THERMAL DECAY OF ISOLATED SINGLE SILICON MOUNDS ON Si(111) SURFACES

Abstract

Isolated three-dimensional (3D) silicon mounds on the Si (111)(7×7) surface have been produced using the tip of a scanning tunneling microscope (STM) at temperatures between 700 K and 750 K. Thermal relaxation processes of the mounds have been investigated by a temperature-variable STM. The 3D mounds formed by the STM tip are like pyramids with certain facets for both surfaces. The indices of the main facets of the mounds on the Si (111) surface are {311}, and those of the small facets are {221} or {331}. Two types of pyramids are produced on the Si (111). The pyramids with a production probability of 75% are normal stacking at the interface between the mound and the substrate, and are called type U. For mounds with a production probability of 25% which are in the twin relation of the type U mounds, there is a stacking fault at the interface, and they are called type F. The formation energy of the stacking fault is estimated from the ratio of the production probability as 4.7 meV/Å2. The decay rate of the type F mounds is about three times larger than that of the type U ones. During decomposition of the type U mounds, the facets of the pyramid are split into two parts. For the type F mounds, the pyramids decay nearly layer by layer without splitting of the facets and step bunching.