Lattice Defect Structure Research Articles

Structural lattice defects in silicon observed at111in by perturbed angular correlation

Probing of structural defects in silicon by the perturbed γγ angular correlation (PAC) technique is demonstrated between 77 K and 1300 K. The behaviour of radioactive111 In probe atoms implanted at 295 K, is monitored during isochronal annealing in n-type, p-type and intrinsic Si. Trapping of defects, produced by the111In implantation itself or by postirradiation is studied in P-doped crystals (1016/cm3-1017/cm3).

Reaction of titanium with nitrogen during heating by radiant energy

Use of radiant energy as a source of heat intensifies the nitriding of titanium. The phase composition, thickness, and properties of diffusion layers depend, at any given temperature, on the nature of the heat source and on the activity of the atmosphere. The mechanism of photoactivation of the surface of a metal specimen consists in changing the concentration of crystal lattice structure defects, which promotes diffusion of nonmetal anions into the specimen.

Lattice defects within grain volumes that affect the electrical quality of cast polycrystalline silicon solar-cell materials

Lattice defect structures within large grains of cast polycrystalline silicon have been investigated using optical microscopy, x-ray topography, and electron-beam-induced conductivity (EBIC) measurements. Optical observations through a series of wafers of an ingot indicate that kinks in high-angle grain boundaries develop by forming straight grain boundaries rather than curved boundaries. It is also observed that a junction of three grain forms a kink in the grain boundary. X-ray topographic observations of lattice defects show that cumulative dislocations are generated at these kinks when the material is subjected to thermal stresses at sufficiently elevated temperatures during solidification. Subsequently the dislocations propagate into the grain volume and form subgrain boundaries. In some cases, they pile up in the coherent {111} twin boundary interfaces. Observed EBIC constrast has shown that both dislocations and subgrain boundaries are electrically active and serve to decrease the effective minority carrier diffusion length.

Nucleation and precipitation in an Al‐Si(1 at.%) alloy investigated by positron annihilation

AbstractIn AlSi alloys incoherent precipitates containing the pure solute element and having diamond cubic crystal structure are formed during a post‐quench annealing without formation of any metastable phase (Mondolfo). Quenched‐in vacancies have a strong effect on rates of precipitation from solid solution by transporting Si atoms as well as by their influence on the nucleation process. One suggestion is the precipitate formation by homogeneous nucleation of small Si clusters rich of vacancies (see for instance Beller). Another picture is the heterogeneous precipitation.Positron annihilation can be expected to be very useful in studying small precipitate nuclei and the role of vacancies in the nucleation process. Positrons provide information of the concentration, configuration and internal structure of such lattice defects in solids, like dislocations, vacancies and vacancy‐clusters (Hautojärvi). The method is also very fruitful in studying small coherent precipitations (Dlubek et al. 1981). The aim of the present work is to study the nucleation and precipitation processes going on in an AlSi (1 at.%) alloy between room temperature and 300 °C by measuring the positron lifetime spectra.The spectra of pure, well annealed metals without any localisation sites are one‐component exponential decay spectra. The time constant is called mean positron lifetime (in Al:τ = 165 ps). It is a measure of the reciprocal electron density. If positrons are localized at a certain kind of traps (such like vacancies or dislocations) a second exponential decay component will appear. The lifetime of the second, longer component is characteristic of the kind of the trap, the intensity of this component is connected with the trap density. It is for instance possible to distinguish clearly between monovacancies, divacancies and small vacancy clusters on the basis of the τ2 values (Hautojärvi).The investigated AlSi(1 at.%) alloy was prepared from 4 N materials. After homogeneisation at 560 °C for some hours the samples were quenched into water at room temperature. Isochronal annealing treatment of samples was performed in 20 K steps (0.5 hours). After each annealing step the samples were slowly cooled down from the annealing temperature to room temperature within 5 minutes. Figure 1 shows the results of the isochronal annealing experiment.

Application of Positron Annihilation Techniques in the Field of Ceramics

The importance of positron annihilation techniques in investigating the defect structure of solids is now well established. The distinct advantage of these techniques in such studies arises due to the sensitivity of positrons to changes in the local electron density near the defect. Metals and alloys are the most extensively studied materials by these techniques. In recent years, however, the interest is steadily growing in the ceramic systems. The present paper highlights the potential of this new and powerful technique in understanding the lattice defect structure of ceramics.

Lattice defect structure of degraded InGaAsP-InP double-heterostructure lasers

Lattice defect structure of degraded InGaAsP lasers has been investigated by scanning and transmission electron microscopy. It is found that although dislocation climb motion in InGaAsP lasers is slow, slip dislocations parallel to the stripe cause rapid degradation of the lasers.

