Temperature dependent morphological evolution of Pt(1 1 1) by ion erosion: destabilization, phase coexistence and coarsening

Abstract

A scanning tunneling microscopy investigation of the morphological evolution of Pt(1 1 1) upon removal of 0.2 to 680 atomic layers by 1 keV Xe + ion bombardment at normal incidence and at temperatures between 600 and 800 K is reported. The surface is found to become unstable in the temperature interval investigated. The destabilization of Pt(1 1 1) is most probably due to a step edge barrier for the attachment of a vacancy to an ascending step. Adatom production during ion bombardment enhances the destabilization of the surface. A qualitative change in roughness evolution is observed around 700 K, signified by an increase of the growth exponent from 0.40 to about 0.58. While below this temperature roughness buildup is due to pit formation, above 700 K it is initiated by remainders, left after vacancy island coalescence. The change in roughness evolution is caused by the onset of step atom detachment. For large removed amounts and above 700 K the surface exhibits an extended temperature regime of phase coexistence between a rough and a flat surface phase. The characteristic length scale of the surface morphology increases with the removed amount according to a power law with a temperature independent exponent of 0.28±0.02. This coarsening is due to step edge diffusion, rather than step atom detachment. The morphologies kinetically facet for the lower investigated temperatures. Possible origins for this slope selection are analyzed.