ANALYSIS OF IN-PLANE STRUCTURES OF THE As-DEPOSITED Si SURFACES USING GRAZING-ANGLE X-RAY STANDING WAVES. O. Sakata, S. Kumano, N. Matsuki, Y. Tanaka, A. M. Nikolaenko, H. Hashizume, Res. Lab. Eng. Mater., Tokyo Institute of Technology, Nagatsuta, Midori, Yokohama 226, Japan

We applied grazing-angle X-ray standing waves to a Si(111):As 1x1 surface to determine the in-plane position and order of As atoms under UHV condition (Sakata & Hashizume (1995)). As K emission profiles showed As atoms located in the threefold coordinated sites of the bulklike Si(111) surface with little disorder. The displacement is smaller than 2% of the d spacing of the (2 20) planes and the coherent fraction is higher than 80%. This technique has now been applied to the Si(100):As surface. The substrate Si surface was cut 4 deg. off the (100) plane to favor the 2x1 structure over the 1x2 structure. The As emission data collected in the vicinities of the 022 and 0 2 2 Bragg peaks under UHV condition at the Photon Factory synchrotron source were fit to a model including parameters for the area ratio of the 2x1 and 1x2 domains (M₂, M₁) and the normalized As-As dimer bondlength (2l). The fits determined [[eta]] parameters defined by [[eta]]=Mi + Mj cos(2[[pi]]1) (i, j = l, 2). Solving the equations using the values of [[eta]]₁=0.42 and [[eta]]₂=0.066 obtained from the fit under the assumption l=0.664, corresponding to 2.55 Å, gave M₁=0.38 and M₂=0.62. This indicates a highly ordered surface with no As atoms in random positions.

Sakata, O. and Hashizume, H. (1995) Acta Cryst. A51, 375-384.