Solubility of Substitutional Impurities in Interstitial Solid Solutions

The solubility coefficient of a substitutional impurity in interstitial solid solutions is calculated within a dynamic model. The presence of an interstitial component increases solubility. In solutions where the interaction between interstitial atoms is negative, a long-range order occurs at interstitial sites at temperatures lower than a certain value. This also causes changes in solubility. An increase in solubility of substitutional impurities is due to ordering at temperatures close to the transition point in the case where the concentration of the interstitial component exceeds 11 at. %. Conversely, solubility decreases due to ordering at lower concentrations. It is shown that an isotopic effect must be observed in solubility of substitutional atoms.     

The thermodynamics of palladium-based solid solutions containing a noble-metal substitutional solute and hydrogen

A cell model for tenary solid solutions containing a substitutional and an interstitial solute species is considered. The interstitial solute is restricted to cells (interstitial sites) in the f.c.c. solvent lattice in which it has either zero or one nearest neighbor substitutional solute atom. The effects of the dilation of the solvent lattice by the substitutional solute are taken into account in an appropriate manner using the currently limited elastic data available.It is shown that the model is in good accord with the measured partial enthalpies and excess entropies in the Pd-Ag-H system, in which the Ag atoms cause a positive lattice dilation, but not for the case of Pd-Cu-H, where there is a contraction.     

Electronic structure calculations of substitutional and interstitial hydrogen in Nb

We report the results of a theoretical study on the effects of substitutional and interstitial hydrogen atoms in niobium. We confirm that any contaminated hydrogen will occupy the interstitial site over the substitutional site in niobium. For interstitial hydrogens, the lattice deformation increases with the percentage content of hydrogen, though it is negligible at low concentrations. Substitutional hydrogens are found to prefer off-center sites in the host lattice.     

In-beam Mössbauer spectroscopy:57Fe in Si and Ge

Fe has been studied in the semiconductors Si and Ge with the Coulomb excitation recoil implantation technique in a wide temperature range. In the case of Fe inSilicon it was found that one third of the implanted atoms land on interstitial sites. The long range diffusion of these atoms could be observed microscopically at temperatures around 600 K. The isomer shift of interstitial Fe in Si was determined. The remaining atoms exhibit a strong quadrupole splitting on disturbed sites. This component seems to relax into a state with higher symmetry above 700 K. InGermanium a similar situation is found. Whereas iron on disturbed sites dominates the spectra, the direct implantation into interstitial sites is also observed below 200 K. At higher temperatures the substitutional position is preferred. The isomer shifts for interstitial and substitutional Fe in Si and in Ge are in good agreement with calculated electron densities.     

Thermodynamics of ternary Fe-Co-N austenites

Gas-solid equilibrium measurements have been used to determine the variation with cobalt concentration in the range 0–9 at. % Co of the partial molar enthalpies and excess entropies in ternary Fe-Co-N austenites in the temperature range 1173–1503 K. The resulting thermodynamic data show a relative invariance in these thermodynamic functions in excellent accord with the cell model for ternary solid solutions containing a substitutional and an interstitial species in which the presence of the substitutional species creates “antitrapping” sites for interstitial atoms.     

Influence of impurities on the work of separation along the interface of joined materials

In this work, on the basis of the thermodynamic approach, we develop a general model for the estimation of the influence of point defects on the work of separation of joined materials. The expressions of the work of separation for the case when defects are atoms of interstitial or substitutional impurities are obtained and analyzed.     

Sites and diffusion for muons and hydrogen in titanium hydrides

Low temperature sites for muons implanted in TiHx have been found to be a mixture of interstitial and substitutional sites, with substitutional occupancy determined by the probability that a muon in an interstitial site will have a vacant nearest neighbor substitutional site. As with ZrHx, activation from the interstitial site is observed below 300 K. From the depolarization rate in the substitutional site, the muon likely displaces the neighboring H atoms by about 0.1 A. Diffusion for the substitutional muons occurs above room temperature with an activation of about 0.38 eV, which is less than the 0.505 eV for hydrogen vacancy motion observed by NMR. To explain this the muon transition rate to a vacancy must be less than that of hydrogen.     

Ab initio thermodynamic characteristics of the formation of oxygen vacancies,and boron,carbon, and nitrogen impurity centers in anatase

Using the ab initio projector augmented wave (PAW) method, calculations are performed for the electronic energy-band structure of titanium dioxide having the structure of anatase doped with boron, nitrogen, and carbon. Thermodynamic characteristics are determined for the formation of impurity centers, such as the preference energy for the interstitial position, the energy of impurity oxidation, and the energy of oxygen vacancy formation. It is shown that under the conditions of thermodynamic equilibrium the interstitial position of boron atoms is stable, whereas carbon atoms, depending on the oxygen pressure, can occupy both interstitial positions and substitutional positions of oxygen atoms, and nitrogen atoms replace oxygen atoms. It is shown that the presence of oxygen vacancies promotes the thermodynamic stability of carbon and nitrogen atoms. The obtained densities of electronic states correspond to ESR spectroscopy data, which indicates the presence of spin-polarized electrons in the states of the oxygen vacancy.     

