• Bulletin of the Korean Chemical Society
• /
• 제18권7호
• /
• pp.743-749
• /
• 1997

Local structure refinement of the BaFe1-xSnxO3-y system (x=0.00-0.50) has been carried out with Fe K-edge x-ray absorpion spectroscopic studies. It is found out that the Fe ions are placed in two different symmetric sites such as tetrahedral and octahedral sites in the compounds by comparison with Fe K-edge x-ray absorption near edge structure (XANES) spectrum of the γ-Fe2O3 compound as a reference. Small absorption peaks of dipole-forbiden transitions appear at a pre-edge region of 7111 eV due to the existence of Fe ions in the tetrahedral and octahedral sites. The peak intensity decreases with the substitution amount of Sn ion. Three different absorption peaks of 1s→4p dipole-allowed transition appear on the energy region between 7123 and 7131 eV. The peaks correspond to 1s→4p main transition of Fe ions in tetrahedral and octahedral sites and 1s→4p transition followed by the shakedown process of ligand to metal charge transfer. The bond distances between Fe ions in the tetrahedral site and nearest neighboring oxygen atom (Fe-4O), and those in octahedral site (Fe-6O) are determined with the extended x-ray absorption fine structure (EXAFS) analysis. Two different interatomic distances increase with the substitution amount of Sn ion and also the bond lengths of Fe-4O are shorter than those of Fe-6O in all compounds.

• 한국진공학회지
• /
• 제13권2호
• /
• pp.86-91
• /
• 2004

전이금속 갈라이드는 고온 응용성이 높은 물질로 관심을 모으고 있다. CsCl구조를 갖는 것으로 알려진 넓은 조성 범위에서 전이금속 갈라이드에 대해 물리적 특성과 전자구조의 상호관계에 대해 체계적인 연구를 하였다. $Co_{l-x}Ga$ $_{x}$ 합금($0.35\leq$x$\leq0.55$)을 arc-melting 방법으로 제작하였으며, 합금 제작 후 시료의 균질성을 높이기 위해 $1000 ^{\circ}C$에서 48시간동안 열처리하였다. 결정 구조를 알아보기 위해 x-ray diffraction을 측정한 결과, 이 조성 범위 안에서 모두 CsCl(B2)구조를 갖는 것으로 밝혀졌다. 화학적 상태와 전자 구조를 알아보기 위해서 x-선 광전자 분광, 그리고 x-선 흡수끝머리 부근 미세구조 (XANES)를 측정하였으며, 조성에 따라 서로 다른 물리적 특성을 보였다. 합금제작 과정에서 시료의 산화가 이루어졌으며 포함된 산소는 Ga과 결합하여 $Ga_2O_3$상을 이루었다. 전자 구조적으로 Co의 d 전자와 Ga의 p 전자사이의 p-d hybridization에 의해 합금이 형성되었다.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 2002년도 추계학술발표회요약집
• /
• pp.319.2-319
• /
• 2002

Synchrotron-based X-ray absorption spectroscopy has been applied to determine the changes in bulk oxidation state of uranium oxides in molten salt. From an analysis of XANES data, one can determine the cahnges in bulk oxidation-state of U compounds in salts(LiCl/KCl). XAFS spectroscpy is a powerful tool for probing the changes in valence state and structure of uranium compounds in colten salt as well as in noncrystalline form and doped in other matrices.

