First-principles study on the effect of the interstitial oxygen ion on the spectral properties of PWO crystal and the origin of the green luminescence band

The electronic structures and absorption spectra of PWO crystals containing interstitial oxygen ions have been calculated using density functional theory code CASTEP with lattice structure optimized. It is shown by calculation that: (1) the interstitial oxygen ion in the perfect PWO crystal doesn’t bring any obvious absorption in the visible region; (2) the green emission of lead tungstate origin is closely related to the interstitial oxygen ion, and probably originates from the center of “ WO₄+O_i”.     

Effect of impurities on the growth of {113} interstitial clusters in silicon under electron irradiation

The growth and shrinkage of interstitial clusters on {113} planes were investigated in electron irradiated Czochralski grown silicon (Cz-Si), floating-zone silicon (Fz-Si), and impurity-doped Fz-Si (HT-Fz-Si) using a high voltage electron microscope. In Fz-Si, {113} interstitial clusters were formed only near the beam incident surface after a long incubation period, and shrank on subsequent irradiation from the backside of the specimen. In Cz-Si and HT-Fz-Si, {113} interstitial clusters nucleated uniformly throughout the specimen without incubation, and began to shrink under prolonged irradiation at higher electron beam intensity. At lower beam intensity, however, the {113} interstitial cluster grew stably. These results demonstrate that the {113} interstitial cluster cannot grow without a continuous supply of impurities during electron irradiation. Detailed kinetics of {113} interstitial cluster growth and shrinkage in silicon, including the effects of impurities, are proposed. Then, experimental results are analyzed using rate equations based on these kinetics.     

Imaging of the interstitial iron concentration in crystalline silicon by measuring the dissociation rate of iron–boron pairs

We present a dynamic approach for measuring the interstitial iron concentration in boron‐doped crystalline silicon using photoluminescence (PL) imaging. This camera‐based technique utilizes the characteristic dependence of the dissociation rate of iron–boron pairs on the interstitial iron concentration. We determine the dissociation rate by measuring the time‐dependent PL signal after complete association of iron–boron pairs in the sample. Since we are only interested in the time dependence of the PL signal, we are able to generate images of the interstitial iron concentration in absolute units without any calibration and without knowing the recombination properties of the interstitial iron or iron–boron pairs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical study on the temperature-induced structural transition of the Si(1 1 3) surface

The temperature-induced structural transition of the Si(1 1 3) surface is investigated by ab initio calculations. In this study, it is found that the room-temperature phase and the high-temperature phase have the 3 × 2 interstitial structure and the 3 × 1 interstitial structure, respectively. The existence of the 3 × 2 and 3 × 1 interstitial structures is supported by the analysis of scanning tunneling microscopy (STM) images and the calculation of surface core level shifts using final state pseudopotential theory. The theoretical STM images of interstitial structures are in good agreement with the STM images suggested by experiments. The analysis of STM images provides an insight into the characteristics of domain boundaries observed frequently in experiments. It is also found that the domain boundary can be formed by local 3 × 1 interstitial structures on the 3 × 2 interstitial surface. The theoretical analysis of the surface core level shifts reveals that the surface core levels in experiment originate from the interstitial structures. The lowest values in the surface core level shifts are found to be associated with the 2p core level shifts of the interstitial atoms.     

LiNH2储氢材料中间隙H与掺杂原子交互作用对其释氢性能影响机理研究

采用基于密度泛函理论的赝势平面波第一性原理方法,研究了LiNH₂缺陷及其掺杂原子交互作用对其释氢影响.通过对其进行优化求得它们的局域最稳定结构并计算了含间隙H原子缺陷的LiNH₂及其掺杂合金的结合能、间隙缺陷形成能、态密度和电荷布居.结果表明: 系统结合能不能反映LiNH₂及其掺杂合金的释氢性质;平衡时,LiNH₂中有一定的间隙氢原子存在,Mg,Ti掺杂使形成能大大降低,大大增大了间隙氢的浓度. 间隙H原子在带隙引入了缺陷能级使带隙大大减小,提高释氢能力.间隙H原子导致[NH₂]^-中N-H原子间相互作用减弱,容易释氢.间隙H与[NH₂]^-中N存在共价作用,可以解释LiNH₂释氢反应中NH₃的放出.当存在掺杂时,N-H键的键强不均衡,部分较弱,部分较强,较弱的N-H键中H容易放出. 关键词： 储氢材料 第一性原理 缺陷 释氢机理     

Mechanism for the enhanced diffusion of charged oxygen ions in SiO2

Based on real-space multigrid electronic structure calculations, we find that a double Si-O-Si bridge structure is the lowest energy configuration of interstitial oxygen ions (O(-) and O(2-)) in SiO2, where two additional Si-O bonds are formed with almost no interaction between the interstitial and host O atoms, while the peroxy linkage is the most stable structure for neutral interstitial O. We propose a diffusion mechanism of interstitial O ions generated from molecular O2 under UV radiation, and find extremely low energy barriers of 0.11--0.27 eV for migration in the form of the double-bridge structure, in good agreement with enhanced oxidation experiments.     

