Nature Of Lattice Defects Research Articles

Cathodoluminescence of Diamond: Features of Visualization

Zonal and sectorial heterogeneities in natural diamonds provide information on the growth conditions and post-growth changes. Cathodoluminescence (CL) microscopy revealed these heterogeneities in a very detailed manner with high spatial resolution. In this study, factors affecting the CL images of two natural diamonds were analyzed and the results of cathodoluminescence studies in steady-state (SS-CL) and scanning modes were compared. SS-CL was observed using an optical microscope, and scanning mode was evaluated via SEM (SEM-CL). It was demonstrated that the relative brightness of the <111> and <100> growth sectors in diamond crystals depends on the nature of defects in them and on the method of image detection (steady-state/scanning versus color/panchromatic). The differences between SS-CL and SEM-CL images can be attributed to the kinetics of luminescence and spectral sensitivity of the detectors. It was established that the nature of lattice defects around small inclusions can be changed (e.g., the intensity of blue luminescence from nitrogen-vacancy defects (N3V) decreases due to their transformation into nitrogen–hydrogen defects (N3VH). The hydrogen disproportion between the sectors is caused by different growth mechanisms. Hydrogen atoms in the diamond matrix can affect the kinetics of transformation of the defects by transforming a part of N3V to N3VH.

Characterizing dislocation loops in irradiated polycrystalline Zr alloys by X-ray line profile analysis of powder diffraction patterns with satellites.

This work extends the convolutional multiple whole profile (CMWP) line profile analysis (LPA) procedure to determine the total dislocation density and character of irradiation-induced dislocation loops in commercial polycrystalline Zr specimens. Zr alloys are widely used in the nuclear industry as fuel cladding materials in which irradiation-induced point defects evolve into dislocation loops. LPA has long been established as a powerful tool to determine the density and nature of lattice defects in plastically deformed materials. The CMWP LPA procedure is based on the Krivoglaz-Wilkens theory in which the dislocation structure is characterized by the total dislocation density ρ and the dislocation arrangement parameter M. In commercial Zr alloys irradiation-induced dislocation loops broaden the peak profiles, mainly in the tail regions, and occasionally generate small satellites next to the Bragg peaks. In this work, two challenges in powder diffraction patterns of irradiated Zr alloys are solved: (i) determination of the M values from the long tail regions of peaks has been made unequivocal and (ii) satellites have been fitted separately, using physically well established principles, in order to exclude them from the dislocation determination process. Referring to the theory of heterogeneous dislocation distributions, determination of the total dislocation density from the main peaks free of satellites has been justified. The dislocation loop structure has been characterized by the total dislocation density of loops and the M parameter correlated to the dipole character of dislocation loops. The extended CMWP procedure is applied to determine the total dislocation density, the dipole character of dislocation loops, and the fractions of 〈a〉- and 〈c〉-type loops in proton- or neutron-irradiated polycrystalline Zr alloys used in the nuclear energy industry.

Three-dimensional X-ray topographic characterization of synthesized diamond crystals

Synthesized diamond crystals grown at high temperatures and high pressures were characterized by three-dimensional X-ray topography. The diffraction planes and wavelength of the monochromatic X-rays used were (004), {111}, and , and 0.0521 nm, respectively. Images of lattice defects in diamond crystals were reconstructed from a stack of about 300 X-ray limited projection topographs using the image processing software Image-J. The three-dimensional structures and nature of lattice defects were identified on the basis of the reconstructed topographs. The pyramidal shape of the four-part stacking fault generated from the seed crystal was identified using the dependence of visible or invisible defect images with diffraction planes. The sector boundary between the [001] and [111] growth directions was also first observed by three-dimensional topography. The image of the sector boundary did not show any dependence on diffraction planes.

Eu2+ doped calcium aluminates prepared by alternative low temperature routes

Eu 2+ doped calcium aluminates, CaAl 2 O 4 :Eu 2+ , were prepared by the Pechini and combustion methods. Very pure monoclinic CaAl 2 O 4 :Eu 2+ was obtained by Pechini method when annealed at 1250 °C. The reaction time was shortened but the annealing temperature was the same as that of the conventional solid state method. By using the combustion method, an additional annealing at 900-1100 °C was needed to crystallize the initially amorphous material. An unusual hexagonal polymorph was then obtained. The luminescence band of the Pechini prepared CaAl 2 O 4 :Eu 2+ peaking at 440 nm corresponded to that of the solid state prepared material. Persistent luminescence spectrum was the same as that of the UV excited one. The thermoluminescence glow curve position, i.e. the nature of lattice defects was not observed to depend significantly on the preparation method.

