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 temper ature. The particles interact through modified Lennard-Jones potential s. The studies focus on how the characteristic features of the surface -surface interatomic potential, specifically its repulsive core, deter mine the variation of surface misfit with temperature, and the stabili ty of the ensuing structural phases and the nature of the observed pha se transitions. The low-temperature phase consists of a striped phase of double-sine-Gordon domain walls oriented along one of the three equ ivalent [110] directions and stacked along the [112] direction. The te mperature evolution of this phase was followed for two typical and dis tinct systems: in one system (system 1), the surface-surface potential was chosen so as to make the effective surface misfit decrease with t emperature, while in the other (system II), the misfit increased or re mained constant with temperature. System I undergoes an incommensurate -commensurate phase transition which appears to be second order in nat ure while system II exhibits an incommensurate-incommensurate phase tr ansition. The temperature evolution of system II closely parallels the behavior of the Au(111) surface with rise in temperature.