Interstitial Trapping Research Articles

Trapping of Interstitials and Vacancies at Solute Molybdenum Atoms in Iron/(0.3 at % Mo)Studied by the Ion-Channelling/Lattice-Location Technique

Trapping of Interstitials and Vacancies at Solute Molybdenum Atoms in Iron/(0.3 at % Mo)Studied by the Ion-Channelling/Lattice-Location Technique

Effects of solute on damage production and recovery in zirconium

Dilute zirconium-based alloys and pure zirconium were irradiated at 10 K with spallation neutrons at IPNS. Four types of alloys, viz., Zr-Ti, Zr-Sn, Zr-Dy and Zr-Au, each with three different concentrations of solute were investigated. Low-temperature resistivity damage rates were enhanced by the presence of each of the four solutes. The greatest enhancement was produced by Au while the least enhancement was produced by Dy. Within each alloy group, damage production increased with increasing concentration but at a decreasing rate. Post-irradiation annealing experiments, up to 400 K, showed that all four solutes suppressed recovery due to interstitial migration which is indicative of interstitial trapping by the solutes. Vacancy recovery was also suppressed by the presence of Sn, Dy or Au. The effect of Ti was to shift this stage to lower temperature. A clear correlation between the results and solute size was not detected.

Electronic structure of the interstitial lithium-associated electron trap in crystalline quartz

A new, paramagnetic ($S=\frac{1}{2}$) defect, designated the ${[\mathrm{S}\mathrm{i}{\mathrm{O}}_{4}/\mathrm{L}\mathrm{i}]}^{0}$ center, consisting of an interstitial lithium "atom," recently has been observed by Jani, Halliburton, and Halperin [Phys. Rev. Lett. 56, 1392 (1986)] in irradiated $\ensuremath{\alpha}$-quartz. A model for this defect has been developed utilizing ab initio self-consistent-field, electronic-structure calculations. In this model, the interstitial lithium nucleus lies on a crystal twofold axis passing through two adjacent silicon ions, and has a nearly neutral charge but very low spin density. The properties calculated using this model are consistent with all the available experimental information for this defect.

Ion implantation in LiF to form F and F2centres

Ion implantation has been used to form colour centres in concentrations as high as 1020 cm-3 in LiF. At low ion doses the F and F2 production is proportional to (dose)0.8 and (dose)1.1 respectively which is interpreted as a consequence of interstitial trapping. The apparent F to F2 dependence is (F2) varies as (F)1.4 but after allowance for overlapping absorption features this corrects to the normal (F2)=K1(F)2 relation. The K1 value is closely linked to the electronic stopping power for energetic proton bombardment.

Interstitial solute trapping by edge dislocations

Interstitial solute trapping in the stress field of edge dislocations is considered when solute atoms interact among each other. The Fermi-Dirac statistics are used to account for the short-ranged repulsive interactions which prevents dual site occupancy. The elastic interaction between solute atoms is described in terms of a mean-field attaction plus a macroscopic interaction mediated by the coherency stress field associated with the nonuniform solute distribution. The enhancement of hydrogen solubility in Pd and α-Fe due to trapping in the strain field of edge dislocations is evaluated and compared with experimental results.

Statistical model for the trapping of interstitials by substitutional (interstitial) atoms in solids.

The distribution of noninteracting interstitial atoms in a lattice containing trapping centers is studied using Fermi-Dirac statistics. Assuming that the energies of free sites and trap sites are distributed according to density-of-states functions, the populations of the various types of clusters are calculated as a function of concentration and temperature; the only form of interaction between interstitials taken into account is represented by the inhibition of some types of clusters. The results are satisfactorily applied to internal friction to explain the anomalous relaxation observed in crystalline and amorphous metal-hydrogen (deuterium) systems.

Intrinsic point defects in niobium: Trapping at100Pd and111In impurities observed by PAC

