Scanning tunnelling 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 about 730 degrees C, c(4 x 4) structures begin to decay. The observed atomic structures are consistent with the mixed ad-dimer model consisting of dimers parallel and perpendicular to the dimers underneath. The parallel dimers form the basic c(4 x 4) periodicity. Based on this periodicity, different c(4 x 4) structures can form with or without perpendicular dimers.