Three compositions with the spinel structure (γ-AIVB2VIO4), MgAl2O4, FeCr2O4 and γ-SiFe2O4, have been irradiated with 1.5 MeV Kr+ ions over a temperature range (20 to 873 K). In situ TEM and HRTEM afterwork were conducted to characterize the effects of the ion irradiation on the microstructure. MgAl2O4 was the most “radiation-resistant” among the three materials. After irradiation to lx1016 ions/cm2 at 20 K, the cations were completely disordered among all possible tetrahedral and octahedral sites, but the oxygen sublattice remained intact. At room temperature, a high density of dislocation loops developed after this same dose, but there was no evidence of cation disordering. However, γ-SiFe2O4, a spinel structure type, formed under high pressure (7.0 GPa), was easily amorphized at low ion doses (σ1014 ions/cm 2) below 723 K, even lower than required for radiation-induced amorphization of its olivine polymorph, fayalite (α-SiFe2O4; HCP). At 873 K, the amorphous phase recrystallized to magnetite (Fe2+Fe 3+2O4, an inverse spinel structure) and quartz (SiO2) during continued Kr+ irradiation. Chromite (ideally FeCr2O4) with an actual composition of (Fe0.6Mg0.4)(Cr0.7A10.3)2O4 amorphized at 6x1015 ions/cm2 at 20 K, a dose about 20 times as high as that required to amorphize most other AB2O4 phases under the same irradiation conditions. A structural parameter, which quantifies the deviation from ideal packing in the spinel structure was developed and correlates with themeasured doses required for amorphization among these three spinel compositions.

Spinel (MgAl2O4) single crystals which had been neutron irradiated at (nominally) 400 and 750°C to high doses (53-250 dpa) were examined using 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). The sensitivity of this procedure to a specific cation (Al) residing in different crystallographic environments allowed us to determine the distribution of the Al between the tetrahedral and octahedral cation sites in the spinel structure. Our results indicate that the Al was distributed nearly equally over both cation sites in the spinel, resulting in a nearly inverse structure.

Analytical electron microscopy (AEM) has been used to investigate precipitates in MgAl2O4 spinel implantated with Al+, Mg+, or Fe2+ ions. Experiments combining diffraction, energy dispersive X-ray spectrometry (EDS), electron energy-loss spectrometry (EELS), and energy-filtered imaging were employed to identify and characterize precipitates observed in the implanted ion region. Diffraction studies suggested these are metallic aluminum colloids, although EELS and energy-filtered images revealed this to be so only for the Al+ and Mg+ implantations, but not for Fe2+ ion implantations. Multiple-least-squares (MLS) fitting of EELS plasmon spectra was employed to quantify the volume fraction of metallic aluminum in the implanted ion region. Energy-filtered plasmon images of the implanted ion region clearly show the colloid distribution in the Al+ and Mg+ implanted spinel. Energy-filtered images from the Fe2+ ion implanted spinel indicate that the features visible in diffraction contrast cannot be associated with either metallic aluminum or iron-rich precipitates.

Microstructural modification of high temperature superconductor (HTS) single-crystal plates of T1-1212 and T1-2212 (numbers designate the Tl/Ba/Ca/Cu cation ratio) was studied during 1.5 MeV Kr+ and Xe+ ion irradiation with in-situ electron diffraction and after ion irradiation with high resolution TEM (HRTEM). Similar in-situ temperature dependence effects are seen for both phases. During irradiations from 22K to 673K, an amorphous halo develops after very low ion dose or fluence (l.7X1012 ions/cm2). During irradiation at 100K and 300K, complete amorphization is obtained, while at 22K and ≥533K, the halo fades slightly and a polycrystalline ring pattern develops, indicating ion irradiation induced crystallization occurred. After a low ion dose (8.5XlO12ions/cm2) at 100K and 300K, HRTEM reveals amorphous regions 5 -20 nm in size which are not columnar and do not all penetrate the entire sample thickness. At 22K and ≥533K, Moire fringes and misoriented crystallites of cascade size are observed. The 4 - 6nm crystallites are thallium-rich.

Electron irradiation damage induced in high Tc superconducing ceramics is studied using microRaman and cathodoluminescence. The formation of extended impurity phases is dominant in BSCCO, while oxygen loss and disorder is the main effect observed in YBCO, in this case the local oxygen loss is quantified.