Structure of lattice defects trapped at in impurities in He-doped Ni and Cu

Structure of lattice defects trapped at in impurities in He-doped Ni and Cu

Structure of lattice defects trapped at In impurities in He-doped Ni and Cu crystals derived from perturbed angular correlation measurements

Abstract “Helium decorated” defects, trapped by 111 In impuriteis implanted in Ni and Cu crystals doped with He, have been observed. This new type of defect possesses a three-fold axis of symmetry along the 〈111〉 direction and is characterized by a strong electric quadrupole interaction and a remarkably high trapping probability: almost 100%.

Relaxation effect of ion-ion and ion-electron emissions of germanium monocrystal

Abstract The first experimental results in investigating the IIE relaxation effect of Ge semiconductor monocrystal when bombarding with accelerated Ar+, Kr+ ions are presented. The interpretation of the observed relaxation effect is held within the theory considering a concentration redistribution processes of both the embedded inert gas ions and the interstitial atoms of Ge itself. The comparison of the relaxational change of IIE coefficient to the analogous change of the IEE coefficient is drawn which shows that IIE is more sensible to the lattice structural defects. The analysis of the relaxation curves showed that the dependence of characteristic relaxation times for IIE and IEE on temperature has the activation character. The activation energies and coefficients of diffusion of embedded Ar and Kr atoms and the activation energy of interstitial Ge atoms migration under the conditions of the ion irradiation are determined.

The construction of central‐force interatomic potentials from whisker deformation data

AbstractStress‐strain curves on single crystal whiskers can extend to the non‐linear region. It is shown that these provide data which can assist in the empirical construction or verification of central force potentials. Potentials constructed in this way are suitable for studying the atomic structure of lattice defects when large deviations from the ideal lattice positions occur in their cores. Furthermore, the effects of high external stresses on crystal defects can be investigated. An example of the latter may be found in the field‐ion microscope and as an application the non‐linear dilatation of the lattice under high hydrostatic tension is calculated, and the possible behaviour of dislocations in FIM specimens is briefly discussed.

Radiative localized centres in Ge-Se glasses observed by photoluminescence

Abstract Emission spectra, decay and fatigue kinetics and their variation witli temperature and composition in glasses of the system Ge x Se1−x reveal two types of radiative recombination centre. The decay of photoluminescence obeys first-order kinetics above 77 K, but deviates from it at lower temperatures. Spectra with two unresolved components and faster fatigue are caused by deviations from the stoichiometric GeSe2, a composition which proved to have limiting values for all the basic photoluminescence characteristics. The experimental data are interpreted in terms of recombination Coulomb centres, the walls of which are modulated by shallow traps due to lattice structure defects and topological random fluctuations.

Impurity-defect configurations in ion-irradiated copper studied by the DPAC-technique with111In

The structure and dynamics of lattice defects in copper are investigated. The defects have been produced by irradiation with heavy ions of 350 keV between 85 K and 300 K. Three different defect configurations are distinguished by the time differential perturbed angular correlation technique (DPAC) with111In as radioactive probe. Their electric quadrupole coupling constantsν Q =e 2 Qq zz /h areν Q1=116(2)MHz,ν Q2=181(3)MHz andν Q3=52(1)MHz. The defects characterized byν Q1 andν Q2 are observed in the temperature range of recovery stage III. The appearance ofν Q3 is closely correlated with recovery stage V. The symmetry axis of the electric field gradient associated with this defect-111In configuration points along a crystallographic 〈111〉 direction. We attribute this defect to a planar faulted loop, presumably of vacancy type. The influence of irradiating particles and dose on the defect configurations is analyzed.

Optically induced charge storage in ion implanted SiO 2

Charge storage in MOS structures with an ion implanted oxide layer has been investigated. The electrons generated by internal photoemission are captured in SiO 2 traps which are created by the implantation of Kr + and N + ions at energies of 50–290 keV and a fluence up to 10 14 cm −2. The charge storage results in a voltage shift of the high frequency C-V-curve. The dependence of electron storage on exposure time has been measured and compared with approximative calculations. The discharge of traps occurs by heating treatment and hints at the existence of deep oxide traps combined with structural lattice defects.

