In-situ transmission electron microscopy and first-principles study of Au (100) surface dislocation dynamics

Abstract

In-situ aberration-corrected transmission electron microscopy combined with density functional theory (DFT) calculations are employed to elucidate the electron beam induced dynamics of surface dislocations on ~4nm×6nm sized Au (100) terraces located on top of hillock shaped Au at room temperature and 77K at video rate (20 frames/s). At room temperature, very small terraces (<4×5 atoms) sink into the lower terrace forming surface dislocations associated with a (5×1) surface reconstruction unit cell. This injection occurs provided that the number of atoms of the terrace fits the number of extra atoms required to form the surface dislocation. The surface dislocation consists of either 5 or 3 (Type I and Type II) hexagonally stacked atom rows. While the surface dislocations tend to reside near terrace edges, in ~20% of the video frames, the surface dislocation resides near the center of the terrace. The occurrence of Type I or Type II structures depends on the terrace width. DFT calculations show that Type I surface dislocations are more stable than Type II, for dislocations that do not span the entire terrace width, in agreement with observations. Surface dislocations are observed to flip by 90° during the experimental observations; the pathway and energy barrier (1.01eV) for such flips is clarified through DFT calculations. At 77K, no injections are observed, but surface dislocations do rarely form from an unreconstructed surface. In addition to dislocation flipping, multiple, dynamic dislocation configurations were observed in conjunction with terrace growth along the dislocation direction.