Quantitative analysis of graded Cu(In1−x,Gax)Se2 thin films by AES, ICP-OES, and EPMA

The overall composition and the compositional profile of the quaternary semiconductor Cu(In_1−x,Ga_x)Se₂ (CIGS) have strong effects on the performance of photovoltaic devices based on it. Recent work that has yielded ∼20% efficient solar cells based on CIGS has forced extra attention on quantitative analysis of the absorber layers. In this paper we present details of the procedures used to generate detailed compositional profiles of graded Cu(In_1−x,Ga_x)Se₂ thin films by Auger electron spectroscopy (AES) that when integrated, agree quantitatively with inductively-coupled plasma optical emission spectrometry (ICP-OES) data on the same films. The effects of sample rotation during sputter depth profiling on the quantification results are described. Details of the procedures used for the ICP-OES and wavelength-dispersed electron probe microanalysis (EPMA) analyses are also presented. Finally, we show why X-ray microanalysis techniques alone should not be used to argue that specific windows of copper and gallium concentrations can yield high performance devices.     

Population analysis solution to hardness enhancement in TiCxN1−x

We investigated the hardness enhancement in titanium carbonitrides (TiC_xN_1−x) by the population analysis method based on first-principles calculations. Populations for bonds TiC and TiN in TiC_xN_1−x (0.25<x<0.75) are all positive. The enhanced hardness for titanium carbonitrides is well explained by overlap population analysis. Intrinsic hardness of TiC_xN_1−x has been calculated based on the obtained overlap populations. The calculated results are in good agreement with the available experimental data.     

Low energy Auger electron spectroscopy of titanium nitrides for quantitative analysis

The potential of the low energy (20–30 eV) region of the Auger spectrum of titanium nitrides for quantitative analysis has been examined. Nitride films were prepared by nitrogen ion implantation and adsorption at 300 and 900 K and subject to Auger electron analysis in both the low and high energy regions, The nitrogen concentration of implanted films will be uniform over the analysed depth and could be determined by spectrum simulation of the high energy region, a technique described previously. This method permitted an internal calibration of the low energy Auger spectrum against nitrogen composition. The low energy spectrum contains two major features which vary in intensity, and energy, with x, the N/Ti atom ratio: Peak A, present in the pure Ti spectrum and assigned to the Ti(3p)Ti(3d)Ti(3d) transition, has an intensity which decreases linearly with x, whereas peak B, present in the stoichiometric nitride and attributed to the Ti(3p)Ti(3d)N(2p) cross transition, has an intensity which reaches a maximum at x = 0.05. The linear decrease in peak A intensity was ascribed to the linear decrease in the number of unoccupied octahedral holes with x. Occupied intrahole and occupied-unoccupied inter-hole transitions make a contribution to peak B and the latter will pass through a maximum at x = 0.5. The low energy spectrum calibration permitted depth profiles to be determined for adsorbed films at 300 and 900 K. In the latter case both methods gave the same result because rapid diffusion produces a film uniform over the analysed depth. For adsorbed films produced at room temperature the high and low energy results were quite different, reflecting the increased depth resolution of the low energy electrons.     

Magnetic,electronic and structural properties of ZnxFe3−xO4

A series of samples Zn_xFe_3−xO₄ have been prepared by the chemical coprecipitation technique and characterized by X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and X-ray photoelectron spectroscopy (XPS). XRD demonstrates all the samples of Zn_xFe_3−xO₄ have a spinel structure same as Fe₃O₄. The magnetic hysteresis loops of Zn_xFe_3−xO₄ obtained from VSM indicate that the saturation magnetization has a maximum when x is ∼1/3. The chemical states of Fe atoms and Zn atoms in zinc ferrites have been measured using XPS and Auger electron spectroscopy (AES). The Fe 2p core-level XPS spectra and Zn L₃M₄₅M₄₅ Auger peaks have been analyzed and the results have been discussed in correlation with the samples’ magnetic properties. These results suggest most of Zn atoms occupy the tetrahedral sites and a small amount of them occupy the octahedral sites.     

