Search results for "angling"
showing 10 items of 99 documents
Molecular polarizability of Si/Ge/GaAs semiconductors clusters
2004
The interacting induced dipole polarization model implemented in our program for the calculation of molecular polarizabilities (POLAR) is used for the calculation of the molecular dipole-dipole polarizability ${\overline{\overline{α}}}$. POLAR is tested with Si$_{n}$, Ge$_{n}$ and Ga$_{n}$As$_{m}$ small 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 in agreement with reference calculations performed with our version of the program PAPID (polarisabilites atomiques par interactions dipolaires) and with reference computations from Dr. J.R. Che…
Oxygen-excess-related point defects in glassy/amorphous SiO2 and related materials
2012
Abstract An insight is given into recent experimental advances in the spectroscopic studies of oxygen-excess intrinsic defects, in glassy SiO 2 and α-quartz. By controlling excess oxygen in a-SiO 2 , and the conditions of F 2 -laser irradiation, SiO 2 glass samples can be obtained with optical absorption almost exclusively dominated by single defect, oxygen dangling bonds (“non-bridging oxygen hole centers” or NBOHCs), without the presence of complementary Si dangling bonds (generic “E′-centers”). This allows for a more accurate determination of the spectral shape of NBOHC optical absorption in UV and vacuum UV spectral regions. The temperature dependence of NBOHC electron paramagnetic reso…
Experimental evidence for two different precursors of E’γ centers in silica
2004
Electron paramagnetic resonance measurements of concentration and line shape of centers induced by γ ray irradiation are presented for natural and synthetic commercial silica with different OH contents. Synthetic materials with OH content >200 ppm by weight show one line shape for all investigated doses. In contrast, the other materials show a different line shape at low irradiation doses. Differences are also observed in the concentration growth of the centers in synthetic wet materials and in the other materials. The results are interpreted as evidence of two centers distinguishable by their line shape and having different precursors.
Luminescence features of nonbridging oxygen hole centres in silica probed by site-selective excitation with tunable laser
2008
Time-resolved photoluminescence at 1.9 eV associated with the nonbridging oxygen hole centre (NBOHC) in silica was investigated under excitation with a ns pulsed laser system, tunable in the visible range. Mapping of the excitation/emission pattern evidences the site-selective excitation of the resonant zero phonon line (ZPL) transition due to its weak coupling with the stretching mode of dangling oxygen. Decay of ZPL follows an exponential law with lifetime of 15.3 μs, which provides a precise measure of the electronic transition probability of a single NBOHC.
Luminescence of non-bridging oxygen hole centers as a marker of particle irradiation of {\alpha}-quartz
2021
The origin of the "red" emission bands in the 600 nm-700 nm region, observed in quartz crystals used for luminescence dating and environmental dosimetry, is still controversial. Their reported spectral and lifetime characteristics are often similar to those of oxygen dangling bonds ("non-bridging oxygen hole centers, NBOHCs") in glassy silicon dioxide. The presence of these "surface radical type" centers in quartz crystal requires sites with highly disordered local structure forming nano-voids characteristic to the structure of glassy SiO2. Such sites are introduced in the tracks of nuclear particles ({\alpha}-irradiation, neutrons, ions). In case of electrons they are created only at large…
Potentials and Electronic Structure Calculations of Non-regular Nanosystems
2017
Methods of numerical investigations of potentials and pseudopotentials for fundamental properties calculations (electronic, vibrational, electron-phonon phenomena, etc.) of condensed matter constitute a basic principle of modelling. It is very essential to find specific analytical approaches to the calculation of atomic and ‘crystalline’ potentials to make the calculations most effective. In particular, we pay attention to the modelling of pure Coulomb contributions and their exchange-correlation corrections in the framework of Xα- и Xαβ-approximations.
Optical absorption band at5.8eVassociated with theEγ′centers in amorphous silicon dioxide: Optical absorption and EPR measurements
2008
Line shape modifications induced by thermal treatment in the optical absorption and electron paramagnetic resonance (EPR) signals associated with the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center are experimentally investigated in various types of $\ensuremath{\gamma}$-irradiated amorphous silicon dioxide $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$. The $g$ values of the EPR main resonance line of the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center show a shift correlated with the peak energy variation of the absorption band at about $5.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ associated with this defect. These spectroscopic changes are proposed to originate from structu…
In situobservation of the formation, diffusion, and reactions of hydrogenous species inF2-laser-irradiatedSiO2glass using a pump-and-probe technique
2006
We quantitatively studied the formation, diffusion, and reactions of mobile interstitial hydrogen atoms $({\mathrm{H}}^{0})$ and molecules $({\mathrm{H}}_{2})$ in ${\mathrm{F}}_{2}$-laser-irradiated silica $(\mathrm{Si}{\mathrm{O}}_{2})$ glass between 10 and $330\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Two key techniques were used: single-pulse ${\mathrm{F}}_{2}$ laser photolysis of silanol (SiOH) groups to selectively create pairs of ${\mathrm{H}}^{0}$ and oxygen dangling bonds (nonbridging oxygen hole centers, NBOHC), and in situ photoluminescence measurements of NBOHCs to monitor their reactions with ${\mathrm{H}}^{0}$ and ${\mathrm{H}}_{2}$ as a function of time and temperature. A smalle…
Elementary Polarizability of Sc/Fullerene/Graphene Aggregates and Di/Graphene–Cation Interactions
2014
Elementary Polarizability of Sc/Fullerene/Graphene Aggregates and Di/Graphene–Cation Interactions Interacting induced-dipoles polarization in code POLAR allows molecular polarizability, which is tested with Scn/Cn [fullerene/ graphene (GR)]/Scn@Cm clusters. Polarizability sees clusters of unlike sizes, parting isomers. Bulk limit is estimated from Clausius– Mossotti relation. Clusters are more polarizable than the bulk. Theory yielded this for small Sin/Gen/GanAsm; however, experiment, reversely for larger Sin/GanAsm/GenTem. Smaller clusters need not act like middle: surface dangling bonds cause small-clusters polarizability that resembles metallic. Code AMYR models GR(2)– Mz+. A 24-atom pl…
Molecular polarizability of semiconductor clusters and nanostructures
2002
Abstract The interacting-induced-dipoles polarization model implemented in program PAPID is used for the calculation of the molecular dipole–dipole polarizability α . The method is tested with Si n , Ge n and GanAsm small clusters. On varying the number of atoms, the clusters show numbers indicative of particularly polarizable structures. The results for the polarizability are in agreement with reference calculations from Chelikowsky. The bulk limit for the polarizability is estimated from the Clausius–Mossotti relationship. The polarizability trend for these clusters as a function of size is different from what one might have expected. The clusters are all more polarizable than what one mi…