The structure of silicon surfaces from (001) to (111)

We describe the structure of silicon surfaces oriented between (001) and (111) as determined by scanning tunneling microscopy (STM) and first-principles, total-energy calculations. In addition to reviewing: and reproducing the structures reported for the few surfaces previously studied, we describe a number of additional surfaces in order to provide a complete overview of the (001)-to(111) surface morphology. As the sample orientation is tilted from (001) to (111) (theta=0 degrees to 54.7 degrees), the surface morphology varies as follows: (1) Si(001) to Si(114)=(001)-like surfaces composed of dimers separated by steps (both rebonded and nonrebonded); (2) Si(114) to Si(113)=mesoscale sawtooth facets composed of the stable (114)-2 x 1 and (113)-3 x 2 planes; (3) Si(113) to Si(5 5 12)=mesofacets composed of (113)-3 x 2 and (5 5 12)-like planes; (4) Si(5 5 12) to similar to Si(223)=nanoscale sawtooth facets composed of (5 5 12)-like and unit-cell-wide (111)-7x7 planes; and (5) similar to Si(223) to Si(111)=(111)-7x7 terraces separated primarily by single-and triple-layer steps. The change in the surface morphology is accompanied by a change in the composition of surface structural units, progressing from (001)-like structures (e.g. dimers, rebonded steps, and tetramers) to (111)-like structures (pi-bonded chains, adatoms and dimer-chain walls). The resultant morphology is a delicate balance between the reduction of dangling bond density achieved by the formation of these structural units, and the resulting surface stress associated with their unusual bond angles and bond lengths. (C) 1997 Elsevier Science B.V.