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－ 75 －Linear-polarization-dependent ARPES measurement of YbB61

M. Arita1, H. Sato1 , K. Shimada1, H. Namatame1, M. Taniguchi1,2, F. Iga3

Hiroshima Synchrotron Radiation Center, Hiroshima University, Kagamiyama , Higashi-Hiroshima 739-0046, Japan
2
Graduate School of Science, Hiroshima University, Kagamiyama , Higashi-Hiroshima 739-0046, Japan
3
College of Science, Ibaraki University, Mito, Ibaraki, 310-8512, Japan

Rare-earth hexaboride forms CaB6-type cubic crystal structure. The unusual physicalproperties appear originated from localized 4f bands. It is known that SmB6 is one of the Kondo
insulators and valence fluctuation materials[1]. In theoretical prediction, SmB6 belongs totopological Kondo insulator in which Dirac-corn-like band structure exists in the c-f
hybridization gap.
Recently similar hexaboride YbB6 the attracted researcher’s interest as candidate material of
topological Kondo insulator. The existence of Dirac-corn-like band structure is predicted in[111] and [110] surfaces in the c-f hybridization gap[2]. Although we have measured theelectronic structure of YbB6 by means of ARPES, Dirac corn has not been observed yet.
In this study, we report that electronic band structures near EF of YbB6 to clarify the in-gapstates. The ARPES measurements have been performed with linear polarized synchrotron
radiation at HiSOR BL-9A. We define the S and P polarization geometries as the perpendicularand parallel polarizations respectively, with respect to the incident plane which corresponds tothe xz plane in Fig 1 (a).
Figures 1 (b) and (c) show the obtained band structure along X with h= 17.0 eV with Sand P geometries, respectively. We found the clear linear polarization dependence around k=0.
Although the hole-like band is observed with S geometry, the spectral intensity disappears near
EF with P geometry. It is considered that the hole-like band character on X (XM) highsymmetry line has the odd symmetry with respect to XMX plane (xz plane). According to theband calculation, the band is mostly derived from B 2p character. Therefore the band in XMX
plain is attributed to py orbital which has node in xz plain.

Fig.1 (a) Experimental S and P polarization geometries as the perpendicular and parallel polarizations
respectively, with respect to the incident plane. ARPES mapping with (b) S geometry and (c) P geometryin (c).
1)
2)

Maxim Dzero et al., Phys. Rev. Lett. 104, 106408 (2010).
Hongming Wen et al., Phys. Rev. Lett. 112, 016403(2014).

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14-A-8 (relevant HiSOR proposal number)

BL-11 (HiSOR beamline number)

Formation of sulfur compounds on the Granulated Coal
Ash covering on organic enriched sediment
Kyunghoi Kima, Tamiji Yamamotob and Shinjiro HayakawacabDepartment of Ocean Engineering, Pukyong National University, Busan 738-737, Korea
Graduate school of biosphere science, Hiroshima University, Higashi-Hiroshima 739-8528, Japanc
Graduate school of engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan

Keywords: Sulfur compounds; granulated coal ash; organic enriched coastal sediment