氧化锌发光中心的统计力学模型

根据ZnO结构的两种空隙(四面体和多面体),提出了一种发光模型.用统计系综求得了上述两种填隙锌的数量计算公式.     

Diffusion of interstitial Mn in the dilute magnetic semiconductor (Ga,Mn)As: the effect of a charge state

Migration barriers for diffusion of interstitial Mn in the dilute magnetic semiconductor (Ga,Mn)As are studied using first-principles calculations. The diffusion pathway goes through two types of interstitial sites: As coordinated and Ga coordinated. The energy profile along the path is found to depend on the ratio of concentrations between substitutional and interstitial Mn in GaAs. Two regions of distinctly different behavior, corresponding to n-type and p-type (Ga,Mn)As, are identified. The difference in mobility is a reflection of the change in the charge state of Mn interstitials (double donors) that occurs in the presence of substitutional Mn impurities (acceptors). In addition, substitutional Mn impurities are shown to act as traps for interstitial Mn. The effective migration barrier for the positively doubly charged Mn interstitials in p-type (Ga,Mn)As is estimated to vary from 0.55 to about 0.95 eV.     

Theoretical study of the effects of vacancy and oxygen impurity on Ti_2GaC

This paper presents the mono-vacancy formation and migration energies of each element Ti, Ga, and C in the MAX phase Ti2GaC, which are obtained by first principles calculations. We also calculate the formation energies of oxygen substituting for Ti, Ga, and C and two formation energies of oxygen interstitial in different sites. The results show that the formation energy of oxygen substituting for Ti is the highest, and the formation energies of the O substitution for Ga atoms decrease as the oxygen concentration increases. The two different formation energies of one oxygen interstitial show that the stable site for the oxygen interstitial is at the center of the triangle composed by three Ga atoms. The effects of vacancy,oxygen substitution, and the interstitial on the electronic properties of Ti2GaC are also discussed in light of the density of states and the electron charge density.     

Atomistic Simulations of the Effect of Helium on the Dissociation of Screw Dislocations in Nickel

The interactions of He with dissociated screw dislocations in face-centered-cubic(fcc) Ni are investigated by using molecular dynamics simulations based on an embedded-atom method model.The binding and formation energies of interstitial He in and near Shockley partial cores are calculated.The results show that interstitial He atoms at tetrahedral sites in the perfect fcc lattice and atoms occupying sites one plane above or below one of the two Shockley partial cores exhibit the strongest binding energy.The attractive or repulsive nature of the interaction between interstitial He and the screw dislocation depends on the relative position of He to these strong binding sites.In addition,the effect of He on the dissociation of screw dislocations are investigated.It is found that He atoms homogeneously distributed in the glide plane can reduce the stacking fault width.     

Fractionation of Oxygen and Hydrogen Isotopes at the Hydrate Gas forming in the Sea Sediments

The paper gives data on isotope composition of interstitial and near-bottom waters sampled in a region of gas-hydrate formation in the Sea of Okhotsk. The studies shows that heavy isotope of oxygen and hydrogen is used in gas-hydrate formation, with the result that isotope composition of its constitution water constitutes δ¹⁸O = +1.99‰, δD = +23‰ relatively to SMOW. Formation of autogenic carbonates leads to isotope exchange with interstitial water wich, in turn, changes its primary isotope composition in the direction of increasing of O-18 content. The near-bottom waters are isotope-light relatively to the SMOW standard and to the mean isotope composition of interstitial water in the studied region of gas-hydrate spreading.     

Effect of lattice deformations on the local,magnetic dipole field of interstitial sites in H.C.P. crystals

It is shown that lattice deformations around interstitial atoms may give a significant contribution to the local magnetic dipolar field at the interstitial site. An analysis of the dipole field measured for mouns on octahedral interstitial sites in Co shows that 1/4 of the dipole field results from lattice deformations. The double force tensor of the muon is found to be nearly isotropic and of the order of magnitude of 4eV.     

Investigation of the guided-mode characteristics of hollow-core photonic band-gap fibre with interstitial holes

This paper investigates the guided-mode characteristics of hollow-core photonic band-gap fibre (HC-PBGF) with interstitial holes fabricated by an improved twice stack-and-draw technique at visible wavelengths. Based on the simulation model with interstitial holes, the influence of glass interstitial apexes on photonic band-gaps is discussed. The existing forms of guided-mode in part band gaps are shown by using the full-vector plane-wave method. In the experiment, the observed transmission spectrum corresponds to the part band gaps obtained by simulation. The fundamental and second-order guided-modes with mixture of yellow and green light are observed through choosing appropriate fibre length and adjusting coupling device. The loss mechanism of guided-modes in HC-PBGF is also discussed.     

