ORIENTATIONAL INSTABILITY OF VICINAL PT SURFACES CLOSE TO (111)

Using scanning tunneling microscopy and thermal He diffraction we have studied the morphology of the vicinal Pt(997) surface, close to the hexagonal close-packed (111) face. While oxygen adsorption induces a step-doubling transition, the clean surface is thermally unstable towards faceting. Above T almost-equal-to 0.5T(m) the surface is found to undergo partial phase separation into large {111} facets and regions of undisturbed step regions. The faceted phase is stabilized by a reduction of surface stress through reconstruction of the (111) faces. The faceting is found to proceed via a nucleation-and-growth mechanism.