Extended X-ray Emission Fine Structure Research Articles

Analysis of coordination environment of aluminum species in zeolites and amorphous silica-alumina by X-ray absorption and emission spectroscopy

The coordination numbers of Al species in zeolites and amorphous silica alumina samples were investigated with three kinds of X-ray spectroscopic technique: namely, X-ray absorption near edge structure (XANES), wavelength dispersive X-ray fluorescence (WD-XRF), and extended X-ray emission fine structure (EXEFS) spectroscopies. XANES, WD-XRF and EXEFS spectra of zeolite samples were identical to those of four-coordinated reference compounds and were distinguishable from those for six-coordinated samples. The energy shift obtained by XANES spectroscopy showed good correlation with those evaluated by WD-XRF and EXEFS.

暴露試験で生じたシリコン添加鋼のさび構造と電気化学特性

The structure of the rust formed on silicon (Si) bearing steel was analyzed by EPMA and FIB-TEM, and the electrochemical behavior of the rust was investigated by the electrochemical impedance spectroscopy (EIS) method after the exposure test. The Si bearing steel showed high corrosion resistance compared to carbon steel (SM) and conventional weathering steel (SMA) in the exposure test. EIS measurement was taken to estimate the rust resistance (Rrust) and corrosion resistance (Rt) of the rusted steel. It was found that Rrust and Rt of Si bearing steel were much larger than those of SMA or SM. EXEFS (Extended X-ray Emission Fine Structure) and the Characteristic X-rays analysis by EPMA and TEM-EELS showed that Si existed as oxidized-state in the inner iron rust layer for Si bearing steel. FIB-TEM showed that nano-scale complex iron oxides containing Si were formed in the inner rust of the Si bearing steel. Finally, it was found that the corrosion resistance of Si bearing steel could be increased by the formation of the nano-scale complex oxides containing Si in inner rust to prevent the penetration of Cl ions.

暴露試験で生じたアルミニウム添加鋼のさび構造

The structure of the rust formed on Al bearing steel was analyzed by EPMA and FIB-TEM, and the electrochemical behavior of the rust was investigated by the electrochemical impedance spectroscopy (EIS) method after the exposure test. The 0.8 mass% Al bearing steel showed high corrosion resistance compared to carbon steel (SM) and conventional weathering steel (SMA) in the exposure test. EIS measurement was taken to estimate the rust resistance (Rrust) of the rusted steel. It was found that Rrust of Al bearing steel was much larger than that of SMA or SM. EXEFS(Extended X-ray Emission Fine Structure)and the X-ray analysis by EPMA and TEM-EELS showed that Al existed in Al3+ oxidized state in the inner iron rust layer for Al bearing steel. TEM showed that nano-scale complex iron oxides containing Al were formed in the inner rust of the Al bearing steel. Finally, it was found that the corrosion resistance of Al bearing steel could be increased by the formation of the nano-scale complex oxide containing Al in inner rust to prevent the penetration of Cl ions.

Radiative Auger Effect and Extended X-Ray Emission Fine Structure (EXEFS)

Radiative Auger spectra are weak X-ray emission spectra near the characteristic X-ray lines. Radiative Auger process is an intrinsic energy-loss process in an atom when a characteristic X-ray photon is emitted, due to an atomic many-body effect. The energy loss spectra correspond to the unoccupied conduction band structure of materials. Therefore the radiative Auger effect is an alternative tool to the X-ray absorption spectroscopy such as EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure), and thus it is named EXEFS (Extended X-ray Emission Fine Structure). By the use of a commercially available X-ray fluorescence spectrometer or an electron probe microanalyzer (EPMA), which are frequently used in materials industries, we can obtain an EXEFS spectrum within 20 min. The radiative Auger effect, as an example, demonstrates that the study on atomic many-body effects has become a powerful tool for crystal and electronic structure characterizations. The EXEFS method has already been used in many industries in Japan. Reviews about the applications and basic study results on the radiative Auger effect are reported in this paper.

Non-destructive Analysis of Buried Interfaces and Surface Layers: X-Ray Emission Spectroscopic Study

Soft X-ray emission spectroscopy (SXES) and extended X-ray emission fine structure (EXEFS) studies have been carried out on a heat-treated thin-film(Ni)/substrate(Si, SiC) contact system using a conventional X-ray micro-analysis (XMA) apparatus. We have successfully deduced information either the chemical bonding or atomic configuration by the former and the latter, respectively. Also, we have succeeded in analyzing an interface buried rather deep below an overlayer, e.g., more than a hundred nm. This is due to the fact that both an X-ray production depth of an energetic electron is much larger than the mean free path of an energetic electron and the mean free path of an X-ray photon in a solid is large. Namely, in the surface, or interface layer, Ni2Si and NiSi2 formation have been clarified for heat-treated Ni/SiC and Ni/Si systems, respectively.

