STM study of Si(111)7x7 reconstructed surface carbonization induced by acetylene

The morphology of the first stages of acetylene reaction with Si(1 1 1)7 x 7 reconstructed surface has been investigated by scanning tunneling microscopy (STM). We studied the surface modification for two substrate temperatures during reaction (650 and 700 degreesC) and as a function of acetylene doses. Both these parameters have been observed to play a crucial role in the carbonization reaction, the formation of nanostructures and their development. For low acetylene exposure, almost the entire surface appears root3 x root3-R30degrees reconstructed but islands, mainly decorating the step edges, are generally surrounded by 7 x 7 reconstructed areas, located deeper with respect to the plane of root3 x root3-R30degrees reconstruction. For highest acetylene dose, the surface is characterized by nanostructures and large holes (as deep as 3-5 nm) that occupy one or more terraces between the original silicon surface step edges with their inner side constituted of islands itself. For intermediate acetylene exposure, the small increase (from 650 to 700 degreesC) of substrate temperature during the reaction is sufficient to make the resulting carbonization mechanism switch towards the highest exposure behaviour. (C) 2004 Elsevier B.V. All rights reserved.