Transmission electron microscopy (TEM) has been used to study the effects of 200 keV proton and 1 MeV fluorine ion irradiation on the microstructure of YBa2Cu3O7-δ (YBCO). Proton irradiation at fluences on the order of 1016 cm−2 results in more visible defects than can reasonably be expected solely from high energy transfer events; medium energy transfer events also contribute to visible defects. Defects arising from cascade events can be as large as 2 to 3 nm, and high resolution imaging suggests that they consist of small volumes of structurally disordered material. Fluorine irradiation to similar displacement levels results in significantly more visible defects.

This is the first report of ESR observations of three distinct paramagnetic centers in TeO29 glasses. One center is intrinsic to the glass and the other two are induced by KrFexcimer-laser radiation. The intrinsic center with a broad ESR spectrum is tentatively identified as an oxygen-associated hole center. One radiation-induced center fades slowly at room temperature; its proposed structure is that of an electron trapped in a diffuse orbital associated with a modifier ion. The other radiation-induced center is stable at room temperature and corresponds to the Vo· center observed in crystalline paratellurite.

The non-uniform distribution of damage with depth and the onset of amorphization produced in Al0.6Ga0.4As/GaAs heterostructures by 1.5 MeV Kr+ ion implantation at 77K have been investigated by using a combination of RBS channeling and cross-sectional high-resolution TEM techniques. The extent of damage increases with increasing depth in the Al0.6Ga0.4As layer. This depth dependence of the damage can be correlated with an increase in the number of recoil events with an energy between 30 and 50 keV. We propose that the amorphization of Al0.6Ga0.4As requires the superposition of cascade-type damage on a background population of point defects which is created by implantation with high energy ions.

We have fabricated optical channel waveguides in planar GaAs/AlGaAs waveguides using 10 MeV oxygen ions at a fluence of 3x1013 and 3x1014 ions/cm2. Although disordering of GaAs/AlGaAs quantum well structures has previously been reported, to the best of the authors' knowledge the fabrication of channel waveguides using high energy oxygen bombardment has not been demonstrated in this material system. This technique may provide a totally new concept of localized material modifications in GaAs/AlGaAs waveguides by creating compositional disordered regions that act as optical confinement channels. The masking technique used to provide selective disordering of the planar waveguide structures will be presented. Optical measurements were performed on the channel waveguides at a wavelength of 1.3 μm.

We investigate the effects of thermal annealing on the structural, elastic and electronic properties of self implanted silicon by tight binding molecular dynamics. The irradiated samples, after a careful relaxation at room temperature, are annealed at different temperatures and for different times and, finally, their properties are carefully monitored during constant temperature simulations. We further provide a characterization of the chemical bonding in the amorphous network and show the evolution of the point defect distribution against maximum annealing temperature.

The concentration of residual defects produced by self ion implantation of silicon has been shown to be a sensitive function of implantation temperature at temperatures near room temperature. In this study samples were heated to temperatures of 20°C and 60°C and implanted with 540 keV Si ions to a fluence of 2x1015Si.cm-2 using a constant scanned ion flux of 0.2 μA.cm-2. The resultant primary defect concentrations, measured by Rutherford backscattering spectrometry and channelling (RBS-C), were 2.3±0.1x1022 cm-l and 1.8±0.2x1021 cm-3, respectively, i.e. a reduction by a factor of σ13 for a temperature increase of 40°C. Such differences were not evident in the concentration of secondary defects formed by annealing these samples at 900°C for 15 minutes: the defect concentrations were equal within the experimental uncertainties of the RBS-C and transmission electron microscopy (TEM) measurements. This result appears to lead to the surprising conclusion that the number of displaced atoms that survive high temperature annealing to form extended defects is largely independent of the dynamic annealing processes operating during implantation but depends instead on parameters which scale with the ion fluence.

The influence of in-situ photoexcitation during low temperature implantation on selfinterstitial agglomeration following annaealing has been investigated using transmission electron microscopy (TEM). A reduction in the level of as-implanted damage determined by RBS and TEM occurs athermally during 150 keV self-ion implantation. The damage reduction following a 300°C anneal suggests that it is mostly divacancy related. Subsequent thermal annealing at 800°C resulted in the formation of 13111 rod like defects or dislocation loops for samples with and without in-situ photoexcitation, respectively. Estimation of the number of self-interstitials bound by these defects in the sample without in-situ photoexcitation corresponds to the implanted dose; whereas for the insitu photoexcitation sample a suppression of ≈2 orders in magnitude is found. The kinetics of the athermal annealing process are discussed within the framework of either a recombination enhanced defect reaction mechanism, or a charge state enhanced defect migration and Coulomb interaction.

