Vacancy-interstitial Annihilation Research Articles

Energetic and kinetic dataset on interaction of the vacancy and self-interstitial atom with the grain boundary in α-iron.

We provide the dataset of the vacancy (interstitial) formation energy, segregation energy, diffusion barrier, vacancy-interstitial annihilation barrier near the grain boundary (GB) in bcc-iron and also the corresponding interactive range. The vacancy-interstitial annihilation mechanisms in the bulk, near the GB and at the GB at across scales were given.

Atomic Scale Simulation of Dislocation Loops Formation in Thin Foil under High Energy Electron Irradiation

Using a personnel computer, we have simulated the diffusion and agglomeration of point defects in thin foil under high energy electron irradiation. The physical model has been developed by using the Monte Carlo technique. Four types of reactions are assumed to take place: di-interstitial creation by agglomeration of two free interstitials, vacancy-interstitial annihilation, interstitial trapping by dislocation loops and interstitial annihilation on the sample surfaces. In the simulation only interstitials are mobile and extended defects are assumed to be interstitial type. We have calculated the concentration of point defects, extended defects and the size of the latter. We compared them to the results of the Chemical Reaction Rate Theory (CRRT). It has been found that the dislocation loops are distributed in the center of material leaving areas denuded close to the surface and the loops radius is also strongly dependent on the location of the defect in thin foil with respect to the results of experimental and CRRT. To explain the origin of these phenomena we have exploited the spatial distribution of vacancies close to free surfaces and around dislocation loops. These types of informations are totally missing in the CRRT and experimental.

Annealing of ion irradiated high TC Josephson junctions studied by numerical simulations

Recently, annealing of ion irradiated high Tc Josephson iunctions (JJs) has been studied experimentally in the perspective of improving their reproducibility. Here we present numerical simulations based on random walk and Monte Carlo calculations of the evolution of JJ characteristics such as the transition temperature Tc′ and its spread ΔTc′, and compare them with experimental results on junctions irradiated with 100 and 150 keV oxygen ions, and annealed at low temperatures (below 80 °C). We have successfully used a vacancy-interstitial annihilation mechanism to describe the evolution of the Tc′ and the homogeneity of a JJ array, analyzing the evolution of the defects density mean value and its distribution width. The annealing first increases the spread in Tc′ for short annealing times due to the stochastic nature of the process, but then tends to reduce it for longer times, which is interesting for technological applications.

Annealing effect on the reproducibility of Josephson Junctions made by ion irradiation

We have studied the annealing effects on the transport properties of High Tc Josephson Junctions (JJ) made by ion irradiation. Several JJ were measured for different annealing times and the experimental data were compared to numerical simulations. We have successfully used a vacancy-interstitial annihilation mechanism to describe the evolution of the JJ coupling temperature (TJ) and the homogeneity of a JJ array, related to the evolution of the defects density mean value and its distribution width. For sufficient long annealing times (t > 600 min), ΔTJ was significatively reduced. This result appears to be very encouraging for future applications where the spread in JJ characteristics has to be as low as possible.

Improving ion irradiated high Tc Josephson junctions by annealing: The role of vacancy-interstitial annihilation

The authors have studied the annealing effect in the transport properties of high Tc Josephson junctions (JJs) made by ion irradiation. Low temperature annealing (80°C) increases the JJ coupling temperature (TJ) and the IcRn product, where Ic is the critical current and Rn the normal resistance. They have found that the spread in JJ characteristics can be reduced by sufficient long annealing times, increasing the reproducibility of ion irradiated Josephson junctions. The characteristic annealing time and the evolution of the spread in the JJ characteristics can be explained by a vacancy-interstitial annihilation process rather than by an oxygen diffusion one.

Molecular dynamics studies on vacancy-interstitial annihilation in silicon

Molecular dynamics (MD) simulation is performed to study the vacancy-interstitial annihilation in crystalline silicon. We choose the Stillinger-Weber potential , which is commonly used for silicon, to describe the interaction between atoms. The system is relaxed under 300K and 1400K respectively. We have found that is the preferred recombination direction and propose the presence of an energy barrier in the direction. From the calculated value of energy barrier alon g we give a reasonable explanation for the difference between Tang's and Z awadzki's data.

