Correlation of ordering formation and surface structure in (GaIn)P using modulated MOVPE

Modulated metalorganic vapour phase epitaxial growth (MOVPE) is used to clarify the role of the surface conditions on the ordering behaviour in ternary (GaIn)P layers. The alternating deposition of GaP and InP layers with individual thicknesses of up to one monolayer is successfully used for the growth of (GaIn)P bulk layers lattice matched to (100) GaAs substrates with various off-orientations. The layer quality and the degree of ordering are investigated using high-resolution X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL), respectively. The application of modulated growth conditions for the deposition of (GaIn)P bulk layers has a strong influence on the degree of ordering achieved in the intermediate growth temperature regime where the highest degree of ordering occurs under continuous MOVPE. Beside a new boundary structure observed in layers grown under modulated flux conditions, the successful growth of highly ordered (GaIn)P layers grown using the modulated MOVPE technique support the model that up to 2 monolayers of the (GaIn)P growth surface are involved in the ordering formation process.     

Surface nanoscale relief of mineral crystals and its relation to nonautonomous phase formation

The features of the nanoscale relief of crystals formed under natural and experimental conditions are considered by examples of pyrite, sphalerite and its solid solutions, and native gold. Nonautonomous phases (NAPs), which differ from the bulk mineral by their chemical composition, stoichiometry, and structure, are fixed within an approximately half-micron surface layer. For pyrite crystals, the NAP composition and morphology vary depending on the genetic conditions. In the case of sphalerite, hierarchical fractal structures arise on the crystal surface due to the formation of NAPs of sulfate or sulfoxide composition. An increased content of admixed elements (Cd, Hg) is observed on the surface at the largest NAP development. Gold sulfide NAPs are observed to be stable at a relatively high temperature under hydrothermal conditions.     

Mathematical modeling and experimental investigation of the effect of temperature gradients on crystallization processes under terrestrial and space conditions

Mathematical modeling of the processes of heat and mass transfer during directed crystallization under terrestrial and space conditions is performed on the basis of experimental data on the temperature distribution (boundary conditions). Convective processes are described by the system of Oberbeck-Boussinesq equations together with the heat-conduction equation (the Stefan problem). A dependence of the intensity of thermal gravitational convection on the radial and axial temperature gradients is established. It is shown that one of the necessary conditions for the growth of homogeneous semiconductor crystals under both terrestrial and zero-gravity (on board spacecraft) conditions is the absence of the free surface of a melt (the Marangoni convection) and optimization of the temperature gradients (first of all, the radial gradient).     

White and Taylor Type Guest Host Displays Without Scattering Effects Using the Tilted Boundary Conditions

White and Taylor type guest host displays using the tilted boundary condition have been reported. The parallel or the perpendicular boundary condition is usually used for these displays and both conditions cause scattering phemomena after the electric field removal. The present paper reports the relaxation processes of samples with the tilted boundary after the field removal. Using the tilted boundary, two types of nonscattering conditions depending on the thickness of the liquid crystal layer (d), the natural pitch (Po) and the boundary condition (φ) exist. Both types of conditions are discussed in detail.     

Differential method for observing defects with the use of a combined polarized radiation

The conditions for observing crystal defects by a new differential method based on the use of combined radiation with two equally intense orthogonally polarized components have been considered. The conditions for recording three groups of defects possessing different optical properties (absorption, scattering, polarizability, and refraction) are indicated. The new method is implemented on the basis of a scanning image converter widely used in optical flaw detection of crystals.     

Specific features of the formation of terrace-step nanostructures on the (0001) surface of sapphire crystals

The terrace-step structures on atomically smooth vicinal surfaces of sapphire crystals subjected to thermal annealing after mechanical and chemical treatments have been investigated by atomic-force microscopy. The influence of the vicinal angles and conditions of thermal treatment (including annealings in air and vacuum) of sapphire plates on the metric parameters of terrace-step structures has been analyzed. It is shown that steps with a height from monoatomic (0.22 nm) to 3 nm or more can be formed on the sapphire surface by changing the vicinal angle and thermal-treatment conditions. The results are interpreted in terms of the minimum surface energy and surface diffusion processes.     

