Lawrence Berkeley National Laboratory

New or modified models have been proposed for the much-studied Si(111)-(2x1) surface structure, including: a reverse-tilted p-bonded chain model (by Zitzlsperger et al); a three-bond scission model (by Haneman et al); and a p-bonded chain model with enhanced vibrations (present work). These models are compared here to the generally accepted modified p-bonded chain model (by Himpsel et al, 1984), by analyzing low-energy electron diffraction (LEED) I-V curves measured earlier. Using the efficient automated tensor LEED technique, the models can be refined to a much greater degree than with earlier methods of LEED analysis. This study distinctly favors the earlier modified p-bonded chain model, but with strongly enhanced vibrations. To compare models that have different numbers of adjustable free parameters a Hamilton ratio test is used: it can distinguish between improvement due to a better model and improvement due only to more parameters.