Thermal decay of isolated single silicon mounds on Si(111) surfaces

Isolated three-dimensional (3D) silicon mounds on the Si(111)(7 x 7) surfac e have been produced using the tip of a scanning tunneling microscope (STM) at temperatures between 700 K and 750 K. Thermal relaxation processes of t he mounds have been investigated by a temperature-variable STM. The 3D moun ds formed by the STM tip are like pyramids with certain facets for both sur faces. 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 p yramids are produced on the Si(111). The pyramids with a production probabi lity 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 stac king fault at the interface, and they are called type F. The formation ener gy of the stacking fault is estimated from the ratio of the production prob ability as 4.7 meV/Angstrom (2). The decay rate of the type F mounds is abo ut 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 splitt ing of the facets and step bunching.