Cw argon laser crystallization of silicon films: Structural properties

This paper deals with the structural characterization of amorphous silicon films deposited on glass in the amorphous state and then post-crystallized using a continuous wave argon laser. In opposite to the excimer laser crystallization method, the processing window is wider. Due to the low cooling rate induced by the continuous irradiation, very large grains are obtained. With an epitaxial growth induced by an adequate overlapping of the laser traces, grains as large as 100 μm can be reached. Electron back-scattered diffraction analysis highlights the single crystalline character of the large size grains crystallized with this kind of laser. The technique is able to produce large area single crystalline regions, suitable to fabricate high speed circuits.     

Structural and electrical properties of epitaxial metal films grown on argon ion bombarded and annealed (001)InP

A study has been made of intimate metal-InP contacts prepared by metal beam epitaxy in ultra-high vacuum Oxygen and carbon contamination was removed from the (001)InP surface by bombardment with 500 eV Ar⁺ ions. On annealing to 250°C, In islands appeared on the surface and c(2×8) reconstruction was observed. Gold and silver films were found to grow epitaxially on the InP at ?40°C but the electrical properties indicate greatly reduced Schottky barrier heights and non-ideal current-voltage characteristics which may be attributed to non-stoichiometry and damage at the semiconductor surface resulting from the ion bombardment.     

Density fluctuations in silicate glasses

The potential use of inorganic glasses as waveguides at optical wavelengths has precipitated the need to understand the relationship between intrinsic optical loss and glass composition. The contribution to optical loss due to scattering from density fluctuations, is analyzed and discussed for various homogeneous (non-phase-separated) silicate glasses. The results show that binary alkali silicates in certain composition ranges form homogeneous glasses with density fluctuations less intense than that of pure silica glass. As third components added to these binary compositions alkali oxides (different from the one already present in the base glass), alkaline earth oxide (CaO) and Al₂O₃ cause further reductions in the magnitude of the density fluctuations.     

The role of argon in yttrium aluminates

Spectral properties of YAG and YAP grown in vacuum or under Ar H₂ protective atmosphere were compared. The latter contained small amounts of argon which was detected by a laser mass spectral analysis. Ar impurity evokes brown colour of unannealed crystals and strenghtens anomalous red colour of annealed (Particularly in O₂) YAP crystals doped with Nd + Cr or Nd + Mo. The same red coloration of the doped YAGs is less stable.     

Local fluctuations and FDR violations in aging glass

Dipolar fluctuations were measured in both macroscopic samples, and locally in mesoscopic volumes of polymer glass. Following a temperature quench, the macroscopic measurements revealed fluctuation–dissipation-relation (FDR) violations with a complex dependence on aging time and measurement frequency. New results on imaging mesoscopic spatio-temporal fluctuations, and the possibility of using this technique to study the heterogeneity of aging and local FDR violations will be discussed.     

On orientational fluctuations in nematic liquid crystals

The factors determining the spectral density of intrinsic optical noise of a nematic liquid crystal (NLC), caused by fluctuations of director orientation in a frequency range of 0.01–1 Hz, have been experimentally established for the first time for (10–100)-μm layers, characterized by rigid anchoring at the boundaries and a quasi-homeotropic macrostructure. A model developed for estimating the spectral density of this noise for an NLC layer with a previously deformed macrostructure and finite molecular anchoring energy has been approved.     

Electron irradiation-induced dynamical fluctuations in amorphous structures

High resolution, transmission electron microscopy results of dynamic observations during the electron irradiation of amorphous phases are presented. The granular image contrast, typical in amorphous structures, fluctuates continuously during high flux irradiation. The fluctuations tend to occur locally in the structure, whereas crystalline regions remain stable. Some local structures are identified during the fluctuations and anisotropic movements are observed at surfaces and interfaces. The phenomenon is attributed to the irradiation-induced instability of a random cluster network, resulting in a decrease of the viscosity and local deformation.     

