Dense amorphous packing of binary hard sphere mixtures with chemical order: The stability of a solute ordered approximant

Recently, Miracle proposed that the intermediate structure in metallic glasses could be usefully characterized as an ordered face centered cubic packing of solute-centered coordination clusters. In this paper we examine the stability of such solute ordered arrangements in binary hard sphere mixtures subject to density maximization through local particle moves.     

MgO films grown on yttria-stabilized zirconia by molecular beam epitaxy

MgO films were grown on (0 0 1) yttria-stabilized zirconia (YSZ) substrates by molecular beam epitaxy (MBE). The crystalline structures of these films were investigated using X-ray diffraction and transmission electron microscopy. Growth temperature was varied from 350 to 550 °C, with crystalline quality being improved at higher temperatures. The MgO films had a domain structure: (1 1 1)[1 1 2¯]_MgO(0 0 1)[1 0 0]_YSZ with four twin variants related by a 90° in-plane rotation about the [1 1 1]_MgO axis. The observed epitaxial orientation was compared to previous reports of films grown by pulsed laser deposition and sputtering and explained as resulting in the lowest interface energy.     

Glasses for lithography

The highest resolution in a lithographic process is often determined by the properties of the resist material. With the currently used polymeric resists, a resolution of better than 100 nm has been achieved under manufacturing conditions, but the future nanoscale devices will require a 10 times superior resolution. In this paper we present an overview of the resist materials, especially with regard to limiting resolution. In principle, inorganic resists should have higher limiting resolution than polymer resists due to smaller fundamental structural units and stronger bonds in the former. However, compositional and/or structural inhomogeneities may limit their ultimate resolution. New results are presented that indicate chalcogenide glasses as promising photo and electron beam resists, which also have the advantages of greater hardness, resistance to acids, easy fabrication in thin film form, and the unique phenomena like radiation enhanced diffusion.     

Fluorine incorporation in silica glass by the MCVD process: Study of fluorine incorporation zone,evaluation of optical properties and structure of the glass

A theoretical approach was made to find out a complete fluorine incorporation zone on a ternary diagram which serves as a useful graphical representation to select the flows of the supplied reagents for incorporation of the suitable amount of fluorine into cladding glass of optical fiber preform made by the MCVD process using CCl₂F₂ as a source of fluorine under oxygen abundance, oxygen deficiency and intermediate oxygen state conditions. The possible mechanism for incorporation of fluorine into cladding glass of optical fiber is also evaluated on the basis of the thermodynamical data. The fluorine incorporation mechanism in silica glass by the MCVD process is found to be dependent on the CCl₂F₂/SiCl₄ ratio in the input gas mixture. Fluorine doping is found to be effective for removing the strained Si–O–Si bonds, which govern the optical transparency in deep ultra-violet (DUV) and vacuum ultra-violet (VUV) regions. The maximum refractive index depression of ?0.5 × 10^?3 is obtained with incorporation of fluorine into silica cladding glass by the MCVD process using CCl₂F₂ as a dopant precursor with suitable flow of SiCl₄ vapor along with O₂ through backward deposition pass. The structure of fluorine doped silica glass preform samples containing 1.70–1.79 mol% fluorine incorporated by the MCVD process based on the analyses of ¹⁹F MAS spectra done by high-resolution ¹⁹F NMR spectroscopy reveal the presence of two distinct types of fluorine environments. The majority of the fluorine environments are formed in SiO_1.5F polyhedral and less abundant species is observed to be highly unusual, yielding a fivefold coordinated silicon of the type SiO₂F polyhedral which become increased with increasing the fluorine content.     

Pseudopotential in the study of superconducting state parameters of metallic glasses

A well recognized model potential is used to study the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ¹, transition temperature T_C, isotope effect exponent α and effective interaction strength N₀V of some binary metallic glasses of simple, non-simple and transition metals. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. Instead of using Vegard’s law, pseudo-alloy-atom model (PAA) in the present investigation is proposed and found successful. The present results of the SSP are found in qualitative agreement with other such earlier reported data wherever exist, which confirms the superconducting phase in the metallic glasses.     

Modulated photocurrent as a powerful method to reveal predominant transport by the majority carriers of disordered semiconductors and to resolve all the kinds of probed gap states

A basic difficulty in the interpretation of photoconductivity measurements may arise from possible mixed contributions of both carriers to the photocurrent. In this work it is demonstrated that a universal behavior in the simulated spectra of the out of phase modulated photocurrent signal is observed in cases where the majority carriers dominate. In these cases, a general formula can be used to evaluate the densities of various species of states using the data from all frequencies. Deviations from the universal behavior can be observed when there are contributions from both carriers. The applicability of our analysis is demonstrated in a-Si:H.     

Specific features of the formation of submicron inclusion in Ti:sapphire

Specific features of the formation of submicron (70–300 nm) inclusions in Ti:sapphire (Al₂O₃:Ti) grown in a carbon-containing medium have been investigated. These inclusions are caused by deviation from the melt stoichiometry and are formed during the melt-crystal phase transition. These defects are submicropores containing excess aluminum and its suboxides; they can be destroyed by thermal loading of a crystal.     

Effect of biotransformation on multispecies plume evolution and natural attenuation

Biological transformation of volatile organic compounds is one of the key factors that influence contaminant-plume evolution and thus natural attenuation. In this study we investigate the effect of biological transformation on the transport of contaminants in the aqueous and gaseous phases. The analysis includes the study of the effect of density-driven advection of contaminants in the gaseous phase on multiphase and multispecies flow, fate and transport modeling in the subsurface. Trichloroethylene (TCE) and its two byproducts, dichloroethylene and vinyl chloride, are analyzed as the target contaminants. Our results indicate that density-driven advection of the gaseous phase, which is initiated by evaporation of TCE as a nonaqueous phase liquid, increases the downward and also the lateral migration of TCE within the unsaturated zone. This process also influences the location of high-concentration zones of the byproducts of TCE in the unsaturated and the saturated zones. Biotransformation of TCE contributes to the reduction of dissolved TCE plume development as expected. The daughter byproducts, which are introduced into the subsurface system, show distinct transport patterns as they are affected by their independent degradation kinetics and density-driven advection. These observations, which are based on our simulation results for biotransformation and transport of TCE and its byproducts, are useful in evaluating the natural attenuation processes, its potential health hazards and also the evaluation of potential plume development at contaminated sites.     

Predicting the onset of DNA supercoiling using a non-linear hemitropic elastic rod

Elastic rod models provide a means to interpret single molecule DNA experiments as well as predict DNA behavior under physiological conditions. Here we use an elastic rod model to predict the stability boundary (critical torque vs. applied tension) for single molecule DNA experiments in which the molecule is subjected to applied tension and twist. We discuss the shortcomings of the usual isotropic rod model. We then derive a consistent non-linear material law from the general representation for a hemitropic (chiral) rod. Finally, we present results of a standard bifurcation analysis predicting the stability boundary. We find results from the non-linear hemitropic rod to match the data closely.     

Analysis of thermally induced multistable composites

This paper models the non-linear flexural response of laminates that have piecewise variation of lay-up in the planform, using finite element analysis. Attention is focused on the effects that thermal stresses have on the potential multiple shapes of a composite structure. Unsymmetric laminates may possess more than a single equilibrium configuration, and during the cool-down the solution thus bifurcates at a critical temperature. In static analyses, numerical solutions are often coaxed to converge into one or the other branch of the solution. A methodology to overcome this problem is presented. Such modelling is necessary to allow application of multistable composite within morphing aircraft structures as multistable composites could provide a viable solution for the realisation of shape-adaptable structures.