Wenjie Zhong

Direct determination of Mn occupations in Ga1-xMnxN dilute magnetic semiconductors by x-ray absorption near-edge structure spectroscopy

X-ray absorption near-edge structure (XANES) spectroscopy is used to study the features of occupation sites of Mn dopants in the Ga1−xMnxN dilute magnetic semiconductors (DMSs) with zinc-blende structure. Theoretical XANES spectra are calculated for representative structure models of Mn atoms in the GaN lattice. It is shown that the substitutional Mn in GaN is characterized by a preedge peak at 2.0eV and a postedge multiple-scattering peak at 29.1eV. The peaks shift in position and drop in intensity dramatically for the interstitial MnI and MnGa–MnI dimer, and then disappear completely for Mn clusters. The experimental spectrum of Ga0.990Mn0.010N is almost reproduced by the calculated XANES spectrum of GaMnN with substitutional Mn.

XAFS applications in semiconductors

X-ray absorption fine structure (XAFS) has experienced a rapid development in the last three decades and has proven to be a powerful structural characterization technique nowadays. In this review, the XAFS basic principles including the theory, the data analysis, and the experiments have been introduced in detail. To show its strength as a local structure probe, the XAFS applications in semiconductors are summarized comprehensively, that is, thin films, quantum wells and dots, dilute magnetic semiconductors, and so on. In addition, certain new XAFS-related techniques, such as in-situ XAFS, micro-XAFS, and time-resolved XAFS are also shown.

Mn Occupations in Ga1-xMnxN Dilute Magnetic Semiconductors Probed by X-Ray Absorption Near-Edge Structure Spectroscopy

X‐ray absorption near‐edge structure (XANES) is used to study the characteristics of different sites of Mn in the Ga1−xMnxN dilute magnetic semiconductor (DMS) with zinc‐blende structure. The XANES spectra of representative Mn occupation sites (substitutional MnGa, interstitial MnI, MnGa‐MnI dimer and Mn cluster) in GaN lattice are theoretically calculated and compared with experimental results. The substitutional Mn in GaN is characterized by a pre‐edge peak at 2.0 eV and a post‐edge multiple‐scattering peak at 29.1 eV. The peaks shift in position and drop in intensity dramatically for the interstitial MnI and MnGa‐MnI dimmer, and disappear completely for Mn clusters. We propose that the distinct characteristics of Mn K‐edge XANES spectra for different Mn sites favor to discriminate Mn occupations in GaMnN DMS.

In‐Situ XAFS Investigation of the Crystallization Mechanism of Ni‐B Nano‐Amorphous Alloy

In‐situ XAFS was used to study the crystallization process of Ni‐B nano‐amorphous alloy by heat treatment from room temperature to 823 K. It was found that the crystallization of the Ni‐B nano‐amorphous alloy is completed in two steps. The first crystallization process starts at 498 K with the main product of Ni3B, and finishes at about 523 K. The second crystallization process begins as the annealing temperature reaches 548 K, at which the crystalline Ni3B is partly decomposed to form crystalline Ni. This second step of crystallization is almost finished at about 623 K with the unique product of crystalline Ni. With further increase in temperature, there is no apparent structural change except the increase of thermal disorder.

EXAFS Study on Atomic Distribution Change during Tensile Deformation of Metallic Glass

The purpose of this research is to investigate the micro-mechanism of anelastic behavior of metallic glass. The changes of atomic arrangement in Cu50Zr50 metallic glass were observed directly by EXAFS method during tensile deformation. The transmission-mode EXAFS measurements around Zr K-edge and Cu K-edge of the sample in various amounts of tensile deformation conditions were done. The interatomic distance between Cu-Zr increased, and that between Zr-Zr decreased simultaneously, with the amount of tensile deformation increase of the sample at first stage of deformation. When the atomic distances reached to certain values respectively, they recovered to the initial values of no tensile deformation condition at first stage, and then the atomic distances changed as same manner as the first stage of deformation, respectively. This is the first observation on the change of atomic arrangement during tensile deformation of metallic glass.