Jiang Yijian

Structural properties of Bi1?xLaxFeO3 studied by micro-Raman scattering

This paper reports that La-doped BiFeO3 (Bi1?xLaxFeO3, x = 0, 0.1, 0.2, 0.3, 0.6, 0.8 and 1.0) were studied by using micro-Raman spectroscopy and x-ray diffraction (XRD). The XRD patterns indicate that the structure of Bi1?xLaxFeO3 changes from rhombohedral BiFeO3 to orthorhombic LaFeO3. The results of Raman spectroscopy show good agreement with the XRD results. Strikingly, the phonon peak at around 610 cm?1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution. The increasing intensity of the 610 cm?1 peak is attributed to the changes in the FeO6 octahedron during the rhombohedral?orthorhombic phase transition. The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure. These results indicate the existence of strong spin?phonon coupling in Bi1?xLaxFeO3, which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi1?xLaxFeO3.

Channel Temperature Measurement of AlGaN/GaN HEMTs by Forward Schottky Characteristics

Channel temperature measurements of multi-finger AlGaN/GaN HEMTs by forward Schottky characteristics are presented. The temperature dependence of the forward gate-source Schottky junction voltage is investigated and it is used as the temperature sensitive parameter (TSP) by pulsed switching technique. The channel-to-mounting thermal resistance of the tested AlGaN/GaN HEMT sample is 19.6°C/W. Compared with both the measured results by micro-Raman method and simulated results of a three-dimensional heat conduction model, the physical meaning of the channel temperature for AlGaN/GaN HEMT tested by pulsed switching electrical TSP method is investigated quantitatively for the first time.

Elastic and Piezoelectric Properties of Ce:BaTiO3 Single Crystals

We investigate magnetic and crystalline microstructures of melt-spun (Fe0.675Pt0.325)(100-x)B-x (x = 12, 14, 16, 18, 20) nanocomposite ribbons after optimal thermal treatment using a magnetic force microscope. The magnetic microstructures are characterized by darker spots adjacent to brighter ones in a sub-micro scale and in random distribution. It is found that the strength of the exchange coupling interaction between the crystals in the 10-100nm scale, implied by the maximum value (delta M)(max) of the Henkel plot, could be roughly described by the ratio of the average width of the magnetic spots (w) over bar to the average crystal size (D) over bar for the ribbons. Moreover, we find that the intrinsic coercivity H-j(c) of the ribbons is sensitive to their crystal sizes, and the smaller (D) over bar, the higher jHc. Finally, by using roughness analysis, the curve of the root mean square values of the phase shift of the magnetic force images versus the boron content x is obtained, which is qualitatively consistent with that of the magnetization sigma(12)kOe of the ribbons versus x.

Analysis of X-Ray Photoelectron Spectroscopy of Polymethyl Methacrylate Etched by a KrF Excimer Laser

The C 1s and O 1s electrons in polymethyl methacrylate etched by different incident laser intensities are analysed by x-ray photoelectron spectroscopy. The results show that when the incident laser fluence increases gradually, the percentage of carbon atoms in C–C bonds decreases while the one in carbonyl group (C=O) and alkoxy group (C–O) increases, and the percentage of oxygen atoms in C=O bonds increases while the one in C–O bonds decreases. Based on the analysis of the chemical structure, the energy level transition, energy diversion, and dissociation of bonds are theoretically examined, which is consistent with the experimental results.

Influences of KrF laser irradiation on the structure and luminescence of ZnO single crystal

In this paper, we investigate the laser irradiation of ZnO single crystals and its influence on photoluminescence. Our study shows that the photoluminescence of ZnO single crystals strongly depends on surface morphologies. The ultraviolet emissions of laser treated-ZnO under 200 mJ/cm2 become stronger, whereas for those deteriorated by irradiation above 200 mJ/cm2, the green emissions centred at 2.53 eV are significantly enhanced with a red-shift to 2.19 eV, probably due to the changes in the charge states of the defects. Enhanced yellow-green emissions are well resolved into four peaks at around 1.98, 2.19, 2.36, and 2.53 eV due to a shallow irradiation depth. Possible origins are proposed and discussed.

Study of (Na 0.5 K 0.5 )NbO 3 -LiNbO 3 ceramics prepared by laser sintering

The unique physical properties of the (1−x)K<inf>0.5</inf>Na<inf>0.5</inf>NbO<inf>3</inf>−xLiNbO<inf>3</inf> (KNN-LN) ceramics prepared by laser sintering were studied by XRD and Raman scattering analysis. The larger substitution of Li⁺ leads to the composition x of the optimized piezoelectric properties (d<inf>33</inf>=65 ∼ 105 pC/N and T<inf>c</inf>= 400 ∼ 440 °C) is down to x = 0.04 from 0.06. Textured structure due to strictly heating directivity of laser irradiation resulted in fine ferroelectric properties of remnant polarization and coercive field are 22.7 µC/cm² and 16.1 kV/cm. The phase transition between tetragonal and orthorhombic phases (T<inf>O-T</inf>) shifting ∼ 0°C from room is beneficial for the increasing of temperature stability of the ceramics in application. It is shown that laser sintering should be one of promising methods in preparation of functional ceramics with applicable physical properties.

Nonlinear Characteristics of an Intense Laser Pulse Propagating in Partially Stripped Plasmas

The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.