Abstract Density Of States Research Articles

DFT Investigation of Structural and Electronic Properties of Modified PZT

Abstract Density of states and geometrical structures of modified Lead zirconate titanate are investigated using density functional theory within local density approximation. The electronic properties and bond length variation have been studied in terms of electronic structure and bonding mechanism principles respectively. Hybridization between Ti 3d - O 2p states and ferroelectric distortion have been addressed as a theoretical approach, to rule the improvement of ferroelectric properties of Lead zirconate titanate. The analysis of Ga, Tl modified Lead zirconate titanate were found to diminish the hybridization between Ti 3d - O 2p states, the relaxed behavior lead to the reversal of the known ferroelectric distortion. Y, Ho, Yb and Lu modified Lead zirconate titanate compounds have a tendency to intense the ferroelectric stability, its exhibit higher hybridization between Ti 3d - O 2p states than pure Lead zirconate titanate, also the arrangement of the ions distortions is strongly the same as the more favoured ferroelectric states of Lead zirconate titanate.

The Effect of Applied Voltage on the Carrier Effective Mass in ABA Trilayer Graphene Nanoribbon

Density of states which is an important parameter for the carrier statistics study of Trilayer Graphene Nanoribbon with ABA stacking is modeled in this paper. Analytical model for the density of states of ABA trilayer graphene nanoribbon is proposed and a numerical solution is obtained. In addition, applied voltage effect on carrier effective mass is simulated. The simulation results indicate that by increasing the applied voltage, the carrier effective mass (m?) increases and thus to obtain equal number of electrons and holes, the location of the intrinsic Fermi level will be moved far from the band gap centre.

Density of States Extraction in Bulk Channel Area of a-Si:H Thin-Film Transistors by Using Low-Frequency Noise Analysis

Density of states in the channel bulk area of a-Si:H thin-film transistors (TFTs) was extracted by using low-frequency noise analysis. The drain current noise power spectral density shows 1/ƒγ behavior at relatively high frequencies (ƒ > 1 kHz), which is due to the exponential distribution of tail states. For the analysis, the modified number fluctuation model which is correlated with mobility fluctuation was used. From the relationship (γ=1- kT/Et ) between exponent γ and the slope of exponential distribution Et of band tail states, the distribution of the band tail near conduction band was extracted.

Density of states in an electrically biased quantum well

Density of states in a quantum well has been studied in the presence of an electric field applied perpendicular to the growth direction. We have shown that an extra quantization is introduced to the motion of the electron due to the discrete energy levels known as Wannier-Stark ladder states and the nature of density of electronic states changes from quasi two-dimensional to quasi one-dimensional.

Order-parameter symmetry manifestation in Josephson junctions

Density of states (DOS) and supercurrents in clean anisotropic superconductor/normal metal/anisotropic superconductor Josephson junctions (weak links with transparent interfaces) are studied theoretically. Two types of anisotropic order parameter are considered: d wave with ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ symmetry and extended s wave with eight nodes ${(s}^{*}$ wave). It is shown that in both cases Andreev bound zero-energy state can appear in the equilibrium state of the junction, and typical differences between d-wave and ${s}^{*}$-wave DOS are presented. Another way to distinguish between the two types of symmetry is found in different anisotropic behavior of the critical current. Possible application to experiments is briefly discussed.

Role of interstitial hydrogen and voids in light-induced metastable defect formation in hydrogenated amorphous silicon: A model

Densities of states of a large set of samples have been measured. Samples were deposited by radio-frequency powered glow discharge under various conditions of temperature, power, gas pressure, and dilution of silane. Density of states was studied in the as-deposited, light-soaked, and annealed states. For all the samples light soaking resulted in an increase of both the deep defect density and of the conduction-band tail states. For samples deposited on the edge of crystallinity and polymorphous materials irreversible modifications of the density of states were observed after light soaking followed by annealing. Since none of the existing models of the metastability can account for this behavior we propose a model. In this model, light induced creation of dangling bonds is mediated by interstitial hydrogen. Hydrogen coming from the breaking of Si-H bonds is trapped into voids or platelets during light soaking and released in the lattice during annealing. This model fully explains our experimental results and also many other experimental observations found in the literature.