• 한국전기화학회:학술대회논문집
• /
• 한국전기화학회 2003년도 춘계총회 및 학술발표회
• /
• pp.22-22
• /
• 2003

• Progress in Superconductivity
• /
• 제14권2호
• /
• pp.99-101
• /
• 2012

Fluorescent yield X-ray absorption fine structure (XAFS) spectroscopy is useful for analyzing local structure of specific elements in matrices. We developed an XAFS apparatus with a 100-pixel superconducting tunnel junction (STJ) detector array with a high sensitivity and a high resolution for light-element dopants in wide-gap semiconductors. An STJ detector has a pixel size of $100{\mu}m$ square, and an asymmetric layer structure of Nb(300 nm)-Al(70 nm)/AlOx/Al(70 nm)-Nb(50 nm). The 100-pixel STJ array has an effective area of $1mm^2$. The XAFS apparatus with the STJ array detector was installed in BL-11A of High Energy Accelerator Research Organization, Photon Factory (KEK PF). Fluorescent X-ray spectrum for boron nitride showed that the average energy resolution of the 100-pixels is 12 eV in full width half maximum for the N-K line, and The C-K and N-K lines are separated without peak tail overlap. We analyzed the N dopant atoms implanted into 4H-SiC substrates at a dose of 300 ppm in a 200 nm-thick surface layer. From a comparison between measured X-ray Absorption Near Edge Structure (XANES) spectra and ab initio FEFF calculations, it has been revealed that the N atoms substitute for the C site of the SiC lattice.

• Journal of Microbiology and Biotechnology
• /
• 제26권12호
• /
• pp.2116-2126
• /
• 2016

Bacterial biofilms are spatially structured communities that contain bacterial cells with a wide range of physiological states. The spatial distribution and speciation of copper in unsaturated Pseudomonas putida CZ1 biofilms that accumulated 147.0 mg copper per g dry weight were determined by transmission electron microscopy coupled with energy dispersive X-ray analysis, and micro-X-ray fluorescence microscopy coupled with micro-X-ray absorption near edge structure (micro-XANES) analysis. It was found that copper was mainly precipitated in a $75{\mu}m$ thick layer as copper phosphate in the middle of the biofilm, while there were two living cell layers in the air-biofilm and biofilm-medium interfaces, respectively, distinguished from the copper precipitation layer by two interfaces. The X-ray absorption fine structure analysis of biofilm revealed that species resembling $Cu_3(PO_4)_2$ predominated in biofilm, followed by Cu-Citrate- and Cu-Glutathione-like species. Further analysis by micro-XANES revealed that 94.4% of copper were $Cu_3(PO_4)_2$-like species in the layer next to the air interface, whereas the copper species of the layer next to the medium interface were composed by 75.4% $Cu_3(PO_4)_2$, 10.9% Cu-Citrate-like species, and 11.2% Cu-Glutathione-like species. Thereby, it was suggested that copper was initially acquired by cells in the biofilm-air interface as a citrate complex, and then transported out and bound by out membranes of cells, released from the copper-bound membranes, and finally precipitated with phosphate in the extracellular matrix of the biofilm. These results revealed a clear spatial pattern of copper precipitation in unsaturated biofilm, which was responsible for the high copper tolerance and accumulation of the biofilm.

• Bulletin of the Korean Chemical Society
• /
• 제19권1호
• /
• pp.5-21
• /
• 1998

The purpose of this paper is to show that X-ray absorption spectroscopy (XANES and EXAFS) is a powerful technique for characterizing both crystalline and amorphous solids from structural (local order) and electronic point of view. The principle of this technique is briefly described by showing the main factors which must be considered for recording and fitting the experimental results. Some non-trivial examples have been selected for demonstrating that XAS spectroscopy is the only technique for bringing a definitive answer as for example: the determination of the local distortion of the $NiO_6$ octahedra in the $Li_{1-z}Ni_{1+z}O_2$ layered oxides and the evidence of the presence of copper pairs in the NASICON-type phosphate $CuZr_2 (PO_4)_3$. Are also reported some significant examples for which XAS spectroscopy is decisive with other characterization methods as (i) Raman spectroscopy for glasses (ii) Mossbauer spectroscopy for $LiNi_{1+z-t}Fe_To_2$ oxides (iii) magnetic measurements for Ce-based intermetallic compounds.

• Bulletin of the Korean Chemical Society
• /
• 제20권12호
• /
• pp.1394-1398
• /
• 1999

The structures of modified Ti$(OPr^i)_4$ with chelating ligands (L) such as ethylacetoacetate (Etac), acetylacetone (Acac) and methylacetoacetate (Mtac) were identified by using IR, ¹H NMR and $^13C$ NMR spectroscopies, and the octahedral structure was confirmed after modification. The pre-edge peaks of XANES spectra of modified metal alkoxides also denoted the mixture of five-fold and six-fold structures. The EXAFS fitting results showed the local structure around Ti atom after alkoxide modification. The hydrolysis-condensation rates of modified Ti alkoxide with organic additives were investigated by ¹H NMR spectroscopy. The Ti$(OPr^i)_4$ modified by Acac was less reactive toward hydrolysis-condensation reaction than those modified by the other alkoxides, which can be attributed to the stable ligand structure between Ti$(OPr^i)_4$ and Acac. The small particle size of modified Ti$(OPr^i)_4$ sol was obtained when Acac was employed.