Defect-Impurity Interactions in Irradiated Germanium

The purpose of these experiments was to formulate a better model for the structures of lattice defects and defect-impurity complexes in irradiated n-type Ge. Single crystals were grown by the Czochralski process from P, As, or Sb-doped melts, and ? 1015 to ? 1017 oxygen cm-3 was added to the furnace chamber after ~ 1/3 of the crystal had been solidified. Hall coefficient and resistivity measurements (at 77°K) were used to determine the initial donor concentration due to the dopant and clustered oxygen, and infrared absorption measurements (at 11.7 ?) were used to determine the dissociated oxygen concentration. Certain impurity and defect-impurity interactions were then investigated that occurred as a consequence of selected annealing, quenching, Li diffusion, and irradiation experiments at ~ 300°K with 60Co photons, 1.5-2.0 MeV electrons, or thermal energy neutrons. Particular attention was given to determining the electrical role of the irradiation produced interstitial and vacancy, and to look for any evidence from electrical and optical measurements of vacancy-oxygen, lithium-oxygen, and lithium-vacancy interactions. A tentative model was developed for the lattice defect and defect-impurity structures, however, it was evident that any interpretation of defect-impurity interactions as a consequence of irradiation or annealing was subject to considerable error if the concentration and electrical role of certain impurities was not determined.

Effects of lattice defects on thermoluminfscence in lithium fluoride crystals

Abstract The thermoluminescent output of ‘pure’ LiF single crystals is studied as a function of annealing temperature and cooling rate. The lattice defect structure is characterized using ionic conductivity measurements. The results show that the sensitivity of such crystals to irradiation is highly dependent on prior history; specifically, the intensity of the observed 105°C thermoluminescence peak depends directly on the concentration of impurity vacany pairs present. The results also show the importance of background impurities in effecting thermoluminescent sensitivity.

Mössbauer Measurements of the Debye‐Waller Factor of Gold in Platinum after Low‐Temperature Neutron Irradiation

AbstractPt197, which decays with 20 h half‐life to Au197, is produced by irradiation of platinum samples with reactor neutrons at 4.6 °K. At the same time structural lattice defects are formed. Using the Mössbauer effect of Au197, the Debye‐Waller factor of the gold atoms is measured. A reduction of up to approximately 10% in the Debye‐Waller factor is found, which is attributed to irradiation‐produced defects. This behaviour is interpreted in terms of an interaction of defects formed by thermal and fast neutrons. A change of the coupling constant of the Au197 atom to its neighbours is assumed to be responsible for the reduction of the Debye‐Waller factor.

Wärmeleitung abschreckend kondensierter Bleischichten

The thermal conductivity of lead containing a large number of structural lattice defects is measured in the temperature range of about 2 to 20 °K. For the first time it is made possible by means of a special technique to investigate quenched films, which have been evaporated on to a cooled substrate in a high vacuum. The thermal conductivity of these films, which is much smaller than that of the bulk material, increases either by annealing or by increasing condensation temperature and film thickness, respectively. For most of the films the heat conduction is shown to be due only to the electrons. Therefore it can be discussed with respect to the validity of Wiedemann-Franz' Law and to deviations from Matthiessen's Rule in the temperature range of small angle scattering between electrons and phonons. The data of the superconducting state can be fitted to the BRT-expression for electronic conduction limited by defect scattering, if an energy gap of 2ɛ0=(4.20±0.15)kTc is chosen. The very small values of the phonon conductivity, estimated for the films with the lowest condensation temperatures, could result from the high concentrations of non-zero dimensional lattice defects, which have been observed earlier in such films.

Band Structure and Nature of Lattice Defects in GeTe from Analysis of Electrical Properties

AbstractThe measured transport properties of non‐stoichiometric GeTe have been satisfactorily analysed on the basis of a two‐carrier model and the various band parameters have been evaluated. In particular the variation of the carrier density of the system with composition has been obtained and then compared to the total number of excess atoms in the non‐stoichiometric lattice. It is found that the defects occurring in GeTe due to these excess atoms are of a complex nature, except for compositions close to stoichiometry where singly ionized vacancies are the dominant defect.

Factors affecting the mechanical behavior of lithium fluoride single crystals

Mechanical properties of lithium fluoride single crystals, taking into account equilibrium lattice defect structures

タングステン-コバルトメッキ層の電子顕微鏡による直接観察

Structure and configuration of lattice defects in tungsten-cobalt electrodeposits were examined under transmission electron microscope. The layer as deposited contained numerous stacking faults and twin faults in each grain, giving martensitelike structure.As the results of electron diffraction analysis, it was found that the crystal structure of the deposits consisted of hexagonal α-Co solid solution oversaturated with tungsten and that after heating at 600°C for 2hr., precipitation of Co3W appeared in α-Co phase. However, the appearance of Co3W phase was not evidently detected under electron microscope, even though it was determined by electron diffraction.Hardening of the deposits after heating seemed to be attributed to the precipitation of Co3W.