Density of states in hexagonal SiC polytypes

Densities of states for the hexagonal polytypes 2H, 4H, and 6H of SiC have been derived for energies within a few hundred meV around the band gaps. The nonparabolic energy dispersions of the valence bands have been taken into consideration, as well as the camel’s back structure of the lowest conduction band in 6H–SiC. The nonparabolicities of the energy bands are shown to strongly influence the densities of states in these polytypes.

Density of states in short-period Si/Ge superlattices.

Densities of states in the Si/Ge (4:4) superlattice have been calculated using a scheme based on empirical local pseudopotentials with spin-orbit coupling. The density of states is decomposed in terms of components originating from different sectors of wave-vector space. Effects of straininduced movements of various bands are discussed in terms of the effects on the densities of states near the valence-band and conduction-band edges.

Vibrational properties of amorphous silicon-germanium alloys and superlattices

Densities of states and localization characteristics have been calculated for vibrational modes in a-${\mathrm{Si}}_{\mathrm{x}}$${\mathrm{Ge}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ alloys and a-Si/a-Ge superlattices, using amorphous tetrahedral networks generated by molecular-dynamics methods. For the alloys, the calculated densities of states agree very well with Raman scattering experiments at all concentrations 0\ensuremath{\le}x\ensuremath{\le}1. We explicitly show that an x-dependent feature at 390 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ arises primarily from Si-Ge bond-stretching motions. The localization of vibrational modes is enhanced in magnitude and in frequency range for the alloys as compared with the pure amorphous materials, but extended modes are still present at all x. To account for the Raman measurements on thin a-Si/a-Ge superlattices, a mixed Si-Ge interfacial region about 5 A\r{} in thickness is indicated by our calculations.

Valence band density of states of 74+as implanted amorphous germanium

Density of states of a-Ge induced by 74+As implantation was measured by means of the photoelectron energy distribution. The result is a very structureless curve. The density of states is very low at 0–5 eV., but larger at 5–9 eV energy regions of the valence band. These data indicate that the As implanted a-Ge is an amorphous state of Ge having distorted tetrahedral coordination.

Electronic structure and magnetic properties of Y2Co14B intermediate compound

Density of states of Y2Co14B and local density of states of Y and Co atoms are calculated by making use of the tight-binding d-band model and by the recursion method. Local magnetic moments on Co atoms are calculated from the calculated local density of states.

Partial LCAO densities of states for ScN, TiN, ZrN and ScP

Densities of states (DOS) and partial densities of states were calculated from self-consistent APW band structure calculations for four transition metal compounds (ScN, TiN, ZrN and ScP) using a recently published improved LCAO interpolation scheme. The total DOS and the LCAO non local partial metal s, p and d and non-metal s and p DOS of these compounds are presented and compared with non local LCAO partial DOS from earlier calculations as well as with local partial DOS obtained directly from the APW or LAPW wave functions. A LCAO charge analysis for all valence states and for the individual valence bands is also given.

The influence of short-range order on electronic properties of transition metals: I. Crystalline systems

Densities of states and electronic parameters related to superconductivity have been calculated for the transition metals Nb and Tc, representing the bulk materials by a finite cluster of atoms. The Schrodinger equation is solved for atomic potentials which have been obtained in a self-consistent band structure calculation. The results show that, in these systems, the electronic structure is determind predominantly by short-range order.

Density of States for a Three-dimensional Disordered Alloy

Abstract Densities of states for three-dimensional models of binary alloys are calculated with a method based on the negative eigenvalue theorem. Comparison is made with the densities of states obtained by diagonalizations of the Hamiltonian for a certain number of physically different clusters of impurities.