Radiation-induced lattice defects in high-purity niobium have been investigated in the temperature range of 30K to 540 K by means of γ-γ perturbed angular correlation (PAC) measurements using the radioactive probes100Pd/100Rh and111In/111Cd. Both probes were produced within the niobium samples by means of heavy-ion nuclear reactions. At the Pd impurities trapping of defects occurred during heavy-ion irradiation at about 30 K in two defined configurations: defect 1(Pd) withv Q1=e 2 qQ/h=42(±2) MHz, η1=0 and defect 2 (Pd) withv Q2=(±2) MHz, η2=1. Two defects were observed at the In impurities in annealing stage III (around 250 K) after heavy-ion as well as electron irradiations: defect 1(In) withv Q1=87(±1) MHz, η1=0 and defect 2(In) withv Q2=105(±2) MHz, η2=0.65(±0.02). A third defect (defect 3(In):v Q3=177(±2) MHz, η3≲0.2) appeared above 260 K after heavy-ion irradiation only. The data are interpreted in terms of interstitial trapping at the Pd impurities and vacancy trapping at the In impurities. Information on the microscopic structure of defect 1(In) and 2(In) is obtained from a PAC-single-crystal experiment. For defect 1(In) axial 〈111〉-symmetry is found, which leads us to identify this defect with a monovacancy as nearest neighbor with respect to the In probe. Defect 2(In) is the trapped divacancy for which an orientation is found that is consistent with both vacancies being nearest neighbor to the probe but second nearest neighbors to each other.

Transient‐Enhanced Diffusion during Furnace and Rapid Thermal Annealing of Ion‐Implanted Silicon

A transient‐enhanced diffusion has been observed during the furnace or rapid thermal annealing of ion‐implanted silicon. We have studied this transient in detail and show that, for doses of Group V dopants sufficient to amorphize the silicon, it arises from the trapping of interstitials by dopant atoms during implantation. These are retained during solid‐phase‐epitaxial (SPE) growth, but can be released by additional thermal processing to cause the observed transient and the formation of a band of extended defects. We have measured the enhanced diffusion coefficients and the duration of the transient for Sb‐implanted Si by careful furnace annealing experiments. We obtain general expressions which predict the effects of the transient during any thermal processing based on SPE growth (furnace, CW laser, or rapid thermal annealing). We show that there is no analogous mechanism of vacancy trapping by Group III elements.

Model for F-center production in alkali halides doped with divalent cation impurities that change their valence state by irradiation.

A model for the radiation-induced F-center coloring in alkali halides doped with doubly valent metal impurity ions (${M}^{2+}$) that can change their valence state by irradiation is proposed in the present paper. The primary event is assumed to be the creation of F centers and interstitial halogen (H) pairs. The thermal- and radiation-induced processes associated with the dynamics of H defects and their trapping at defects leading to the stabilization of their counterpart F centers are taken into account during the three stages of the F-coloring curve. The fundamental traps for the interstitials are assumed to be the ${M}^{2+}$-cation vacancy dipoles. Therefore, a heterogeneous nucleation process around these complexes is one of the assumptions on which the model is based. It is proposed that stage I of the F-coloring curve is reached with the single process of the capturing of one H defect by a dipole producing an ${S}_{1}$ center. The trapping of one additional interstitial by ${S}_{1}$ generates a less stable center, ${S}_{2}$. The trapping of one or more interstitials by ${S}_{2}$ gives a stable aggregate center denoted by A, which is responsible for stage III. On the other hand, another way in which these dipoles may vary is through the capture of free electrons during the irradiation process to become either ${M}^{+}$ or ${M}^{0}$ states. It is assumed that these latter states have different capabilities for the trapping of interstitials than those of ${M}^{2+}$. The possibility of hole capture by these reduced states, which would allow them to return to the original ${M}^{2+}$ state, is also included in the model. These basic assumptions are used to postulate a set of ten differential equations which we have solved numerically using a Runge-Kutta iteration program. The numerical solutions of the equations are in good qualitative agreement with the more important features of the experimentally determined effects of room-temperature x-ray irradiation in europium- and lead-doped alkali halides. In some cases, semiquantitative agreement with experiment is obtained.

Trapping of Interstitials During Ion Implantation In Silicon

ABSTRACTThe solid phase epitaxial regrowth of silicon implanted with a group V dopant, such as antimony, results in excellent incorporation of the dopant atoms into silicon lattice sites. However, annealing at higher temperatures or longer times results in transient dopant precipitation with a diffusion coefficient up to five orders of magnitude above that of tracer diffusion and with a reduced activation energy.This precipitation is accompanied by the nucleation of dislocation loops that are interstitial in nature, and the transient ceases as the dislocation loops develop. It is believed that Si interstitials are trapped in a stable defect complex during the implantation process.Although they survive SPE these complexes dissolve at higher temperatures and release a large supply of interstitials which serve to promote dopant migration via an interstitialcy mechanism until they condense to form the observed dislocation loops. By following the Sb implantation with an implantation of B to an equivalent concentration profile the loop formation is efficiently suppressed. For higher B concentrations the Sb precipitation is no longer observed. Results for As implantation are similar to Sb except that As precipitates can not be directly observed. Calculations of the dopant and interstitial concentration depth distributions were also performed.

