Quan Xie

INFLUENCE OF Fe/Si THICKNESS RATIO ON STRUCTURAL AND MAGNETIC PROPERTIES OF Fe3Si FILMS FABRICATED BY SPUTTERING

The structural and magnetic properties of Fe3Si films fabricated by layered sputtering on Si substrates dependent on the Fe/Si thickness ratio varying from 2:1 to 4:1 were investigated. X-ray diffraction (XRD) results show that over the whole range of the Fe/Si thickness ratio considered, all films consist of the polycrystalline Fe3Si phase. The film produced with the Fe/Si thickness ratio of 3:1 shows relatively high structural quality. Scanning electron microscopy (SEM) images reveal that the film layer can be clearly observed and the thickness of the film layer at Fe/Si thickness ratio of 3:1 is the thinnest. From the analysis of the magnetization curves, all of these films exhibit ferromagnetic behavior at room temperature. The sample at Fe/Si thickness ratio of 3:1 shows a high Ms value of ∼831emu/cm3, which is slightly lower than the bulk value of Fe3Si. The variety of its coercive force Hc is associated with the change of grain size D through Hc∝1∕D, and the discrepancy between the Hc values of these films and the bulk Fe3Si is due to defects pinning magnetic domain. Meanwhile, the electrical resistivity remarkably decreases with the increase of the Fe/Si thickness ratio.

The Influence of Lattice Vacancy on Electrical and Optical Properties of Mg2Si

A detailed theoretical study on the influence of lattice vacancy on structural and optical properties of the magnesium silicide Mg2Si has been performed based on the first-principles pseudopotential method. The results show that Mg2Si has changed from indirect band gap semiconductor to direct band gap semiconductor because of Mg vacancy. Compared with the dielectric function, absorption coefficient, refractive index, reflectivity and photon conductivity of Mg2Si, those peaks of Mg15Si8 appear from 0 to 1.8 eV. And the loss function’s biggest peak of Mg15Si8 moves to the direction of high energy.

Preparation of the Kondo Insulators FeSi by Magnetron Sputtering

The Kondo insulator FeSi was prepared by DC magnetron sputtering and the effects of sputtering parameters on the formation of FeSi were investigated in detail. The formation of monosilicide FeSi was clarified using X-ray diffraction (XRD) and its microstructure was characterized by scanning electron microscopy (SEM). The results indicate that the sputtering gas pressure, the sputtering power and the Ar flux all have significantly effects on formation of FeSi and the crystalline of the film. The sputtering gas pressure has effects on sputtering yields, depositing rate and the energy of sputtering atoms, the sputtering power has effects on the kinetic energy and the diffusion ability of deposing atoms and the gas flux has the effects on the flowing state of Ar gas. The most optimal sputtering parameters for the preparation of the Kondo insulator FeSi by DC magnetron sputtering are given: 1.5 Pa for sputtering Ar pressure, 100 W for sputtering power and 20 SCCM for sputtering Ar flux.

Simulation Study of Microstructure Transition of Liquid Ge during Rapid Cooling Solidification

Structural and dynamical properties of the rapid solidification process of liquid Ge have been investigated by molecular-dynamics calculations based on the Stillinger-Weber potential. The variations of microstructures during the solidification process are analyzed by the self-diffusion coefficient D(T), pair correlation function g(r) curves and the HA bond-type index method. The melting point implicated in D(T) is about 2100 K. The pair correlation function g(r) obtained by the simulated in liquid Ge is good agreement with experiment, the fist-peak of g(r) gradually becomes higher and sharper with the temperature decreasing, when temperature drops to 1400 K, the second-peak of g(r) begins to split. The change of HA bond-type indicated that the most important structural change occurs in the temperature range 1400 K-700 K.