Materials Literature
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Ferroelectric thin films are currently being used to develop tunable microwave circuits based on the electric-field dependence of the dielectric constant. (Ba0.5Sr0.5)TiO3 (BST) films prepared by sputtering on Pt/TiO2/SiO2/Si substrates are found to exhibit a capacitance change (tunability) of nearly 4:1. Higher tunab…
We compute the thermodynamic properties of the glass phase in a binary mixture of soft spheres. Our approach is a generalization to mixtures of the replica strategy, recently proposed by Mezard and Parisi, providing a first principle statistical mechanics computation of the thermodynamics of glasses. The method starts…
We propose a simple and efficient one-way multigrid method for self-consistent electronic structure calculations based on iterative diagonalization. Total energy calculations are performed on several different levels of grids starting from the coarsest grid, with wave functions transferred to each finer level. The onl…
We describe the object-oriented implementation of a higher-order finite-difference density-functional code in Fortran 90. Object-oriented models of grid and related objects are constructed and employed for the implementation of an efficient one-way multigrid method we have recently proposed for the density-functional…
High real-space resolution atomic pair distribution functions PDFs from the alloy series $\mathrm{Ga}{}_{1\ensuremath{-}x}{ln}_{x}\mathrm{As}$ have been obtained using high-energy x-ray diffraction. The first peak in the PDF is resolved as a doublet due to the presence of two nearest neighbor bond lengths, Ga-As and I…
The optic vibrational (confined and interface) modes and the electron-phonon and hole-phonon interactions are obtained, in the dielectric continuum model, for two diluted magnetic semiconductor structures: a single well of Cd1-xMnxTe/Cd1-yMgyTe with the magnetic ions in the well, and a double well of CdTe/Cd1-xMnxTe,…
We investigate the behavior of three-dimensional (3D) exchange-correlation energy functional approximations of density functional theory in anisotropic systems with two-dimensional (2D) character. Using two simple models, quasi-2D electron gas and two-electron quantum dot, we show a {\it fundamental limitation} of the…
We have calculated the effects of structural distortions of armchair carbon nanotubes on their electronic and electrical properties. We found that the bending of the nanotubes decreases their transmission function in certain energy ranges and leads to an increased electrical resistance. Electronic structure calculatio…
A local-density-approximation (LDA) and $\mathrm{LDA}+U$ band structure study of various phases of ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ shows that the most prominent (spin- $\frac{1}{2}$) models used to describe the semiconductor-metal transition are not valid. We find that the large on-site Coulomb and exchange interac…
Medium and high-energy x-ray diffraction has been used to study the atomic structure of pure amorphous Si prepared by MeV Si implantation into crystalline silicon. Both as-implanted and annealed samples were studied. The inelastically scattered x rays were removed by fitting the energy spectrum for the scattered x ray…
We study the phase diagram of a system of spherical particles interacting in three dimensions through a potential consisting of a strict hard core plus a linear repulsive shoulder at larger distances. The phase diagram (obtained numerically, and analytically in a limiting case) shows anomalous properties that are simi…
Two types of polymer–silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO2 nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol–gel polym…
We present first-principles charge- and spin-self-consistent electronic structure computations on the Heusler-type disordered alloys ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ for three different metalloids $X=(\mathrm{Si},\mathrm{Ga},$ and Al). In these calculations we use the methodology based on the Korrin…
We use a simple picture based on the $\ensuremath{\pi}$ electron approximation to study the band-gap variation of carbon nanotubes with uniaxial and torsional strain. We find (i) that the magnitude of slope of band gap versus strain has an almost universal behavior that depends on the chiral angle, (ii) that the sign…
A model of relaxor ferroelectrics based on the interacting polar clusters picture has been formulated. The electric dipole moment of a nanosized polar domain is allowed a large number of discrete orientations and its length is assumed to fluctuate in a broad interval. Introducing a set of quasicontinuous order paramet…
The radiative lifetime, ${\ensuremath{\tau}}_{R},$ of the ${}^{5}{D}_{0}$ metastable excited state of ${\mathrm{Eu}}^{3+}$ ions in nanocrystalline monoclinic ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ samples is about four times longer than that in the micron size powder of the same material. The ${\mathrm{Eu}}^{3+}$ radiativ…
Electronic structure calculations of $\ensuremath{\beta}\ensuremath{-}{\mathrm{BaB}}_{2}{\mathrm{O}}_{4}$ from first principles are performed based on a plane-wave pseudopotential method, and the linear optical properties are then obtained. The static second-harmonic generation (SHG) coefficients are calculated at the…
Femtosecond (fs) broad-band transient absorption (TA) is used to study the intraband relaxation and depopulation dynamics of electron and hole quantized states in CdSe nanocrystals (NC's) with a range of surface properties. Instead of the drastic reduction in the energy relaxation rate expected due to a ``phonon bottl…
A fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders. The fabricated displays were fully scalable at low temperature, below 415 °C, and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1 V…
Aluminosilicate zeolites such as UTD-1 (structure shown) belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange. During the last decade, the rate of discovery of new open-framework materials based, for example, on phosphates, sulfides, halides, nitrides, and c…