| AVS 54th International Symposium | |
| Surface Science | Tuesday Sessions |
| Session SS2-TuM |
| Session: | Surface Structure and Growth on Metals |
| Presenter: | J. Martínez-Blanco, Universidad Autónoma de Madrid, Spain |
| Authors: | J. Martínez-Blanco, Universidad Autónoma de Madrid, Spain V. Joco, Universidad Autónoma de Madrid, Spain C. Quirós, Universidad de Oviedo, Spain P. Segovia, Universidad Autónoma de Madrid, Spain E.G. Michel, Universidad Autónoma de Madrid, Spain |
| Correspondent: | Click to Email |
The crystalline structure of 0.5 monolayer of Sn atoms adsorbed on Cu{100} has been studied by surface X-ray diffraction (SXRD) measurements. This surface undergoes a temperature-induced phase transition at 360 K from a single domain (√2 x √2)R45° phase at high temperature to a two rotated domains (3√2 x √2)R45° phase at low temperature. In a previous work1 this phase transition was identified as being due to the stabilization of a charge density wave (CDW), with gapping of nested regions of the high temperature Fermi surface in excellent agreement with the CDW periodicity. We performed temperature-dependent SXRD measurements in order to obtain information on the atomic displacements across the phase transition and to understand the nature of the two phases observed. A full data set including in-plane reflections, superstructure rods and crystal truncation rods was measured for each phase. The optimization method employed for fitting the experimental data for both the high and low temperature phases is a type of genetic algorithm called Differential Evolution,2 used in this work for the first time to extract crystallographic information from SXRD data. For the low temperature phase, we compare the model obtained with a previous surface structure model.3 Our results confirm the removing of every third row of copper in the alloyed top layer and a concomitant pairing of Sn atoms as the origin of the triple periodicity. However, we obtain slightly different values for the atomic displacements in deeper layers. For the high temperature phase, the overall dependence of the measured structure factors with the perpendicular momentum transfer is similar to the values extracted from the low temperature phase, suggesting a disordered nature for the high temperature phase. We propose a detailed model for this phase and for the nature of the thermal induced disorder. We discuss possible mechanisms to keep the local structure across the phase transition and the nature of the high temperature disordered phase.
1J. Martínez-Blanco et al., Physical Review B, 72 (2005), 041401(R)
2M. Wormington et al., Phil. Trans. Roy. Soc. London Sers A, 357 (1999), 2827-2848
3K. Pussi et al., Surface Science, 549 (2004), 24-30.