Unstable neck formation between two isolated particles was analyzed by considering the effects of both faceted and rounded (i.e., "atomically rough") surfaces. Mathematical descriptions of both neck growth and rupture are developed here. Calculations conducted with these formulations can explain the neck instability observed by Rankin and Boatner. The analysis and the experimental data suggest that the energy barrier associated with forming a new atomic layer on top of a faceted surface can restrict the shape evolution of a crystalline particle, even at moderately high temperatures. The analysis also indicates that this energy barrier can be overcome when the positive curvature which initially exists at a facet/rough surface boundary reverses as a result of neck growth. This latter effect offers an explanation for neck rupture which is consistent with the experimental results. In addition to providing an explanation for this phenomenon, the analyses presented here also demonstrate that surface phase boundaries and step energy barriers can have a significant effect on microstructure evolution during solid-state sintering.

An experimental study of electric field induced surface diffusion is presented. A stability analysis of conductive surfaces subjected to a normal uniform electric field shows that sufficiently strong electric fields can destabilize a flat surface, similar to strain induced surface evolution in strain mismatched semiconductor thin films. Further, electric field gradients such as those under a sharp electrode or in the fringe field in a capacitor can drive surface diffusion, leading to nano-scale and micro-scale surface structure growth. Experiments are conducted on gold surfaces at elevated temperatures around 250-350°C, subjected to electric fields of the order of 10 8 -10 9 V=m. Growth of islands as ridges was observed, the height of which was as high as 200 nm. A description of the initial surface normal velocity is developed by using the MaxwellRowgoski solution for the fringe field at the edge of a parallel plate capacitor.