Recovery of electrical resistivity in ni alloys after neutron irradiation at low temperature

Abstract The isochronal annealing curves of the electrical resistivity in dilute Ni alloys have been measured after fast neutron irradiation at about 5 K. The suppression of the stage I recovery in dilute alloys is due to the trapping of interstitials at solute atoms. The trapping ability of interstitials in Ni alloys is very small as compared with that in Cu alloys. The substages in the stage II recovery are discussed in relation to the release of interstitials from solute atoms. In some concentrated alloys the retention of defects after annealing at 400 K is smaller than that in dilute alloys and pure Ni.

Enhanced diffusion from interstitial trapping during solid-phase-epitaxial growth of silicon alloys

During the recrystallization by solid-phase-epitaxial (SPE) growth of supersaturated silicon alloys, a high concentration of interstitials is trapped. These are released by subsequent heating causing a transient (greatly enhanced) diffusion of the substitutional dopant by an interstitialcy mechanism. The enhancement may be as much as five orders of magnitude over tracer values, and shows an activation energy of only 1.8±0.2eV. Following the transient, the interstitials condense into loops, allowing an independent estimate to be made of their concentration. From these observations, we propose that during ion implanted dopants can acquire their natural valency, and retain it as the crystallization interface passes. For group V dopants this creates the trapped interstitials, giving transient enhanced diffusion when they are released by subsequent annealing.

The selective trapping of mobile group-V interstitials by impurities in electron-irradiated GaAs and GaP

Irradiation of GaAs or GaP by 2 MeV electrons at room temperature leads to the generation of group-V interstitials. These defects are immobile in n-type material but once the Fermi level is lowered to a critical position, corresponding to a threshold dose of irradiation, they diffuse through the crystal and may be trapped by isoelectronic boron BGa, carbon acceptors CV- and boron impurity antisite defects BV as monitored by the infrared vibrational absorption arising from these light atoms. Other defects, including (BV--donor) pairs are also destroyed. The relative cross sections for these processes do not differ significantly and it is concluded that the interactions are dominated by elastic size effects rather than by a Coulombic field. The implication is that group-V interstitials are negatively charged in n-type material and neutral in high-resistivity irradiated samples. It is explained how the critical threshold dose for interstitial mobility may be used to explore the mechanism for production of other defects such as the AsGa antisite defect.

Direct evidence for several impurity-interstitial configurations in molybdenum

Abstract 3 MeV electron irradiations on Mo57Co Mössbauer samples were performed with various fluences at 100 K irradiation temperature. Using the Mossbauer technique the trapping of interstitials, mobile at irradiation temperature, in different configurations around the 57Co impurities, could be directly observed from the appearance of additional absorption lines in the Mössbauer spectra. Analysing the irradiation dose dependent population of these defect lines, four different stable sites for trapped single interstitials and two di-interstitial sites were found. They are characterized by a nearly unique isomer shift of +0.46 mm/s relative to a substitutional lattice site and large quadrupole splittings ranging from 1.82 to 0.81 mm/s. At higher irradiation doses interstitial clustering at the 57Co impurities was found, resulting in a defect line with 0.39 mm/s quadrupole splitting and a broadened line width. The general trapping behaviour of the Mo57Co system could be described by the unsaturable trap model with a trapping radius of rco/rv = 0.23. The microscopic picture for the population of the observed trapping sites for interstitials is discussed within this model.

Interstitial trapping in Fe-implanted Al after excimer laser annealing

Laser annealing was used to create a supersaturated solution of Fe atoms in Al, in order that channeling measurements of self-interstitial trapping could be made. A single crystal of Al was implanted with 40 keV 56Fe to a fluence of 1.6×10 15 ions cm −2. A 4 mm diameter region of the crystal was annealed in air with a XeCl excimer laser at an energy density of ∼ 6 J cm −2. This treatment produced a relatively perfect crystal; the normalized yield of 1 MeV He + ions from near-surface Al atoms for 〈110〉 alignment at 35 K was 0.04. The Fe atoms were ∼ 90% substitutional, corresponding to a solubility of ∼ 0.3 at%, as compared with only ∼ 0.02 at% obtained by a water quench from 873 K. The crystal was then irradiated with 1 MeV He + at 70 K to a fluence of ∼ 5 × 10 15 ions cm −2, in order to create mobile Al self-interstitial atoms which could be trapped by the Fe atoms. A channeling analysis of the resulting displacement of Fe atoms indicated that they trapped self-interstitials strongly, as observed for other small solute atoms in Al. As no flux peaking in the backscattering yield from Fe atoms was observed for a 〈110〉 angular scan, the results indicate that the trapping configuration may differ from that observed for Cr, Mn or Cu solute atoms in Al. The trapped interstitials were annihilated by vacancy migration near 200 K.