The effect of substitutional impurity atoms on the diffusivity of an interstitial species

A model has been developed to treat the problem of the effect of substitutional solute elements on the diffusion of an interstitial species. The calculation applies only to cases where the substitutional solute creates “antitrapping” sites, whose energies are higher than the “normal” interstitial sites in the defect-free solvent lattice.The model predicts that, for sufficiently “high” antitrapping sites, there will be substantially no effect of composition or even solute atom type on the mobility of the interstitial species even up to about 20 atm% of substitutional solute.It is also possible for a given substitutional solute to act both as an accelerator or retarder with respect to the diffusivity of the interstitial species, depending upon temperature.     

Interaction between interstitial hydrogen and substitutional solute atoms in solid solutions of niobium-base ternary alloys

The interaction between interstitial hydrogen and substitutional solute atoms has been investigated by the measurements of the hydrogen solubility and the influence of hydrogen charging on the half-width of the X-ray reflection lines in pure Nb, Nb-5%V, Nb-5%Mo and Nb-5%Ta alloys. In Nb-5%V and Nb-5%Mo alloys, the solubility considerably increases with respect to pure Nb. On the other hand, the solubility hardly changes in Nb-5%Ta alloy. With addition of hydrogen, the half-widths in pure Nb and Nb-5%Ta alloy show a monotonic increase, but in Nb-5%V and Nb-5%Mo alloys they show a minimum. The results are explained by the interaction of hydrogen with substitutional solute atoms. The interaction is considered to be caused by the internal strain induced by the difference in atomic radii between substitutional and solvent (Nb) atoms.     

Dynamical theory of diffraction of plane and spherical waves by a periodic system of scatterers with isolated defects

Using the T-matrix formalism a method known from the crystal lattice dynamics is applied to the study of the diffraction of radiation by a crystal with isolated defects. The following cases are discussed: substitutional foreign atoms or vacancies without lattice deformation, lattice deformation, interstitial atoms. Plane or spherical primary incident scalar waves are considered.     

Substitutional-interstitial interactions in niobium-titanium alloys: An internal friction study

The influence of additions of interstitial oxygen and nitrogen on the internal friction spetrum of the niobium-1 at-% titanium alloy was studied. The nature of the various observed relaxation processes introduced by the presence of substitutional titanium is discussed. A thermodynamic analysis was carried out for two pronounced interaction peaks attributed to the stress-induced reorientation of single oxygen or nitrogen atoms around single titanium atoms and the respective binding energies were estimated. It was also found that, over the range of oxygen concentration studied, interstitial oxygen is completely removed from random migration by substitutional titanium atoms acting as trapping centres, whilst nitrogen population is always partitioned between mobile and trapped atoms even at very low relative nitrogen concentrationsC _N/C _Ti. A possible reason for the different behavior of oxygen and nitrogen is suggested.     

Early stages of vanadium deposition on Si(1 1 1)-7 × 7

We investigate the low-coverage regime of vanadium deposition on the Si(1 1 1)-7 × 7 surface using a combination of scanning tunnelling microscopy (STM) and density-functional theory (DFT) adsorption energy calculations. We theoretically identify the most stable structures in this system: (i) substitutional vanadium atoms at silicon adatom positions; (ii) interstitial vanadium atoms between silicon adatoms and rest atoms; and (iii) interstitial vanadium - silicon adatom vacancy complexes. STM images reveal two simple vanadium-related features near the Si adatom positions: bright spots at both polarities (BB) and dark spots for empty and bright spots for filled states (DB). We relate the BB spots to the interstitial structures and the DB spots to substitutional structures.     

In-beam Mössbauer spectroscopy on single iron atoms in alkali metals

In-beam Mössbauer spectroscopy is applied to study implanted Fe atoms in the alkali metals Li, Na and K. From the Mössbauer parameters we infer that the Fe implants take up substitutional as well as interstitial sites. The strongly increased electron density at the interstitial position is qualitatively explained by the pressure resulting from the small interstitial volume. It is concluded that recently reported local moment formation in these systems cannot be due to substitutional Fe only.     

