SURFACE-MORPHOLOGY CHANGES UPON LASER-HEATING OF PT(III)

The surface morphology of Pt(111) has been studied as a function of irradiation energy produced by a pulsed laser at 1064 nm. Substantial changes from the ideal crystal structure are observed at temperatures greater than approximately half the melting point. These changes are due to the nucleation of dislocations associated with the large temperature gradient normal to the surface. Using scanning tunneling microscopy, we observe dislocations with near-atomic resolution. Stress caused by the normal temperature gradient is relieved by slip parallel to the (111) planes inclined to the surface. Increasing the stress by increasing the maximum temperature to which the surface is heated increases the density of dislocations rather than the average slip along a dislocation. For maximum surface temperatures below 1000 K, atomic diffusion along steps does not occur during the 5 ns during which the surface is heated. For T-max above 1100 K, this diffusion becomes rapid. For T-max above values leading to surface damage in the form of slip bands which are visible by light microscopy, the surface is highly disordered.