Energy Differences Between the Si and the Ge Dangling Bond Defects in a-Si1-xGex Alloys

1992 ◽  
Vol 258 ◽  
Author(s):  
S.M. Cho ◽  
B.N. Davidson ◽  
G. Lucovsky
Keyword(s):  
Nearest Neighbor ◽  
Bond Angle ◽  
Local Density ◽  
Bethe Lattice ◽  
Structural Disorder ◽  
Energy Difference ◽  
Amorphous Semiconductors ◽  
Dangling Bond ◽  
Lattice Method ◽  
The Difference

ABSTRACTWe have investigated the difference in the electronic energies of neutral Si and Ge dangling bond states in undoped a-Si1-xGex alloys as a function of the alloy composition, x, and local bond-angle distortions. The local density of states, LDOS, in a-Si1-xGex alloys has been calculated using nearest-neighbor interactions, and employing the Cluster Bethe Lattice method. We conclude that for ideal, tetrahedrally bonded amorphous semiconductors alloys, the Ge dangling bond energy is lower than that of Si dangling bonds by ∼ 0.13 eV, independent of the specific nearest neighbors to the dangling bond (3 Si-atoms, 2 Si-atoms and 1 Ge-atom, etc.), but that the spread in dangling bond energies associated bond-angle variations of the order of 6–8 degrees can be larger than this energy difference (∼0.3 eV or greater). This means that structural disorder, rather than chemical disorder causes Si and Ge-atom dangling bond states to overlap in their energy distributions.

Defect States and Structural Disorder in a-Si.

1992 ◽  
Vol 258 ◽  
Author(s):  
B. N. Davidson ◽  
G. Lucovsky ◽  
J. Bernholc
Keyword(s):  
Standard Deviation ◽  
Nearest Neighbor ◽  
Bond Angle ◽  
Local Density ◽  
Tight Binding ◽  
Bethe Lattice ◽  
Structural Disorder ◽  
Defect States ◽  
Lattice Method ◽  
The Relationship

ABSTRACTWe have examined the distribution of the neutral dangling bond defect states, T30, as a function of the local disorder. T30 defects in a-Si play an important role in many of the current models of the metastable photoconductivity. To understand the relationship between the T30 defect and its bonding environment, the Local Density of States (LDOS) for under-coordinated Si atoms in disordered environments are calculated using the cluster-Bethe lattice method, CBLM. Our Hamiltonian employs the tight-binding parameters of an sp3 orbital basis containing both 1st and 2nd nearest-neighbor interaction terms fit to c-Si band structure. Averaged LDOS of atoms with various bond angle distortions are calculated in order to demonstrate the relationship between the standard deviation in bond angle and the width of the defect states. The CBLM is also used to determine the extent of the valence band tails as a function of the standard deviation in bond angle. In addition, the LDOS of clusters with 2 dangling bonds are examined to determine the degree that their energy levels split due to their interaction with each other.

Effect of the Local Disorder in a-Si on the Electronic Density of States at the Band Edges.

1991 ◽  
Vol 219 ◽  
Author(s):  
B. N. Davidson ◽  
G. Lucovsky ◽  
J. Bernholc
Keyword(s):  
Density Of States ◽  
Nearest Neighbor ◽  
Bond Angle ◽  
Local Density ◽  
Tight Binding ◽  
Bethe Lattice ◽  
Neighbor Interaction ◽  
Lattice Method ◽  
Electronic Density ◽  
Interaction Terms

ABSTRACTWe have systematically investigated the formation of electronic states in the region of the conduction and valence band edges of a Si as functions of variations in the bond angle distributions. Local Density of States (LDOS) for Si atoms in disordered environments have been calculated using the cluster Bethe lattice method with a tight-binding Hamiltonian containing both first and second nearest neighbor interaction terms. LDOS for atoms with bond angle dis ortions in the nearest neighbor and second neighbor shells are compared and contrasted, both showing an influence on the LDOS near the gap. We also consider the role of the second neighbor term in the Hamiltonian by comparing the DOS for a distoned infinite Bethe lattice using Hamiltonians with and without the second neighbor interactions. It is found that in this case the second neighbor interaction terms cause greater conduction band tailing than using the nearest neighbor interaction terms alone.

