Title: Photoemission Study of GaSe bilayer passivated Si(111)

Author:  Shuang Meng, B.R. Schroeder, A. Bostwick, Marjorie A. Olmstead
              Physics Dept., Univ. of Washington
	 Eli Rotenberg, Advanced Light Source, Lawrence Berkeley
		National Lab
	 F.S. Ohuchi, Dept. of Mat. Sci. & Eng., Univ. of Washington
	   

Si(111) 7x7 can be passivated by a GaSe bilayer grown at
T$_{substrate}\ge$ 525$^o$C. The passivation is achieved by a
single-domained GaSe bilayer bonding to surface Si and leaving Se
lone-pairs on the surface. The atomic structure has been studied by
component-resolved photoelectron diffraction (PED) and low-energy
electron diffraction. We find that Ga sits directly atop surface Si with
the Ga-Se bond aligned with the substrate Si-Si bond. Core-level
photoemission shows Si to be in an extremely bulk-like environment, but
angle-resolved photoemission spectroscopy indicates that GaSe has a long
range influence on the Si bands. PED shows strong (>20%) angular
variation of the Ga 3d spin-orbit branching ratio, though not of the Se
3d ratio. This surprising result arises from spin-orbit variations in the
complex photoionization matrix element amplified by subsequent
scattering, as shown by relativistic multiple-scattering calculations. 

*  Supported by NSF DMR9801302