TABLE OF CONTENTS ( Edited by R.J Nemanich)
V. Zielasek, Feng Liu and M.G. Lagally
November 1998
Starting with bulk silicon, the creation of any surface necessarily cuts some of the highly directional covalent bonds between Si atoms, leaving energetically unfavourable dangling bonds at the surface. To lower the surface energy, Si(001), Si(111) and Si(110) exhibit surface reconstructions, i.e. atomic rearrangements, that reflect the balance between a reduction of dangling bonds and the minimisation of surface stress [1].
The increasing importance of surfaces and interfaces in semiconductor devices has stimulated extensive studies of low-index silicon surfaces over the years. Their reconstructions not only determine the surface electronic structure in detail but are also important for elementary processes of epitaxial growth, like adsorption, surface diffusion, and island formation.
On a bulk-terminated (001) surface each atom of the topmost layer would have two dangling bonds, i.e. sp 3 hybrid orbitals occupied by only one electron ('bulk-terminated' means all atoms forming the surface remain at positions they would occupy in the bulk). The formation of surface dimers, as first proposed by Schlier and Farnsworth [2] and first directly observed by means of scanning tunnelling microscopy (STM) [3,4], eliminates half of the dangling bonds and reduces the overall surface free energy by about 1 eV per surface atom [5 9]. The decrease in electronic energy by dimerisation (2 eV per atom [10]) is partly compensated by an increase in strain energy...
