Properties Of Lattice Defects Research Articles

David John Hugh Cockayne. 19 March 1942 — 22 December 2010

David Cockayne had a wide-ranging and lasting impact on electron microscopy in materials science. He had dual UK and Australian nationality, and his professional career was divided between the two countries. His research was exceptional. His most important scientific contribution was the development (with I. L. F. Ray and M. J. Whelan in Oxford) of the dark-field ‘weak-beam’ technique of transmission electron microscopy, which improved by an order of magnitude (to 1.5 nm) the resolution at which complex crystal lattice defect geometries could be studied. The technique had a significant impact on advancing our understanding of the structure and properties of lattice defects in many materials, and became established as a routine tool in laboratories all over the world; it is still widely used today. With D. R. McKenzie in Sydney he developed a powerful high-precision electron diffraction technique within an electron microscope to study small volumes of amorphous material, orders of magnitude smaller than is possible with X-rays or neutrons, giving nearest-neighbour distances accurate to 0.001 nm. As Director of the University of Sydney Electron Microscope Unit from 1974 to 1999, he led the development of the Unit to provide a first-class centralized service of electron microscopy for the university as a whole. This stimulated other Australian universities to follow his example.

Production and spectral properties of lattice defects in natural fibrous gypsum colored electrolytically at near room temperature using a pointed anode

Natural fibrous gypsum is colored electrolytically at near room temperatures and under various voltages using a pointed anode and a flat cathode. The SO4-, SO3-, SO2- and O− lattice defects are produced in the colored natural fibrous gypsum. No visible characteristic absorption band in the ultraviolet and visible wavelength regions is observed in the optical absorption spectrum of the natural fibrous gypsum before the electrolytic coloration. The characteristic absorption bands of the SO4-, SO3-, SO2- and O− lattice defects are observed in the optical absorption spectra of the colored natural fibrous gypsum. The production of the lattice defects is explained. Current–time curve for the electrolytic coloration of the natural fibrous gypsum and its relationship with the electrolytic coloration processes are given.

First-principles modeling of lattice defects: advancing our insight into the structure-properties relationship of ice

We discuss a number of examples that demonstrate the value of computational modeling as a complementary approach in the physics and chemistry of ice I h , where real-life experiments often do not give direct access to the desired information or whose interpretation typically requires uncontrollable assumptions. Specifically, we discuss two cases in which, guided by experimental insight, density-functional-theory-based first-principles methods are applied to study the properties of lattice defects and their relationship to ice I h s macroscopic behavior. First, we address a question involving molecular point defects, examining the energetics of formation of the molecular vacancy and a number of different molecular interstitial configurations. The results indicate that, as suggested by earlier experiments, a configuration involving bonding to the surrounding hydrogen-bond network is the preferred interstitial structure in ice I h . The second example involves the application of modeling to elucidate on the microscopic origin of the experimental observation that a specific type of ice defect is effectively immobile while others are not. Inspired by previous suggestions that this defect type may be held trapped at other defect sites and our finding that the bound configuration is the preferred interstitial configuration in ice I h , we use first-principles modeling to examine the binding energetics of the specific ice defect to the molecular vacancy and interstitial. The results suggest a preferential binding of the immobile defect to the molecular interstitial, possibly explaining its experimentally observed inactivity.

Brother Silicon, Sister Germanium

Material and lattice defect properties of silicon and germanium relevant for device processing are discussed and compared with respect to their impact on crystal pulling, device processing, and diode leakage current. It is shown that both semiconductors are very similar when comparing their material properties at the same temperature normalized to the melt temperature . In other respects, however, like the diffusion of dopants, Ge behaves quite differently. With respect to diode leakage, germanium is more sensitive to metal contamination than silicon at the same device operation temperature.

Brother Silicon, Sister Germanium

Material and lattice defect properties of silicon and germanium relevant for device processing are discussed and compared. It is shown that both semiconductors are very similar when comparing their material properties at the same temperature T normalized to the melt temperature Tm. In other respects, however, like the diffusion of dopants, Ge behaves quite differently.