Characterization of In/Pd and Pd/In/Pd thin films by ellipsometric, XRD and AES methods

In/Pd and Pd/In/Pd thin films were prepared by thermal evaporation on the SiO₂ substrate in a vacuum. The structural and optical properties of the films were investigated by means of X-ray diffractometry (XRD), Auger electron spectroscopy (AES) and spectroscopic ellipsometry (SE). Auger depth profile studies were performed in order to determine the composition of elements in the Pd-In systems. Interdiffusion of metals was detected at room temperature. Optical properties of Pd-In composite layers formed due to the interdiffusion were derived from ellipsometric quantities Ψ and Δ measured in the photon energy range 0.75-6.50 eV at different angles of incidence. The effective optical spectra show absorption peaks dependent on the composition of nonuniform films. The XRD patterns indicated formation of Pd_1−xIn_x intermetallic phases in the samples.     

SCANNING AUGER ELECTRON SPECTROSCOPIC INVESTIGATIONS OF MAGNETOSTRICTIVE NANOSCALE MULTILAYERS

The characterisation of thin magnetostrictive multilayers in the nanometerscale range [(4,5nmTb₄₀Fe₆₀/9nmFe)×100] demands a surface sensitive analytical technique. A suitable technique is scanning Auger Electron Spectroscopy (AES) to determine the elemental composition, the thickness, the presence of interdiffusion between thin layers, or the presence of contamination at interfaces.Auger sputter depth profiles are obtained by using Xe-Ion bombardment to etch the sample.Sample rotation during sputtering produces shallow craters, minimises roughening and enhances depth resolution. In addition, Auger maps of the craters are used to reveal the separated magnetostrictive Tb₄₀Fe₆₀ layers and soft magnetic Fe layers.     

Structural characterization of InxGa1−xAs/Inp layers under different stresses

In_xGa_1−xAs layers on InP substrate can be subjected to compressive or tensile strain due to lattice parameter differences depending on the alloy composition. In order to examine in details the strain of InGaAs/InP epiatxial layers and its evolution after subjecting the layers to annealing at high pressure, X-ray synchrotron topography, high resolution X-ray diffraction and atomic force microscopy have been employed. The data show that the changes of structural properties of the InGaAs layers subjected to high temperature-high pressure treatment at 670 K-1.2 Gpa, strongly depend on initial strain state and defect structure. The annealing of samples under high pressure results in change of strain in tensile layers only. The behaviour of observed defects is discussed.     

Chemical vapor deposition of ZrxTi1−xO2 and HfxTi1−xO2 thin films using the composite anhydrous nitrate precursors

Zr-Ti and Hf-Ti composite nitrates were successfully developed as single-source precursors for the chemical vapor deposition (CVD) of Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ thin films. The Zr-Ti nitrate can be assumed as a solid solution of the individual Zr and Ti nitrates, and the Zr/Ti molar ratio in the deposited Zr_xTi_1−xO₂ films is consistent with that in the precursor. The Hf-Ti nitrate appears to be a mixture of the Hf and Ti nitrates and the composition of the deposited Hf_xTi_1−xO₂ films depends remarkably on the heating time of precursor. Both Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ films exhibit trade-off properties between band gap and dielectric constant. The obtained results suggest that Zr_xTi_1−xO₂ and Hf_xTi_1−xO₂ films are promising candidates for gate dielectric application to improve the scalability and reduce the leakage current of the future complementary metal-oxide-semiconductor (CMOS) devices.     

Auger parameters of ternary Pd–Ni–P amorphous alloys

A series of bulk ternary amorphous alloys of Pd_{100?3 x} Ni_{2 x} P _x were prepared and their amorphicity checked by X-ray diffraction (XRD) and neutron scattering. Auger parameters of these alloys have been derived from X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectra (AES). Experiments of XPS and AES on each elemental metal and Ni₂P were also performed for comparison. The results show a clear compositional dependence for the 3d binding energies and the MNN Auger energies of Pd on alloying, while Ni 2p core levels and the Ni LMM Auger lines show a weaker variation. Analysis of the data using “excited atom” models indicates electron transfer from Pd, with P carrying negative charge, but the differences in behaviour of the two metallic species suggests that covalent bonding changes may be significant.     

Spin resonant optical four wave mixing in Pb1−xSnxTTe epitaxial layers and in Pb1−xSnx/PbTe superlattices

Spin resonances of the third-order non-linear susceptibility of epitaxial layers of n- and p-type Pb_1?xSn_xTe and Pb_1?xSn_xTe/PbTe superlatttices have been observed by four photon mixing of the radiation of two CO₂-lasers. Precise data on the effective g-values of the electrons and holes of Pb_1?xSn_xTe were obtained. These data and the results of magneto-optical interband absorption measurements are used to obtain k·p parameters within the Mitchell and Wallis band model. In the Pb_1?xSn_xTe/PbTe superlattices, the same g-values for electrons as in the Pb_1?xSn_xTe films with the same composition x are found. Consequently, the electrons in the superlattices are confined within the Pb_1?xSn_xTe layers. Therefore the Pb_1?xSn_xTe/PbTe system forms a type I and not a staggered superlattice.     