Role of oxygen and carbon on donor formation in step-annealed CZ-silicon

Step-annealing schedules for two different annealing chains, i.e. 450-650-450 and 650-450-700 °C have been followed to study the effect of oxygen and carbon on donor formation in carbon-rich Czochralski-silicon. It has been found that the annealing time does not have reasonable effect on substitutional carbon atoms. On the other hand, interstitial oxygen atoms are drastically reduced depending on annealing temperature. Carbon concentration does not exhibit any relationship with new donor (ND) concentration. The result suggests that the ND formation is not controlled by the substitutional carbon concentration directly, but by a density of some unknown embryos. The energy of formation of NDs was found to be 1.84 eV. All these results with plausible explanation are reported here.     

硅中的过渡元素杂质能级

本文提出了半导体中过渡元素杂质的一个简单模型,用格林函数方法计算了硅中替代和间隙原子产生的杂质能级和波函数。发现两者的性质有很大的差别。替代原子只有当d原子能级V_d低于价带顶时才能产生杂质能级。它的波函数主要是悬键态,当能级靠近导带边时变成正键态。间隙原子只有当V_d高于价带顶时才能产生杂质能级。它的波函数主要是中心原子d态,当能级靠近导带边时变成弱反键态。最后定性地说明了过渡元素杂质能级的化学趋势和一些实验事实。 关键词：     

替位杂质对低能Pt原子与Pt(111)表面相互作用影响的分子动力学模拟

采用嵌入原子方法的原子间相互作用势，通过分子动力学方法模拟了低能Pt原子与Cu，Ag，Au，Ni，Pd替位掺杂Pt(111)表面的相互作用过程，系统研究了替位原子对表面吸附原子产额、溅射产额和空位缺陷产额的影响规律，分析了低能沉积过程中沉积原子与基体表面的相互作用机理以及替位原子的作用及其影响规律.研究结果显示：替位原子的存在不仅影响着沉积能量较低时的表面吸附原子的产额与空间分布，而且对沉积能量较高时的低能表面溅射过程和基体表面空位的形成产生重要影响.替位原子导致的表面吸附原子产额、表面原子溅射以及空位形 关键词： 分子动力学 低能粒子 替位掺杂 表面原子产额 溅射 空位     

Annealing of point defects in p-type germanium after electron irradiation at liquid nitrogen temperature

Annealing of radiation induced defects in p-type germanium was studied by measuring Hall coefficient and conductivity. The dopant was gallium or indium. It was concluded that the annealing stage between 80° and 140°K is caused by migration of the vacancy to the sink of an impurity atom. In this stage the vacancy migrates to a substitutional impurity atom and makes an association. The activation energy of the stage was found tO be 0.1 ev ad it is regarded to be that of the vacancy migration. The model for the annealing stage which occurs in the range 220 to 270°K is proposed as follows: An interstitial impurity atom migrates to a substitutional impurity atom and makes an association. From the activation energy of the stage, the migration energy of the interstitial impurity atom was concluded to be about 0.4 eV for gallium and 0.7 eV for indium atoms.     

Effect of crystal potential on electric field gradient calculations due to impurities in cubic metals

The electric field gradients caused by interstitial and substitutional point defects in f.c.c. metals have been studied. The perturbation on the host electron distribution has been calculated self-consistently using density functional formalism. The effect of strain caused by size difference between host and impurity atoms is treated in the point-ion model. The influence of the host potential on impurity perturbation is incorporated within the spherical solid approximation. The theory is applied to positive muon and mono-vacancy in Al and Cu hosts. The theoretical results are in good agreement with experiment and illustrate the importance of both strain and conduction electron contribution to the electric field gradient.     

Effect of thermal annealing on sub-band-gap absorptance of microstructured silicon in air

The optical absorption properties of femtosecond-laser-made “black silicon” as a function of the annealing conditions were investigated. We found that the annealing process changes the surface morphology and absorption spectroscopy of the “black silicon” samples, and obtained a maximum sub-band-gap absorptance value of approximately 30% by annealing at 1000 °C for 30 min. The thermal relaxation and atomic structural transformation mechanisms are used to describe the lattice recovery and the increase and decrease of the substitutional dopant atom concentration in the microstructured surface during the annealing. Our results confirm that: i) owing to the thermal relaxation, the lattice defects decrease with the increase of the annealing temperature; ii) the quasi-substitutional and interstitial configurations of the doped atoms transform into substitutional arrangements when the annealing temperature increases; iii) the quasi-substitutional and interstitial configurations with higher energies of the doped atoms transform into interstitial configurations with the lowest energy after high-temperature annealing for a long period of time, causing the deactivation or reactivation of the sub-band-gap absorptance by diffusion. The results demonstrate that the annealing can improve the properties of “black silicon”, including defects repairing, carrier lifetime lengthening, and retention of a high absorptive performance.