采用MOCVD方法在GaAs衬底上生长ZnO(002)和ZnO(100)薄膜

采用金属有机化学汽相沉积生长法（MOCVD）,在不同的衬底表面处理条件和生长温度下,在GaAs衬底上生长出了ZnO薄膜。随着化学腐蚀条件的不同,可生长出优先定位不同的ZnO（100）和ZnO（002）薄膜。该薄膜的晶体结构特性是由X光衍射谱仪（XRD）所获得的,而其光学特性是由光荧光谱仪（PL）来测的。与ZnO（002）相比,ZnO（100）薄膜具有更优越的晶体结构特性,并且在同样的生长温度下都具有相似的光学特性。对于腐蚀条件不同的GaAs衬底所进行的XPS分析结果表明,ZnO薄膜优先定位变化的主要原因在于腐蚀过程中形成的富As层。     

Dynamic interaction of dislocations with impurity subsystem in crystalline materials

The entrainment of impurities by moving dislocations results in the accumulation of impurities in dislocation cores, which eventually significantly modifies the dynamic properties of dislocations. In the framework of the kink mechanism, the possible modes of motion are found self-consistently and the conditions for dislocation immobilization are determined. The dependence of the immobilization stress (the parameter that is most important for ??defect engineering?? in semiconductors) on the material parameters and experimental conditions is calculated.     

溶胶-凝胶低温自蔓延工艺合成Co0.5Ni0.5Mn2O4纳米粉体的过程稳定性研究

本文研究了溶胶-凝胶低温自蔓延工艺合成Co0.5Ni0.5Mn2O4纳米粉体过程中柠檬酸-硝酸盐体系的稳定性.研究结果表明:柠檬酸盐的析出是造成溶胶-凝胶体系不稳定主要因素;加入乙二醇与柠檬酸形成网络结构、以及金属离子与柠檬酸羧基之间形成的配位键是保证溶胶-凝胶体系稳定的两个必不可少的条件.     

Growth of (Perylene)2 [Pd(mnt)2] crystals

The conditions for the growth of (Perylene)₂ [Pd(mnt)₂] crystals either by chemical oxidation and electrochemical routes are described. The electrocrystallisation is limited by close proximity of the oxidation potentials of the perylene donor and [Pd(mnt)₂]^? anion, and depending on the experimental conditions different morphologies can be obtained. (Per)₂ [Pd(mnt)₂] crystals obtained by elecrocrystallisation were found to be mainly of the β-polymorph with properties comparable to the Cu, Ni and Pt analogues previously described at variance with those obtained by chemical oxidation which are mainly of the α-polymorph .     

Structure and Ordering Principles of Ultrathin Organic Molecular Films on Surfaces of Layered Semiconductors Organic-on-Inorganic MBE

Epitaxially ordered thin films of large planar organic molecules can be obtained on layered inorganic semiconductors by organic molecular beam deposition in UHV. Analysis by low energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS) yields structural parameters and binding energies. The conditions necessary for order formation are analyzed. Epitaxial data are given for hexabenzocoronene (HBC) and naphthalene-tetracarboxylic-dianhydride (NTCDA) on graphite, MoS₂ and GeS.     

Liquid Crystal Channel Waveguides: A Monte Carlo Investigation of the Ordering

We present detailed Monte Carlo (MC) simulations of a nematic cell with homeotropic boundary conditions at the four confining surfaces. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the cell anchoring. We have investigated the model using a standard Metropolis Monte Carlo method to study the optical transmission and the ordering through the cell.     

Polymer Composite Based on DAST Submicron Crystals: Technology and Properties

We propose a new nonlinear optical material, a polymeric nanocomposite based on DAST submicron crystals (trans-4’-(dimethylamino)-N-methyl-4-stilbazolium tosylate). The method and the preparation conditions for films based on a mixture of polymer solutions and a DAST powder are studied. Polymer matrices of various types, solvent ratio for the pair DAST/polymer, and electrical poling conditions are investigated. Absorption and luminescence spectra and the second harmonic generation have confirmed the creation of red-form DAST nanocrystals in polymer films. The figure of merit for a resulting polymer film is approximately 400 times higher than that for LiNbO₃ at a wavelength of 1.32 microns.     

