Effect of substrate temperature on the properties of reactively sputtered TiN/NbN multilayers

TiN/NbN multilayer coatings were deposited with various substrate temperatures by DC reactive magnetron sputtering method onto Si (111) and glass substrates. The effect of substrate temperature on the structural and optical properties of TiN/NbN multilayers was investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, Field emission scanning electron microscopy and Photoluminescence measurements. The composition was analyzed by X‐ray photoelectron spectroscopy. X‐ray diffraction results showed that the layers crystallized in cubic structure for TiN and hexagonal structure for NbN. It was found that grain size increased with increase in substrate temperature. The surface morphology of the TiN/NbN thin films showed a dense and smooth surface with substrate temperature upto 200 °C but after 300 °C, the grains became larger and coarse surface was observed. The TiN/NbN multilayer coatings exhibited the characteristic peaks centered at 180, 210 and 560 cm^‐1. Red band emission peaks were observed in the wavelength range of 700‐710 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology and Microstructure of TiN and Ti(N,C) Thin Layers

Thin layers of TiN and Ti(N, C) solid solution were obtained by the CVD process, making use of the following gas mixtures: TiCl₄–N₂–H₂ for TiN and TiCl₄–CCl₄–N₂–H₂ for Ti(N, C). The thin layers deposition processes were carried out in the temperature range from 900–1450 °C. As growth substrates were used polycrystalline Al₂O₃, graphite, W, Mo and Cu plates and also single crystal Al₂O₃ (leucosapphire), (111) Cu and (111) Si plates. The influence of certain technological factors on the morphology of the layers obtained was studied. TEM examinations were also made of the microstructure of the thin TiN layers and the Ti(N, C) solid solution layers deposited on polycrystalline and single crystal Cu plates. Factors responsible for the presence of a high density of dislocations in the tested films were ascertained.     

Growth of Epitaxial Layers of GaN from GaBr3 · 4 NH3 Complex

A method of obtaining GaN from GaBr₃ · 4 NH₃ by radiation heating of the substrate is described. The results of investigations are given concerning the growth rate of polycrystalline GaN layers on [111] oriented silicon substrates in dependence on the changes of the temperature of reaction, evaporation temperature of GaBr₃ · 4 NH₃, and the rate of gas flow. The results of X-ray investigations and light absorption coefficient are described. Some facts were observed, namely a considerable influence of the nozzle form on the kinetics of the transporting gas stream on the growth rate of GaN, as well as the fact that not the whole complex undergoes pyrolysis on the substrate at temperatures below 500°C.     

Influence of substrate temperature on the structure of ZnO:Al thin films

ZnO: Al films were prepared using low cost spray pyrolysis technique. The dependence of the physical properties on the substrate temperature was studied. The best films obtained at 500°C substrate temperature with preferred [002] orientation. The sheet resistance decreases with increased substrate temperature, and values as low as R_sh = 207 Ω/cm² are reached for substrate temperature of 500°C. The optical transmittance of films increased by increasing the substrate temperature and received to 75% at 500°C. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low temperature epitaxial growth of Ge on CaF2 buffered cube-textured Ni

Quasi-single crystal Ge films were grown on cube textured Ni substrate at a temperature of 350 °C using an insulating buffer layer of CaF₂. A direct deposition of Ge on Ni at 350 °C was shown to alloy with Ni. From x-ray pole figure analysis, it was shown that Ge grew epitaxially with the same orientation as CaF₂ and the dispersions in the out-of-plane and in-plane directions were found to be 1.7±0.1° and 6±1°, respectively. In the out-of-plane direction, Ge[111]6CaF₂[111]6Ni[001]. In addition, the Ge consisted of four equivalent in-plane oriented domains such that two mutually orthogonal directions: Ge〈2?11〉 and Ge〈01?1〉 are parallel to mutually orthogonal directions: Ni〈1?10〉 and Ni〈1?1?0〉, respectively, of the Ni(001) surface. This was shown to originate from the four equivalent in-plane oriented domains of CaF₂ created to minimize the mismatch strain between CaF₂ and Ni in those directions.     

