Materials Literature
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Finding the most stable structure of a solid is one of the central problems in condensed matter physics. This entails finding both the lattice type (e.g., fcc, bcc, and orthorhombic) and (for compounds) the decoration of the lattice sites by atoms of types $A$, $B$, etc. (``configuration''). Most approaches to this pr…
Resonant electronic transmission through graphene-based double barriers (wells) is studied as a function of the incident wave vector, the widths and heights (depths) of the barriers (wells), and the separation between them. Resonant features in the transmission result from resonant electron states in the wells or hole…
Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO3/Pt FTJ as a model system, we show that the polarization of the BaTiO3 barrier leads to a substantial drop in the tunneling conductance due to…
We describe a possible pathway to new magnetic materials with no conventional magnetic elements present. The substitution of nitrogen for oxygen in simple nonmagnetic oxides leads to holes in N 2p states which form local magnetic moments. Because of the very large Hund's rule coupling of Nitrogen and O 2p electrons an…
The authors have fabricated ultraviolet (UV) laser diodes based on ZnO∕BeZnO films. The devices have p-n heterojunction structures with a multiple quantum well (MQW) active layer sandwiched between guide-confinement layers. The MQW active layer comprises undoped ZnO and BeZnO, while the two guide-confinement layers we…
Low energy collective angular momentum states of the Tb3+ ions in Tb2Ti2O7 are classified according to the irreducible representations of the octahedral point group. Degeneracy lifting due to the exchange interaction is discussed. Diffuse neutron scattering intensity patterns are calculated for each collective angular…
We have selectively grown thin epitaxial GaAs films on Ge substrates with the aid of a 200 nm thin SiO2 mask layer. The selectively grown structures have lateral sizes ranging from 1 um width up to large areas of 1 by 1 mm2. The growth is fully selective, thanks to an optimized growth procedure, consisting of a 13 nm…
Plasmon modes of a two-dimensional lattice of long conducting circular wires are investigated by using an embedding technique to solve Maxwell's equations rigorously. The frequency-dependent density of states is calculated for various values of the wave vector and the filling fraction. At low filling fractions, collec…
We have selectively grown thin epitaxial GaAs films on Ge substrates with the aid of a 200 nm thin SiO2 mask layer. The selectively grown structures have lateral sizes ranging from 1 um width up to large areas of 1 by 1 mm2. The growth with the standard growth procedure for GaAs growth on Ge substrates reveals a limit…
Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650C by organometallic vapor phase epitaxy (OMVPE) on Ge substrates and extensively analyzed by low-temperature photoluminescence (PL) spectroscopy.
The near-field scanning optical microscopy images of excitonic wavefunctions in self-assembled InAs/GaAs quantum dots are calculated using an empirical pseudopotential method, followed by the configuration interaction (CI) treatment of many-particle effects. We show the wavefunctions of neutral exciton $X^0$ of differ…
Pieces of eight: Single-crystalline Au nano-octahedra with well-defined shape and tunable size can be synthesized by a modified polyol process. The octahedral Au nanocrystals have sharp corners and display optical properties that are sensitive to the crystal sizes and the truncation of the tips.
Defects in graphene are of crucial importance for its electronic and magnetic properties. Here, impurity effects on the electronic structure of surrounding carbon atoms are considered and the distribution of the local densities of states is calculated. As the full range from near field to the asymptotic regime is cove…
Bi Fe O 3 is an interesting multiferroic oxide and a potentially important Pb-free ferroelectric. However, its applications can be limited by large leakage currents. Its band gap is calculated by the density-functional based screened exchange method to be 2.8eV, similar to experiment. The Schottky barrier height on Pt…
In the FEM analysis of structure response under dynamic loading such as high velocity impact, the failure parameter is a important aspect of material behavior. With split Hopkinson tension bar tests and static material test at various stress states and temperatures, the effects of high strain rate, elevated temperatur…
We have investigated the magnetic properties of a GaN/Ga1-xMnxN (x = 0.1) digital ferromagnetic heterostructure (DFH) showing ferromagnetic behavior using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The Mn L2,3-edge XAS spectra were similar to those of Ga1-xMnxN random alloy…
We have systematically studied the transport properties of the La$_{2-x}$Y$_{x}$CuO$_{4}$(LYCO) films of T'-phase ($0.05\leq x \leq 0.30$). In this nominally "undoped" system, superconductivity was acquired in certain Y doping range ($0.10\leq x \leq 0.20$). Measurements of resistivity, Hall coefficients in normal sta…
We find an unconventional nucleation of low temperature paramagnetic metal (PMM) phase with monoclinic structure from the matrix of high-temperature antiferromagnetic insulator (AFI) phase with tetragonal structure in strongly correlated electronic system $BaCo_{0.9}Ni_{0.1}S_{1.97}$. Such unconventional nucleation le…
Understanding radiation-induced defect formation in carbon materials is crucial for nuclear technology and for the manufacturing of nanostructures with desired properties. Using first principles molecular dynamics, we perform a systematic study of the non-equilibrium processes of radiation damage in graphite. Our stud…
We develop a theory to represent dislocated single crystals at the mesoscopic scale by considering concentrated effects, governed by the distribution theory combined with multiple-valued kinematic fields. Our approach gives a new understanding of the continuum theory of defects as developed by Kroener (1980) and other…