TEMPERATURE-DEPENDING GROWTH AND SURFACE-STRUCTURES OF LOW-COVERAGE AL PHASES ON SI(100) OBSERVED BY SCANNING-TUNNELING-MICROSCOPY

The surface structures of Al on the Si(100) surface, at coverages less than one monolayer deposited at various temperatures, were studied by scanning tunneling microscopy (STM). Surface structures of 2 x 2 and 2 x 3 phases formed at temperatures below 350-degrees-C consist of Al- dimer lines with the dimerization parallel to that of the Si-dimers. F rom the STM images, we can find that a filled state of Al-Si backbonds and an empty state of Al-Al dimer bonds are observed prominently at a bout -3 and +1 eV at positions on the Si-dimer rows and between the Si -dimer rows, respectively. For deposition above 500-degrees-C, the Al- dimer lines change into molecular clusters, each one of them consistin g of five or six Al atoms. These molecules form the c(4 x 2n) structur e with buckling of underlying Si-dimer rows. At the same time, two-dim ensional (2D) Si and Al islands with 2 x 1 and 2 x 2 structures were f ormed in the second layer on the c(4 x 2n) structure. The local struct ures of the low-coverage Al phases on Si(100), depending on the deposi tion temperature and coverage, are analyzed by STM.