The use of positron annihilation to study vacancy defects and some recent results are reviewed. For metals, theoretical calculations have reached the leyel where they can reliably predict lifetime values of positrons trapped at vacancy defects of various size, geometry and impurity environment. Experimental results are shown on vacancy recovery and vacancysolute interaction in electron irradiated Fe, Nb, and Ta. During last years the technique has been applied also to semiconductors. Positron trapping in Si is discussed and some results are given on native and irradiation induced vacancies in GaAs. A beam of slow positrons is a new tool to probe nearsurface regions and thin films. Examples are shown on Mo(111) surface sputtered with Ar+ ions and on Si(100) implanted with 35 keV H+ ions.

Most of the Interpretation of positron annihilation results to date have been done within the context of the simple trapping model which assumes a uniform spatial distribution of defects within the specimen examined. While this assumption is often justifiable there are numerous metallurgical defect configurations which are markedly nonuniform. In this work some of the appropriate trapping models which have previously appeared in the literature will be briefly reviewed. Additional models which are currently being developed will be presented and the series of experiments which are being used to test the trapping models will be described.

Positron annihilation lifetime spectroscopy has proven to be sensitive to glass transitions and other free volume dependent phase transitions in amorphous and semicrystalline polymers. The thermal dependence of the lifetime spectra of positrons in compression-molded poly(bisphenol-A carbonate) has been measured from 253K to 323K, then modelled using a three component fit. The longest-lived component lifetime τ3 was found to vary linearly with increasing temperature independent of thermal history. The corresponding component intensity I3 was found to vary in a non-linear fashion with increasing temperature, exhibiting a significant dependence on thermal history. The observed thermal response of τ3 and I3 is discussed in terms of both molecular relaxation and the ductile-to-brittle transition behavior of poly(bisphenol-A carbonate).

In applications of the perturbed angular correlation (PAC) technique to the characterization of defect structures in materials conclusions are drawn from the local electric field gradient measured at the site of a radioactive probe atom. In metals, PAC has been very successful in labeling and identifying simple probe atom-defect pairs. Based on these results, new experiments were performed on defect structures in cold-worked samples, on the dynamics of He-defect interactions and on the growth of vacancy clusters. Recent results on interactions between the acceptor atom In and different donor atoms or intrinsic defects in Si indicate that PAC may provide atomistic information also in the case of semiconductor materials.

Following nanosecond-duration laser surface-melting, lattice locations of illIn probe atoms in Ni and Pt samples were studied using the technique of perturbed gamma-gamma angular correlations (PAC). After melting and annealing, no probe atoms were observed to become associated with unique vacancy clusters observed after other methods of damaging, while many probe atoms were found on non-unique sites. 111In probe atoms were observed to move to the surface and to be expelled at anomalously low temperatures. These observations are partially reconciled by the hypothesis that probe atoms diffusing in the molten surface layer become trapped on dislocations during resolidification, and during later annealing return to the surface via pipe diffusion.

The effects of target-atom vibrations on nuclear reaction kinetics have been examined. In particular, Doppler broadening of resonance-type and elastic- scattering reactions has been considered in detail. Depending on the specific process parameters, the resulting energy widths can be many orders of magnitude larger than the energies of the vibrational states of the target solid. Comparison of experimental results on a hydrogen-bearing thin target with the theoretical predictions shows excellent agreement. We will show the importance of this effect in hydrogen profiling measurements and point out the feasibility of vibrational spectroscopy on hydrogen in solids.

Recent results on the diffuse scattering from single crystals of Fe1−xO at high temperatures reveal that the defect structure is in striking agreement with embedded cluster calculations by Ellis et al. The dominant defect is an imperfect 7:2 cluster. Mixtures of this and a larger complex (13:4) can explain the electrical properties. XANES studies of this oxide are in agreement with Ellis' theoretical work. However, in both FOx and MnxO it is not possible to use the shift of the cation K absorption edge to characterize valence. In fact in the latter case the shift passes through a minimum, perhaps indicating the onset of clustering.

Large-angle diffuse scattering has been investigated for the purpose of studying coherent precipitates in a crystal lattice. Detailed calculations have been made of the scattering near Bragg reflections from cobalt precipitates in a copper host lattice. These calculations have been compared to x-ray diffuse scattering measurements made on aged (570°C for 17 hr.) Cu-0.95%Co crystals with x-rays of three different wavelengths at the NSLS. The results indicate that the size distribution, the concentration, and the internal strain of the precipitates can be determined from such diffuse scattering measurements.

A detailed comparison of small-angle scattering (SANS) and large angle x-ray diffraction methods of characterization of precipitates was undertaken. Cobalt-rich precipitates on the order of 50 Å developed after a 17 hour anneal at 570°C were studied in a single crystal sample with SANS and with diffuse x-ray scattering near the (400)Bragg peak. Each scattering data set was analyzed independently in terms of a distribution of precipitate sizes; a detailed comparison is made of the size distribution obtained. A small interparticle interference effect is seen.

In Al-Cu alloys containing Guinier-Preston zones, the scattering contributions due to short-range order and atomic displacements vary differently when the scattering contrast between Al and Cu is changed. The diffuse neutron scattering of Al-Cu single crystals containing 63Cu or 65Cu is compared and evaluated to test the current methods of separating the two scattering contributions. - The nature of a sugggtted ordered state in α-brass is also studied by neutron scattering, using Cu to enhance the scattering contrast in a Cu-30 at.% Zn alloy. A broad diffuse peak is found in powdered, appropriately aged samples, confirming that the first Warren-Cowley short-range order parameter is negative.

