Search results for "Dangling bond"
showing 10 items of 52 documents
An increased F2-laser damage in ‘wet’ silica glass due to atomic hydrogen: A new hydrogen-related E′-center
2006
Abstract A dramatic increase of F2-laser induced room temperature-stable point defects in ‘wet’ synthetic silica glass occurs when irradiation temperature is lowered to 80 K. Contrary to the predictions based on the established models of defect processes, a large part of defects induced at 80 K remains stable also at the room temperature. The intensities of the laser-induced optical absorption bands of the non-bridging oxygen hole centers (2.0 and 4.8 eV) and E′-centers (5.8 eV) are comparable to those created by neutron irradiation (1018 n/cm2). A growth of infrared absorption peak at 2237 cm−1 indicates creation of silicon hydride (SiH) groups. A study of irradiation dose dependences and …
Temperature dependance of the generation and decay of E’ centers induced in silica by 4.7eV laser radiation
2009
We report a study of the generation of silicon dangling bonds (E' centers) induced in fused silica by 4.7 eV laser irradiation in the 10 200 K the induced defects undergo a post-irradiation decay due to their reaction with mobile H(2). The interplay between generation and annealing gives rise to a bell-shaped temperature dependence of the concentration of induced E' centers, peaking at 250 K
Effects of temperature on electron paramagnetic resonance of dangling oxygen bonds in amorphous silicon dioxide
2011
The properties of electron paramagnetic resonance (EPR) signal of oxygen dangling bonds in amorphous SiO2 ("non-bridging oxygen hole centers", NBOHC) in excimer laser-irradiated amorphous SiO2 were studied in the temperature range 20K to 295K. NBOHCs strongly affect optical and chemical properties of amorphous SiO2 -based (nano) structures and their surfaces. The behaviour of their EPR signal is complicated due to a nearly degenerate electronic ground state. It was found that EPR signal has a non-Curie (~1/T) T-dependence down to 40K, indicating that EPR-based concentration estimates routinely obtained at T = 77K underestimate the center concentrations at least by a factor of 1.7. The estim…
Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review
2008
This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO 2 (a-SiO 2 ). The most common form of interstitial oxygen species is oxygen molecule (O 2 ), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial 0 2 provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O 2 in long-range oxygen transport in a-SiO 2 ; formation of the Frenkel defect pair (Si-Si bond and interstitial oxygen atom, 0°) by dense electronic excitation; efficient photolysis of interstitial O 2 into O° with F 2 laser light (λ= 157…
Structural, chemical and dynamical trends in graphene grain boundaries
2010
Grain boundaries are topological defects that often have a disordered character. Disorder implies that understanding general trends is more important than accurate investigations of individual grain boundaries. Here we present trends in the grain boundaries of graphene. We use density-functional tight-binding method to calculate trends in energy, atomic structure (polygon composition), chemical reactivity (dangling bond density), corrugation heights (inflection angles), and dynamical properties (vibrations), as a function of lattice orientation mismatch. The observed trends and their mutual interrelations are plausibly explained by structure, and supported by past experiments.
Role of Mobile Interstitial Oxygen Atoms in Defect Processes in Oxides: Interconversion between Oxygen-Associated Defects inSiO2Glass
2004
The role of mobile interstitial oxygen atoms (${\mathrm{O}}^{0}$) in defect processes in oxides is demonstrated by interconversion between the oxygen dangling bond and the peroxy radical (POR) in ${\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ glass. Superstoichiometric ${\mathrm{O}}^{0}$ was created by ${\mathrm{F}}_{2}$ laser photolysis of the interstitial ${\mathrm{O}}_{2}$. On annealing above $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, ${\mathrm{O}}^{0}$ migrated and converted the oxygen dangling bond to POR. Exposure to 5.0 eV light converted POR back to a pair of the oxygen dangling bond and ${\mathrm{O}}^{0}$ (quantum yield: $\ensuremath{\sim}0.1$). These findings suggest that…
Ab initio calculation of wurtzite‐type GaN nanowires
2007
Ab initio calculations of wurtzite-type GaN nanowires have been performed using density functional theory. Different shapes of nanowires of with similar diameters of around 2 nm have been considered to determine the stability of the structures. The quantitative similarities in the local properties obtained and dangling bond energies of nanowires and bulk surfaces have lead to a simple model model for a calculation of effective Young's modulus of nanowires of arbitrary diameters and shapes. The size dependence of the Young's modulus reveals a softening of GaN nanowires with the decrease of the diameter. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Crucial dependence of excimer laser toughness of “wet” silica on excess oxygen
2011
Creation of point defects by ArF (6.4 eV) and F2 laser (7.9 eV) irradiation in synthetic “wet” silica glass thermally loaded with interstitial O2 molecules was studied by optical absorption, electron paramagnetic resonance and infrared absorption. The presence of excess oxygen caused a significant increase of laser-induced ultraviolet (UV) absorption, which was 4 times (7.9 eV-irradiation) and > 20 times stronger (ArF irradiation) as compared to O2-free samples. The spectral shape of photoinduced absorption nearly completely coincided with the spectral shape of oxygen dangling bonds (NBOHC) in 3 to 6.5 eV regions. The contribution of Si dangling bonds (E' centers) was less than few % and wa…
Molecular polarizability of fullerenes and endohedral metallofullerenes
2002
The interacting induced dipoles polarization model implemented in our program POLAR is used for the calculation of the molecular dipole µ and tensor quadrupole moments and also the dipole–dipole polarizability . The method is tested with Scn, Cn (fullerene and graphite) and endohedral Scn@Cm clusters. The polarizability is an important quantity for the identification of clusters with different numbers of atoms and even for the separation of isomers. The results for the polarizability are of the same order of magnitude as from reference calculations performed with our version of the program PAPID. The bulk limit for the polarizability is estimated from the Clausius–Mossotti relationship. The…
Generation of defects in amorphous SiO(2) assisted by two-step absorption on impurity sites.
2011
Generation of the Si dangling bond defect in amorphous SiO(2) (E' centre) induced by tunable pulsed UV laser radiation was investigated by in situ optical absorption measurements. The defect generation efficiency peaks when the photon energy equals ∼5.1 eV, it depends quadratically on laser intensity and is correlated with the native linear absorption due to Ge impurities. We propose a model in which the generation of E' is assisted by a two-step absorption process occurring on Ge impurity sites.