Systematic Study Related to the Role of Initial Impurities and Irradiation Rates in the Formation and Evolution of Complex Defects in Silicon for Detectors in HEP Experiments*

The influence of oxygen and carbon impurities on the concentrations of defects in silicon for detector uses, in complex fields of radiation, characteristic to high energy physics experiments, is investigated in the frame of the quantitative phenomenological model developed previously by the authors and extended in the present paper. Continuous irradiation conditions are considered, simulating realistically the environments for these experiments. The generation rate of primary defects is calculated starting from the projectile–silicon interaction and from the recoil energy redistribution in the lattice. The mechanisms of formation of complex defects are explicitly analysed. Vacancy-interstitial annihilation, interstitial and vacancy migration to sinks, divacancy, vacancy- and interstitial-impurity complex formation and decomposition are considered. Oxygen and carbon impurities present in silicon could monitor the concentration of all stable defects, due to their interaction with vacancies and interstitials. Their role in the mechanisms of formation and decomposition of the following stable defects: V2, VO, V2O, Ci, CiOi, CiCs and VP, is studied. The model predictions cover a generation rate of primary defects between 102 pairs/cm3/s and 1011 pairs/cm3/s, and could be a useful clue in obtaining harder materials for detectors for space missions, at the new generation of accelerators, as, e.g. LHC, Super-LHC and Eloisatron, or for industrial applications.

Reduction of grown-in defects by vacancy-assisted oxygen precipitation in high density dynamic random access memory

The silicon ingot growing scheme has been investigated to reduce the grown-in defect. It is found that a fast cooling rate suppresses the further growth of crystal-originated particles (COPs) after supersaturating vacancies by increased pulling speed. This reaction makes the COP-rich region with the high density and smaller size extend to wafer edge. Initially higher COPs decrease by subsequent annealing in oxygen ambient through the vacancy-interstitial annihilation mechanism. Since vacancies assist oxygen precipitation, bulk microdefect is easily formed and the intrinsic gettering during the denudation process becomes more efficient. Based on this principle, the ingot growing scheme with a 1.8 mm/min-pulling speed and 9.8 °C/min cooling rate in the range of 1000 to ∼1200 °C is suggested, and its superiority is verified through the improvement of the tail component of retention time by 40% in high density dynamic random access memory.

Microscopic modelling of defects production and their annealing after irradiation in silicon for HEP particle detectors

In this contribution, the production of defects in radiation fields and their evolution toward equilibrium in silicon for detector uses has been modelled. In the quantitative model developed, the generation rate of primary defects is calculated starting from the projectile–silicon interaction and from recoil energy redistribution in the lattice. Vacancy–interstitial annihilation, interstitial migration to sinks, divacancy and vacancy–impurity complex (VP, VO, V2O,CiOi and CiCs) formation are considered.The results of the model support the experimental available data. The correlation between the initial material parameters, temperature, irradiation and annealing history is established. The model predictions could be a useful clue in obtaining harder materials for detectors at the new generation of accelerators or for space missions.

Radiation defects in neutron irradiated silicon with high oxygen concentration

In silicon material with oxygen concentration in the range (4–9)×1017cm−3, grown by the CZ method and irradiated by reactor neutrons, the interstitial oxygen mainly participates in A-center (V+O) creation. A-center concentration is linearly dependent on neutron fluence up to Φ=1018n/cm2, value at which saturation occurs caused not by the exhaustion of dissolved oxygen but rather by vacancy-interstitial atom annihilation competitive mechanisms. A-center annealing (T>300°C) does not lead to the full restoring of interstitial oxygen concentration. Repeating neutron irradiation and annealing causes a decrease of oxygen complex activity and the silicon behaves as a low-oxygen material.

Long-term Damage Induced by Hadrons in Silicon Detectors for Uses at the LHC-accelerator and in Space Missions

In the present paper, the phenomenological model developed by the authors in previous papers has been used to evaluate the degradation induced by hadron irradiation at future accelerator facilities or by cosmic protons in high resistivity silicon detectors. The damage has been analysed at the microscopic (defects production and their evolution toward equilibrium) and at the macroscopic level (changes in the leakage current of the p–n junction). The rates of production of primary defects, as well as their evolution toward equilibrium have been evaluated considering explicitly the type of projectile particle and its energy. Vacancy-interstitial annihilation, interstitial migration to sink, divacancy and complex (VP, VO, V2O, CiOi, CiCs) formation are taken into account for differently doped initial silicon material. The influence of these defects on the leakage current density has been compared with experimental data from the literature, and predictions for the LHC (Large Hadron Collider) radiation fields, as well as for space missions in the near Earth orbits have been done, in the frame of the Schokley–Read–Hall model.

