The structure and oxidation of tin single crystal surfaces

Low energy electron diffraction (LEED), low energy electron loss spectroscopy (ELS) and Auger electron spectroscopy (AES) have been used to study the structure of clean (101), (100) and (110) tin single; crystal surfaces and their oxidation characteristics. The surface structure of a foil sample was also studied and a high degree of surface crystallite orientation exposing predominantly (001) planes was noted. The three single crystal surfaces displayed different degrees of reconstruction which seemed to be related to the packing density of the exposed crystal plane. The (100) surface, which was the most closely packed, showed minor relaxation interpreted as displacement of some of the surface atoms away from the bulk. The reconstruction of the (110) surface involved greater surface upheaval and two models have been proposed to account for the changes observed in LEED as a function of temperature. The true (101) surface was never seen since the surface was always facetted. The argon ion beam which was used to clean the surface in situ was thought to be responsible for this. The reconstruction of the facetted (101) surface below 270K has been explained as the formation of a surface layer of a-Sn, the nonmetallic phase which is stable below 290K. Oxidation experiments were conducted in 5 x 10-7 Torr of oxygen and the oxidation rates of the surfaces measured. The LEED and ELS data were used to identify the oxide species formed at different temperatures on each of the surfaces. Each surface produced a characteristic LEED pattern when oxidized, but the patterns could all be resolved into one of two basic components. The oxide structure preferentially formed at room temperature has been identified as distorted SnO(001), and the structure formed at higher temperatures has been interpreted as a suboxide containing a mixture of Sn(II) and Sn(IV) atoms. LEED in particular has provided information which supplements the results of other workers and resolves some of the ambiguities concerning the oxidation of tin surfaces.