The role of argon in plasma-assisted deposition of indium nitride

Radiofrequency (RF) nitrogen plasma sources are commonly employed in the growth of group III-nitrides by molecular beam epitaxy and reactive evaporation. These sources produce atomic nitrogen and excited molecules (N₂*). In this work the relative flux of these two species produced by an RF source was studied by emission spectroscopy as a function of power, pressure, and argon dilution. Polycrystalline indium nitride thin films were synthesized under the same conditions. It was found that argon dilution had a strong influence on the production of active nitrogen, with maximum fluxes obtained around ∼40% N₂. Film properties, as measured by X-ray diffraction, atomic force microscopy and Hall effect, were also optimized at this condition. It was observed that the Hall mobility scaled with the sum of N and N₂* emission, suggesting that both species may be beneficial for InN growth.     

Role of concentration fluctuations in metallic glass formation

The glass forming composition range in several binary metallic systems is correlated with the composition dependence of S_cc(0), the concentration-concentration fluctuation structure factor at its long wavelength limit. The magnitude of S_cc(0) has been evaluated for the liquid phase from available thermodynamic data. It has been observed that S_cc(0) exhibits a maximum and tends to the ideal value in the glass forming composition range. Significant and systematic negative deviations from ideal values or the tending to zero of S_cc(0) are observed at the stoichiometry corresponding to complexes in the liquid state in the case of compound forming or associated systems. These observations are discussed in terms of the chemical short-range order in the liquid state. It is concluded that while a reasonable degree of order may exist for the compound forming compositions, in the glass forming region itself the liquids are nearly random mixtures of complexes and unassociated component atoms.     

Structure and thermal fluctuations in thin films of smectic liquid crystals

Thermal fluctuations of the smectic layers in freely suspended thin liquid crystalline films have been studied by the methods of X-ray diffraction and reflectometry. The fluctuation dynamics is studied by the methods of photon correlation spectroscopy with the use of a source of coherent synchrotron radiation. In freely suspended smectic films, the typical relaxation times are of the order of several microseconds. In thin liquid crystalline films, the simultaneous damped and oscillatory behavior was observed for the layer undulations.     

The influence of heat-dissipation and temperature fluctuations on SbSI crystallization in thin layers

Single crystal films of SbSI 5 to 100 μ in thickness have been obtained by crystallization from melts in a close spacing. The films crystallized under conditions under conditions of direct heat -dissipation and periodical fluctuations of temperature near the melting point. The phase transition in the films was revealed by means of capacity measurements at temperatures of ∼ 20 °C.     

Effect of fragility on relaxation of density fluctuations in glass

Density fluctuations play a crucial role in governing the optical, mechanical, thermodynamic, and kinetic properties of glass. The relaxation of density fluctuations displays an inherently nonmonotonic behavior, yielding a minimum in fluctuations following a quench and isothermal hold. Here we investigate the impact of liquid fragility on the relaxation of density fluctuations in the nonequilibrium glassy state. While fragility has a direct impact on the kinetics of the relaxation process, the minimum level of density fluctuations is unaffected by changes in fragility alone. The magnitude of density fluctuations can be minimized by tailoring the thermal history of the glass.     

Volume fluctuations in potassium silicate glass studied by molecular dynamics

Potassium-silicate glass, 0.05K₂O·0.95SiO₂, was prepared by molecular dynamics under three different regimes (cooling rates, simulating box sizes) to study their influence to temperature regimes of volume fluctuations. Partial volume fluctuations (VF) were introduced with the help of Voronoi polyhedra tessellation. Dynamic and static fluctuations were suggested as a measure for time- and space-related fluctuations. Separation of the dynamic and static VFs anticipates glass transition. The glass transition was related with the change of the temperature course of the static VFs. The dynamic VFs changed their temperature regimes well below the glass transition and the transition temperature was related with the change of the transport regime. Glass transition cages the atoms but Voronoi polyhedra are definitely shaped well below the glass transition temperature.     