Atomistic simulation of lattice defects in nano-scale semiconductors: minimal-basis TBMD method

The atomistic properties of lattice defects in the nano-scale semiconductor crystallites are studied using the improved nonorthogonal tight-binding molecular-dynamics (TBMD) method. This nonorthogonal TB theory, with only three adjustable parameters gives values of the energies and bonding distances which are in excellent agreement with the ab initio results for small semiconductor clusters. We apply this type of MD scheme for the calculations of lattice defects (dislocations) and γ-surface in the small semiconductor crystallites with the size of N ∼ 200. We have found that there are marked differences in the properties of lattice defects between those in the bulk and those in the nano-scale crystallites.

Origin of ordering in B2-type transition-metal aluminides: Comparative study of the defect properties of PdAl, NiAl, and FeAl.

The physical mechanism for ordering and the properties of lattice defects in {ital B}2-type transition-metal (TM) aluminides are presented. It is shown that the size effect is inadequate in explaining the defect structure (and ordering) in these intermetallics. Such is the case evident in the prototypical example of PdAl, which is found to exhibit all the physical characteristics of strongly ordered alloys even though the difference in atomic radii between constituent Pd and Al atoms is very small. We obtain a high heat of formation, high antiphase boundary energies associated with the partial 1/2{l_angle}111{r_angle} slip, and the existence of triple defect (for the point defect structure) in PdAl. Comparative analyses are presented for PdAl, NiAl, and FeAl, and results reveal that the electronic structure at the TM sites plays a decisive role in the energetics (and types) of defects. The strong ordering in late TM aluminides of the {ital B}2 type is due to the {ital lack} of electronic screening from the TM {ital d} band to compensate the energetically unfavorable nearest-neighbor interaction between Al atoms when ordering is disrupted.

Structural, electronic, and magnetic properties of 3d transition-metal aluminides with equiatomic composition.

First-principles calculations have been performed to study the chemical bonding trends and the phase stability of 3[ital d] transition-metal (TM) aluminides with equiatomic composition. The physical mechanisms for ordering in both the [ital L]1[sub 0] and [ital B]2-type aluminides are presented. It is shown that the dominant factor for early TM aluminides is the directional bonding between the [ital d] orbitals of TM atoms, whereas for late TM aluminides, charge transfer and hybridization between Al [ital s] and [ital p] states, and TM [ital d] states play more important roles in the bonding mechanism and the properties of lattice defects. Our calculations also show the existence of a ferromagnetic phase for MnAl in the [ital L]1[sub 0] structure, which is stabilized by the formation of a magnetic moment on the Mn sites (with a value of 2.0 [mu][sub [ital B]]). The chemical trends in the structural stability and heats of formation of 3[ital d] TM aluminides are found to correlate well with the densities of states at the Fermi level.

Optical properties of lattice defects in α-Al2O3

Experimental optical properties of lattice vacancy defects in single crystal α-Al2O3 are reviewed. Specific ultraviolet absorption and luminescence bands are associated with F-type centers. Following extended exposures to epithermal neutron sources, photobleaching and anisotropic properties allowed the association of several of the visible and near infrared bands with F2-type centers. Photoconductivity, photostability and charge state considerations provided tentative placement of defect energy levels with respect to the conduction band edge.

Static Lattice Defects in a Quasi‐Continuum

AbstractA new method for the description of the properties of lattice defects in a quasi‐continuum with long‐range elastic interactions is presented. The method is based on the application of the Fourier transformation for the solution of the equation of classical elasticity and takes into account the fact that the wavelength of the elastic waves in a real material cannot be arbitrarily small. The method is applied for the description of the properties of a dilatation centre and a screw dislocation.

Electronic properties of lattice defects studied with Synchrotron Radiation

Abstract Synchrotron Radiation is extensively used in defect research to study the electronic properties of defects and impurities. After a rapid survey of the principles and characteristics of the source, are shown some techniques recently used in this field: excitation of luminescence of ion impurities and excitions, time decay investigation, Augee-free luminescence, two-phot on spectroscopy and defect creations processes.