The influence of initial impurities and irradiation conditions on defect production and annealing in silicon for particle detectors

Silicon detectors in particle physics experiments at the new accelerators or in space missions for physics goals will be exposed to extreme radiation conditions. The principal obstacles to long-term operation in these environments are the changes in detector parameters, consequence of the modifications in material properties after irradiation. The phenomenological model developed in the present paper is able to explain quantitatively, without free parameters, the production of primary defects in silicon after particle irradiation and their evolution toward equilibrium, for a large range of generation rates of primary defects. Vacancy–interstitial annihilation, interstitial migration to sinks, divacancy and vacancy–impurity complex (VP, VO, V 2O and C iO i, C iC s) formation are taken into account. The effects of different initial impurity concentrations of phosphorus, oxygen and carbon, as well as of irradiation conditions are systematically studied. The correlation between the rate of defect production, the temperature and the time evolution of defect concentrations is also investigated.

Radiation Defects in Silicon due to Hadrons and Leptons, their Annealing and Influence on Detector Performance

A phenomenological model was developed to explain quantitatively, without free parameters, the production of primary defects in silicon after particle irradiation, the kinetics of their evolution toward equilibrium and their influence on detector parameters. The type of the projectile particle and its energy is considered in the evaluation of the concentration of primary defects. Vacancy-interstitial annihilation, interstitial migration to sinks, vacancy-impurity complexes (VP, VO, V2O), and divacancy (V2) formation are taken into account in different irradiation conditions, for different concentrations of impurities in the semiconductor material, for 20 and 0°C. The model can be extended to include other vacancy and interstitial complexes. The density of the reverse current in the detector after irradiation is estimated. Comparison with experimental measurements is performed. A special application considered in the paper is the modelled case of the behaviour of silicon detectors operating in the pion field estimated for the LHC accelerator, under continuum generation and annealing.

Tight-binding molecular dynamics study of vacancy-interstitial annihilation in silicon

We have studied the annihilation of a tetrahedral interstitial by a vacancy using molecular dynamics and a tight-binding model due to Goodwin-Skinner-Pettifor. At both 1473 and 1173 K, the annihilation process was dominated by the movement of the faster-diffusing vacancy. Once the vacancy moved to a nearest-neighbor position relative to the interstitial, annihilation was inevitable. As the initial distance between the T-interstitial and the vacancy increased, the number of pathways by which annihilation occurs increased accordingly. Fast and slow annihilation pathways were identified. The process was found to be highly stochastic in nature, requiring multiple simulations to provide adequate statistics. System size was not a factor in altering the results. The capture radius, within which annihilation is assured, was found to be between 5--6 \AA{} at 1473 K, although it is clear from the orientation dependence of the results that a spherically symmetric view of the capture radius is somewhat inappropriate. Limited investigation of annihilation between a (110) split interstitial and a vacancy confirmed the basic results of Tang et al. (Ref. 21) (using a Kwon tight-binding model) that the formation of a double-vacancy: double-interstitial configuration, dubbed a ``bond-defect'' by those authors, occurs in some but not all cases as part of the annihilation mechanism.

Recovery behavior of tellurium irradiated with 20-MeV electrons and the influence of lattice defects on the transport properties

The reaction kinetics of the 50-K recovery stage of tellurium irradiated with 20-MeV electrons can be explained by correlated vacancy-interstitial annihilation. Moreover, the influence of the doping on the transport properties of irradiated tellurium crystals was investigated. It turned out that the assumption of a reduction of the dislocation scattering potential by vacancy trapping as proposed in previous papers is insufficient. The experimental findings are comprehensible if screening of the dislocations by free carriers is assumed to be the predominant mechanism. With this model the doping dependence of the mobility in unirradiated tellurium crystals can also be understood.

Kinetics of externally stimulated interstitial release followed by vacancy-interstitial annihilation

The radiation-damage annealing kinetics are described for the case of interstitial release from impurity-defect complexes followed by interstitial-vacancy annihilation. Several externally induced annealing experiments in Ge and Si are discussed in which retrapping of interstitials at the complexes is unlikely. The solutions presented are fit to these experimental data. It is shown that a surprising number of optical, subthreshold-electron-irradiation, ion-irradiation, or minority-carrier injection-stimulated annealing situations exist in Si, Ge, GaAs, and GaP and can perhaps be described by the rather simple annealing-kinetics model presented here. It is also possible that certain chemical reactions in the field of radiation and catalytic chemistry could follow these same kinetics equations.