1. Introduction
Hydrogen sulfide is formed in organically enriched sediments through the reduction of sulfate ions by sulfate
reducing bacteria under anoxic condition and it is highly toxic and fatal to living organisms, and consumes
oxygen when it is oxidized. Thus, it is important to reduce hydrogen sulfide concentration in the sediments torestore and maintain healthy aquatic ecosystems.
Granulated Coal Ash is a product which is the mixture of fly ash and cement as a binder. Previous studies inbatch experiments using hydrogen sulfide solution revealed that GCA could effectively reduce hydrogen sulfide;in this process, manganese oxide contained in the GCA may have oxidized the hydrogen sulfide to sulfur(Asaoka et al., 2012).
However, removal mechanism should depend on the sediment conditions such as pH, ORP, and concentrationof hydrogen sulfide. In order to develop technology for remediation of organic enriched sediment using GCA, it
is necessary to clarify the mechanism of hydrogen sulfide removal with GCA in the condition of organicenriched sediment.
In the present study, we investigated the formation of sulfur compounds onto the GCA covering on organic
enriched coastal sediment by XAFS analyses.
2. Materials and methods
The pH and ORP in the sediment of Fukuyama Inner Bay were 6.89 and -402 mV and maximum
concentration of hydrogen sulfide in Fukuyama Bay were about 300 mg/l. The Ignition Loss and Particulate
Organic Sulfur in the sediment of Fukuyama Inner Bay ranged 10 - 30% and 8 - 18 mg/g, respectively.
GCA samples for XAFS analysis were collected using acrylic pipes (Φ=15 cm, 20 cm long) by a diver atFukuyama inner bay (Fukuyama GCA) 3 years later the GCA covering was conducted for the sediment
remediation. The GCA samples were sealed in a plastic bottle with mud to prevent oxidation after measuring pHand ORP (PS-112C, RM1; TOA Electronics, Ltd., Tokyo, Japan). Sulfur K-edge measurement was carried out
using wet GCA immediately after the mud was gently removed with paper.
Sulfur K-edge measurements (range 2460-2485 eV) were made with BL11 in Hiroshima Synchrotron
Research Center, HiSOR (Hayakawa et al., 2008). The synchrotron radiation from a bending magnet was
monochromatized with a Si(111) double-crystal monochromator. The sample chamber was filled with He gas tosuppress any X-ray absorption and scattering from air, and XAFS spectra were measured both by a X-ray
fluorescence yield (XFY) mode using a SDD detector (XR-100SDD; AMPTEK) and a conversion electron yield(CEY) mode. The step size for measurement was 0.25 eV. The sulfur K-edge was calibrated with cupric sulfate(CuSO4·5H2O) peak set at 2481.6 eV (Backnaes et al., 2008). As references, humic acid, FeS, MnS weremeasured by the CEY mode.
XAFS spectra were analyzed with a XAFS spectra processing software (REX2000 ver. 2.5: Rigaku co. Ltd.).
A background adsorption was approximated by a least-square fitting. An adsorption edge (Eo) was defined as
the inflection point in the spectrum.

－ 97 －3. Results and discussion
The sulfur K-edge XANES spectra were measured for the GCAs (Fig. 1). The initial GCA has a peak at2482 eV representing sulfate. New peak at 2469 eV was observed for the Fukuyama GCA and the peak at 2482
eV observed for the initial GCA shifted to 2481.5 eV. The peak at 2469 eV is identified as that of FeS, and theshift of the peak from 2482 eV to 2481.5 is judged to be influenced by the peak of FeS (eq 1).
Fe2+ + HS- → FeS + H+(1)New small peak at 2472 eV was observed for Fukuyama GCA. This means that hydrogen sulfide wasadsorbed onto the granulated coal ash (MnS) and the oxidation reaction of hydrogen sulfide was coupling withreduction of manganese oxide (eq 2; Asaoka et al., 2012).
Mn2O3 + H2S + 4H+ → 2Mn2+ + S + 3H2O

(2)Peaks at 2473 eV and 2475.5 is coincided with that of Humic acid indicating adhesion of organic matter.

FIGURE 1. Sulfur K-edge XANES spectra of the sampled GCA with several sulfur standards.

REFERENCES
1. S. Asaoka, S. Hayakawa, K.H. Kim, K. Takeda, M. Katayama, and T. Yamamoto, J. Coll. Int. Sci.377, 284-290 (2012).
2. L. Backnaes, J. Stelling, H. Behrens, J. Goettlicher, S. Mangold, O. Verheijen, R. G. C. Beerkens, J. Deubener, J.
American Cer. Soc. 91, 721-727 (2008).
3. S. Hayakawa, Y. Hajima, S. Qiao, H. Namatame, and T. Hirokawa, Anal. Sci. 24, 835-837 (2008).

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