Textural properties of AISb films

Textural studies have been carried out in AlSb films deposited by coevaporation method under high vacuum at different substrate temperatures between 450° to 625 °C. The films have been examined by X-ray and electron diffraction techniques. It was observed that the films deposited around 550 °C were found to exhibit [110] and [111] textures and the films deposited at higher substrate temperatures (above 600 °C) were found to exhibit only [111] textures.     

Epitaxy of CdTe on sapphire substrates with titanium buffer layers

The formation of a developed electrical relief on the sapphire substrate surface is investigated. A technique is proposed for introducing Ti⁴⁺ impurity atoms into the sapphire crystal lattice by depositing titanium layers with a thickness of about 5 nm and their annealing in air (oxidizing atmosphere) to a temperature of 1400°C. It is shown that this preliminary treatment of the sapphire substrate surface results in epitaxial growth of (111) СdTe films parallel to the sapphire (0001) plane at a temperature of 350°C.     

The Morphology of Hydrothermally Grown Plagioclase

Plagioclase crystals Ab₂₀An₀₀ and nearly pure anorthite were grown on the surface of artificial melts by hydrothermal treatment at 2 kb. The average crystal size was 0.002 to 0.008 mm. In the temperature range of 400° to 600°C a pseudohexagonal habit was observed for anorthite while a lath-like habit due to the prevalence of {010} was found for the Ab₂₀An₈₀ composition. Dominating faces are {010} {130} {110} {100} {110} {130} in the zone [001] and {021} {111} {111} {021} {111} {111} together with {001}.     

Kinetics of dissolution and calcium sulphate growth on {111} faces of calcium fluoride crystals etched in sulphuric acid

The effect of temperature (20–100°C) and concentration of H₂SO₄ etching solutions on the etching behaviour of {111} faces of calcium fluoride crystals is investigated. Whisker growth of calcium sulphate is observed. Temperature of the etchant also has an effect on their formation. The kinetics of dissolution at the sites of dislocations and general dissolution have been studied. Studies on induction period and its dependence on the concentration of the acid and temperature are also described. It is observed that: (i) at low and high acid concentrations, the dissolution is diffusion controlled while it is predominantly reaction-rate controlled in the intermediate concentration range and (ii) the growth rate of calcium sulphate whiskers decreases with time and their induction period decreases with increase in the temperature of the solution. The implications are discussed.     

Deformation behaviour of single crystals of GaP in uniaxial compression

LEC n-GaP:S single crystals were deformed in uniaxial compression parallel [321] and [110] direction. Plastic deformation by (111) slip has been observed between 511 °C and 717 °C. Indications for (111) twinning were obtained. Yield stress exhibits activation enthalpies U = Q(m + 2) and stress exponents m of U₃₂₁ = (0.54 ± 0.05) eV, U₁₁₀ = = (0.46 ± 0.05) eV, m = 1.1 ± 0.2 and m = 3 ± 1, respectively.     

Electrical and optical properties of titanium nitride coatings prepared by atmospheric pressure chemical vapor deposition

In order to examine the possibility for TiN coatings to be low-E, TiN coatings were deposited on the glass substrates by atmospheric pressure chemical vapor deposition using titanium tetrachloride (TiCl₄) and ammonia (NH₃) as precursors. X-ray diffraction, sheet resistance measurement, optical transmittance spectroscopy and infrared reflectance spectroscopy were carried out to determine the relationships between the preparation parameters and the microstructure, electrical and optical properties of the coatings. The results showed that the concentration of crystals increased with increasing the substrate temperature and the flow of TiCl₄, resulting in a decrease of the electrical resistivity. The optical transmittance of TiN thin films was strongly dependent on the gas flow and the substrate temperature. Under optimum conditions, continuous polycrystalline TiN coatings with FCC structure were obtained with an electrical conductivity around 34.5 Ω/□, an optical transmittance around 50% in the visible range, and an infrared reflectance higher than 50% above 3000 nm. This indicates that TiN coated glasses may be possible candidates for high IR reflectance windows.     

