CHEMISORPTION PROPERTIES AND STRUCTURAL EVOLUTION OF PT-SI INTERMETALLIC THIN-FILMS PREPARED BY THE ACTIVATED ADSORPTION OF SIH4 ON PT(111)

The reaction of a silicon adlayer deposited on Pt(111) by chemical vap or deposition (CVD) using silane (SiH4) is described. Data from Auger electron spectroscopy (AES) reveal that Si readily diffuses into the P t substrate and sequentially forms at least two unique intermetallic P t-Si surface structural phases with (root 7 x root 7)R19.1 degrees and (root 19 x root 19)R23.4 degrees real space unit cells as characteriz ed by low-energy electron diffraction (LEED). The chemisorption proper ties of each of the ordered overlayers were studied using CO as a mole cular probe. Reflection-absorption infrared spectroscopy (RAIRS) and t emperature-programmed desorption (TPD) studies indicated that CO was m ostly limited to chemisorption at ''atop'' Pt sites in the root 7 phas e with a significant reduction of the heat of adsorption with respect to the Pt(111) surface. The root 19 phase also showed a significant mo dification of the chemisorption properties although it is not as prono unced as that seen for the root 7 structure. The relevance of these st udies to intermetallic thin film growth is discussed.