SCANNING-TUNNELING-MICROSCOPY STUDY OF SI(100)-C(4X4) STRUCTURE FORMATION BY ANNEALING OF SI EPITAXIAL-FILMS

c(4 x 4) reconstructions have been prepared by 600 degrees C annealing a number of different Si(100) surfaces upon which about one monolayer thick Si films had been deposited at several temperatures. Nucleation , extension and disappearance of these structures have been studied by scanning tunnelling microscopy. Initially small regions of the c(4 x 4) reconstructions prefer to nucleate at step edges and then grow when being annealed for a long time. Subsequently, these structures remain stable at annealing temperatures of up to about 700 degrees C. At abo ut 730 degrees C, c(4 x 4) structures begin to decay. The observed ato mic structures are consistent with the mixed ad-dimer model consisting of dimers parallel and perpendicular to the dimers underneath. The pa rallel dimers form the basic c(4 x 4) periodicity. Based on this perio dicity, different c(4 x 4) structures can form with or without perpend icular dimers.