Atomic Resolution In-Situ Dynamics of Dislocation Kinks in Silicon

This dissertation concerns atomic resolution imaging of moving dislocations in silicon. The aim of the work is to understand obstacles to dislocation motion, since these control the strength of materials. This research reports the first direct observations of moving kinks on dislocation lines. These observations were used to study the mechanism and energetics of kink motion. Direct measurements of dislocation kink velocities in silicon have been obtained using a novel electron microscope imaging technique. Movements of 90^circ partial dislocation segments have been recorded for distances as small as one Peierls valley (3.3 A) by imaging normal to the glide plane with (242)/3-type "forbidden" reflections produced by intrinsic stacking faults. The relaxation of nonequilibrium dissociated 60^circ dislocations was studied at elevated temperatures, driven by the stress on the 90^circ and 30^ circ partials bounding the stacking faults. Kinks and superkinks along the partials are observed by this imaging method and have been analyzed in terms of the defect geometry and the atomistics of dislocation motion. Using video rate image collection, high-resolution TEM observations of dislocation segment unpinning and subsequent motion were recorded in real time at elevated temperatures (600^circC) with the beam normal to the dislocations. Estimates of the unpinning energy are compared to existing theoretical and experimental values and the nature of the pining sites is examined. Difference images are used to minimize noise from surface roughness and to identify motion. The applicability of Radiation Enhanced Dislocation Glide (REDG) for 90^circ partial dislocations was assessed using low temperature relaxation in the absence of electron irradiation. The activation energy for kink motion and the formation energy for double kinks are calculated and it is found that the nucleation of double kinks, rather than the migration of kinks, is rate controlling in silicon for these experimental conditions.