M. W. C. Dharma-wardana

Optical properties of structurally relaxed Si / SiO 2 superlattices: The role of bonding at interfaces

We have constructed microscopic, structurally relaxed atomistic models of

Idealized slab plasma approach for the study of warm dense matter

\mathrm{Si}/{\mathrm{SiO}}_{2}

Magnetism and structure at vacant lattice sites in graphene

superlattices. The structural distortion and oxidation-state characteristics of the interface Si atoms are examined in detail. The role played by the interface Si suboxides in raising the band gap and producing dispersionless energy bands is established. The suboxide atoms are shown to generate an abrupt interface layer about 1.60 \AA{} thick. Band structure and optical-absorption calculations at the Fermi golden rule level are used to demonstrate that increasing confinement leads to (a) direct band gaps, (b) a blue shift in the spectrum, and (c) an enhancement of the absorption intensity in the threshold-energy region. Some aspects of this behavior appear not only in the symmetry direction associated with the superlattice axis, but also in the orthogonal plane directions. We conclude that, in contrast to Si/Ge,

Substrate and capping layer effects on the phonon spectrum of ultrathin superlattices

\mathrm{Si}/{\mathrm{SiO}}_{2}

Electronic structure of InNxAs1−x alloys from tight-binding calculations

superlattices show clear optical enhancement and a shift of the optical spectrum into the region useful for many opto-electronic applications.

ELECTRONIC STATES AND OPTICAL PROPERTIES OF SI/SIO2 SUPERLATTICES

Recently, warm dense matter has emerged as an interdisciplinary field that draws increasing interest in plasma physics, condensed matter physics, high pressure science, astrophysics, inertial confinement fusion, as well as material science under extreme conditions. To allow the study of well-defined warm dense matter states, we introduced the concept of idealized slab plasma (ISP) that can be realized in the laboratory via (1) the isochoric heating of a solid and (2) the propagation of a shock wave in a solid. The application of this concept provides new means for probing AC conductivity, equation of state, ionization, and opacity. These approaches are presented here using results derived from numerical simulations.

Equation of state and the Hugoniot of laser shock-compressed deuterium: Demonstration of a basis-function-free method for quantum calculations

Abstract The electronic structure, bonding and magnetism in graphene containing vacancies are studied using density-functional methods applied to finite- as well as periodic simulation cells. The single-vacancy graphene ground state is spin polarized and structurally flat. The unpolarized state is non-planar only for finite segments. Systems containing periodic arrays of vacancies display magnetic transitions and metal–insulator transitions.

Quasimetallic behavior of carrier-polarized C60 molecular layers: Experiment and theory

GemSin ultrathin superlattices have been grown on (001) Si substrates and partly capped with Si. Raman scattering from acoustic phonons in the long‐wavelength region shows unexpectedly intense broad peaks that develop into an increased number of sharper intense peaks on capping. We identify these peaks with resonant phonon modes and use a linear chain model to expose the importance of substrate‐superlattice‐capping layer interactions in these multilayer structures.

Molecular electronics, negative differential resistance, and resonant tunneling in a poled molecular layer on Al∕LiF electrodes having a sharp density of states

We present tight-binding band-structure calculations for InNxAs1−x alloys as a function of the nitrogen concentration. The high-concentration regime is found to be extremely sensitive to x. The low-concentration region (0<x<0.25) is of technological interest and is examined in detail. Effects of clustering, percolation, and the dependence of the energy gap on the assumed valence-band offsets on the band gap are reported.

Electron confinement and optical enhancement in S i / S i O 2 superlattices

We study the electronic structure of {Si}m{SiO2}n superlattices (SLs) grown along the [001] direction, using tight-binding methods. Detailed atomic models of the Si/SiO2 interface are considered. A clear feature of the results is the essentially direct band-gap structure with flat bands along the ZΓ symmetry line of the SL-Brillouin zone which has a blueshifted energy gap due to quantum confinement. The calculated densities of states are enhanced at the valence and conduction band edges, as compared with silicon. The optical properties of the SLs are calculated using a parametrization of the imaginary part of the dielectric function of bulk Si. The strong confinement of the electron–hole pairs in the Si wells and their tendency to localize at the low-dielectric {SiO2} interfaces due to the mutual Coulomb attraction lead to strong electrostatic effects. These produce an interplay of several length scales in determining possible regimes of high radiative efficiency. Our results have implications for the und...