EXTENDED X-RAY EMISSION FINE STRUCTURE (EXEFS) AND X-RAY ABSORPTION NEAR EDGE STRUCTURE (XANES) OF SOIL SAMPLES

Silicon K X-ray fluorescence spectra of soil samples in a volcano island are measured using a commercially available wavelength dispersive X-ray fluorescence spectrometer for elemental analysis. EXEFS (extended X-ray emission fine structure) are found at the low energy side of the K X-ray fluorescence diagram lines. Synchrotron radiation XANES (X-ray absorption near edge structure) spectra are measured for the same samples and for aerosols collected in the same island. The EXEFS spectra are compared with the XANES spectra. The EXEFS method becomes an easy-to-perform alternative of XANES measurements using a similarity between EXEFS and XANES. We analyze the chemical state of Si in the soil samples.

New method of chemical state imaging by EPMA-EXEFS

A novel two dimensional imaging technique of the chemical bonding state was developed by combining the extended X-ray emission fine structure method with an electron probe X-ray microanalyzer mapping technology. With this method, chemical state images of some aluminum standard samples were obtained. It was confirmed that the obtained images provide correct information of chemical states.

Extended x‐ray emission fine structure and high‐energy satellite lines state measured by electron probe microanalysis

AbstractThe Kα satellite or shake‐off lines can be observed by wavelength‐dispersive spectrometry on the high‐energy side of the main Kα peak. Occasionally, chemical state analysis of an emitting atom has been attempted using the shape and position of these lines. Recent extensive theory and experiment have shown that it is fruitful to take a similar approach using extended x‐ray emission fine structure (EXEFS) arising from the radiative Auger effect (RAE). This fine structure is found in a low‐intensity spectrum on the low‐energy side of the Kα peak.We have studied the RAE spectra of the Kα lines of the elements F through to Ca by EPMA. The RAE peaks have energies close to the KLL energies of Auger transitions. In the lighter elements in this series, it was found that the difference between Kα and the RAE peak energies becomes quite small. For elements lighter than fluorine, it is difficult to observe the RAE peaks because they are overlapped by the main Kα line. At the higher energy end of the series, the intensity of the RAE lines becomes very small. The utility of the RAE lines for state analysis is limited, in practice, to the elements F through to Ca. The extended x‐ray emission fine structure (EXEFS) of the RAE spectra has been used to calculate local bonding parameters.Both shake‐off and RAE spectra associated with the F Kα line have been studied experimentally in the rare earth fluorides. The KLL RAE moves to lower energy as the atomic number of the rare earth cation increases. This has been confirmed theoretically by calculating electron energies using discrete variational Xα molecular orbital theory. The shake‐off peaks increase in intensity relative to the main Kα peak because atomic number increases, contrary to expectation. It is considered that this could be due to temporary covalency. The EXEFS of the RAE spectra has been used to calculate local bonding parameters. Copyright © 2001 John Wiley & Sons, Ltd.

High spatial resolution extended x‐ray emission fine structure (EXEFS) spectra of an electronic device measured by electron probe microanalysis (EPMA)

AbstractSilicon K x‐ray emission spectra of a model electronic device are measured using a commercial electron probe microanalyser equipped with a wavelength‐dispersive spectrometer. Extended x‐ray emission fine structure (EXEFS) is observed at the low‐energy side of the K x‐ray emission diagram lines. The EXEFS spectra are known to be similar to the XANES (x‐ray absorption near‐edge structure) spectra. The measured silicon K x‐ray EXEFS spectra are compared with Si, SiC, Si3N4 and SiO2 EXEFS spectra. The EXEFS spectra at two places on the electronic devices are different from each other; one is similar to the spectrum of SiO2 and the other is the sum of SiO2 and Si. These results correspond well to the multilayer structure of the measured points. The present results demonstrate that a high spatial resolution chemical‐state analysis is possible using the XANES‐like EXEFS spectra. Copyright © 2001 John Wiley & Sons, Ltd.

Micro-XANES by EPMA spectrometer.

XANES (X-ray absorption near edge structure) spectrum of an area of a few tens of square micrometers of MgO is measured with an EPMA (electron probe X-ray microanalyzer) using a novel method -EXEFS (extended X-ray emission fine structure) method -proposed by the present authors. The EXEFS method has the following six remarkable characteristics: (1) high energy resolution, (2) high spatial resolution, (3) short measuring time, (4) easy sample preparation, (5) convenient without using synchrotron radiation facilities, and (6) good at measuring soR X-ray absorption spectra.

A survey of novel X-ray analysis methods

Five novel X-ray analysis methods recently developed in the author's research group are surveyed: extended X-ray emission fine structure (EXEFS), depth-selective X-ray absorption fine structure (XAFS), X-ray fluorescence holography (XFH), X-ray Raman and total reflection X-ray photoelectron spectroscopy (TRXPS). Some of these methods are completely new and others are modified existing methods, and all of them are easily applicable to practical chemical state analysis.

Extended X-ray emission fine structure (EXEFS)

We show that a similar structure to the extended X-ray absorption fine structure (EXAFS) is observable in the line shape of X-ray fluorescence spectra. Using this similarity, we can measure the soft X-ray EXAFS using a hard X-ray beam line. The incident beam energy is required only to be high enough to excite the characteristic X-ray line. Therefore a monochromatized incident beam is not required. Measurement of the Al K-edge EXAFS of AlN excited by X-rays from an Rh anode X-ray tube using this method is described as an example.