Wave-vector dependence of spin-wave line-width in yttrium iron garnets

The wave-vector dependence of the spin-wave line-width in yttrium iron garnets has been studied for samples of grain diameter varying from 1·2μm to 12μm. An expression for the spin-wave line-width as a function of wave-vector and grain diameter has been obtained, which agrees satisfactorily with experiment.     

Sputter deposition of bismuth and aluminum substituted dysprosium iron garnet films using sol-gel derived targets

Bismuth and aluminum substituted dysprosium iron garnet (Bi, Al:DylG) films were prepared by r.f. sputtering using sol-gel derived targets. The sol-gel derived target was coating on a rigid wafer. The coating was derived from the paste formed by a mixture of powders and viscous sol, which were prepared by the sol-gel process using nitrates as precursors, in appropriate stoichiometric ratios of . X-ray diffraction (XRD) patterns show that the crystallized films sputtered from the sol-gel derived targets are single phase garnet in nature, indicating that the sol-gel derived target is indeed a feasible alternative to a ceramic target. Magneto-optical measurements show that the prepared garnet film exhibits a strongest Faraday rotation of about 4.5°/m at a wavelength of 550 nm. It is believed that this sol-gel method for preparing the sputtering targets comprised of multi-component oxides provides a low cost target preparation process.     

Liquid phase epitaxy growth of bismuth-substituted yttrium iron garnet thin films for magneto-optical applications

The novel Bi-substituted rare-earth iron garnet films were grown by the modified liquid phase epitaxy (LPE) technique for use as a 45° Faraday rotator in optical isolators. First, single crystals of Y₃Fe₅O₁₂ (YIG), with a lattice constant of 1.2378 nm, were grown by means of the Czochralski method. Using the seed crystal of YIG instead of the conventional non-magnetic garnet of Gd₃Ga₅O₁₂ as a substrate, a film of BiYbIG was grown by means of the LPE method from Bi₂O₃–B₂O₃ fluxes. The structural, magnetic and magneto-optical properties of BiYbIG LPE film/YIG crystal composite have been investigated using directional X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and near-infrared transmission spectrometry. The saturation magnetization 4πM_s has been estimated to be approximately 1200 G. The Faraday rotation spectrum was measured by the method of rotating analyzer ellipsometry with the wavelength varying from 800 to 1700 nm. The resultant Bi_0.37Yb_2.63Fe₅O₁₂ LPE film/YIG crystal composite showed an increased Faraday rotation coefficient due to doping Bi³⁺ ions on the dodecahedral sites of the magnetic garnet without increasing absorption loss, therefore a good magneto-optic figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved of 21.5 deg/dB and 30.2 deg/dB at 1300 nm and 1550 nm wavelengths, respectively, at room temperature. Since Yb³⁺ ions and Y³⁺ ions provide the opposite contributes to the wideband and temperature characteristic of Faraday rotation, the values of Faraday rotation wavelength and temperature coefficients were reduced to 0.06%/nm and 0.007 deg/°C at 1550 nm wavelength, respectively.     

脉冲激光沉积制备立方AlN薄膜的研究

采用脉冲激光沉积(PLD)方法,在SrTiO3(100)衬底上在650℃、10Pa N2条件下成功制备了立方结构的AlN薄膜.高能电子衍射(RHEED)及X射线衍射(XRD)分析表明立方AlN和SrTiO3的外延关系为AlN[100]∥SrTiO3[100]和AlN(200)∥SrTiO3(100).其AlN(200)衍射峰的摇摆曲线半高宽(FWHM)为0.44°,说明薄膜结晶性能良好.原子力显微镜(AFM)表明外延的立方AlN薄膜表面具有原子级平整度,其表面均方根粗糙度(RMS)为0.674nm.通过X光电子能谱(XPS)分析AlN薄膜表面成分,结果表明AlN薄膜表面没有被氧化.     

