Search results for "angling"

Density functional study of gold atoms and clusters on a graphite (0001) surface with defects

2006

Adsorption of gold atoms and clusters $(N=6)$ on a graphite (0001) surface with defects has been studied using density functional theory. In addition to perfect graphite (0001), three types of surface defects have been considered: a surface vacancy (hole), a pyridinelike defect comprising three grouped nitrogen atoms, and a substitutional doping by N or B. Results for Au and ${\mathrm{Au}}_{6}$ indicate that the surface vacancy can form chemical bonds with Au as the three nearby carbons align their dangling bonds towards the gold particle (binding energy 2.4--$2.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$). A similar chemically saturated holelike construction with three pyridinic N atoms resul…

Electronic Structure of Oxygen Dangling Bond in GlassySiO2: The Role of Hyperconjugation

2003

The electronic structure and the nature of optical transitions in oxygen dangling bond in silica glass, the nonbridging oxygen hole center (NBOHC), were calculated. The calculation reproduced well the peak positions and oscillator strengths of the well-known optical absorption bands at 2.0 and 4.8 eV, and of the recently discovered absorption band at 6.8 eV. The 2.0 eV band was attributed to transition from the $\ensuremath{\sigma}$ bond between Si and dangling oxygen to nonbonding $\ensuremath{\pi}$ orbital on the dangling oxygen. The uniquely small electron-phonon coupling associated with the 2.0 eV transition is explained by stabilization of Si-O bond in the excited state by hyperconjuga…

<title>Advances in silica-based glasses for UV and vacuum UV laser optics</title>

2003

The origins of pre-existing and laser-induced ultraviolet (UV) and vacuum ultraviolet (VUV) optical absorption in state-of-the-art glassy silicon dioxide and the ways to improve it are reviewed. The main causes of pre-existing absorption in UV/VUV are oxygen vacancies, hydroxyl (silanol) groups, and strained bonds/localized states due to glassy disorder. The main absorption bands induced by UV/VUV excimer lasers are due to oxygen vacancies and due to silicon and oxygen dangling bonds (E'-centers and non-bridging oxygen hole centers, respectively). The optimized glasses are achieved via an intricate balance between a good stoichiometry, use of network modifiers (F or OH) to reduce the number…

DFT studies of OH-functionalized open-ended zigzag, armchair, and chiral single wall carbon nanotubes

2011

The functionalization of single-wall carbon nanotubes (SWCNTs) by attaching various molecules or molecular groups to the exterior walls or tips has attracted much attention, because it offers a possible way to modify their electronic, chemical, optical and mechanical properties. In this contribution the results of DFT studies of pristine and OH-modified open-ended zigzag (9,0), armchair (5,5) and chiral (8,2) nanotubes are reported. The calculations have been performed for partially and fully functionalized at one end model SWCNTs with dangling bonds saturated with hydrogen atoms and a nonadditive dependence of attachment energy on the number of substituents was observed.

Mismatch strain versus dangling bonds: formation of "coin-roll nanowires" by stacking nanosheets.

2010

Anisotropic optical response of GaN and AlN nanowires.

2012

We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire. For both GaN and AlN nanowires, we have found a remarkable anisotropy of the optical absorption when the light-polarization changes, showing in the case of GaN a dependence on the nanowire size.

<title>Quantum chemical simulation of silicon nanostructures</title>

1999

The point defects in silicon, their migration, geometry and electronic structure, as well as some models for nanowires, were studied. The ab initio Self Consistent Field Molecular Orbital method and the molecular cluster model were used. Hydrogen pseudoatoms were used to saturate dangling bonds of the cluster. The influence of the compression onto defect structure and properties was simulated by changing the bond length value. The silicon interstitial migration activation energy, calculated as the difference between the total energies of the cluster with interstitial in tetrahedral and hexagonal positions, is 4.21 eV, and it does not depend on local pressure. The influence of high pressure …

Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides

2020

The present work elaborates on the correlation between the amount and ordering of the free carbon phase in silicon oxycarbides and their charge carrier transport behavior. Thus, silicon oxycarbides possessing free carbon contents from 0 to ca. 58 vol.% (SiOC/C) were synthesized and exposed to temperatures from 1100 to 1800 &deg

Intrinsic defect formation in amorphousSiO2by electronic excitation: Bond dissociation versus Frenkel mechanisms

2008

Two competing mechanisms of intrinsic defect formation in amorphous ${\text{SiO}}_{2}$ $(a{\text{-SiO}}_{2})$, i.e., the vacancy-interstitial (Frenkel) mechanism and Si-O bond dissociation to form silicon and oxygen dangling bonds, were compared under $\ensuremath{\gamma}$-ray electronic excitation. The Frenkel mechanism was found to be dominant. The concentrations of both kinds of defects strongly correlate with the degree of the structural disorder of $a{\text{-SiO}}_{2}$, providing experimental evidence that both types of intrinsic defect pairs are formed mainly from the strained Si-O-Si bonds. The bond dissociation mechanism is more susceptible to the structural disorder than the vacanc…

-ray-induced intrinsic defect processes in fluorine-doped synthetic SiO2 glasses of different fluorine concentrations

2009

Fluorine-doped synthetic SiO2 glass is suitable for investigating intrinsic defect processes in SiO2 glass because of the high radiation hardness and the low concentrations of defect precursors such as the strained Si O Si bonds and impurity-related network modifiers including SiOH, SiH, and SiCl groups. When the concentrations of the defect precursors are minimized by moderate fluorine doping into SiO2 glass, formation of oxygen vacancy–interstitial pairs (Frenkel pairs) is the primarily Co60γ-ray-induced defect process. However, heavy fluorine doping tends to degrade the radiation hardness and enhance the formation of the silicon and oxygen dangling bonds, suggesting the presence of anoth…