Single crystals of Al were irradiated up to 480 ppm of Frenkel defects using a specially developed irradiation facility for high dose electron irradiation of large samples below 20 K. Diffuse inelastic neutron scattering measurements have been performed at these samples to study the dynamics of single self interstitial atoms. The measurements were made at 6 K on the sample before annealing and after annealing at 46 K (above stage I) and at 300 K (after complete recovery). The irradiated samples showed a significant increase of the inelastic scattering intensity at transferred energies between 0.7 and 2 THz. By comparison with the results of computer calculations the different frequencies of the energy loss spectrum could be attributed to the different vibration modes of interstitial atoms. The frequencies of the most significant modes of the self interstitial atom are determined to be υ = 0.75 THz and υ = 1.35 THz for the translation-(A2u) and libration-(Eg) mode, respectively.

High-resolution, neutron time-of-flight Bragg scattering measurements have been carried out on polycrystalline CeO2 as a function of temperature (20<T<1200C). Systematic deviations between theory and experiment for the integrated intensities of the Bragg reflections were observed; these deviations increased with increasing temperature. The deviations result from cubic anharmonic interactions that appear only on the oxygen sublattice. The results are discussed in terms of higher order cumulant tensor representations. We observe that these anharmonic interactions exhibit the same symmetry as those associated with defects incorporated into the fluorite lattice when CeO2 is made nonstoichiometric.

We have studied the atomic states of arsenic (As) and phosphorus (P) in SiO2 using X-ray photoelectron spectroscopy (XPS). Silicon dioxide implanted with As or P shows multiple XPS core level peaks corresponding to the impurity atoms located in two distinct atomic sites. The binding energies of the two arsenic 3d core levels occur at 45.8 and 42.3 eV and the two phosphorus 2p core levels occur at 134.7 and 130.3 eV. When the implanted oxides are annealed in an oxygen ambient between 900°C and 950°C, only the highbinding- energy peaks of P and As are observed. This identifies the highbinding- energy core level peaks as being associated with the impurity (P or As) on silicon sites. Annealing in nitrogen at 950° C results in an increase in the low-binding-energy signal. The low-binding-energy peaks are associated with the impurity (P or As) bonded to silicon neighbors. The relative amounts of dopants in silicon and oxygen sites depend on ambient purity and processing details. Reference to previous work shows that the presence of As or P on silicon sites in SiO2 corresponds to a fast diffusing state whereas As or P on oxygen sites corresponds to a slow diffusing state [1].

Signal-to-noise ratios for Si <110> lattice images are measured for a variety of different specimen preparation techniques, including ion-milling, chemical polishing, cleavage and in-situ surface cleaning by heating. The noise levels are significantly lower in the latter, possibly permitting new classes of experiments in image quantitation and impurity imaging.

RBS/Channeling measurements have been used to characterize the Si recrystallization and As substitutionality of <100> Si wafers implanted with 100 keV As at two doses after multiple thermal anneals. It is found that low temperature thermal treatment after a high temperature rapid thermal anneal results in deactivation of the implant, presumably due to Arsenic clustering. The ion channeling results indicate the growth of a disordered layer in the silicon after the second anneal at a depth corresponding to the peak of the Arsenic implant concentration. The number of displaced Si atoms is found to be 5-10 times greater than the number of displaced As atoms. This indicates that both As clustering and growth of Si defects should be considered as possible mechanisms for the electrical deactivation of the implanted Si after post anneal.

The surface layer of single crystal GaAs that has been bombarded with high energy (2-15 MeV) ions is strained and contains many defects, but it remains crystalline. We have studied the isochronal annealing behavior of this layer using phonon shifts and widths, which were detected by Raman measurements. We do not find any sharp annealing stages to 500 C, at which temperature the phonons have returned to their positions in the unbombarded crystals. These results are consistent with the idea that the phonon shifts are primarily due to antisites and their complexes with other primary defects. However, other extended defects may still be present, and the Raman data show some evidence for this.

In-situ time resolved reflectivity, Rutherford backscattering and channeling and transmission electron microscopy have been employed to characterise the evolution of Ar+ ion implantation damage in GaAs as a function of ion dose at various irradiation temperatures. Specific reflectivity signatures have been identified and characterised in terms of observed structural changes to the GaAs. Reflectivity provides a simple and convenient means of monitoring damage build up during ion implantation. In contrast to accepted models for amorphous phase formation in semiconductors, GaAs has been observed to undergo a sudden transformation from a crystal containing a dense network of extended defects to an amorphous phase under elevated temperature irradiation conditions.

Semi-insulating and SI-doped <100> GaAs have been irradiated to a dose of 1016 protons cm−2. Samples have been annealed for 20 minutes at 400,500 and 600°C. Cross-sectional TEN has shown the as-implanted and 400°C annealed GaAs to contain no visible damage. After 500 and 600°C anneals a heterogeneous distribution of planar raft-like defects apears on {(11} and {110}. The density of these defects is much lower in the Si-doped material.

Three hundred angstrom Zr films were deposited on A12O3 substrates and irradiated with 300 keV Xe ions to a dose of 1 × 1016 /cm2. The irradiation was carried out at 77 K, 300 K (ambient temperature), and 800 K. Changes in the deposited film and the Zr-A12O3 interface were examined by comparing Rutherford backscattering spectra from irradiated and unirradiated regions of the samples. Ion beam induced reactions were observed at all three temperatures. The systematics of the temperature dependence of ion beam mixing are discussed.

This paper presents an analytical model for the application of capacitance DLTS on the normally-on HEMT structure. Based on the charge conservation law, the DLTS signal is derived by taking into account both the Schottky gate and the heterojunction depletion layer capacitances. It is shown that the anomalous features observed by using the conventional DLTS technique on a HEMT structure can be reasonably explained with this model. Some results obtained by simulation of typical measurements are presented, which confirm our conclusions.