Study of manganese oxide thin films grown by pulsed laser deposition

In this paper, we report on the growth of manganese oxides thin films by Pulsed Laser Deposition using an MnO target at various oxygen pressures and substrate temperatures ranging from 550 to 800 °C. Grazing Incidence X-Ray Diffraction measurements on the grown films revealed that, at low deposition temperature, the dominant phase is Mn₂O₃, but as the deposition temperature was raised above 700 °C, a phase transformation occurred leading to the formation of Mn₃O₄. In a qualitative comparison, in the temperature range of 500-850 °C, and at a pressure below 13 Pa, the phase diagram of bulk manganese oxides and our grown films show a fair correlation. The films grown near the transition temperature (T = 700 °C) were found to be very thin compared to those grown at lower or higher temperatures, but the surface roughness was found to increase with temperature, as determined by Atomic Force Microscopy.     

Microstructure of homoepitaxial strontium titanate films grown by pulsed laser deposition

Homoepitaxial strontium titanate (SrTiO₃) thin films have been grown by pulsed laser deposition in order to identify those defects which are intrinsic to the growth of SrTiO₃. The pulse rate and oxygen annealing pressure were varied, although the oxygen pressure had no effect under these conditions. Columnar growth was common. The nature of the columns is described, but the reason for their presence is not fully understood. They can be suppressed using a high laser pulse rate.     

Structural investigations of InZnO films grown by pulsed laser deposition technique

Thin films of indium zinc oxide were grown from targets with In atomic concentration [In/(In + Zn)] of 2.8%, 4.3%, and 16.8%, respectively, by pulsed laser deposition technique (KrF laser, 10 Hz, 4 J/cm² fluence) on Si(001) and glass substrates that were heated at 500 °C. X-ray diffraction investigations showed that targets that had an atomic In concentration of 2.8% exhibited only the wurtzite-type ZnO lattice, while the targets that contained In concentrations of 4.3% and 16.8% consisted of a mixture of the wurtzite-type ZnO and the homologous compound Zn₇In₂O₁₀. All deposited films exhibited only the wurtzite-type ZnO lattice, being c-axis textured. The increase of the In concentration resulted in films less textured that also exhibited increased lattice parameters a and c. X-ray photoelectron spectroscopy investigations showed slight changes of the In 3d and Zn 2p binding energies for increased In content, consistent with an In doped ZnO lattice.     

Microstructural evolution in lubricious ZnO films grown by pulsed laser deposition

Zinc oxide (ZnO) is well known to the electronic industry as a piezoelectric material. Recent research from this laboratory also indicates the potential of ZnO as a tribological material. The current work describes the evolution of microstructure with deposition parameters in pulsed laser deposited ZnO thin films, specifically targeted for friction and wear applications. Films were characterized by high resolution scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Friction and wear measurements were made using a ball-on-disk tribometer. Films were grown in vacuum (V) as well as in 5 mTorr of oxygen (O₂), while the substrates were kept at room temperature (RT). The RT/V ZnO films have (002) columnar texture with an average column width of 20 nm. The RT/O₂ films also are nanoclumnar with (002) texture, but each column is a mosaic of low-angle boundaries. Deformation mechanisms associated with nanocrystalline grain structure were analyzed with particular reference to sliding contact. Mechanisms to provide the observed low friction of RT/O₂ films (μ=0.15–0.20) have been activated by its mosaic structure.     

Nonlinear optical properties of thin iron films grown on MgO (100) by pulsed laser deposition

Thin films of iron were fabricated on MgO (100) substrates using pulsed laser deposition technique. The crystalline property and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. It was found that the morphology of the Fe film deposited at room temperature was characteristic of continuous metal film. Increasing the deposition temperature caused the smooth Fe film to break up, and nanoscale Fe islands were formed. We performed the z-scan measurements to study the third-order optical nonlinearity of the continuous approximately 9-nm-thick iron film. The results show that the ultrathin iron film exhibits large nonlinear refractive coefficient, n₂=7.09×10⁻⁵ cm²/kW, and nonlinear absorption coefficient, β=−5.52×10⁻³ (cm/W), at the wavelength of 532 nm.     

