A. George

On the yield point of floating-zone silicon single crystals. I: Yield stresses and activation parameters

Abstract In initially dislocation-free silicon single crystals deformed in compression (single slip) at low strain rates, the lower yield stress τ1y exhibits a three-stage temperature dependence with a plateau (1170K ≲ T ≲ 1320 K at [ydot]≅ 2 × 10−5 s−1) between the low- and high-temperature regimes, where τ1y decreases with increasing T. Pre-strained silicon crystals were deformed in the temperature range of dislocation velocity measurements (820 K ≲ T ≲ 1070 K). With the assumption that pre-straining, which minimizes yield-point phenomena, ensures dislocation structures (i.e. internal stresses) that are at worst only weakly dependent on the deformation conditions, the activation Gibbs free energies derived from activation volumes measured at the lower yield point are found to be in very good agreement with activation energies for dislocation velocity at the same stresses.

Observation par topographie aux rayons X des configurations de dislocations développées a l'extrémité d'une fissure dans le silicium

Resume Des monocristaux de silicium, prefissures a temperature ambiante, sont charges en mode 1, a 800°C, la charge appliquee correspondant a un facteur dintensite de constrainte KI < K IC. Les configurations de dislocations developpees a lextremite de la fissure sont etudiees par topographie aux rayons X. Les dislocations sont contenues dans les plans {111} qui coupent le front de fissure. Dans un type de plan donne, deux vecteurs de Burgers sont en general observes. La forme des lignes de dislocations et le choix des systemes de glissement sont discutes a partir du calcul des cissions resolues en tout point de leprouvette.

Observation des dislocations dans l'indium par topographie aux rayons x

Resume Nous avons etudie par topographie aux rayons X et a temperature ambiante ( 0,7 T ƒ ) des monocristaux dindium a tres faible densite de dislocations. Les dislocations observees sont le plus souvent rectilignes et traversent le cristal dune face a lautre. Les vecteurs de Burgers sont du type 1 2 〈110〉 ou du type 1 2 〈110〉 . Lorientation preferentielle des segments de dislocation correspond a un minimum de lenergie elastique. Nous avons observe le glissement de ces dislocations, vraisemblablement provoque par les contraintes exercees sur le cristal par son propre poids, ce qui a permis didentifier les systemes de glissement 〈110〉 {1 1 1}, 〈101〉 {11 1 }, 〈101〉 {10 1 }. Ces resultats sont compares avec ceux obtenus par dautres auteurs dans lindium et les metaux cfc.

Dislocations and Slip Systems in Indium Single Crystals

ABSTRACT Indium single crystals have been studied by X-ray topography at room temperature. Dislocations usually appear as straight segments, with Burgers vectors of the ½ or ½ types, the orientation of which minimizes the elastic energy. Dislocation glide has been observed which could be due to the stresses arising from the crystal weight. slip systems were identified.

Mechanical Behavior of Polycrystals and Single Crystals of Silicon

ABSTRACT Mechanical behavior of poly-and single crystals of silicon has been studied by compression tests between 1023 K and 1623 K. Polycrystals were tested along two orientations parallel and normal to the axis of texture for as-grown and annealed material. Single crystals were tested along , and orientations. In polycristals a weak effect of the texture and a marked softening by annealing were observed. The flow stress of polycrystals were related to those of single crystals according to Taylors theory.