STM investigation on the normal and CDW phases of Sn/Cu(100)

J. MARTÍNEZ BLANCO; H. ASCOLANI; J.E. GAYONE; E.A. SÁNCHEZ; P. SEGOVIA; E.G. MICHEL

San Carlos de Bariloche, Argentina

Conferencia; 13th International conference on solid films and surfaces (ICSFS13); 2006

Centro Atómico Bariloche (CNEA)

Two-dimensional 2D phase transitions triggered by a gain in electronic energy have deserved ample attention during recent years. The most important example of this kind is the formation of a charge-density wave (CDW). The CDW state is an easily accessible, macroscopically coherent state with very interesting properties. As the CDW sets in, the lattice reorders slightly, giving rise to a periodic lattice distortion PLD and a new supercell. The loss of elastic energy is compensated in the new supercell by a gain in electronic energy related to the opening of a band gap 2W. This process is favoured when a significant fraction of electrons is affected, i.e., if there are large parallel portions of the Fermi surface separated by 2kF  nesting. Then, the spatial periodicity of the PLD is 2p/2kF and the nested portions of the Fermi surface are eliminated in the CDW state. In this work we report and STM study on the properties of the normal and CDW phases for 0.5 ML of Sn atoms on Cu(100). The CDW phase is observed below 360 K and it has a (3√2x√2)R45° structure. There are atomic models for this phase in the literature. Above 360 K, a new phase with (√2x√2)R45° structure is formed. STM images measured on the two phases involved are consistent with the stabilization of a CDW. Interestingly, the lateral distortions observed in the  (3√2x√2)R45° phase are much smaller than the vertical corrugation observed for this phase. The structural models of each phase obtained from the STM pictures are compared also with the results from surface x-ray diffraction experiments, which provide us with a consistent picture on the structural behaviour of this surface.TIPO DE PRESENTACION: POSTER