VLS Growth of ITO Whiskers Prepared by the Electron Shower Method

Indium tin oxide (ITO) whiskers were grown by VLS (vapour-liquid-solid) mechanism, using the electron shower method. The whiskers were grown above 200 °C, and the deposition rate was above 0.6 nm/s. The electron shower controlled the size of the whiskers, and the size was 30 nm in diameter and 600 nm in length. The whiskers grew along the substrate at t < 300 s, but grew in a direction perpendicular to the substrate at t > 300 s. When the ITO whiskers grown along the substrate were used as NO₂ gas sensor, the sensitivity was 340, and about 300 times higher than those of the whiskers grown in a direction perpendicular to the substrate and plate-like ITO crystallites.     

The influence of low-temperature annealings on the structural and superconducting properties of Bi 2212 and Bi 2201 whiskers

The influence of post-growth short-term low-temperature annealings (O₂, 400°C, 5–15 min) on the composition, crystal structure, and superconductivity of Bi₂Sr₂CaCu₂O_{8 + δ} and Bi₂Sr₂CuO_{6 + δ} oxycuprate whiskers freely grown in gas cavities has been investigated. The optimal conditions for growth in closed gas cavities in a flux and post-growth annealing in oxygen were found, making it possible to obtain high-quality superconducting Bi 2212 and Bi 2201 whiskers in a wide doping range (from heavily underdoped to optimally doped) with a small rocking curve half-width (～0.1^°–0.2^°) and narrow superconducting transition (ΔT = 1.5–2 K).     

Effects of CdCl2 treatment on properties of CdTe thin films grown by evaporation at low substrate temperatures

The structural, morphological and optical properties of vacuum‐evaporated CdTe thin films were investigated as a function of substrate temperature and post‐deposition annealing without and with CdCl₂/treatment at 400°C for 30 min. Diffraction patterns are almost the same exhibiting higher preferential orientation corresponding to (111) plane of the cubic phase. The intensity of the (111) peak increased with the CdCl₂/annealing treatment. The microstructure observed for all films following the CdCl₂/annealing treatment are granular, regardless of the as‐deposited microstructure. The grain sizes are increased after the CdCl₂/annealing treatment but now contain voids around the grain boundaries. The optical band gaps, E_g, were found to be 1.50, 1.50 and 1.48 eV for films deposited at 200 K and annealed without and with CdCl₂/treatment at 400°C for 30 min respectively. A progressive sharpening of the absorption edge upon heat treatment particularly for the CdCl₂/treated was observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and dielectric properties of Ta2O5 single crystal by the floating zone method

Large Ta₂O₅ single crystal with high‐dielectric permittivity was successfully grown by floating zone (FZ) method under air atmosphere. The grown crystal that has been obtained was typically about 8 mm in diameter and 90 mm in length. The crystal growth parameters were optimized. The crystal symmetry, characterized by means of X‐ray diffraction (XRD), was found to be tetragonal. The relative permittivity and loss tangent along growth and [001] direction were measured in the temperature range between ‐200 °C and 200 °C, which showed a strong dielectric anisotropy. At a frequency of 1 MHz and 20 °C, the dielectric permittivity along the growth direction and [001] direction are 81.17 and 25.04 respectively. The stabilization of high‐temperature phase can explain the dielectric enhancement.     