scholarly journals Electronic and Magnetic Properties of Building Blocks of Mn and Fe Atomic Chains on Nb(110)

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1933
Author(s):  
András Lászlóffy ◽  
Krisztián Palotás ◽  
Levente Rózsa ◽  
László Szunyogh
Keyword(s):  
Ground State ◽  
Nearest Neighbor ◽  
Local Density ◽  
Building Blocks ◽  
Orbital Decomposition ◽  
Atomic Chains ◽  
Physical Insight ◽  
The Difference ◽  
Atomic Coordination ◽  
Spin Spiral

We present results for the electronic and magnetic structure of Mn and Fe clusters on Nb(110) surface, focusing on building blocks of atomic chains as possible realizations of topological superconductivity. The magnetic ground states of the atomic dimers and most of the monatomic chains are determined by the nearest-neighbor isotropic interaction. To gain physical insight, the dependence on the crystallographic direction as well as on the atomic coordination number is analyzed via an orbital decomposition of this isotropic interaction based on the spin-cluster expansion and the difference in the local density of states between ferromagnetic and antiferromagnetic configurations. A spin-spiral ground state is obtained for Fe chains along the [11¯0] direction as a consequence of the frustration of the isotropic interactions. Here, a flat spin-spiral dispersion relation is identified, which can stabilize spin spirals with various wave vectors together with the magnetic anisotropy. This may lead to the observation of spin spirals of different wave vectors and chiralities in longer chains instead of a unique ground state.

MODIFICATION OF CASIMIR FORCES DUE TO BAND GAPS IN PERIODIC STRUCTURES

2002 ◽  
Vol 17 (06n07) ◽  
pp. 798-803 ◽  
Author(s):  
C. VILLARREAL ◽  
R. ESQUIVEL-SIRVENT ◽  
G. H. COCOLETZI
Keyword(s):  
Density Of States ◽  
Casimir Force ◽  
Periodic Structures ◽  
Local Density ◽  
Band Gaps ◽  
Basic Unit ◽  
Local Density Of States ◽  
Casimir Forces ◽  
Unit Cells ◽  
The Difference

The Casimir force between inhomogeneous slabs that exhibit a band-like structure is calculated. The slabs are made of basic unit cells each made of two layers of different materials. As the number of unit cells increases the Casimir force between the slabs changes, since the reflectivity develops a band-like structure characterized by frequency regions of high reflectivity. This is also evident in the difference of the local density of states between free and boundary distorted vacuum, that becomes maximum at frequencies corresponding to the band gaps. The calculations are restricted to vacuum modes with wave vectors perpendicular to the slabs.

Reduction of Computing Time and Improvement of Convergence Stability of the Monte Carlo Method Applied to Radiative Heat Transfer With Variable Properties

1989 ◽  
Vol 111 (1) ◽  
pp. 135-140 ◽  
Author(s):  
M. Kobiyama
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Computing Time ◽  
Energy Difference ◽  
Radiative Properties ◽  
Radiative Energy ◽  
Control Element ◽  
The Monte Carlo Method ◽  
The Difference ◽  
Convergence Stability

A modified Monte Carlo method is suggested to reduce the computing time and improve the convergence stability of iterative calculations without losing other excellent features of the conventional Monte Carlo method. In this method, two kinds of radiative bundle are used: energy correcting bundles and property correcting bundles. The energy correcting bundles are used for correcting the radiative energy difference between two successive iterative cycles, and the property correcting bundles are used for correcting the radiative properties. The number of radiative energy bundles emitted from each control element is proportional to the difference in emissive energy between two successive iterative cycles.

