W. Paszkowicz

Extremely low temperature growth of ZnO by atomic layer deposition

We report on the zinc oxide (ZnO) thin films obtained by the atomic layer deposition (ALD) method using diethyl zinc and water precursors, which allowed us to lower deposition temperature to below 200 °C. The so-obtained “as grown” ZnO layers are polycrystalline and show excitonic photoluminescence (PL) at room temperature, even if the deposition temperature was lowered down to 100 °C. Defect-related PL bands are of low intensity and are absent for layers grown at 140−200 °C. This is evidence that extremely low temperature growth by ALD can result in high quality ZnO thin films with inefficient nonradiative decay channels and with thermodynamically blocked self-compensation processes.

Genetic Algorithms, a Nature-Inspired Tool: Survey of Applications in Materials Science and Related Fields

Genetic algorithms (GAs) are a helpful tool in optimization, simulation, modelling, design, and prediction purposes in various domains of science including materials science, medicine, technology, economy, industry, environment protection, etc. Reported uses of GAs led to solving of numerous complex computational tasks. In materials science and related fields of science and technology, GAs are routinely used for materials modeling and design, for optimization of material properties, the method is also useful in organizing the material or device production at the industrial scale. Here, the most recent (years 2008–2012) applications of GAs in materials science and in related fields (solid state physics and chemistry, crystallography, production, and engineering) are reviewed. The representative examples selected from recent literature show how broad is the usefulness of this computational method.

ZnO grown by atomic layer deposition: A material for transparent electronics and organic heterojunctions

We report on zinc oxide thin films grown by atomic layer deposition at a low temperature, which is compatible with a low thermal budget required for some novel electronic devices. By selecting appropriate precursors and process parameters, we were able to obtain films with controllable electrical parameters, from heavily n-type to the resistive ones. Optimization of the growth process together with the low temperature deposition led to ZnO thin films, in which no defect-related photoluminescence bands are observed. Such films show anticorrelation between mobility and free-electron concentration, which indicates that low n electron concentration is a result of lower number of defects rather than the self-compensation effect.

Rietveld refinement for indium nitride in the 105–295 K range

Results of Rietveld refinement for indium nitride data collected in the temperature range 105–295 K are presented. Acicular microcrystals of indium nitride prepared by reaction of liquid indium with nitrogen plasma were studied by X-ray diffraction. The diffraction measurements were carried out at the Swiss-Norwegian Beamline SNBL (ESRF) using a MAR345 image-plate detector. Excellent counting statistics allowed for refinement of the lattice parameters of InN as well as those of the metallic indium secondary phase. In the studied temperature range, the InN lattice parameters show a smooth increase that can be approximated by a linear function. Lattice-parameter dependencies confirm the trends indicated earlier by data measured using a conventional equipment. The relative change of both the a and c lattice parameters with increasing the temperature in the studied range is about 0.05%. The axial ratio slightly decreases with rising temperature. The experimental value of the free structural parameter, u=0.3769(14), is reported for InN for the first time. Its temperature variation is found to be considerably smaller than the experimental error. The thermal-expansion coefficients (TECs), derived from the linearly approximated lattice-parameter dependencies, are aa=3.09(14)x10-6 K-1 and ac=2.79(16)x10-6 K-1. The evaluated TECs are generally consistent with the earlier data. For the present dataset, the accuracy is apparently higher for both, the lattice parameters and thermal-expansion coefficients, than for the earlier results. The refined lattice parameter cIn of the indium secondary phase exhibits the known strongly nonlinear behavior; a shift (∆T equal about -50 K) of the maximum in cIn(T) dependence is observed with respect to the literature data..

X-ray powder diffraction data for indium nitride

X-ray powder diffraction pattern for InN synthesized using a microwave plasma source of nitrogen is reported. The data were obtained with the help of an automated Bragg-Brentano diffractometer using Ni-filtered Cu K α radiation. The lattice parameters for the wurtzite-type unit cell are a o =3.5378(1) A, c o =5.7033(1) A. The calculated density is 6.921±0.002 g / cm 3 .

XPS and XRD study of crystalline 3C-SiC grown by sublimation method

Abstract Preliminary XPS and XRD studies of the 3C-SiC polycrystals (with the grain size of order of 100 μm) grown by the sublimation method were performed. The XRD data proved a dominant 3C-SiC structure accompanied by an admixture of the residual 6H-SiC phase. The main core-level photoelectron spectra were analysed in detail. In particular, the C 1s level spectrum revealed a three peaks structure containing the peak indicative of free carbon as well as the remaining two identified as the carbidic components, centered at E B a =282.3 eV and E B b =283.4 eV. The fact, that the most intensive peak ‘a’ was found especially well resolvable in the acquired spectrum (as not observed in the earlier reports) was linked with a dominance of 3C-SiC phase and a relatively high lattice perfection of the crystals studied. Therefore, it enabled us a reliable identification of the main C 1s line component (peak ‘a’) as related to the C-Si bond in cubic Si 1− x C x crystal with slight deviation from stoichiometry (0.5 x ⪝0.54). On the other hand, the minor carbidic component (peak ‘b’) was ascribed to the C-Si bond in the highly C-saturated cubic Si 1− x C x ( x ≃0.6) compound that is present in the surface region.

Rietveld refinement for CuInSe2 and CuIn3Se5

Rietveld refinements for copper indium selenides CuInSe2 and CuIn3Se5 and their mixture were performed using data collected at a Bragg–Brentano diffractometer. The values of lattice parameters, axial ratio and positional parameters are discussed and compared to available literature data for single crystals and polycrystals. Results for CuInSe2 give a0=5.78149(1) A and c0=11.61879(4) A. The positional parameter x is determined to be equal 0.2271(4). Refinements for CuIn3Se5 give an indication concerning the choice of a structural model for this compound. Namely, the best fit is obtained for a model based on I42m space group, yielding a composition close to the experimental one and the lattice parameters a0=5.75812(2) A and c0=11.53593(7) A. Parameters of this model are discussed.

Composition dependence of the unit cell dimensions and the energy gap in Zn1-xMgxSe crystals

Zn1-xMgxSe mixed crystals were grown by the high-pressure Bridgman method in the x range 0.06 to 0.285. X-ray investigations show that with increasing Mg content the transition from a sphalerite structure to wurtzite occurs at x=0.185+or-0.03. After annealing in liquid zinc or zinc vapour, investigated crystals exhibit n-type conductivity as well as blue-violet and orange photoluminescence in the temperature range from 40 K to room temperature.

Magnetic properties of ZnMnO films grown at low temperature by atomic layer deposition

The authors demonstrate that by lowering deposition temperature of ZnMnO films (T<500°C) they can avoid Mn clustering and creation of inclusions of Mn oxides, which are frequently formed in ZnMnO layers grown by high temperature methods. Low temperature growth is achieved using atomic layer deposition and organic zinc and manganese precursors.

Raman scattering in α-In2Se3 crystals

Abstract A directional freezing method was used to obtain In 2 Se 3 crystals. Rietveld refinement of the diffraction data was performed. The Raman spectra of the α-phase of In 2 Se 3 were measured with polarized light in different configurations of the crystals. Phonon modes were assigned to the Raman tensors of the R3m space group. LO-TO splitting of the A modes were determined.