Scanning tunneling microscopy study of Pd adsorption on Pt(111)

The structure of palladium deposited on the Pt(111) surface has been studied by scanning tunneling microscopy (STM). Palladium of 99.99% purity was evaporated at a rate of about 6.7 x 10(-3) ML/min onto the Pt(l 11) crystal at a substrate temperature of room temperature (RT). The palladium atoms migrated along island edges leading to a smoother structure. It was found that the palladium atoms occupy the fcc-adsorption sites with an outward displacement of approximately 0.06 nm, and mainly leading to the terraces from the steps of Pt(111) surfaces at a coverage of 0.57 ML palladium. The palladium islands exhibit a fractal character, and a fractional dimension p of 4.39 +/- 0.81 at a coverage of 0.13 ML palladium. This result shows that palladium islands grow an equilateral triangle structure (rho = 4.55), and indicates that palladium islands have 6-fold rotation axis with respect to the first layer of Pt atoms.