Metal Precursor Influence on Performance of CuIn1-xGaxSe2 Films

CuIn_1-xGa_xSe₂ (CIGS) films were prepared by a two-stage method, in which Cu-In-Ga metallic precursors were firstly deposited on unheated Mo-coated soda lime glass substrates by direct current sputtering CuGa (20%Ga) and radio frequency sputtering In targets inan Ar atmosphere, followed by selenization at 520 oC for 40 min in Se vapor. By adjust-ing the sputtering thickness ratio of surface CuGa (20%Ga) and bottom CuGa (20%Ga) alloy layers in metal precursor, different CIGS thin films were fabricated. Through X-ray diffraction spectra, Raman spectra, local energy dispersive spectrometer, planar- and cross-sectional views of scanning electron microscopy measurements, it revealed that the CIGS thin films from selenization of metal precursor with CuGa:In:CuGa thickness ratio of 7:20:3 (sample-2-se) was of chalcopyrite structure with the preferred (112) orientation, and the grains sizes ranged from 0.5 μm to 2 μm, and sample-2-se had no binary compound phase of In-Se and order defect compound phase. Consequently, the results of illuminated current-voltage curve and quantum efficiency measurements showed that the CIGS film device made from sample-2-se had relative higher photo-electric conversion efficiency (3.59%) and good spectrum response.     

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb₂₅Fe₆₁Co₁₄ thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb₂₅Fe₆₁Co₁₄ films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.     

High thermoelectric power in a NaxCoO2 thin film prepared by sputtering with rapid thermal annealing

Na_xCoO₂ thin films were fabricated by means of RF-magnetron sputtering. We measured and analyzed the thermal properties and changes of the Na_xCoO₂ crystal structure by XRD, SEM, Raman spectra, and XPS analyses. Sodium ions diffused from the bulk of the thin film to the surface as the temperature increased. The diffused Na ions reacted with oxygen ions and Na₂O was formed on the surface of the thin film, resulting in a decrease of the carrier concentration and a change of the crystal structure from a layer to a spinel structure. The Seebeck coefficient of the Na_xCoO₂ thin film annealed at 550 °C is larger than the value (100 μV/K) for single crystal NaCo₂O_4.     

Modeling of SIMS profiles at low energy: Application to algaas

Abstract

This work proposes an original solution to model Secondary Ions Mass Spectrometry. This modeling allows the accurate determination of both the thickness and the composition of AlGaAs samples.     

Growth and optical properties of Fe2O3 thin films: A study of quantum confinement effects by experiment and theory

Thin iron films in the thickness range 0.7–48 nm have been deposited on high quality Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The films were then oxidized by annealing at temperatures of 400−450 °C in a furnace in air. X-ray diffraction experiments revealed the formation of single-phase α-Fe₂O₃. The films were continuous and present negligible surface roughness. Ultraviolet-visible light absorption spectroscopy has shown a blue shift of both, the indirect and direct band gaps of hematite. The experimental results are interpreted as evidences of quantum confinement effects. This is facilitated by theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation. The agreement between theory and experiment supports the quantum confinement interpretation.     

The effect of SiO2 buffer layer on the electrical and structural properties of Al-doped ZnO films deposited on soda lime glasses

In this paper, the influence of SiO₂ buffer layer on electrical and structural properties of AZO films on soda lime glasses has been investigated. The results showed that the Hall mobility and carrier concentration of AZO films deposited on soda lime glasses at high temperature could be enhanced by introducing SiO₂ layers. The optical absorption edges of AZO films with SiO₂ buffer layer are blue shifted compared with that of buffer layer free due to the increase of carrier concentration. SiO₂ layers prepared at 400 °C more effectively suppress the diffusion of Na atoms into AZO films compared with that prepared at room temperature. On the other hand, the in-plane stress dependence of optical band gap is linear for AZO films deposited on quartz glass substrates, but is deviated from linearity in the case of soda lime glass substrates.     

Vacuum ultra-violet spectroscopic ellipsometry study of sputtered BeZnO thin films

This paper reports on a systematic investigation of the optical properties of BeZnO thin films fabricated by radio frequency reactive magnetron sputtering technique using vacuum ultraviolet spectroscopic ellipsometry (VUV-SE). The thicknesses and optical constants of the thin films were determined in the wavelength range 138–1650 nm, using VUV-SE through the Tauc–Lorentz and Gaussian models. Refractive indices and extinction coefficients of the thin films were determined to be in the range n = 1.58–1.99 and κ = 1.0 × 10⁻²⁷–0.37, respectively. The absorption coefficient and the optical bandgap energy were then calculated. Measurement of the polarized optical properties reveals a high transmissivity (>90%) and very low absorptivity (<4%) for BeZnO films in the visible and near infrared regions at different angles of incidence. From the angle dependence of the p-polarized reflectivity we deduced a Brewster angle of about 58.5°.     

Annealing of defect clusters in irradiated tungsten

Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in tungsten irradiated at reactor ambient tempeaature, ～ 70°C. Annealing, consisting of the growth and eventual elimination of the clusters, is observed to occur in two stages, one at temperatures below 435°C and one at temperatures above 740°C, which are interpreted as being due to interstitial and vacancy migration, respectively. The changes in defect cluster size and density are paralleled by similar changes in the measured strength of the material, and can be quantitatively correlated with the shear stress on the basis of a model of dislocation movement through a random array of obstacles.     

Accommodation coefficients for low-energy ions on metal surfaces

The interaction of low-energy ions (E = 3 to 100 eV) with the surface of a solid cannot be treated in terms of gas dynamics. The scattering of particles at an energy of E _o > 20 eV may be explained in terms of binary collisions with the atoms of the target. The validity of the single collision model with free surface atoms for medium energies from 10 to 100 eV and even down to 1 eV was confirmed on the basis of both experimental and computational data. This paper describes experimental studies of the secondary ion emission from the (100) and (110) faces of a Mo single crystal and both experimental and theoretical studies of alkaline ion accommodation coefficient on polycrystalline Mo within the energy range E = 3 to 50 eV with a varying direction of the primary ion beam from normal to the glancing angle of incidence (ρ = 0 to 75°). On the basis of the retarding potential method using a spherical condenser whose central electrode was the target, we measured the energy distribution of secondary ions. Calculations have been performed for the energy of scattered ions and the high energy portion of accommodation coefficient on the basis of single and double binary collisions using the Born-Mayer potential and taking into consideration the influence of adsorption forces at the surface of the target.     

Anisotropic angular distribution of sputtered atoms

The sputtering yield angular distributions have been calculated on the basis of the ion energy dependence of total sputtering yields for Ni and Mo targets bombarded by low-energy Hg⁺ ions. The calculated curves show excellent agreement with the corresponding Wehner's experimental results of sputtering yield angular distributions. This fact clearly demonstrates the intrinsic relation between the ion energy dependence of total sputtering yields and the sputtering yield angular distribution. This intrinsic relation had been ignored in Yamamura's papers [Yamamura, Y. (1982). Theory of sputtering and comparison to experimental data, Nucl. Instr. and Meth., 194, 515–522; Yamamura, Y. (1981). Contribution of anisotropic velocity distribution of recoil atoms to sputtering yields and angular distributions of sputtered atoms, Rad. Eff., 55, 49–55.] due to some obvious mistakes.