Radiance-based monitoring of the extent of tissue coagulation during laser interstitial thermal therapy

Optical monitoring relates the dynamic changes in measured light intensity to the extent of treatment-induced coagulation that occurs during laser interstitial thermal therapy. We utilized a two-region Monte Carlo simulation to elucidate the nature of the changes in interstitial radiance and fluence that result from the formation of a volume of thermal coagulation surrounding a cylindrical emitter. Using simulation results, we demonstrate that radiance sensors are more sensitive than traditional fluence sensors to coagulation-induced scattering changes. Radiance measurements take advantage of directional detection angles that are more receptive to the onset and passing of the coagulation boundary. We performed experiments with albumen phantoms to demonstrate the practicality of the radiance method for monitoring interstitial laser thermal therapy.     

Application of a solvation shell analysis to the diffusivity of an interstitial species in binary substitutional solutions

A model is presented for the effect of substitutional solute elements on the diffusion coefficient of an interstitial species for low concentrations of both solutes. The model is based on the theory of absolute reaction rates and a Wagner random, noninteractive model for the substitutional solution, with Maxwell-Boltzmann statistics for the distribution of the interstitial atoms. Simplifying assumptions are made concerning the configuration of activated complexes, treating them as formed by the interstitial atom and the two nearest lattice atoms. The calculations are compared with experimental data reviewed for the diffusivity of carbon in Fe-Cr, Fe-Mn, Fe-Co and Fe-Ni alloys.     

Novel sb induced reconstruction of the (113) surface of ge

Sb induces on Ge(113) a c(2 x 2) reconstruction in which Sb breaks one Ge-Ge bond and occupies an interstitial site, in contrast to Sb adsorption on other Si or Ge surfaces. Sb saturates the three dangling bonds per unit cell of the (113) surface inducing a large strain which is released by occupation of the interstitial site. Two neighboring Sb at interstitial sites form a dimer. The structure has been determined by x-ray diffraction, applying direct methods, and ab initio density-functional-theory calculations. The adsorption geometry and the high binding energy lead one to expect that Sb cannot be used as a surfactant for the growth of Si/Ge layers on the (113) surface.     

On the theory of interactions and thermodynamic properties of carbon atoms in hcp and fcc iron

General expressions are derived for deformational interactions of interstitial atoms in an hcp interstitial alloy MeX _c taking into account Me-X interactions of any range. These expressions are used for obtaining quantitative estimates of both deformational and chemical interactions of carbon atoms in hcp iron-carbon alloys. The results show that the interactions of interstitial atoms in hcp alloys noticeably differ from analogous interactions in cubic alloys, being more anisotropic, more extended, and more sharply oscillating with increasing distance. Analytical expressions are obtained for the thermodynamic contribution of interstitial atoms in disordered MeX _c alloys using both the simple mean field approximation and more exact cluster methods. Comparison of the results of such calculations for austenite with the results of simulation based on the Monte Carlo technique and with experimental data shows that the accuracy of the mean field approximation for MeX _c alloys is very low due to strong repulsion of neighboring interstitial atoms. On the other hand, the accuracy of cluster methods remains high for all temperatures and concentrations under consideration.     

间隙原子对ZnNb2O6光电特性影响的第一性原理研究

基于密度泛函理论第一性原理,研究Zn、Nb、O间隙原子对ZnNb2 O6体系光电特性的影响.分析显示:间隙原子对体系晶格畸变的影响与间隙原子几何尺寸有关.缺陷结构中,由于间隙原子电负性存在差异,也是产生晶格畸变的因素.光电特性分析显示:含有Zn、Nb间隙原子的体系表现为n型简并半导体.且Nbi表现出较强的介电效应,主要...     

Influence of hydrostatic pressure on the native point defects in wurtzite ZnO: Ab initio calculation

The formation energies and transition energy levels of native point defects in wurtzite ZnO under applied hydrostatic pressure are calculated using the first-principle band-structure methods. We find that the pressure coefficient of the (2+/0) level for oxygen vacancy is larger than that of the (2+/1+) level for zinc interstitial, which demonstrates that the donor level of oxygen vacancy is deeper than that of zinc interstitial, therefore the latter is the more probable electron resource in native n-type ZnO. And the significantly different pressure dependence of the transition levels between them can be used to determine the origin of the green luminescence center in ZnO. Zinc octahedral interstitial and oxygen tetrahedral interstitial configurations became the dominant defects under 5 GPa at their favorable growth conditions, respectively. The formation of defects under applied pressure is the result of fine interplay between internal strains, charges on the defects and applied external pressures.