A parametric study of AlN thin films grown by pulsed laser deposition

High quality AlN thin films were grown at 200–450°C on sapphire substrates by laser ablation of Al targets in nitrogen reactive atmosphere. The nitrogen pressure was varied between 10⁻³ and 10⁻¹ mbar. The reactive gas pressure during irradiation and the temperature of the substrate were found to essentially influence the quality of the layers. X-ray diffraction analysis evidenced the formation of highly orientated layers for a very restrictive set of parameters. Other analysis techniques, like X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, optical transmission spectroscopy have been used to evidence the good stoichiometry and purity of the films. The characteristics of these films were compared with those of AlN thin films deposited in similar experimental conditions, on Si (100) and Si (111) substrates.     

Epitaxial EuO thin films by pulsed laser deposition monitored by in situ x-ray photoelectron spectroscopy

We have grown EuO thin films on silicon [001] and yttrium aluminate [110] from a europium metal target using pulsed laser deposition. In situ x-ray photoelectron spectroscopy has been used to determine the parameter window for stoichiometric EuO deposition. EuO is observed to grow in the relatively high pressure regime of 10⁻⁶-10⁻⁵ mbar, due to the large Eu flux during ablation. EuO is proven to grow epitaxially on yttrium aluminate [110]. Magnetization measurements confirm the stoichiometry of the film.     

On the optical properties of bismuth oxide thin films prepared by pulsed laser deposition

The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorption in the photon energy range 2.50-4.30 eV and optical functions (n, k, ?₁, and ?₂) in the domain 3.20-6.50 eV, have been investigated. As-prepared films (d=0.05-1.50 μm) are characterized by a mixture of polycrystalline and amorphous phases. The fundamental absorption edge is described by direct optical band-to-band transitions with energies 2.90 and 3.83 eV. The dispersion of the optical functions provided values of 4.40-6.25 eV for electron energies of respective direct transitions. In the spectral range 400-1000 nm, bismuth oxide films show a normal dispersion, which can be interpreted in the frame of a single oscillator model.     

Influences of oxygen pressure on optical properties and interband electronic transitions in multiferroic bismuth ferrite nanocrystalline films grown by pulsed laser deposition

Bismuth ferrite (BiFeO(3)) nanocrystalline films with the crystalline size of 27-40 nm have been grown on c-sapphire substrates under various oxygen pressures of 1 × 10(-4) to 1 Pa by pulsed laser deposition. The X-ray diffraction spectra show that the films are polycrystalline and present the pure rhombohedral phase. It was found that the Raman-active phonon mode E(TO1) shifts towards a higher energy side from 74 to 76 cm(-1) with increasing oxygen pressure, indicating a larger tensile stress in the films deposited at higher oxygen pressure. The X-ray photoelectron spectroscopy analysis suggests that the concentrations of both Fe(2+) ions and oxygen vacancies in the BiFeO(3) films increase with decreasing oxygen pressure. Moreover, the dielectric functions in the photon energy range of 0.47-6.5 eV have been extracted by fitting the transmittance spectra with the Tauc-Lorentz dispersion model. From the transmittance spectra, the fundamental absorption edge is observed to present a redshift trend with increasing the temperature from 8 to 300 K. Note that the optical band gap (E(g)) decreases with increasing the temperature due to the electron-phonon interactions associated with the interatomic distance in the BiFeO(3) films. However, the E(g) decreases from 2.88 to 2.78 eV with decreasing oxygen pressure at 8 K, which can be attributed to the increment of oxygen vacancies leading to the formation of some impurity states between the valence and conduction band. It can be concluded that the oxygen pressure during the film fabrication has the significant effects on microstructure, optical properties, and electronic band structure modification of the BiFeO(3) films.     

