Depth-selective X-ray absorption spectroscopy by detection of energy-loss Auger electrons

Isomura, Noritake; Soejima, Narumasa; Iwasaki, Shiro; Nomoto, T.; Murai, Takaaki; Kimoto, Yasuji

doi:10.1016/j.apsusc.2015.07.110

Cited by 19 publications

(9 citation statements)

References 19 publications

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“…Using high-resolution soft X-ray, PES and NEXAFS are powerful tools to elucidate the electronic structures near the VBM and the CBM in detail. However, since PES 27 and NEXAFS acquired in partial electron yield mode 28 are surface-sensitive techniques, we must pay attention to the off-stoichiometric, that is, the extrinsic influence in the spectra. To elucidate the intrinsic electronic structure, it is desired to use well-defined surfaces without contamination and atomic defects, such as a cleaved surface 29 or a fractured surface 17 of a single crystal.…”

Section: Resultsmentioning

confidence: 99%

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

et al. 2017

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The electronic structure of ternary tin oxide with pyrochlore structure, Sn 2 Nb 2 O 7 , which has the contribution of the Sn 5s orbitals in the valence band, is examined by synchrotron-radiation-excited photoelectron spectroscopy and X-ray absorption spectroscopy together with ab initio calculations. The empirical spectra are qualitatively consistent with the calculated density of states with the exception of a striking discrepancy in the electronic structure around the valence band maximum (VBM). The band calculation suggests the presence of a sharp peak around the VBM, mainly due to dispersionless bands that are derived from hybridization of Sn 5s orbitals and O 2p orbitals close to the Sn atom. However, the photoelectron spectra show no such characteristic spectral feature. From the theoretical prediction about the orbital origin of the localized VBM and the experimental estimation of the elemental composition by chemical analysis, it seems reasonable to conclude that the discrepancy of the electronic structure around the VBM is caused by the off-stoichiometric effect due to the point defects such as oxygen vacancies close to Sn 2+ , Sn 2+ vacancies, and Sn 4+ -on-Nb 5+ substitutional defects. Oxides with such localized VBM are not considered to be suitable for practical p-type oxide semiconductors. Therefore, the disappearance of the theoretically predicted localized VBM suggests the possibility to improve the mobility of hole carriers, and is considered to be closely related to our success in the development of the p-type oxide semiconductor Sn 2 Nb 2 O 7 .

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Section: Resultsmentioning

confidence: 99%

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

et al. 2017

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“…For the N K-edge, the oscillation range used for the Fourier transform was k = 2.6-7.8 Å À1 with a relatively good signal-tonoise ratio, and the phase shift and backward scattering factor values were calculated using FEFF (Zabinsky et al, 1995;Ankudinov et al, 1998). The Si K-edge was measured at the BL6N1 beamline of AichiSR (Yamamoto et al, 2014;Isomura et al, 2015), and the obtained TEY-EXAFS spectrum included no other edge (no data shown), enabling EXAFS analysis. The first nearest-neighbor distances were calculated via a fitting analysis using the ARTEMIS program (Ravel & Newville, 2005).…”

Section: Resultsmentioning

confidence: 99%

A new EXAFS method for the local structure analysis of low-Z elements

Isomura

Kamada²,

Nonaka

et al. 2016

J Synchrotron Radiat

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A unique analytical method is proposed for local structure analysis via extended X-ray absorption fine structure (EXAFS) spectroscopy. The measurement of electron energy distribution curves at various excitation photon energies using an electron energy analyzer is applied to determine a specific elemental Auger spectrum. To demonstrate the method, the N K-edge EXAFS spectra for a silicon nitride film were obtained via simultaneous measurement of the N KLL Auger and background spectra using dual-energy windows. The background spectrum was then used to remove the photoelectrons and secondary electron mixing in the energy distribution curves. The spectrum obtained following this subtraction procedure represents the `true' N K-edge EXAFS spectrum without the other absorptions that are observed in total electron yield N K-edge EXAFS spectra. The first nearest-neighbor distance (N-Si) derived from the extracted N K-edge EXAFS oscillation was in good agreement with the value derived from Si K-edge analysis. This result confirmed that the present method, referred to as differential electron yield (DEY)-EXAFS, is valid for deriving local surface structure information for low-Z elements.

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“…The experiments were performed at the soft X-ray XAS beamline BL6N1 of the Aichi Synchrotron Radiation Center (AichiSR) (Yamamoto et al, 2014;Isomura et al, 2015), which has an electron storage ring with a circumference of 72 m and is operated at an electron energy of 1.2 GeV with a current of 300 mA. White light from a bending magnet was monochromated by an InSb(111) double-crystal monochromator.…”

Section: Methodsmentioning

confidence: 99%

“…Stö hr (1979) proposed a method to avoid photoelectron crossing by detecting secondary electrons with ISSN 1600-5775 # 2017 International Union of Crystallography low energy. However, these secondary electrons, which are electrons that have lost energy in the solid bulk, originate primarily from Auger electrons, suggesting a greater depth than the AEY (Isomura et al, 2015). In most cases, PEY measurement is performed using X-ray absorption near-edge structure (XANES) spectroscopy, which does not require a wide-energy-range spectrum and is analyzed by comparison with the spectra of standard materials.…”

Section: Introductionmentioning

confidence: 99%

Surface EXAFS via differential electron yield

Isomura

Murai²,

Nomoto³

et al. 2017

J Synchrotron Radiat

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Surface-sensitive analysis via extended X-ray absorption fine-structure (EXAFS) spectroscopy is demonstrated using a thickness-defined SiO (12.4 nm)/Si sample. The proposed method exploits the differential electron yield (DEY) method wherein Auger electrons escaping from a sample surface are detected by an electron analyzer. The DEY method removes local intensity changes in the EXAFS spectra caused by photoelectrons crossing the Auger peak during X-ray energy sweeps, enabling EXAFS analysis through Fourier transformation of wide-energy-range spectral oscillations. The Si K-edge DEY X-ray absorption near-edge structure (XANES) spectrum appears to comprise high amounts of SiO and low Si content, suggesting an analysis depth, as expressed using the inelastic mean free path of electrons in general electron spectroscopy, of approximately 4.2 nm. The first nearest neighbor (Si-O) distance derived from the Fourier transform of the Si K-edge DEY-EXAFS oscillation is 1.63 Å. This value is within the reported values of bulk SiO, showing that DEY can be used to detect a surface layer of 12.4 nm thickness with an analysis depth of approximately 4.2 nm and enable `surface EXAFS' analysis using Fourier transformation.

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Depth-selective X-ray absorption spectroscopy by detection of energy-loss Auger electrons

Cited by 19 publications

References 19 publications

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

A new EXAFS method for the local structure analysis of low-Z elements

Surface EXAFS via differential electron yield

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Depth-selective X-ray absorption spectroscopy by detection of energy-loss Auger electrons

Cited by 19 publications

References 19 publications

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn2Nb2O7

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn2Nb2O7

A new EXAFS method for the local structure analysis of low-Z elements

Surface EXAFS via differential electron yield

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Product

Resources

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Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