Search results for "Crystallographic"
showing 10 items of 202 documents
Fast and robust phase-shift estimation in two-dimensional structured illumination microscopy.
2019
A method of determining unknown phase-shifts between elementary images in two-dimensional Structured Illumination Microscopy (2D-SIM) is presented. The proposed method is based on the comparison of the peak intensity of spectral components. These components correspond to the inherent structured illumination spectral content and the residual compo- nent that appears from wrongly estimated phase-shifts. The estimation of the phase-shifts is carried out by finding the absolute maximum of a function defined as the normalized peak intensity difference in the Fourier domain. This task is performed by an optimization method providing a fast estimation of the phase-shift. The algorithm stability an…
Modelling of silver adhesion on MgO(100) surface with defects
1999
We show how surface defects (especially Fs 0 and Vs 0 centres) can play a major role in the adhesion of Ag (at 1:4 and 1:1 coverages) on the MgO(100) surface. Our calculations use a periodic (slab) model and an ab initio Hartree-Fock approach with a posteriori electron correlation corrections. We are able to analyse the interatomic bond populations, effective charges and multipole moments of ions, in combination with the interface binding energy and the equilibrium distances. Both surface defects cause strong redistributions of the electron density which increase the binding energy of metal atoms by more than an order of magnitude. This implies radiation-induced strengthening of metal adhes…
Ab InitioModeling of Metal Adhesion on Oxide Surfaces with Defects
2000
Our ab initio studies show that surface defects cause redistribution of the electron density which can increase substantially the binding energy of metal atoms to oxide surfaces. The results for electron $({F}_{s}^{0})$ and hole $({V}_{s}^{0})$ centers in the adhesion of Ag atoms (at 1:4 and 1:1 coverages) to a MgO(100) surface, combined with previous studies for charged defects, support earlier ideas of the mechanism of radiation-enhanced adhesion of nonreactive metals on oxide substrates. The results suggest that some optical control of adhesion energies is possible through charge transfer.
Investigation on the microscopic structure of E' center in amorphous silicon dioxide by electron paramagnetic resonance spectroscopy
2006
The E′δ center is one of the most important paramagnetic point defects in amorphous silicon dioxide ( a-SiO 2) primarily for applications in the field of electronics. In fact, its appearance in the gate oxide of metal-oxide-semiconductor (MOS) structures seriously affects the proper work of many devices and, often, causes their definitive failure. In spite of its relevance, until now a definitive microscopic model of this point defect has not been established. In the present work we review our experimental investigation by electron paramagnetic resonance (EPR) on the E′δ center induced in γ-ray irradiated a-SiO 2. This study has driven us to the determination of the intensity ratio between…
Electron paramagnetic resonance investigation on the hyperfine structure of the center in amorphous silicon dioxide
2007
Abstract We report an experimental investigation by electron paramagnetic resonance (EPR) spectroscopy on the hyperfine structure of the E δ ′ center in γ-ray irradiated amorphous silicon dioxide materials. This study has driven us to the determination of the intensity ratio between the hyperfine doublet and the main resonance line of this point defect. This ratio was obtained for a variety of silica samples and compared with the analogous ratio obtained for the E γ ′ defect. The comparison definitively confirms that the electronic wave function involved in the E δ ′ center is actually delocalized over four nearly equivalent Si atoms.
Effects of Mn doping on dielectric properties of ferroelectric relaxor PLZT ceramics
2017
This work has been supported by Latvian state research program IMIS2 .
Radiation induced generation of non-bridging oxygen hole center in silica: Intrinsic and extrinsic processes
2007
Abstract The generation of non-bridging oxygen hole center ( Si–O ) was investigated in a wide variety of natural (fused quartz) and synthetic silica samples exposed to different γ- and β-irradiation doses by looking at its optical bands. We distinguish two different generation processes: intrinsic associated with the cleavage of Si–O bond and characterized by a sublinear law and extrinsic due to the conversion of OH precursor characterized by a growth curve with a saturating tendency. The interplay between the two processes and the role of H are discussed.
Large-scale ab initio modelling of defects in perovskites: Fe impurity in SrTiO3
2002
Abstract Using the unrestricted Hartree–Fock method and supercells containing up to 160 atoms, we calculated the energy level positions in the gap and atomic geometry for the Fe4+ impurity substituting for a host Ti atom in SrTiO3. In agreement with experiment, the high-spin (S=2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacement mode of the six nearest O ions which is a combination of the Jahn–Teller and breathing modes. A considerable covalent bonding between the Fe ion and the four nearest O ions takes place.
A First Principles Study on Charge Dependent Diffusion of Point Defects in Rutile TiO2
2010
A first principles theoretical study on the diffusion mechanism of Ti interstitials and O vacancies in rutile TiO2 is reported. We find that the diffusion depends strongly on the defect charge. Wea...
Defects in glasses
1995
Abstract The absence of long range order in the glass structure allows to define only point defects in these materials. They are: 1) intrinsic defects—atomic size local deviation from short range order; 2) impurity defects—isolated impurity atoms or ions in the glass network; 3) intrinsic impurity defects—complexes consisting of the impurity atoms chemically bonded to one of the intrinsic defect atoms. The latter defects are characteristic for the doped glasses. Presence of point defects in glasses introduces new spectroscopic properties of these solid materials. Defect generation, interaction and recombination reactions resulting from the external influence causes the glass spectroscopic p…