Characterization of metal alloy systems by scanning tunneling microscopy and low-energy ion backscattering

Low-energy ion backscattering and scanning tunneling microscopy (STM) can be used in combination to study the surface crystallography of single crystals, in particular also for alloy and ordered intermetallic compound systems. The elemental composition as well as the location of the atoms is determined by low-energy noble gas impact collision ion scattering spectroscopy with neutral detection (NICISS). Microscopic information on an atomic scale is obtained with the help of STM. The influence of adsorption-induced surface modifications is investigated at Cu3Au and compared with Cu surfaces. From the NICISS investigation the Au-Cu termination is inferred for clean Cu3Au(100) and (110). After careful preparation of the clean Cu3Au(110) surface the prominent (2 x 1) LEED superstructure changes into a pronounced (4 x 1) LEED pattern. The (4 x 1) structure can be explaining by row pairing of Cu-Cu and Au-Au rows in the topmost layer. Upon oxygen exposure of the Cu,Au compounds, Cu tends to segregate to the surface. In case of Cu3Au(110) a (2 x 1)-O superstructure appears which is in part similar to the known added row structure obtained for Cu(110)-(2 x 1)-O. Comparison with the Cu(110)-O surface shows, however, that the known periodically ordered structure of Cu-O stripes at undersaturation with oxygen does not show up at Cu3Au(110)-O.