Effect of coimplantation of iron and chromium ions on the optical properties of aluminum oxide

The optical absorption of leucosapphire and polycrystalline corundum (polycor) upon coimplantation of iron and chromium ions and subsequent annealing in vacuum is studied. The structure of the states localized in the band gap induced by radiation defects exhibits a higher stability to annealing as compared to implantation of other types of ions into aluminum oxide and to separate irradiation with iron and chromium ions. The governing contribution to the exponential and interband absorption is made by substitutional defects of either type, their clusters, and impurity-vacancy complexes. The effect of incorporated iron ions on the population of levels of chromium-containing defect clusters, on their recharge, and on interaction with intrinsic radiation and biographical defects is revealed. Mixed clusters of substitutional defects are optically active in a spectral range of 2.0–4.0 eV after annealing at a temperature of 1300–1600 K.     

XRD AND EXAFS INVESTIGATION OF THE DECOMPOSITION OF Co-Cu SOLID SOLUTION PREPARED BY MELT SPINING

High solid-solubility Co₁₅Cu₈₅ alloys were prepared by melt spining and then submitted to isothermal and anisothermal annealing to obtain granular alloys. The synchrotron radiation X-ray diffraction patterns and extended X-ray absorption fine structure (EXAFS) spectra were measured to investigate the decomposition of supersaturated solid solution upon annealing. Experimental results indicated the precipitation of ultrafine Co-rich particles occurred at about 500℃ and the annealing had a great influence on the middle-range order of Co atoms. While the fitted EXAFS spectra showed that the interfaces of Co precipitates seem to be enriched with vacancy-type defects, leading to distorted interfaces.     

Optical properties of polycrystalline alumina after irradiation with iron ions and annealing

Optical absorption of polycrystalline corundum (polycor) after irradiation with iron ions and subsequent annealing in vacuum was studied. It was found that substitutional, intrinsic radiation, biographical defects, and complexes on their basis have an effect on the absorption parameters and optical transitions between localized states and allowed bands. The contributions to changes in the optical properties of individual substitutional defects, their clusters, and complexes with the participation of substitutional defects and radiation defects were singled out. The influence of defects and iron oxides formed upon annealing on absorption was estimated. The most proable nature of clusters of substitutional defects and impurity-vacancy complexes was identified.     

Free volumes in bulk nanocrystalline metals studied by the complementary techniques of positron annihilation and dilatometry

Free-volume type defects, such as vacancies, vacancy-agglomerates, dislocations, and grain boundaries represent a key parameter in the properties of ultrafine-grained and nanocrystalline materials. Such free-volume type defects are introduced in high excess concentration during the processes of structural refinement by severe plastic deformation. The direct method of time-differential dilatometry is applied in the present work to determine the total amount and the kinetics of free volume by measuring the irreversible length change upon annealing of bulk nanocrystalline metals (Fe, Cu, Ni) prepared by high-pressure torsion (HPT). In the case of HPT-deformed Ni and Cu, distinct substages of the length change upon linear heating occur due to the loss of grain boundaries in the wake of crystallite growth. The data on dilatometric length change can be directly related to the fast annealing of free-volume type defects studied by in situ Doppler broadening measurements performed at the high-intensity positron beam of the FRM II (Garching, Munich, Germany).     

Laws of changing the structure and properties of metallic glasses upon annealing and local mechanical loading

The behavior of metallic glass structure and properties upon annealing and local mechanical loading is investigated. Based on the results obtained, an energy model of plasticity behavior upon annealing and an atomic reorganization model upon local mechanical loading are suggested.     

Molecular dynamics simulations of lanthanum oxide surfaces

Classical molecular dynamics was used to investigate the equilibrium state of the surface region of as-grown La₂O₃. It is currently thought that bulk and epitaxial thin film La₂O₃ surfaces exhibit amorphous structures in the as-prepared state that yield bulk crystal states upon postdeposition annealing. The focus of the study is to determine if the as-prepared surface region of La₂O₃ is purely amorphous as indicated from prior experimental results. Using simulation cells sufficiently large to accommodate the formation of defects, phase segregation, compositional migration, and site defects, our results show that crystalline phases are evident from simulated X-ray diffraction patterns. Although the phase of these crystallites is unresolved, we suggest that combinations of distorted hexagonal, cubic, and nonstoichiometric phases are formed in the as-prepared state prior to annealing. These crystallites likely serve as nucleation site for long-range ordered crystal growth upon annealing.     

High temperature reaction and defect chemistry at the Si/SiO2 interface

The generation of structural and electrical defects in Si/SiO₂ structures upon high temperature annealing by the oxide decomposition reaction Si+SiO₂→2SiO ↑ has been studied using scanning electron microscopy (SEM) and ramped current-voltage measurements. The SiO decomposition is nucleated at crystalline defects in the substrate and results in the formation of voids in the oxide. The voids grow laterally with annealing time, independent of the nature of the defect. Prior to the formation of physical voids in the oxide, defects become electrically active, leading to low field dielectric breakdown. The breakdown degradation is prevented when the O₂ pressure in the annealing ambient is sufficient to reverse the decomposition reaction by reoxidizing the SiO product at the interface.     

