DETERMINATION OF THE STRUCTURE OF SUBSURFACE LAYERS BY MEANS OF COAXIAL TIME-OF-FLIGHT SCATTERING AND RECOILING SPECTROMETRY (TOF-SARS)

It is demonstrated that both surface and subsurface structural information can be obtained from Si(100)-(2 x 1) and Si(100)-(1 x 1)-H by coupling coaxial time-of-flight scattering and recoiling spectrometry (TOF-SARS) with three-dimensional trajectory simulations. Experimentally, backscattering intensity versus incident alpha angle scans at a scattering angle of almost-equal-to 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 been introduced for quantitative evaluation of the agreement between experimental and simulated scans. For the case of 2 keV He+ scattering from Si{100}, scattering features can be observed and delineated from as many as 14 atomic layers (approximately 18 angstrom) below the surface. The intradimer spacing D is determined as 2.2 angstrom from the minimum in the R-factor versus D plot.