M. Ajmal Khan

Effect of organic ligands (L-Proline and L-Methionine) on growth, structural, vibrational, crystalline perfection, SHG efficiency, microscopic and optical properties of KDP single crystals.

The effect of L-Proline (LP) and L-Methionine (LM) doping on the various properties of KDP single crystals grown by slow evaporation solution technique has been investigated. The external morphology of the grown crystals was found to vary due to different dopants and doping concentrations. The change in powder X-ray diffraction intensity patterns due to doping shows the lattice distortion within resolution limit and confirms that there is no extra phase. Further, the same was confirmed by FT-Raman analysis. Infra red microscopic study also exhibits the effectiveness of doping in terms of varying surface morphology. Crystalline perfection of KDP crystals with LP and LM doping was examined by high-resolution X-ray diffraction. This shows very interesting features on the ability of accommodating the dopants in the crystalline matrix. Second harmonic generation efficiency was also found to be in similar fashion as of crystalline perfection. The optical transparency of doped crystals was tested.

Quantum confinement effects on the band structure and dielectric properties of nanostructured GaAs

The electronic band structure and dielectric properties of a GaAs quantum well have been investigated using the pseudopotential approach. The effect of quantum confinement on the electronic and dielectric properties of GaAs has been examined. It is found that significant variations in the studied properties occur at quantum well widths below 5 nm. The information may be useful in obtaining derived electronic and dielectric properties, which was not possible in the unconfined (bulk) GaAs compound semiconductor.

Molecular Dynamics Simulation of ZnS using Interatomic Potentials

Constant temperature molecular dynamics simulations have been performed on ZnS at different temperatures ranging from 300 K to 1400 K with the objective of establishing and validating the temperature dependent structural and thermodynamic properties. The simulations were carried out in canonical ensemble (NVT) using Lennard‐Jones pair potential. Radial distribution functions have been calculated. RDF peaks are found to be broadened and decrease in heights with increasing temperature, reflecting enhanced atomic motions. Energy temperature graph does not show any break, however a break in the specific heat curve and a λ type transformation are observed indicating second order phase transformation. Mean Square Displacement (MSD) for Zn and S atoms separately have been measured and almost identical graph were obtained. The MSD curve exhibits the existence of maximum disorderness at 1100 K and 1400 K which indicates phase transformations around them.

Composition dependence of penetration range and backscattering coefficient of electrons impinging on SixGe1−x and GaAsxN1−x semiconducting alloys

The alloy composition dependence of penetration range and backscattering coefficient of electrons normally impinging on SixGe1-x and GaAsxN1-x semiconductor alloys targets for beam energies in the range 0.5-3.5 keV has been investigated. The electron penetration range is calculated using the Ashleys model. The electron backscattering coefficient is determined using both the Vicanek and Urbassek theory where the transport cross-sections are obtained more accurately via an improved approximation and Monte Carlo method in which the inelastic scattering processes are treated via Ashleys optical model. Our results regarding the electron backscattering coefficient for Si and Ge targets are found to be much higher than those of experiment when using the Vicanek and Urbassek theory. However, the use of Ashleys model via Monte Carlo method gives results that are in reasonably good accord with the experimental data reported in the literature in the low energy regime being considered here.

Elastic constants and mechanical stability of InxAl1 − xAsySb1 − y lattice-matched to different substrates

ABSTRACT Based on a pseudopotential approach under the virtual crystal approximation, the elastic modulus of InxAl1 − xAsySb1 − y quaternaries lattice-matched to InP, GaSb and InAs substrates has been investigated. Our findings show a reasonably good accord with experiment. The dependence of the elastic features of interest on the indium concentration x shows a monotonic behaviour when InxAl1 − xAsySb1 − y is lattice-matched to InP substrate. In that case, the elastic constants have larger values and the material system of interest becomes less harder and its rigidity becomes weaker. The mechanical stability criteria is verified in terms of elastic constants and shows that InxAl1 − xAsySb1 − y is mechanically stable for each x and substrate being considered here. The change in indium content x and the substrate is found to have no much effect on both the Poisson ratio and machinability. The present study showed that a proper choice of the indium composition x and substrate may provide more diverse opportunities as regards the elastic modulus of InxAl1 − xAsySb1 − y.