COAXIAL SCATTERING PROBE OF THE SURFACE AND SUBSURFACE STRUCTURE OF THE SI(100)-(2 X-1) AND SI(100)-(1 X 1)-H PHASES

It is demonstrated that both surface and subsurface structural informa tion can be obtained from Si{100}-(2 x 1) and Si{100}-(1 x 1)-H by cou pling coaxial time-of-flight scattering and recoiling spectrometry (TO F-SARS) with three-dimensional trajectory simulations. Experimentally, backscattering intensity versus both incident alpha and azimuthal del ta angle scans at a scattering angle of approximately 180-degrees have been measured for 2 keV He+ incident on both the (2 x 1) and (1 X 1)- H surfaces. Computationally, an efficient three-dimensional version of the Monte Carlo computer code RECAD has been developed and applied to simulation of the TOF-SARS results. An R (reliability) factor has bee n introduced for quantitative evaluation of the agreement between expe rimental and simulated scans. For the case of 2 keV He+ scattering fro m Si{100}, scattering features can be observed and delineated from as many as 14 atomic layers (almost-equal-to 18 angstrom) below the surfa ce. The sensitivity of the alpha and delta scans to the amplitudes of both surface and bulk vibrations, the interlayer spacings, the intradi mer spacing (in the (2 x 1) reconstructed phase), and the presence of hydrogen atoms (in the (1 x 1) phase) is explored. The intradimer spac ing D is determined as 2.2 angstrom from the minimum in the R-factor v ersus D plot.