Defect trapping by100Pd in fcc metals

Lattice defects in Al, Cu, Ag and Au were studied by the perturbed γ γ angular correlation technique (PAC) using the probe atom100Pd/100Rh. The comparison of data obtained on interstitial trapping in Cu and Au at different probe atoms (100pd,111In) allows defect characterisation less affected by the respective probe. The trapping efficiency of100Pd for vacancy like defects is quite different to that of111In atoms.

Trapping of Interstitials in Metals

The term trapping is used extensively to refer to the fact that interstitial atoms often find interstices associated with lattice imperfections to be energetically preferable to normal sites. This preference results in a delay of diffusion of interstitial atoms near these sites. As understanding of the details of lattice imperfections has improved, understanding of the effect of traps on the diffusion process has increased. Trapping is often illustrated by the use of a potential energy diagram. This simple model is characterized by a potential energy well deeper than those of surrounding interstitial sites. The energy required for the interstitial to jump into the trap is the same as that required for jumping into other adjacent interstitial sites, but that required for jumping out is greater. The additional energy required to leave the site is often designated as the trap binding energy, E/sub B/. Potential energy diagrams appropriate for most traps in metals are likely to be more complicated, but this simple model is a starting point for more sophisticated models of trapping. Imperfections may occasionally produce interstitial sites less favorable than normal sites and thus be less preferred. Little experimental exploration of this anti-trapping phenomenon has been carried out, however.more » Developments in understanding at various levels of trapping of interstitial impurities by lattice imperfections are examined.« less

Study of defect formation in irradiated KI and KI(Pb) by raman scattering and optical absorption techniques

Abstract Studies of the growth of halogen molecular complexes induced in KI and KI(Pb) have been made by Raman scattering and optical absorption techniques. Their behaviour is consistent with the ideas of halogen cluster development resulting from the sequential trapping of halogen interstitials. Comparison of the results with recently published studies of KI and KI(Ca) shows that the defects responsible for the Raman scattering (I3- and higher order interstitial complexes) have the same basic nature independent of the presence of nearby impurities. Evidence that lead impurities stabilize halogen interstitials is presented.

On the study of interstitial trapping in dilute alloys by resistivity measurements

Abstract The determination of the trapping properties of solute atoms (t) for self-interstitials (i) in dilute alloys via resistivity measurements has been done up to now by assuming that the resistivity of the small complexes (tin ) is the mere sum p(t) + n p(i). However, for deep trapping configurations where the formerly substitutional impurity becomes part of the interstitial defect, the resistivity of the complex ti may be significantly smaller than p(t) + p(i). Then the extra resistivity is no longer a measure of the defect concentration. The present work analyses the implications of such situations, in particular as concerns the determination of trapping radii, rt , of self-interstitials by impurity atoms. It shows that different experimental methods such as the damage rate method and the recovery method will provide different information since they are operating in different conditions. The damage rate method usually leads to an upper limit of Rt (= rt/rv where rv is the capture radius of a self-i...

Radiation damage studies in BCC metals by Mössbauer spectroscopy

Trapping of interstitials at impurity atoms can be observed directly by Mössbauer spectroscopy. This was proven in studies on the dilute bcc alloys Mo 57Co, Nb 57Co, W 57Co and V 57Co, where the trapping leads to additional quadrupole split defect lines. In contrast to similar investigations in the fcc systems Al 57Co and Ag 57Co, quite large quadrupole splittings were found for the interstitial-impurity complexes in the bcc metals. This made it possible to separate different configurations of interstitials around the 57Co impurities in the Mössbauer spectra. Pursuing the population and decay of these configurations after different irradiation conditions as well as after isochronal annealing, detailed information about the defect mobility, the fractions of defects with impurities and the stability of impurity-defect complexes could be obtained. This is shown for the system Mo 57Co.