Microstructural evaluation of reactive ion etched - regrown GaAs

Reactive ion etching (RIE) is a preferred dry process step for fabrication of submicron III-V semiconductor device structures. This kinetically assisted chemical dry etch process offers several important advantages over other etching methods, namely etch anisotropy, etch rate control, selectively, accuracy, uniformity across the wafer and reproducibility. As a result of these desirable characteristics, a number of semiconductor device designs involve REE in their device fabrication process. Some of the more novel designs involve lateral quantum well arrays, whereby fabrication requires molecular beam epitaxial (MBE) regrowth on RIE semiconductors.A major drawback of RIE is the potential lattice damage introduced by energetic ion bombardment and contamination. This material damage may lead to deterioration of device performance. It is important to identify and understand this RIE induced damage in order to develop and refine the RIE process, i.e. minimize crystal damage and thus optimize device performance. This study identifies and analyzes the damage associated with various RIE parameters used for quantum well fabrication. Microstructural characterization via TEM is used to identify the nature of lattice defects, their distribution, and density. Optical methods, Photoluminescence and Raman spectroscopy are used to evaluate the crystal damage and serve as a reliable comparators for the TEM results.

Ion Implantation Damage and its Annealing Characteristics in an AlAs/GaAs Layer Structure

ABSTRACTThe implantation of Ar+ ions into AlAs/GaAs layered samples is shown to give very different damage structures in the two materials. While the GaAs is relatively easily amorphised, the AlAs is quite resistant to damage accumulation and remains crystalline for the ion doses employed in these investigations. The behaviour of the different damage structures when subjected to rapid thermal annealing treatments is described in some detail. It is demonstrated that differences in the initial damage state have a strong influence upon the nature of lattice defects produced by annealing.

Diffuse X-Ray Scattering for the Study of Defects in Silicon

ABSTRACTX-ray diffuse scattering can be used to study the size, concentration, and nature of lattice defects and defect clusters in crystalline materials. The availability of analytical models and detailed numerical calculations for the “Huang” diffuse scattering close to Bragg reflections and the “asymptotic” diffuse scattering at somewhat larger distances from Bragg reflections has made it possible to carry out detailed analyses of the intensity and angular distribution of the diffuse scattering in terms of specific defect parameters. Accordingly, diffuse scattering has been used to study point defects, dislocation loops, and precipitates in metals, semiconductors, and insulators and has provided information on defect geometries, size distributions, and concentrations. In this paper, the theoretical framework necessary for the interpretation of the “Huang” and “asymptotic” diffuse scattering from defect clusters is presented and examples of diffuse scattering calculations for defects in silicon are given. Diffuse scattering from clustered defects in silicon is discussed in terms of the type of information available from this scattering and the relative merits of diffuse scattering as an investigative tool for defect clusters. Diffuse scattering analysis techniques for the determination of separate size distributions for vacancy and interstitial dislocation loops in silicon are presented and applied to diffuse scattering measurements on neutron irradiated silicon. Dislocation loop densities and sizes determined in the as-irradiated state and after thermal anneals are compared with electron microscopy results.

Positron annihilation — a localized probe of lattice defects in metals

It is evident that positron annihilation spectroscopy has become a valuable technique for the study of metals. Owing to the ability of the positron to localize in a variety of metal defects where its subsequent annihilation yields information regarding its local electronic environment, we now have a new and unique tool available with which to probe the nature of lattice defects in metals, which supplements previously available methods. Many new PAS experimental and theoretical techniques and additional applications to problems concerning defects and microstructures in metals are evolving in this rapidly developing area. It seems clear that in the future, the usefulness of PAS for the study of defects in metals will continue to increase.

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.

The Nature of Lattice Defects in Silver Bromide Crystals

The Nature of Lattice Defects in Silver Bromide Crystals