J. Phys.: Condens. Matter 12 (2000) 10045–10058. Printed in the UK PII: S0953-8984(00)17587-3 Dislocation multiplication in silicon at the onset of plasticity observed by in situ synchrotron x-ray topography Alain Jacques†§, Fr´ ed´ eric Vallino†§, Francisco Serbena‡§ and Amand George†§ † Laboratoire de Physique des Mat´ eriaux, UMR CNRS No 7556, Ecole des Mines de Nancy, Nancy, France ‡ Universidade Estadual de Ponta Grossa, Department de Fisica, Ponta Grossa, Brazil § European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France Received 13 September 2000 Abstract. In situ observations by synchrotron x-ray topography were performed on initially dislocation-free silicon single crystals deformed in creep conditions at temperatures between 975 K and 1075 K, and tensile stresses equal to 22 MPa or 44 MPa, in order to study the multiplication of dislocations during the very first stages of plastic deformation. It could be seen that the first dislocations, created at Vickers micro-indents or at residual surface damage, did not develop in a strictly planar way: prismatic half loops, gliding simultaneously on two {111} planes, were commonly observed. Cross-slip events appeared to be quite frequent, in the bulk as well as at free surfaces. Groups of similar dislocations soon exhibited irregular shapes with cusps and trailing dipoles, which was taken as an indication that they developed jogs during their motion. Several configurations of dislocation sources formed by the mobile dislocations were observed and are described in detail. The formation of new sources usually involved cross-slip. The role of jogs formed by forest-cutting seems important. The efficiency of sources was strongly limited by the lack of stability of the cross-slipped segments, which acted as poles for the Frank–Read mechanism. 1. Introduction Dislocation multiplication in deforming crystals proceeds via Frank–Read sources, consisting of mobile dislocation segments bowing out between fixed poles, under the action of shear stresses, so as to form spirals or concentric closed loops of fresh dislocations. Fixed poles, around which mobile segments turn, are assumed to be dislocation nodes of the three- dimensional Frank network, which is present in well annealed metals. In later stages of plastic deformation new sources continuously form due to intersections of primary dislocations with trees having other Burgers vectors. The first convincing experimental proof of such a Frank–Read source was probably obtained by Dash in silicon [1], in crystals twisted at high temperatures and observed by infrared light after copper decoration of dislocations. Yet, dislocation multiplication during the very first stages of deformation is still poorly understood in present day Si crystals, which, in contrast to those of Dash, are initially dislocation free and do not contain any Frank network. In their model of the yield stage, Alexander and Haasen [2] used an empirical multiplication law of the form dρ dt = ˙ ρ = Kρvτ eff 0953-8984/00/4910045+14$30.00 © 2000 IOP Publishing Ltd 10045