Effects of the structural state of a W — Re solid solution on the Fe-57 Mössbauer spectrum

Mössbauer spectra for iron-57 are reported for alloys containing up to 27 at.% rhenium. The cobalt-57 was introduced by diffusion annealing as the parent isotope for the iron-57. Diffusion annealing at 1080°C for 16 hr causes the cobalt to diffuse mainly along lattice defects (dislocations and grain boundaries). These defects give rise to regions whose electronic structure differs from that of the matrix. The precise type of structure and the number of such regions are complex functions of the alloy composition and structural state. Results are given on the iron-57 spectra for tungsten, rhenium, the σ phase, and an alloy in the two-phase region.     

Enhanced infrared response of Si base p-n diode with self-assembled Ge quantum dots by thermal annealing

The effects of thermal annealing in Si base p-n diode with self-assembled Ge dots stacked in eight layers structure are investigated. The effects of annealing are discussed based on the photovoltage spectra, the PL spectra and the Raman spectra. Three main effects occur after thermal annealing: the reduction of point defects, the intermixing of Si-Ge and the strain relaxation. The experimental result shows that 800 °C might be a suitable annealing temperature for photovoltaic applications.     

Structure, electrical and magnetic properties, and the origin of the room temperature ferromagnetism in Mn-implanted Si

The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 10¹⁶ cm^?2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account for only a few percent of the total Mn content. The main part of Mn is fixed in Mn₁₅Si₂₆ nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than by a Mn impurity.     

Effect of annealing on the structural and optical properties of (3 1 1)B GaAsBi layers

The influence of post-growth annealing on the microstructure and photoluminescence (PL) of GaAsBi alloys grown on (3 1 1)B GaAs is analyzed. Conventional transmission electron microscopy (TEM) performed on as-grown samples evidence the presence of structural defects and a mosaic structure in the GaAsBi layer. A sequence of stacking faults at regions close to the GaAs/GaAsBi interface are observed in high resolution TEM images. After annealing at 473 K during 3 h the mosaic structure disappears, the presence of defects is reduced and the PL peak intensely enhances.     

Temperature-dependent texture, stress and resistivity in melt spun Cu0.95Co0.05 ribbon

Ribbon samples of Cu_0.95Co_0.05 were prepared by melt spinning method to perform systematic investigations on structure and transport properties as a function of annealing temperature. X-ray diffraction study shows that the ribbon is polycrystalline with a strong 2 0 0 texture along the surface normal of the as-quenched Cu_0.95Co_0.05 ribbon and the degree of texture is enhanced upon annealing. The compressive stress, which relaxes upon annealing, is observed in as-quenched ribbon. The resistivity, which is higher in as-quenched ribbon, decreases toward the bulk value of Cu upon annealing. The compressive stress and higher resistivity in as-quenched ribbon are attributed to the incorporation of Co atoms/particles in Cu matrix. The decrement of the stress and resistivity upon annealing is due to the precipitation of Co atoms from the Cu matrix, segregating as Co or Co-rich Cu grains as observed from the transmission electron microscopy measurements.     

Positron annihilation in electron-irradiated n-type gap crystals

Abstract

The defects in n-GaP crystals irradiated by 2.3 MeV electrons up to 1 × 10¹⁹ cm^?2 at RT were studied by means of positron annihilation (angular correlation) and electrical property measurements. It was found that positrons are trapped in some radiation-induced vacancy-type defects (acceptors) but that the effect saturates at high electron fluences (D1 × 10¹⁸ cm^?2). The trapping rate in irradiated samples increases with temperature in the range 77–300 K. Post-irradiation isochronal annealing reveals the positron traps clustering at about 200–280°C. All positron sensitive radiation-induced defects disappear upon annealing up to 500°C.     

非故意掺杂4H-SiC外延材料本征缺陷的热稳定性

采用电子顺磁共振（ESR）和低温光致发光（PL）技术,研究了退火温度对低压化学气相沉积法（LPCVD）制备的非故意掺杂 4H-SiC材料中本征缺陷稳定性的影响.结果发现,当退火时间为10 min和30 min时,本征缺陷浓度均随着退火温度的升高而增大,当退火温度达到1573 K时材料中本征缺陷浓度达到最大,继续升高退火温度将使材料中本征缺陷浓度迅速降低.退火温度对材料中本征缺陷的影响主要是由于退火中本征缺陷的稳定化过程及本征缺陷之间发生强烈的相互作用引起的. 关键词： 高温退火 本征缺陷 电子顺磁共振谱 光致发光     