scholarly journals Tool Wear Assessment Approach Based on the Neighborhood Rough Set Model and Nearest Neighbor Model

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Ren Sheng ◽  
Xiaoran Zhu
Keyword(s):  
Rough Set ◽  
Nearest Neighbor ◽  
Milling Process ◽  
Two Dimension ◽  
Assessment Approach ◽  
Intersection Area ◽  
Neighborhood Rough Set ◽  
The Difference ◽  
Boundary Curves ◽  
Baseline State

In order to assess the degree of wear of tool for milling process quantitatively, a new assessment approach is proposed. Firstly, making full use of the neighbor information, two sensitive features are selected by using the neighborhood rough set model, and then, boundary curves are established by using the nearest neighbor model with noncounter data in two dimension spaces. Secondly, the intersection area or expanding area is used to describe the difference between two boundary models because the intersection area or expanding area can consider the effect of distance and angle simultaneously in two dimension spaces. Thirdly, after determining a baseline state, a new quantitative assessment indicator (QAI) can be calculated based on the intersection area or expanding area. The QAI can directly measure the difference between the model of baseline state and the model of unknown state and indirectly measure the degree of wear of tool. Finally, the effectiveness of the assessment approach is proven by using the Milling Dataset which was provided by the NASA Ames Research Center.

TIME-DEPENDENT DENSITY FUNCTIONAL STUDY OF MULTIELECTRON TRANSFER IN Cq+–Na4 COLLISIONS

2010 ◽  
Vol 24 (24) ◽  
pp. 4811-4820
Author(s):  
Y. P. ZHANG ◽  
F. S. ZHANG ◽  
Y. GAO ◽  
H. W. CHANG ◽  
G. Q. XIAO
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Local Density ◽  
Time Dependent ◽  
Functional Study ◽  
Density Approximation ◽  
Functional Theory ◽  
The Difference ◽  
Multielectron Transfer ◽  
Dependent Density

The process of multielectron transfer from a Na 4 cluster induced by highly charged C 6+, C 4+, C 2+ and C + ions is studied using the method of time-dependent density functional theory within the local density approximation combined with the use of pseudopotential. The evolution of dipole moment changes and emitted electrons in Na 4 is obtained and the time-dependent probabilities with various charges are deduced. It is shown that the Na 4 cluster is strongly ionized by C 6+ and that the number of emitted electrons per atom of Na 4 is larger than that of Na 2 under the same condition. One can find that the detailed information of the emitted electrons from Na 4 is different from the same from Na 2, which is possibly related to the difference in structure between the two clusters.

Electron-Phonon Coupling Strength of Specific Phonons from First Principles Lapw Calculations

1988 ◽  
Vol 141 ◽  
Author(s):  
H. Krakauer ◽  
R. E. Cohen ◽  
W. E. Pickett
Keyword(s):  
Coupling Strength ◽  
First Principles ◽  
Mode Coupling ◽  
Local Density ◽  
Matrix Elements ◽  
Dual Representation ◽  
Electron Phonon Interaction ◽  
Electron Phonon Coupling ◽  
Coupling Strengths ◽  
The Difference

AbstractElectron-phonon matrix elements, phonon linewidths and mode coupling strengths are being calculated for La2-xMxCuO4 (M-divalent cation, for paramagnetic x-0.0 and for x-0.15 in a rigid band picture) from first principles local density calculations. The change in potential due to a particular phonon mode is calculated from the difference of self-consistent one-electron potentials, and appropriate Fermi surface averages are carried out for selected modes, allowing us to obtain the phonon linewidth due to the electron-phonon interaction, and the corresponding coupling strength λQ. Here we establish the numerical accuracy within the dual representation of the potential used in the Linearized Augmented Plane Wave (LAPW) method. Evaluations of phonon linewidths and mode coupling strengths are presented for Al and Nb and compared with previous information on these modes. We present preliminary results for the full matrix elements and coupling of the La2CuO4 oxygen planar X-point breathing mode, and compare with a simpler approximation.

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