. Nat. Mater. 9, 797 (2010).
3. K. I. Kobayashi, T. Kimura, H. Sawada, K. Terakura andY. Tokura, Nature 395, 677 (1998).
4. D. Choudhury et al. Phys. Rev. Lett. 108, 127201 (2012).

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