Solid phase epitaxial regrowth of spatially isolated amorphous regions in Si, Ge and GaP has been stimulated by using an electron beam with energies in the range of 50 to 300 keV. In all materials, the rate at which the amorphous zones disappear decreases as the energy of the electron beam increases from 50 keV reaching a minimum below the threshold displacement voltage before it again increases with increasing electron energy. The experimental results are interpreted in terms of creation and motion of defects (dangling bonds, charged defects) along the amorphouscrystalline interface.

Concurrent irradiation with ions and electrons has been done in a high voltage electron microscope interfaced with an ion accelerator. The objective is to clarify the stability of cascades in Ge in terms of the elementary processes associated with the concurrent irradiation. Amorphous-like cascade contrast is observed under ion irradiation and increases in number eventually leading to saturation. The cascade contrast is produced within cascade regions through sequential overlaps of cascades and heavier ions form more stable cascade regions. The concurrent or subsequent electron irradiation recrystallizes cascade regions through shrinkage of the cascade contrast. Point defects and their diffusion induced by electrons contribute to the recrystallization of cascade regions.

In order to explain the relatively easy laser-induced desorption of hydrogen implanted in silicon, and particularly the lower temperature needed for desorption at higher implantation energy, the microstructural modifications produced by laser pulses were studied by means of transmission electron microscopy. The structural damage, such as defect clusters and hydrogen gas bubbles was observed. In the case of low dose implantation (H/Si ≤ 15&), most of the bubbles were produced during laser annealing rather than during implantation. This bubble formation in the course of desorption explains the higher temperature needed. When blisters are already present on the as-implanted surface, desorption starts at a lower temperature.

Thermal helium desorption spectrometry and positron beam analysis have been used to monitor the growth of helium vacancy clusters during room temperature helium irradiation of silicon and during subsequent annealing to 1300 K. Experimental results obtained with hydrogen irradiation show that also hydrogen can be used to create cavities. There is a rather sharp threshold dose for creating cavities that will survive 1300 K annealing. It appears that positrons form a sensitive probe for the trapping and release of impurities inside the cavities. Results of atomistic calculations are used to discuss thermal stability of helium vacancy complexes. The results are related to recent impurity gettering studies based on impurity trapping at helium induced gettering centers.

Solid phase epitaxial regrowth of ion-implanted relaxed Si1-xGex layers was studied as a function of alloy composition (0.15< x <0.5) by a combination of Rutherford backscattering/ channeling spectrometry and transmission electron microscopy. The samples were grown by molecular beam epitaxy on compositionally graded buffers at different growth conditions. It was found that the regrowth velocity follows an Arrhenius curve in the investigated composition range and increases with increasing Ge content. The activation energies of the epitaxial regrowth were found to be higher than those expected from a linear interpolation between the values for pure Si and Ge. It is demonstrated that the regrowth velocities in the samples grown at 550 and 750°C and with low-rotational speed of the substrate during growth depend on the lateral position on the wafer and that they can be reduced by a preannealing treatment at high temperatures (σ920°C). We suggest that these effects arise from a compositional modulation in the alloy layer and, therefore, from a symmetrized strain, which can be reduced by a high temperature annealing.

We have examined the damage produced by Si-ion implantation into strained Si1-xGex epilayers. Damage accumulation in the implanted layers was monitored in situ by time-resolved reflectivity and measured by ion channelling techniques to determine the amorphization threshold in strained Si1-xGex, (x = 0.16 and 0.29) over the temperature range 30-110°C. The results are compared with previously reported measurements on unstrained Si1-xGex, and with the simple model used to describe those results. We report here data which lend support to this model and which indicate that pre-existing strain does not enhance damage accumulation in the alloy layer.

Positron annihilation lifetime spectroscopy (PALS) is a unique technique for detection of vacancy related defects in both as-grown and irradiated materials. We present a systematic study of vacancy defects in stoichiometrically controlled p-type Gallium Arsenide grown by the Hot- Wall Czochralski method. Microstructural information based on PALS, was correlated to crystallographic data and electrical measurements. Vacancies were detected and compared to electrical levels detected by deep level transient spectroscopy and stoichiometry based on crystallographic data.

Semi-insulating gallium arsenide has been irradiated by protons and by gamma-rays with different doses. The irradiation-induced deep level defects have been investigated by current transient spectroscopy to find their energy, capture cross sections and generation rate.Two electron traps at Ec+0.14eV(E13) and Ec-0.70eV(E4) and a hole trap at Ec-0.14eV(H2) in addition to the levels existing before the irradiation have been detected in the irradiated samples. These findings have been related to the performance of gallium arsenide charge particle detectors.