Structural study of fractal silica humid gels

The structures of gels of silica obtained from solutions of TMOS, methanol and water have been studied by small angle X-ray scattering (SAXS) using synchrotron radiation. The SAXS results indicate that all the gels studied exhibit fractal structures. It is inferred that gels obtained under basic conditions are volume fractals built up by surface and volume fractal units for high and low water content, respectively. The gels obtained under acidic conditions are all volume fractals having structural units much smaller than those of basic gels. The influence of aging on the structure of basic gels has also been established.     

Molecular beam epitaxy of single phase GeMnTe with high ferromagnetic transition temperature

Ferromagnetic Ge(1-x)Mn(x)Te is a promising candidate for diluted magnetic semiconductors because solid solutions exist over a wide range of compositions up to x(Mn)≈0.5, where a maximum in the total magnetization occurs. In this work, a systematic study of molecular beam epitaxy of GeMnTe on (1?1?1) BaF(2) substrates is presented, in which the Mn concentration as well as growth conditions were varied over a wide range. The results demonstrate that single phase growth of GeMnTe can be achieved only in a narrow window of growth conditions, whereas at low as well as high temperatures secondary phases or even phase separation occurs. The formation of secondary phases strongly reduces the layer magnetization as well as the Curie temperatures. Under optimized conditions, single phase GeMnTe layers are obtained with Curie temperatures as high as 200?K for Mn concentrations close to the solubility limit of x(Mn)=50%.     

Eutectic structures in the Ni–Co–Cr–Al system obtained by plasma spraying and by Bridgman growth

Formation of a regular fibrous two-phase microstructure was found in low-pressure plasma spray (LPPS) deposited Ni–Co–Cr–Al–Y coatings by transmission electron microscopy and analyzed by energy dispersive spectroscopy. The structure is compared to aligned lamellar three-phase structures of an Ni–Co–Cr–Al alloy obtained on Bridgman growth under slow unidirectional solidification (UDS) conditions. The composition of the Ni–Co–Cr–Al alloy for UDS experiments has been identified by DTA. The conditions for the formation of both the LPPS and the UDS structures are discussed.     

Thermal properties of nano crystalline CdS

Nano CdS samples are synthesized by precipitation method for different growth conditions. Thermal diffusivity and conductivity on these nano CdS are measured by photo acoustic technique. The results are compared with bulk and discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth from the vapour by surface nucleation

The experimental conditions under which cadmium sulphide is grown from the vapour to form crystals having a (11.0) singular growth faces are calculated. This is done assuming that growth proceeds on these faces by one-dimensional surface nucleation. Calculations based on this assumption are compared with experimental observations on the habit of CdS, and the relationship between growth rate and supersaturation, and shown to be consistent with these.     

Realization of optically active strained InAs island quantum boxes on GaAs(100) via molecular beam epitaxy and the role of island induced strain fields

We report here the realization of strained InAs three-dimensional islands on GaAs(100) with optical characteristics that reveal lateral quantum confinement (i.e. quantum box behavior). The importance of the cap layer growth conditions and methodology in achieving optically active InAs islands and the existence, range, and impact of island-induced strain fields on the cap layer growth are uncovered via marker layer experiments. Strong optical emission from the InAs islands is observed in correlation with the transmission electron microscope (TEM) observation of uniform coherent islands under optimized growth conditions. Photoluminescence excitation (PLE) spectroscopy reveals the presence of the energy transitions due to the three-dimensional electronic confinement in such InAs islands. The InAs islands buried under the GaAs were found to be quite stable upon annealing to 100°C higher than the growth temperature.     

Dynamic response of glass panels subjected to shock loading

A controlled study has been performed to understand fracture and damage in glass panels subjected to air blast. A shock tube apparatus has been utilized to obtain the controlled blast loading. Five different panels, namely plain glass, sandwiched glass, wired glass, tempered glass and sandwiched glass with film on both the faces are used in the experiments. Fully clamped boundary conditions are applied to replicate the actual loading conditions in windows. Real-time measurements of the pressure pulses affecting the panels are recorded. A post-mortem study of the specimens was also performed to evaluate the effectiveness of the materials to withstand these shock loads. The real time full-field in-plane strain and out-of-plane deformation data on the back face of the glass panel is obtained using 3D Digital Image Correlation (DIC) technique. The experimental results show that the sandwich glass with two layers of glass joined with a polyvinyl butyral (PVB) interlayer and protective film on both the front and back faces maintains structural integrity and outperforms the other four types of glass tested.