Relaxation of Nanostructures on the Si(111)(7×7) Surface by High Temperature Scanning Tunneling Microscopy

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Abstract
Single silicon islands have been produced on the Si(111)(7 × 7) surface by a scanning tunneling microscope (STM) tip. Thermal relaxation of the isolated islands is observed by temperature variable scanning tunneling microscopy with strong tip effects. The sizes of islands depend on time t with a functional form of (t0-t)α. It is found that α≃2/3 for single bilayer islands, and α≃1 for three-dimensional ones. During the decomposition of three-dimensional islands, step bunching of over-layers takes place, while the islands have certain facets, like a pyramid just after the creation. At the final stages of the three-dimensional island decompositions, two-dimensional ones with 5 × 5 structure always appear. We have found that characteristic 5 × 5 islands with a long lifetime are formed during relaxation, but the 7 × 7 islands have mostlt a short lifetime. Rotation of small islands is also observed during relaxation. We discuss the results in terms of two-dimensional vapor phase processes.