Defect Structure of Strained Heteroepitaxial In(1—x)Al(x)P Layers Deposited by MOVPE on (001) GaAs Substrates

Weak-beam, large angle convergent beam electron diffraction and high resolution transmission electron microscope experiments have revealed, that after strain relaxation due to plastic deformation dislocation networks can be observed in In_(1—x)Al_(x)P heteroepitaxial layers grown on (001) GaAs substrates under compressive stress. The 60° slip dislocations are mostly dissociated into partials of Shockley type whereas in the particular case of layers grown under tension twins are predominantly formed by successive nucleation and slip of 90° Shockley partials on adjacent {111} glide planes lying inclined to the (001) surface. When a few 90° Shockley partials pile up during extension of twins, then planar incoherent twin boundaries with {112} coincidence planes have been formed during strain relaxation. Due to the space group symmetry ((InAl)P belongs to the space group F4-3m) there is a striking asymmetry in defect formation, i.e. defect nucleation and slip on the planes (111) and (1-1-1) slip of the [1-10] zone are preferred to nucleation and slip on the {111} planes of the [110] zone. Apparently, the occupacy of the atomic sites in the dislocation core with either group-III or group-V atoms is responsible for this behaviour. The nature of the defects implies that their spontaneous nucleation should have taken place at the growing surface. Under tensile strain the 90° Shockley partial is nucleated first and the 30° one trails. Under compressive strain this sequence is reversed. It is evident, for dissociated dislocations lying at the interface always the 30° partial, i.e. the partial with less mobility or with higher friction force, is detained near or directly in the interface. Thus, in layers grown under tension the stacking fault associated with the dissociated 60° dislocation lies inside the GaAs substrate. For layers grown under compression it is located inside the ternary layer.     

A Gamma-ray Diffraction Study of MBE-Grown CaF2/Si(111) Heterostructures

MBE grown epitaxial films of CaF₂ onto Si(111) substrates were investigated by gamma ray diffraction to obtain assertions about the real structure and the strain situation in the epitaxial systems. It were measured the integral reflection coefficient R_i and the angle distribution of the reflected intensity of both (111) and (333) reflections. It was found that (i) a high temperature annealing step during the wafer preparation (1200 °C) causes a drastical increase of real structure defects in the substrate material, (ii) expitaxial layers of 18 nm thickness are grown pseudomorphically, layers having a thickness of 30 nm are relaxed, (iii) the misfit dislocation network formed during the relaxation process is localized not in the deposit but in the substrate material.     

Study of imperfections in iron whiskers

Iron whiskers grown by hydrogen reduction of ferrous chloride were studied by several X-ray and optical techniques, particularly by X-ray diffraction topography. 36 whiskers with [100], [110] and [111] axis directions, from 20 μm to 260 μm in thickness were investigated. They were of different degree of perfection with dislocations nonuniformly distributed. Three [111] whiskers showed a lattice twist around the axis. Burgers vectors of several frequent types of dislocations were found.     

Growth of tungsten whiskers oriented in <111> direction

The electron micro diffraction technique and pseudopotential ab initio calculations were implemented to study in details the formation and mechanism of growth of the tungsten whiskers during the reduction of nickel tungstate by CO gas. It has been shown that the W whiskers prefer to grow as crystals oriented in the <111> direction, and this process may be considered as the epitaxial growth on the hexagonal planes of Ni₄W particles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of KGd(WO4)2 single crystals studied by Brillouin spectroscopy

The results of a study of KGd(WO₄)₂ single crystals by Brillouin scattering method are presented. The Brillouin spectra for the acoustic phonons propagating in the [100], [010], [001], [110] and [101] directions, taken in 90° and 180° scattering geometry at room temperature have been recorded. Using the Brillouin spectroscopy the refractive indices for some directions of KGd(WO₄)₂ crystals were determined. The refractive indices were also calculated for the same directions by the rotation transformation of the principal optical axes of the optical indicatrix to the crystallographic directions of KGd(WO₄)₂ crystals. Moreover, some anomalies of the acoustic phonons propagating connected with birefringence of KGd(WO₄)₂ crystals were discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)