O. Hardouin Duparc

High-resolution transmission electron microscopy observations and atomic simulations of the structures of exact and near Σ = 11, {332} tilt grain boundaries in nickel

Abstract A Σ = 11, {332} nickel bicrystal was grown by solidification. The aim of this paper is to show the evolution of the grain-boundary (GB) structure depending upon the position in the bicrystal of the extracted sample. Conventional transmission electron microscopy and high-resolution transmission electron microscopy (HRTEM) observations were used to characterize the GBs on microscopic and nanoscopic scales respectively. The detailed atomic structures of the exact {332} and the asymmetrical {111}‖{331} GBs were investigated by numerical calculations and compared with the HRTEM images. There is a perfect agreement between the calculated and the experimental image for the symmetrical {332} GB at the head of the bicrystal. The high GB defect density in the asymmetrical GBs at the end of the bicrystal makes the comparison less straightforward. It is, however, noteworthy that two complete periods of the calculated structure are actually observed in the experimental image. In order to approach the atomic description of the {111}1 ‖{hkl}2 asymmetrical tilt GBs, it is proposed to use for each side the structural units which appear in the corresponding symmetrical {111} and hkl tilt GBs respectively.

CORRELATION BETWEEN THE GETTERING EFFICIENCIES AND THE ENERGIES OF INTERFACES IN SILICON BICRYSTALS

A comparative study of the gettering efficiency of the twin grain boundaries Σ=25, Σ=13, and Σ=9 has been carried out by means of electron‐beam‐induced current measurements performed on quenched silicon bicrystals precontaminated by Cu or Ni. The extent of the denuded zone appearing on both sides of each interface type has been considered as the ‘‘rating’’ of its gettering efficiency. For both contaminants, the same scaling of the gettering efficiencies of the boundaries has been observed and was found to be in the order Σ=9≪Σ=13<Σ=25. To account for this ranking, we have correlated the gettering efficiency to the excess energy of the grain boundary with respect to the bulk energy, as theoretically calculated. The computational procedures have been performed by means of molecular‐dynamics simulations using several potentials. On the basis of the specific disorder affecting the Σ=25 structure upon heat treatment, our calculations provided the same progression for the interfacial energies as that observed e...

A new type of periodie boundary condition useful for high-temperature atomistic simulations of grain boundaries: Applications in semiconductors

A new type of boundary condition, named Möbius or antiperiodic boundary conditions, is proposed and tested, both analytically and within the context of numerical simulations. It is shown that these boundary conditions are very useful for twist grain boundary atomistic simulations. By contrast to the use of the ordinary Born von Kármán periodic boundary conditions, they allow only one grain boundary per box instead of two. The risk of migration and overinteraction of two grain boundaries at high temperature is thus avoided while more complex grain boundaries can also be tackled at the same computer price. Such examples are presented and discussed.

The Preston of the Guinier-Preston Zones. Guinier

Almost all materials scientists know about the Guinier–Preston (GP) zones, which were discovered in age-hardened aluminum-copper alloys in 1938. One of the discoverers, the French André Guinier, is rightly well known. The other discoverer, the British G.D. Preston, is totally ignored, even in English scientific biographies. I wish here to partly make up for this “oblivion” by giving elements about George Preston’s life (August 8, 1896 to June 22, 1972) and scientific work. Born in Ireland to the physicist Thomas Preston and deceased in Scotland, G. Preston carried out his scientific achievements in England, mainly studying the crystallographic structure of metals, metallic alloys, and thin films of metal oxides in a pioneering way. He also discussed the atomistic structure of twins in 1927. He mastered many kinds of X-ray and electron diffraction techniques up to diffuse scattering, which allowed him to detect the GP zones. Although he was involved in several controversies, including one about diamonds, he always remained a forthright person until his final professorship in Dundee. André Guinier’s career is briefly recalled in a parallel way.

The atomic structure of Σ=33{144}〈011〉 (θ=20.05°) tilt grain boundary in germanium

Abstract By combining high resolution transmission electron microscopy images with energy calculations of relaxed structures described using semi-empirical potentials, we show that the atomic structure of the Σ=33{1 4 4}〈0 1 1〉 ( θ =20.05°) tilt grain boundary in germanium contains a glide mirror symmetry and not a mirror plane symmetry as was proposed earlier in literature.

Alan Cottrell, a fundamental metallurgist. In memoriam

We recall the early scientific achievements of the great fundamental metallurgist Sir Alan Howard Cottrell (1919–2012), until about 1960, as a supplement to the Tributes written by his friends and colleagues from Cambridge for his funeral.

Analysis of dissociated dislocations in a deformed bicrystal close to the rhombohedral twin orientation in α-alumina

Abstract A bicrystal close to a rhombohedral twin orientation in α-alumina has been deformed by compression at high temperature. After deformation the twin contained a periodic array of intrinsic dislocations. This configuration is interpreted by the decomposition of incoming basal lattice dislocations into interfacial disconnections and further interactions between sessile and glissile products. The dislocations are widely dissociated and the separation width between partials being close to 30 Å. The translation state of the interfacial structure between partials is different from those of the perfect twin. Possible structural models are envisaged and simulated using ab initio calculations and the less efficient Streitz and Mintmire modelling. One model in particular fits the experimental image rather well. The interfacial energies are higher than those estimated using elasticity theory.

Correlation between electrical activity and various structures of Ge grain boundaries

The links between the electrical activity and the atomic structure of various Ge grain boundaries (GBs) are investigated. The atomic structure is studied using high resolution electron microscopy, while the electrical activity is evaluated thanks to the measurement of minority carrier lifetime by means of the contactless microwave phase shift technique. Results show that in the Σ = 51 GB the electrical activity depends on the atomic structure connected to the configuration of the grain boundary, i.e. tilt, twist or mixed. Lower energy structures such as Σ = 3 and 9 GBs appear not to be recombinant.

Total-energy tight-binding modelisations of silicon

We present a systematic comparison of several tight-binding total-energy modelisations of silicon. These modelisations include the tight-binding electronic cohesive energy and a phenomenological description of a repulsive term. We examine both the electronic band gap and various structural properties such as structural stability, bulk modulus, elastic constants, four typical vibrational modes and their Gruneisen constants. We then apply these models to the calculations of the minimised energies of some multivariant grain boundaries. We discuss the influence of the choice of cut radii.