TDPAC study of lattice defects and solutes in cadmium and cadmium alloys

The technique of the time differential perturbed angular correlation (TDPAC or PAC) is applied to study the properties of lattice defects or solutes in Cd with 111In( 111Cd) as the probe nucleus. First, a theoretical expression of the PAC spectrum for the probe nucleus in a single crystal, which is vitally important for the PAC technique to determine the structure of a defect-probe atom complex, is examined. Here the PAC spectrum of 111In in a single crystal of Cd is measured as a function of the crystal orientation relative to the detectors. Next, the technique is applied to study the radiation damage in Cd after a proton irradiation. Here the introduction of damages and probe nuclei are performed at the same time at 77K. Finally, the tecnique is applied to Cd-In and CD-Rh alloys to study the solute-solute interactions. The results of these experiments are reviewed and discussed.

Studies on the origin of subgrain boundaries in cast polycrystalline silicon using ebic and X-ray topography

X-ray topography and low-temperature EBIC measurements have been used in a complementary way to study the structural and electrical properties of lattice defects in cast polycrystalline silicon material. The origin of subgrain boundaries in the material and their effect on excess carrier recombination is discussed.

Electrical Noise Produced by Lattice Defects in Metals

The relevant aspects of electrical noise in metals related to the kinetic properties of lattice defects are presented. Two basic phenomena are considered: (a) resistivity fluctuations in thermal equilibrium associated with vacancy creation and annihilation processes, (b) resistivity fluctuations generated by collective dislocation rearrangements during plastic deformation. It is shown that, through the characterization of the fluctuations with a suitable statistical model, information can be obtained on the physical properties of these defects. In particular, vacancy parameters, such as the migration energy, the average life-time and the resistivity contribution of unit vacancy concentration can be experimentally determined. Moreover, the relevant features associated with dislocation rearrangement processes during plastic deformation are put in evidence.

Electrical Properties of Dislocations and Boundaries in Semiconductors

ABSTRACTSimple models have been suggested to predict electronic properties of lattice defects in semiconductor crystals: dislocations ought to act via the acceptor character of dangling bonds, and small-angle grain boundaries ought to consist of regular arrays of dislocations. The actual situation in most semiconductors is, however, much more complicated. The observed electrical effects of dislocations do not confirm the dangling-bond concept, they are affected by dissociation and reconstruction. There appear to be differences between straight and kinked dislocations. Dislocations owe much of their electronic behavior to clouds and precipitates of impurities; oxygen in silicon plays a significant role. This review summarizes the present status of experimental methods and results, including luminescence and capacitance spectroscopy as well as mapping and imaging techniques using electron-microscopes.

Local strain effects for isolated pairs of ortho-H2 molecules in para hydrogen

The crystal fields resulting from the local strains associated with a defect consisting of an isolated pair of ortho-H2 molecules in solid para hydrogen are calculated. The Kanzaki method for the determination of the static properties of lattice defects is used. It is found that the crystal field parameters depend on the pair state |F,±M > and differ considerably for in-plane and out-of-plane pairs. Theories of Luryi, et al. and Harris, et al. for the energy levels of pairs of ortho-H2 molecules in nearly pure para hydrogen are compared with our results.

Textures and collective properties of lattice defects (External surface, grain boundaries...)

Textures and collective properties of lattice defects (External surface, grain boundaries...)

Sensitivity of lattice defect calculations for fcc metals to empirically derived interatomic potentials

Abstract The relevant factors which must be considered for the empirical fitting of a two-body interatomic interaction to the elastic moduli and phonon dispersion relations are discussed. It is shown that for nickel and copper there is no necessity to use any more complex interaction than a near-neighbor central force. There is, however, no unique way to determine an appropriate potential from perfect lattice data alone, since the interaction must be known at distances which do not occur in the perfect lattice for the calculation of lattice defect properties. A set of three potentials for copper, all of which are equivalent for the perfect lattice, were used to investigate the sensitivity of vacancy and interstitial formation and migration energies to the details of the potential. Vacancy calculations were not very sensitive, the ratio E v/(E +E v) varying from about 0.4 to 0.5. The interstitial results showed an overall greater sensitivity, as the relative formation energy of different defect configurati...