A542

344

The influence of internal surfaces on the (2 × 1) cleavage reconstructions for Si ( l l l ) Y.M. Huang, J.C.H. Spence, Otto F. Sankey and G.B. Adams Department of Physics, Arizona State University, Tempe, A Z 85287, USA Received 28 December 1990: accepted for publication 30 April 1991

Surface Science 256 (1991) 344-353 North-Holland

shuffle and glide

l 'he surface reconstructions which occur when a parallel-sided gap opens up between the (111) planes of silicon are computed using the ab initio total-energy and lattice dynamics method of Sankey and Niklewski (1989). This allows the time-evolution of the surface structures to be observed. The shuffle and glide terminations are compared, and found to differ in energy by 0.17 eV/(surface atom), with the shuffle termination having lower energy. The Haneman (2 × 1) buckled row reconstruction is found to occur at a certain critical gap d, = 0.46 nm, and acts as a precursor for the Pandey (2 x 1) 7r-bonded chain model, which occurs at larger gaps. Charge-density maps are shown, and the results related to cleavage in real crystals. The surface energy of (2 × 1) reconstructed Si(111 ) is calculated to be 1340 erg/cm 2 (1.07 eV per surface atom) in good agreement with experiment.

354 Surface Science 256 (1991) 354-360 North-HoUand

Scanning tunneling microscopy and spectroscopy of cubic B-SiC(111) surfaces C.S. Chang, I.S.T. Tsong, Department of Physics, Arizona State University, Tempe, AZ 85287-1504, USA

Y.C. Wang and R.F. Davis Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907, USA

Received 2 April 1991; accepted for publication 30 April 1991

Scanning tunneling microscopy (STM) images show a 6 x 6 reconstruction of the fl-SiC(111) surface annealed at 1150-1200 o C. Contrast reversal is observed as tunneling voltage bias is reversed. Spectroscopic I / V data indicate the presence of a graphite layer on the top surface. A model of the surface is proposed where an incommensurate graphite monolayer is grown over a (1 × 1) Si-terminated fl-SiC(111) surface. This model helps to explain the discrepancy between the 6¢'3 × 6Vr3 geometry observed by LEED

and the 6 × 6 geometry observed by STM on the same surface.

Surface Science 256 (1991) 361-369 361 North-Holland

Initial stage of thermal-oxidation reactions on Cl-adsorbed Si surfaces Nahomi Aoto, Hirohito Watanabe and Takamaro Kikkawa Microelectronics Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa 229, Japan

Received 18 December 1990; accepted for publication 1 May 1991

The oxidation of Si-surfaces terminated with chlorine and the incorporation of chlorine into oxide layers are studied by applying AES, LEELS, and XPS. It is found from the heating of C1/Si surfaces in 02 atmospheres that adsorbed CI atoms suppress oxidation. In the first step of oxidation CI atoms desorb by heating, and in the second step the Cl-free areas thus react with O z followed by further oxidation proceeding to back-bonds of surface Si atoms. The Si-CI bonds did not directly react with 02. On oxide surfaces formed by heating C1/Si surfaces in 1% C12/O 2, the dominant chlorines were the ones remaining on the surface after heating, even though a little CI is additionally incorporated into the surface from the atmosphere. The amount of CI in the deeper regions or at the oxide/Si interface is below the detection level by XPS. No CI incorporation at the interface occurs by heating thin-oxide/Si surfaces in a C12-contained 02 atmosphere.