Materials Science Forum Vols. 475-479

Abstract: The microstructure, optical absorption properties and luminescence function of GaN thin films grown on the sapphire substrate with the buffer layer of GaN by metal-organic chemical vapor deposition (MOCVD) have been studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared transmission spectrum, ultraviolet-visible absorption spectrum and photoluminescence. XRD results show that the crystal structure of GaN is hexagonal wurtzite structure. The thin films have preferred orientation in c axis with very high quality. TEM images of the cross-sectional specimen show that the thickness of every layer in the superlattice are uniform with the average period of 13.3 nm, but there are high-density dislocations in the superlattices region. From related optical experimental data, it is found that optical absorption edge is at about 370 nm. The theory calculation indicates that the five samples are direct transition semiconductor and band-gaps are about 3.4 eV. The refractive indexes of the samples increase with photon energy enhancing and decrease with the wavelength increasing. The results show that the extinction coefficients reach the lowest point at 370 nm. Photoluminescence test results show that superlattice has preferable luminescence property. In addition, the yellow luminescence is found in all samples.

Abstract: The MOCVD-growth and annealing of InN films have been studied in this work. The XRD spectra of InN films grown at 350 °C~500 °C indicate that the diffraction of In increases with increasing the growth temperature to 425 °C and the temperature higher than 425 °C causes the decrease of In diffraction. The corresponding SEM images show that In grains disappear from the surface as the growth temperature is higher than 425 °C. These are attributed to the increase of the desorption of In with the growth temperature. In addition, the SEM images of the annealed InN films also show that the In grains decrease gradually as the annealing temperature is higher than 425 °C. Thus, it is concluded that the desorption of In is the main process as the temperature is higher than 425 °C.

Abstract: In this paper, the optical properties and structure of CdS films were investigated by SEM, X-ray diffraction, and x-ray photoelectron spectroscopy. The CdS films in this study were deposited on the plane transparent glass by chemical bath deposition technique. The experimental results have shown that the annealing treatment has an important effect on the optical properties and structure of CdS films. This may be ascribed to decreasing surface contaminations and oxide content in the films.

Abstract: 185 nm-thick Ni76Fe24 films were deposited on SiO2/Si(100) substrates at room temperature by DC magnetron co-sputtering and they were annealed in a vacuum of 5×10-4 Pa at 300 , 400 and 480 °C for 1 hour, respectively. The as-deposited film grows with thin columnar grains and has void networks in the grain boundaries. As the annealing temperature increases, the grain size gradually increases and the void networks decrease. Besides, the void networks shorten and widen with annealing temperature. The resistivity of the film decreases with increasing annealing temperature. The magnetic hysteresis loop of the as-deposited film shows a hard magnetization requiring a saturation field of 1050 Oe while that of the film annealed at 480 °C represents an easy magnetization. For the film annealed at 480 °C the coercivity is 78 Oe and the ratio of remanent magnetization to saturation magnetization is 0.72. The as-deposited and annealed films have an isotropic magnetization characteristic.

Abstract: FePt/C mutilayer films were successfully prepared by using RF and DC magnetron sputtering system. FePt nanoparticles embedded in a C matrix were formed by consequently annealing. X-ray diffraction (XRD) results show the degree of atomic ordering of the L10 structure increases with higher temperature annealing. Room temperature magnetic measurements reveal that in-plane coercivity HC, and squareness Mr/MS depend on the thickness of carbon layer. Relatively High HC (3245.1Oe) and squareness (0.67) were obtained when the thickness of C layer is 2.0 nm. The carbon layer not only isolates the FePt grain, but also suppresses the growth of fct FePt grains. When the thickness of carbon layer is 2.0 nm, the FePt grain size decreases down to ~20 nm measured by Scan Probe Microscope (SPM). Interactions between particles can be tuned to near zero when we select the proper thickness of C layer.

Abstract: A series of (Fe50Ni50)xCu1-x granular films were prepared using magnetron controlled sputtering method. The magnetic-transport and microstructure of FeNi-Cu films deposited at room temperature and then annealed at various temperatures were investigated through TEM, XRD and conventional four probes method under room temperature, respectively. The giant magnetoresistence (GMR) as a function of FeNi volume fraction for as-deposited FeNi-Cu films reached a maximum of about 1.8 % at the volume fraction of 32 %. With increasing the annealing temperature, the GMR of films with the volume fraction less than 26 % reaches a peak at certain annealing temperature. While for films with the volume fraction larger than 26 %, the GMR have almost no changes at first and then decrease with increasing the annealing temperature. In addition, the relationship between magneto-transport and the microstructure, morphology of granular films is discussed.

Abstract: Granular C/Co/C films have been prepared by magnetron sputtering from C and Co onto glass substrates at room temperature and subsequent in situ annealing. C and Co targets use an RF and DC facing deposition mode respectively. The structural and magnetic properties of films at room temperature were investigated as functions of Co layer thickness, C layer thickness and annealing temperature. X-ray diffraction (XRD) shows the majority Co nanograins are formed as the hexagonal-close-packed (hcp) structure annealing at 400 °C. Vibrating sample magnetometer (VSM) measurements indicate that the magnetic moment lies well in the film plane. Hc reaches maximum near 20 nm-thick Co layer and 30 nm-thick C layer with annealing temperature of 400 °C for 30 min. Remanent squareness (S) close to 1 was achieved for the film in which C layer thickness is 45 nm. Scanning probe microscope (SPM) was used to scan surface morphology and magnetic domain structures. The average grain size varies from 10 nm to 15 nm after annealing.

Abstract: In this paper, the influences of annealing temperature on TbFe magnetostrictive film magnetic and magnetostrictive characteristics were discussed. TbFe films were prepared by RF magnetron sputtering. XRD patterns indicate that polycrystalline films consisting mainly of a-Fe and TbFe2 Laves phase could be obtained through rapid cycle annealing process (RCAP) at higher annealing temperature. Grain sizes could be controlled through varying annealing temperature. From film hysteresis loops measured by VSM, it has been found that the annealing treatment can improve TbFe film in-plane magnetization at 1600 kA.m-1 external field, and decrease in-plane coercivity. Magnetostriction of annealed TbFe films measured by optical cantilever deflectometer is better than as-deposited films at 40 kA.m-1 external magnetic field.

Abstract: In this paper, based on 4×4 matrix method, we present theoretical calculations of the polar magneto-optical Kerr effect for Co/Pt and MnBi multilayered films, and NixSiO2(1-x) granular films. The calculated results indicate that, (1) the simulated Kerr spectra as a function of photo-energy are in good agreement with experimental ones; (2) the maxima and the periodical and damped oscillation appear in the Kerr spectra curve with the magnetic thickness, which is important for design of the material in the future; (3) the structure of interfacial layer affect greatly the Kerr spectra, which is significant for the processing of magneto-optical material.

Abstract: In recent years, much work has been done on microwave absorbing materials, and anisotropy magnetic materials are expected to have excellent microwave absorbing properties. We have prepared well-aligned ZnO whiskers on glass substrate by atmospheric MOCVD. In the present work, Fe2O3 film is deposited by this technique. The phase composition, orientation and morphology of deposited products are studied by XRD and SEM. The effects of the deposition conditions (such as vaporizing temperature, substrate temperature, distance from nozzle to substrate, and carrier gas flux) are investigated. The optimal conditions for the preparation of orientated Fe2O3 film and even well-aligned whisker array are discussed.