Optimization of growth parameters for MOVPE-grown GaSb and Ga1−xInxSb

The triethylgallium/trimethylantimony (TEGa/TMSb) precursor combination was used for the metal-organic vapour phase epitaxial growth of GaSb at a growth temperature of 520 °C at atmospheric pressure. Trimethylindium was added in the case of Ga_1−xIn_xSb growth. The effects of group V flux to group III flux ratio (V/III ratio) on the crystallinity and optical properties of GaSb layers are reported. It has been observed from the crystalline quality and optical properties that nominal V/III ratios of values greater than unity are required for GaSb epitaxial layers grown at this temperature. It has also been shown that Ga_1−xIn_xSb can be grown using TEGa as a source of gallium species at atmospheric pressure. The relationship between Ga_1−xIn_xSb vapour composition and solid composition has been studied at a V/III ratio of 0.78.     

Surface TiHn as the catalytically active species for the hydrogen absorption by TiFe; a SX-APS investigation supplemented by AES

The interaction of hydrogen with the surface of previously cleaned TiFe samples was investigated by means of Soft X-Ray Appearance Potential Spectroscopy (SX-APS) and Auger Electron Spectroscopy (AES). The access of oxygen (air) was carefully prevented by performing all experiments “in-situ” in an UHV-chamber. At about 800°C the hydrogen interaction with the TiFe surface leads to extensive Ti segregation. As observed by SX-APS, iron is displaced by titanium on the whole surface of the sample (about 1.5 cm²). From AES depth profiles the Ti overlayer is estimated to have a thickness of about 100 monolayers. In this region Fe is completely absent. No enrichment of Fe beyond this region could be detected; the Fe concentration increases monotonously from zero to the bulk value. From these results it is obvious that the hydrogen absorption/desorption of TiFe is catalytically activated by Ti species rather than by Fe species. The chemical state of the surface is discussed.     

Molecular dynamics simulations on local structure and diffusion in liquid TixAl1−x alloys

The microscopic structure and dynamics of liquid Ti_xAl_1-x alloys together with pure liquid Ti and Al metals were investigated by means of molecular dynamics simulations. This work gives the structural properties, including pair-correlation function, bond-angle distribution function, HA and Voronoi indices, and their composition dependence. The dynamical properties have also been studied. The calculated pair-correlation function, bond-angle distribution function, and HA and Voronoi indices suggest that the stoichiometric composition Ti_0.75Al_0.25 exhibits a different local structure order compared with other concentrations, which help us understand the appearance of the minimum diffusion coefficient at this composition. These results indicate that the mobility of atoms strongly depends on their atomic local structure.     

Preparation and annealing study of TaNx coatings on WC-Co substrates

To prevent Co diffusion from cemented carbides at high temperatures, we fabricated TaN_x coatings by reactive direct current (d.c.) magnetron sputtering onto 6 wt.% cobalt cemented carbide substrates, to form diffusion barrier layers. Varying the nitrogen flow ratio, N₂/(Ar + N₂), from 0.05 to 0.4 during the sputtering process had a significant effect on coating structure and content. Deposition rate reduced as the nitrogen flow ratio increased. The effects of nitrogen flow ratio on the crystalline characteristics of the TaN_x coatings were examined by X-ray diffraction. The TaN_x coatings annealing conditions were 500, 600, 700, and 800 °C for 4 h in air. We evaluated the performance of the diffusion barrier using both Auger electron spectroscopy depth-profiles and X-ray diffraction techniques. We also investigated oxidation resistance of the TaN_x coatings annealed in air, and under a 50 ppm O₂-N₂ atmosphere, to evaluate the fabricated layers effectiveness as a protective coating for glass molding dies.     

