atomic and molecular physics by rajkumar

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Abstract
: Self-assembled germanium islands have been grown on Si (001) substrates using solid source molecular beam epitaxy. A series of annealing experiments have been performed at a temperature 650°C in order to clarify some issues related to island stability and coarsening mechanism. The shape and size distribution of Ge islands as a function of annealing time up to 90 min have been studied through atomic force microscopy. Foot-prints of the annealed and etched islands have demonstrated that the coarsening is dominated by coalescence mechanisms rather than the Ostwald ripening. A detailed Raman characterisation, using optical phonons as efficient probes in analysing self-organised Si1-xGex islands, is reported. The alloy composition has been determined from the Raman intensities. The experimental results are in good agreement with the strain relaxation obtained from X-ray rocking curve and data from AFM topographic images. The generic mechanisms for the growth of self-assembled Ge islands as a function of growth parameters and post-growth treatment are also reviewed.


The conformational analysis of 2-amino-6-methoxy-3-nitropyridine molecule (AMNP) has been carried out using density functional theory calculations. The vibrational spectra of the molecule is simulated theoretically and compared experimentally, and the vibrational frequencies are assigned on the basis of potential energy distribution calculations. Electronic properties of the molecule derived from the theoretical ultraviolet-visible spectrum are validated experimentally. The higher non-linear optical activity of the molecule is indicated in the first-order hyperpolarizability calculations. The natural bond orbital and Mulliken atomic charge distribution analysis confirm intramolecular charge transfers and intramolecular interactions. The Frontier molecular orbitals are plotted, and the related molecular properties are calculated and discussed. The molecular electrostatic potential contour map is simulated. As the presence of intramolecular interactions and the associated charge transfers between the pyridine ring of AMNP molecule and the lone pair of oxygen is a common molecular feature of a pharmaceutical compound, this investigation paves the way for its possible biomedical applications. Further, the considerably higher non-linear optical (NLO) activity of the molecule identified suggests its potential applications in the design of new optical materials.


Large-scale molecular dynamics simulations are performed to investigate the atomiclevel stresses on InAs/GaAs mesas. The simulations are based on an interatomic-potential scheme for InAs/GaAs systems which depends on the local chemical composition. Multiresolution techniques are used to speed up the simulations. InAs/GaAs square mesas with  101 -type sidewalls are studied. The atomic-level pressure distribution and surface atomic stresses on the sidewalls with 12, 10, 8 and 6 monolayers of InAs overlayers have been calculated.
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Atomic And Molecular Physics By Rajkumar

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