Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 89: Metal Substrates: Epitaxy and Growth

O 89.3: Talk

Friday, February 29, 2008, 10:00–10:15, MA 041

SXRD study at both sides of a temperature induced surface phase transition on Sn/Cu(001) — •jesus martinez-blanco¹, victor joco², carlos quiros³, pilar segovia², and enrique g michel² — ¹Fritz Haber Institut, Berlin, Germany — ²Universidad Autonoma de Madrid, Spain — ³Universidad de Oviedo, Spain

The crystalline structure of 0.5 monolayer of Sn atoms adsorbed on Cu(001) 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×√2)R45^∘ phase at high temperature to a two rotated domains (3√2×√2)R45^∘ phase at low temperature. 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, used in this work for the first time to extract crystallographic information from SXRD data. For the low temperature phase, our results confirm the removing of every third row of copper in the alloyed top layer. 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.