Thermal Neutron damage in cadmium

The isochronal annealing of the damage produced by thermal neutron irradiation of cadmium at 3.6 °K has been studied for several initial doses which vary by a factor of 1000. The recovery results show a strong dependence upon initial dose. This effect, which is not seen to this extent in the fcc metals, cannot be accounted for by an irradiation annealing mechanism. In contrast to the observation of two processes involving long range defect migration for several fcc metals only one process, at high temperatures, is discernable from isochronal annealing of Cd. The presence of another process at low temperatures is clearly established by other means. Irradiation annealing effects observed during the production of damage at high defect concentrations indicate that the spontaneous annihilation volume between the defects of a new capture event and the defects from an earlier event is 80 atomic volumes. Other results suggest that damage production and recovery mechanisms may be associated with the anisotropic nature of the cadmium hexagonal lattice.     

Evolution of SiGe nanoclusters and micro defects in the Si1−xGex layer fabricated by two-step ion implantation and subsequent thermal annealing

The Si_1−xGe_x thin layer is fabricated by two-step Ge ion implantation into (0 0 1) silicon. The embedded SiGe nanoclusters are produced in the Si_1−xGe_x layer upon further annealing. The number and size of the nanoclusters changed due to the Ge diffusion during annealing. Micro defects around the nanoclusters are illustrated. It is revealed that the change of Si-Si phonon mode is causing by the nanoclusters and micro defects.     

A systematic analysis of defects in ion-implanted silicon

A classification scheme for the different forms of implant-related damage which arise upon annealing consisting of five categories is presented. Category I damage is subthreshold damage or that which results prior to the formation of an amorphous layer. If the dose is increased sufficiently to result in the formation of an amorphous layer then the defects which form beyond the amorphous/crystalline (a/c) interface are classified as category II (end of range) damage. Category III defects are associated with the solid phase epitaxial growth of the amorphous layer. The most common forms of this damage are microtwins, hairpin dislocations and segregation related defects. It is possible to produce a buried amorphous layer upon implantation, If this occurs, then the defects which form when the two a/c interfaces meet are termed category IV (clamshell, zipper) defects. Finally, category V defects arise from exceeding the solid solubility of the implanted species in the substrate at the annealing temperature. These defects are most often precipitates or dislocation loops.In addition to presenting examples of this classification scheme, new results emphasizing category II, IV, and V defects will be presented. For category II defects, the source, dose and mass dependence as well as the influence of pre- and post-amorphization is discussed. The category IV defects which arise from buried amorphous layers in {100} oriented As implanted samples is presented. Half loop dislocations which arise during annealing of high dose As implants, are shown to originate in the category V defects and grow upon dissolution of As clusters and precipitates.     

Study of “uncorrelated” radiation damage inNi 111In

With 1.5 MeV deuterons lattice defects have been introduced into diffused sources of¹¹¹In in Ni. Defect structure and annealing behavior were found in all respects comparable to previous work in Groningen using ion-implantation. The results suggest that the defect structure in Ni and other fcc metals is not strongly dependent on the manner in which the defects are introduced.Research supported in part by the National Science Foundation.     

Effect of XeCl laser irradiation on the defect structure of Nd:YAG crystals

This paper presents the effect of XeCl laser irradiation on Nd:YAG single crystal samples with various number of pulses at different repetition rates and laser fluences. Effects of the irradiation on the optical and structural properties of the crystal are analyzed by UV–vis-NIR spectroscopy. Annihilation of some point defects of the crystal structure is observed following laser irradiation at a fluence of 100 mJ cm⁻² with 100 and 500 pulses. Increasing the laser fluence and pulse numbers leads to saturation and new defects are found to be formed in the crystal. Additional absorption spectra of the irradiated samples show that oxygen vacancies in the Nd:YAG crystals are removed during the low-dose irradiation. The laser irradiation is compared to the thermal annealing process for Nd:YAG crystal modification. Additional absorption spectrum of an annealed sample reveals that induced negative absorption band at 236 nm is correlated with the annihilation of the oxygen vacancy center. Our results also demonstrate that XeCl laser treatment has several advantages upon annealing at high temperatures in the Nd:YAG crystal quality improvement. Thus, the present work can give a new approach to modify Nd:YAG crystals to be used in a wide variety of solid-state laser engineering.     

Extended defects in shallow implants

Extended defects are often found after ion implantation and annealing of silicon and they are known to affect dopant diffusion. The article reviews the structure and energetics of the most often found extended defects and describes the mechanisms by which all these defects grow in size and transform during annealing. Defects grow by interchanging the Si atoms they are composed of and thus maintain large supersaturations of free Si interstitials in the region. A model has been developped to describe such an evolution in presence of a free surface. It is shown that after low energy implantation, the surface of the wafer may recombine large amounts of these free Si interstitials, driving defects into dissolution before transformation into more stable forms. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +33-56/2257-999, E-mail: claverie@cemes.fr