• 대한화학회지
• /
• 제43권6호
• /
• pp.636-643
• /
• 1999

PDP(plasma display panel)의 녹색 광원으로 유망한 $Zn_{2-x}Mn_xSiO_4$ 헝광체를 1300$^{\circ}C$에서 고상반응법으로 제조한 후 900$^{\circ}C$에서 후속 열처리를 실시하면 녹색 형광의 강도가 현저히 증가한다. 열처리를 통한 형광 강도의 향상과 망간의 산화 상태 및 국부 구조 변화와의 관계를 파악하고자 망간 K 흡수단의 엑스선 흡수 스펙트럼을 분석하였다. $1s{\rightarrow}3d$ 전이에 해당하는 프리엣지(preedge) 봉우리와 XANES 스펙트럼을 분석한 결과, 망간은 열처리와 무관하게 +2가의 산화 상태를 유지하였으며 Zn 자리를 치환하는 것으로 밝혀졌다. 또한 EXAFS 스펙트럼의 분석을 통하여, Mn은 $MnO_4$ 사면체를 형성하고 Mn-O 쌍의 결합 길이와 디바이월러 인자(Debye-Waller factor)는 열처리 후 공히 감소함을 알 수 있었다.

• 한국결정학회:학술대회논문집
• /
• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
• /
• pp.5-6
• /
• 2002

The new spectrometer for X-ray Induced Electron Emission Spectroscopy (XIEES) .has been recently developed in KRISS in collaboration with PTI (Russia). The spectrometer allows to perform research using the XAFS, SXAFS, XANES techniques (D.C.Koningsberger and R.Prins, 1988) as well as the number of techniques from XIEES field(L.A.Bakaleinikov et all, 1992). The experiments may be carried out with registration of transmitted through the sample x-rays (to investigate bulk samples) or/and total electron yield (TEY) from the sample surface that gives the high (down to several atomic mono-layers in soft x-ray region) near surface sensitivity. The combination of these methods together give the possibility to obtain a quantitative information on elemental composition, chemical state, atomic structure for powder samples and solids, including non-crystalline materials (the long range order is not required). The optical design of spectrometer is made according to Johannesson true focusing schematics and presented on the Fig.1. Five stepping motors are used to maintain the focusing condition during the photon energy scan (crystal angle, crystal position along rail, sample goniometer rail angle, sample goniometer position along rail and sample goniometer angle relatively of rail). All movements can be done independently and simultaneously that speeds up the setting of photon energy and allows the using of crystals with different Rowland radil. At present six curved crystals with different d-values and one flat synthetic multilayer are installed on revolver-type monochromator. This arrangement allows the wide range of x-rays from 100 eV up to 25 keV to be obtained. Another 4 stepping motors set exit slit width, sample angle, channeltron position and x-ray detector position. The differential pumping allows to unite vacuum chambers of spectrometer and x-ray generator avoiding the absorption of soft x-rays on Be foil of a window and in atmosphere. Another feature of vacuum system is separation of walls of vacuum chamber (which are deformed by the atmospheric pressure) from optical elements of spectrometer. This warrantees that the optical elements are precisely positioned. The detecting system of the spectrometer consists of two proportional counters, one scintillating detector and one channeltron detector. First proportional counter can be used as I/sub 0/-detector in transmission mode or by measuring the fluorescence from exit slit edge. The last installation can be used to measure the reference data (that is necessary in XANES measurements), in this case the reference sample is installed on slit knife edge. The second proportional counter measures the intensity of x-rays transmitted through the sample. The scintillating detector is used in the same way but on the air for the hard x-rays and for alignment purposes. Total electron yield from the sample is measured by channeltron. The spectrometer is fully controlled by special software that gives the high flexibility and reliability in carrying out of the experiments. Fig.2 and fig.3 present the typical XAFS spectra measured with spectrometer.