The Location of Displaced Impurity Atoms in Irradiated Aluminum Crystals by Backscattering

The energy spectra of 1 MeV He+ ions backscattered from single crystals of Al alloys containing 0.09 at.% Mn, 0.09 at.% Zn, 0.08 at.% Ag, or 0.03 at.% Sn have been examined in different crystallographic directions. For the annealed crystals, the minimum yield of back-scattered He+ ions from Al atoms at 40 K in a [Formula: see text] direction was [Formula: see text], and the corresponding yield from Mn, Zn, or Ag impurity atoms was (χmin)i ≤ 0.06, indicating that at least 96% of these impurity atoms had replaced Al atoms at normal lattice sites. For the Al–0.03 at.% Sn alloy, the substitutional fraction of Sn atoms was only ~50% for a slowly cooled crystal, but was increased to ~90% by a rapid (water) quench from 600 °C. Irradiation of the crystals at 40–70 K with 0.3–1.0 MeV He+ ions to doses of 1015–1016/cm2 caused the Mn, Zn, and Ag atoms to be displaced from lattice sites by the trapping of self-interstitial Al atoms. From an analysis of [Formula: see text], [Formula: see text], {100}, and {111} channeling, it was shown that the trapping configuration was the [Formula: see text] dumbbell. Both the irradiation induced dechanneling and the displacement of these impurity atoms annealed out in recovery stage III, from 180–220 K, because of vacancy interstitial annihilation. The Sn atoms were not displaced appreciably by He+ ion irradiation at 40–70 K, but a displacement occurred during stage III recovery.

On the nature and mechanism of surface polygonization of NaCl and KCl single crystals produced by electron bombardment and illumination

Abstract The polygonization phenomenon observed on alkali halide surfaces, irradiated with electrons and subsequently illuminated, was studied by optical and electron microscopy. For the explanation of the nature and mechanism of this process, we have investigated the influence of light (containing the F−centre absorption band) on the development and annihilation in time of some polygonization lines, as well as the correlation of the polygonization patterns with dislocation etch pits and subgrain boundaries revealed by a selective chemical etching. Preceded by an optical bleaching effect which locally induces surface potential changes, the polygonization process is explained taking into account the mobility of unpinned charged dislocations and the surface atom migration. The disappearance of some polygonization lines may be produced by a vacancy-interstitial annihilation process. No identification was found between the polygonization patterns and the subgrain boundaries.

Kinetics of Vacancy-Interstitial Annihilation. III. Interstitial Migration to Sinks

The kinetics of vacancy-interstitial annihilation when interstitials are permitted to anneal at sinks has been studied both by analytic and computer techniques. During the annealing the interstitial concentration decays to zero but the vacancy concentration approaches a terminal value governed by an analytic relation between the concentration of interstitials and vacancies, valid at all times, and independent of the annealing temperature but a function of the sink and initial defect concentration. The growth of defect concentration during irradiation at a temperature where the interstitials are mobile has also been studied. The interstitial concentration goes through a maximum as a function of irradiation time. Past this maximum a steady-state approximation is valid and the subsequent growth of the vacancy concentration can be described by a simple relation. The vacancy growth in steady state is independent of the temperature and is only a function of the integrated exposure. The rate of vacancy accumulation during continuous irradiation is compared to that arising from intermittent irradiations (low temperature) and annealings.

Kinetics of Vacancy-Interstitial Annihilation. II. Di-Interstitial Formation

The equations for the kinetics of vacancy-interstitial annihilation with diinterstitial formation have been solved on an analog computer. At low temperature, or for high diinterstitial binding energy, the decomposition reaction can be neglected. Analytic approximations have been found and shown to be valid in this case. Conventional methods of activation energy determination are valid in this region for evaluating the interstitial migration energy. At high temperature, or for low binding energy, the diinterstitial concentration may be neglected and the resulting kinetics is the simple quadratic interstitial-vacancy annihilation governed by the interstitial migration energy. In the intermediate region no analytic approximations have been found and the rate constants, therefore, cannot be evaluated.