Epitaxial growth and annealing control of FMR properties of thick homogeneous Ga substituted yttrium iron garnet films

Homogeneous, 30 μm to 70 μm thick Ga substituted yttrium iron garnet films have been grown on Y or Al substituted gadolinium gallium garnet substrates having lattice parameters matched to that of the films. Resonance field and FMR linewidth measurements as a function of frequency and annealing experiments revealed that the magnetization and cubic anisotropy of the films are identical to data from flux grown bulk single crystals, the FMR losses of the films are only slightly higher. For films grown with supercooling ΔT < 50 °C a negative, growth induced, uniaxial anisotropy was found which could be removed by annealing in air at 1100 °C. A compensation of the temperature drift of the FMR frequency can be adjusted in the Ga substituted films by changing the frozen-in Ga-Fe cation distribution by annealing and quenching from different temperatures > 800 °C.     

Structural and optical properties of neodymium-doped lutetium fluoride thin films grown by pulsed laser deposition

Neodymium-doped lutetium fluoride (Nd³⁺:LuF₃) thin films were successfully grown on MgF₂ (0 0 1) substrates by pulsed laser deposition (PLD). It is void of cracks that are otherwise prevalent due to structural phase transitions in Nd³⁺:LuF₃ during thin film deposition and bulk crystal growth. Cathodoluminescence (CL) spectra revealed multiple emission peaks, with a dominant peak in the vacuum ultraviolet (VUV) region at 179 nm. This peak has a decay time of 6.7 ns. The ability to grow high quality Nd³⁺-doped fluoride thin films would enable fabrication of VUV light-emitting devices that will enhance applications requiring efficient VUV light sources.     

The effects of buffer growth parameters on heteroepitaxial ZnO films grown by pulsed laser deposition

The effects of buffer layer deposition conditions on subsequent ZnO epitaxy on sapphire (0001) were examined. An initial ZnO buffer layer improves surface roughness for a wide range of buffer layer growth temperatures and pressures. Changes in buffer layer growth pressure and temperature have a moderate effect on the roughness of subsequent film growth. However, the conditions for buffer layer deposition have a large impact on crystallinity of subsequent films. In particular, the out-of-plane X-ray diffraction rocking curve full-width half-maximum decreased as buffer deposition temperature or O₂/O₃ pressure increases. Carrier mobility in the subsequent thick ZnO film was enhanced with increase in buffer layer deposition temperature. Carrier concentration decreased with increasing buffer layer deposition pressure.     

Effects of stress on the structure of indium-tin-oxide thin films grown by pulsed laser deposition

The effects of stress in pulsed laser deposited (PLD) indium-tin-oxide (ITO) films formed on glass substrate at 200 °C and oxygen pressures (P_{o 2}) ranging from 0.1 to 2.7 Pa are discussed. Grazing incidence X-ray diffraction (GIXRD) investigations of the ITO films show splitting of the diffraction peaks and significant changes in the lattice constants for films deposited at low P_{o 2} and when the thickness of the films is larger than 150 nm. These features were due to intrinsic stress caused by the incidence of energetic particles on the substrate during growth. The splitting of the peaks only occurred in the bulk of the films, while near the surface, single peaks were evidenced, indicating the existence of two layers. No apparent splitting of the diffraction peaks or shifts in peak positions occurred in the ITO layers with thickness less than 100 nm. In spite of the presence of stress in the ITO films, resistivity less than 3 10, ^-4 cm was obtained. © 2001 Kluwer Academic Publishers     

Highly oriented metallic SmS films on Si(100) grown by pulsed laser deposition

Stoichiometric and highly oriented in (100) direction SmS films in the metallic phase have been grown on Si(100) substrate at room temperature by pulsed laser deposition (PLD) as revealed from lattice parameter, reflectivity and electrical resistivity measurements. Above-critical compressive stress P = 0.9 GPa in as grown film was determined from sample curvature measurements and attributed to stress building up in PLD process further accompanied by stress due to SmS versus Si lattice parameter mismatch. Stress relaxation and subsequent metal-to-semiconductor phase transition occurred following annealing at T = 900 K as evident from consistent changes of SmS/Si sample curvature, structural, optical and electrical properties.