Molecular-dynamics studies of temperature-dependent structural transitions on fcc(111) metallic surfaces

We present molecular-dynamics studies of structural transformations on metallic fcc(111) surfaces as a function of surface misfit and temperature. The particles interact through modified Lennard-Jones potentials. The studies focus on how the characteristic features of the surface-surface interatomic potential, specifically its repulsive core, determine the variation of surface misfit with temperature, and the stability of the ensuing structural phases and the nature of the observed phase transitions. The low-temperature phase consists of a striped phase of double-sine-Gordon domain walls oriented along one of the three equivalent 〈110〉 directions and stacked along the 〈112〉 direction. The temperature evolution of this phase was followed for two typical and distinct systems: in one system (system I), the surface-surface potential was chosen so as to make the effective surface misfit decrease with temperature, while in the other (system II), the misfit increased or remained constant with temperature. System I undergoes an incommensurate-commensurate phase transition which appears to be second order in nature while system II exhibits an incommensurate-incommensurate phase transition. The temperature evolution of system II closely parallels the behavior of the Au(111) surface with rise in temperature.