The estimation of concentration fluctuations in liquid Ag–Si and Au–Si alloys

The specific electrical resistivity was measured for liquid states of Ag–Si and Au–Si with deep eutectic points for which the ‘electron atom ratio’ at the eutectic composition is 1.33 and 1.56, respectively. On lowering the temperature, the specific electrical resistivity deviates from the straight line, which was obtained by extrapolating its behavior from high to low temperatures. The concentration dependence of this deviation at the liquidus shows the largest value at the eutectic composition. The analysis based on the effective medium theory tells us that the volume fraction of concentration fluctuation in the homogeneous liquid phase is largest at the eutectic composition. The degree of concentration fluctuation was summarized on one systematic trend among metal–semiconductor eutectic systems. It is concluded that the large concentration fluctuation develops in the homogeneous liquid phase of eutectic systems. The possibility of the poor supercooling tendency of homogeneous liquids at the eutectic composition was revealed with relation to this concentration fluctuation.     

Structural and optical properties in gadolinium-aluminum-lead-germanate quaternary glasses

Glasses in the quaternary system 0.05Al₂O₃·0.95[xGd₂O₃·(100-x)(7GeO₂·3PbO)] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. In this paper, we investigated structural and optical properties in gadolinium-alumino-lead-germanate glasses through investigations of FTIR (Fourier-Transform Infrared Spectroscopy) and UV-VIS (Ultra-Violet) spectroscopy.The observations presented in these mechanisms show that by increasing Gd₂O₃ content up to 40 mol%, the glass network modification has taken place mainly in the germanate part, while the excess of oxygen can be accommodated in the host network by the creation of shorter rings of [Ge₂O₇] structural units and the formation of [AlO₄] structural units. The affinity pronounced of the gadolinium cations towards germanate structural units produces the formation of the Gd₂Ge₂O₇ crystalline phase.The UV-VIS spectroscopy data show the charge transfer transitions of Pb^+ 2-O^− 2, Al^+ 3-O^− 2 and Gd^+ 3-O^− 2, respectively. The additional absorption in the range of 300 to 600 nm was attributed to other types of defects such as: non-bridging oxygen ions, change in valency of ions and other color centers.The values of the direct optical band gap of the glasses are determined from the optical absorption spectra. By increasing Gd₂O₃ content in the glass matrix, the optical band gap energy increases indicating changes of the lattice parameters by Gd₂O₃ incorporation.     

Structural defects and their genesis in corundum monocrystals

Besides the formation of dislocations and block boundaries behind the crystallization front, there is much experimental evidence indicating the presence of rather big aggregates in various crystal-forming media. Experimental facts are given proving them to exist in Al₂O₃ melt. The perfection of a grown crystal depends on aggregation degree of the melt which can be controlled by both impurity cncentration and supercooling of the melt. E.g. in Verneuil-grown crystals a change in Cr concentration from 1 ṁ 10⁼³ to 1% leads to a change in aggregate sizes from 100 to 1000 Å. With Stepanov-, Czochralski-, and horizontally directed crystallization methods a variation in supercooling the melt enables to change the size of the aggregates from 150 to 400 Å. High values of the diffusion coefficient are accounted for by a higher concentration of the holes. The main reason increasing the number of holes in the crystals grown by the mentioned methods is the presence of the boundaries between incoherently accreted aggregates.     

Optical and structural proprieties of nc-Si:H prepared by argon diluted silane PECVD

Using argon as a diluent of Silane, hydrogenated amorphous and nanorocrystalline silicon films Si:H were prepared by radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD). The deposition rate and crystallinity varying with the deposition pressure and rf power, were systematically studied. Structural analysis (Raman scattering spectroscopy and X-ray diffraction), combined with optical measurements spectroscopy were used to characterize the films. The argon dilution of silane for all samples studied was 95% by volume, and the substrate temperature was 200 °C. The deposition pressure was varied from 400 mTorr to 1400 mTorr and varying rf power from 50 to 250 W. The structural evolution studies, shows that beyond 200 W of rf power, an amorphous-nanocrystalline transition was observed, with an increase in crystalline fraction by increasing rf power and working pressure. The films were grown at high deposition rates. The deposition rates of the films near the amorphous-nanocrystalline phase transition region were found in the range 6–10 Å/s. A correlation between structural and optical properties has been found and discussed.