The structure and luminescence properties of long afterglow phosphor Y3−xMnxAl5−xSixO12

A series of phosphors with the composition Y_3−xMn_xAl_5−xSi_xO₁₂ (x=0, 0.025, 0.050, 0.075, 0.150, 0.225, 0.300) were prepared with solid state reactions. The X-ray powder diffraction analysis of samples shows that the substitution of Mn²⁺ and Si⁴⁺ does not change the garnet structure of phosphors, but makes the interplanar distance decrease to a certain extent. The emission spectra show that Mn²⁺ in Y₃Al₅O₁₂ emits yellow-orange light in a broad band. With the increment of substitution content, the emission intensity of the phosphors increases firstly then decreases subsequently, and the emission peak moves to longer wavelength. Afterglow spectra and decay curves show that all the Mn²⁺ and Si⁴⁺ co-doped samples emit yellow-orange light with long afterglow after the irradiation of ultraviolet light. The longest afterglow time is 18 min. Thermoluminescence measurement shows that there exist two kinds of traps with different depth of energy level and their depth decreases with the increment of substitution content.     

Hall to drift mobility ratio in Ga1−xAlxAs alloys

Hall concentration measurements as a function of temperature ($\text{750 ? T ? 77}\text{K}$) on n-type epitaxial layers of Ga_1?xAl_xAs in the composition range $\text{0 ? x ? 0.78}$, have been used to evaluate the composite dependence of the Hall to drift mobility ratio in this alloy at 300 K. This ratio is found to be close to unity for alloy compositions $\text{0 ? x ? 0.25}$ and $\text{0.6 ? x ? 0.78}$, but attains a maximum value of 3.8 at x = 0.42 due to the multiconduction Hall effect.     

A neutron powder diffraction study of the helimagnetic structure of TlCo2Se2−xSx

The magnetic layer structure of TlCo₂Se_2−xS_x has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged within the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo₂Se₂ form a helix along the c-axis with a turning-angle of ∼119° at 1.4 K. This kind of helical structure prevails for 0≤x≤1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34°, showing an almost linear relationship with the interlayer distance of Co-Co. For x≥1.75 the interlayer coupling changes to ferromagnetic. Unexpectedly, two helices were found to coexist at x=0.5 and x=1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106°, resp., 73°) together with a commensurate angle of 90°. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites.     

Synthesis and ferroelectric properties of bismuth layer-structured (Bi7−xSrx)(Fe3−xTi3+x)O21 solid solutions

Bismuth layer-structured (Bi_7−xSr_x)(Fe_3−xTi_3+x)O₂₁ (BSFT) ceramics were synthesized and the ferroelectric properties and crystal structure were investigated. X-ray powder diffraction profiles and refinement of the lattice parameters indicated single phase BSFT was obtained in the composition range 0-1.5. The lattice parameter b of BSFT remained almost constant, while a slight decrease in the lattice parameter a was observed by the Sr and Ti substitution for Bi and Fe, respectively, which indicated an increase in the orthorhombicity. The dependence of the BSFT lattice parameter on temperature implied a phase transition from the orthorhombic to the tetragonal phase, which was in good agreement with the Curie temperature. The remnant polarization P_r, of BSFT was significantly improved by the Sr and Ti substitution for Bi and Fe, and ranged from 9 to 16 μC/cm², although no remarkable variation in the coercive field E_c was observed. As a result, a well-saturated P-E hysteresis loop of BSFT ceramic was obtained at x=0.5 with a P_r of 30 μC/cm at an applied voltage of 280 kV/cm.     

Soft x-ray absorption and high-resolution powder x-ray diffraction study of superconducting CaxLa1−xBa1.75−xLa0.25+xCu3Oy system

We have studied the electronic structure of unoccupied states measured by O K-edge and Cu L-edge x-ray absorption spectroscopy (XAS), combined with crystal structure studied by high resolution powder x-ray diffraction (HRPXRD), of charge-compensated layered superconducting Ca_xLa_1−xBa_1.75−xLa_0.25+xCu₃O_y (0≤x≤0.4 and 6.4≤y≤7.3) cuprate. A detailed analysis shows that, apart from hole doping, chemical pressure on the electronically active CuO₂ plane due to the lattice mismatch with the spacer layers greatly influences the superconducting properties of this system. The results suggest chemical pressure to be the most plausible parameter to control the maximum critical temperatures (T_c^max) in different cuprate families at optimum hole density.     

Evidence by Raman scattering on In1−xGaxAsyP1−y of the two-mode behaviour of In1−xGaxP

We report the Raman scattering study of optical vibrations in indium rich In_1?xGa_xAs_yP_1?y epitaxial layers grown on InP. We evidence the splitting of the LO line of InP even for very small x and demonstrate it is due to the presence of gallium in the samples. These results lead us to ascribe to In_1?xGa_xP a somewhat modified two-mode behaviour and to In_1?xGa_xAs_yP_1?y a four-mode behaviour.