THE UNRECONSTRUCTION-RECONSTRUCTION PHASE-TRANSITION OF THE PT(110) SURFACE

Ar ions with appropriate kinetic energy bombarding on a clean Pt(110)-(1 x 2) surface without further annealing produce a (1 x 1) bulklike LEED pattern. Atoms at the topmost layer of this (1 x 1) surface must be random. The phase transition temperature from unreconstruction (1 x 1) to reconstruction (1 x 2) of the Ar+ bombarded (1 x 1) surface and the conventional CO-induced (1 x 1) surface occur at 440 K and 360 K respectively. Both transitions are irreversible. A reversible transition (1 x 2) reversible (1 x 1) occurs at 1050 K that belongs to a order-disorder phase transition. From the behaviour of the phase transition, the LEED spot profile and comparable studies with oxygen chemisorbed on two (1 x 1) unreconstructed surfaces and a (1 x 2) reconstructed the surface, we conclude that atoms on the topmost layer of the Pt(110)-(1 x 1) surface induced by CO are random in position.