Structural analysis of GaAs(0 0 1)-c(4×4) with LEED IV technique

By means of low energy electron diffraction intensity versus voltage (LEED IV) analysis with the help of scanning tunneling microscope (STM), the crystallography of GaAs(0 0 1)-c(4×4) surface has been determined. STM images indicate that the atomic structure of the surface at room temperature does not have rigorously a p2mm symmetry, which has been assumed in all the analyses conducted so far. Asymmetric three-dimer model, which consists of three As dimers in the unit cell on an As-terminated unreconstructed surface, has led to the best fit between the experimental and calculative IV curves with the Pendryʹs reliability factor of 0.27. The center dimer among the three is tightly dimerized with the bond length of 2.13 إ, while the outer two have achieved less complete dimerization with the bond length of 3.02 إ. Contrary to the case for the Si(0 0 1), it is not buckling perpendicular to the surface but in-plane twisting that dominantly makes the dimers asymmetric, which involves remarkably short bond length for some of the backbonds.