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 vapor deposition (CVD) using silane (SiH₄) is described. Data from Auger electron spectroscopy (AES) reveal that Si readily diffuses into the Pt substrate and sequentially forms at least two unique intermetallic Pt-Si surface structural phases with (√7 × √7)R19.1° and (√19 × √19)R23.4° real space unit cells as characterized by low-energy electron diffraction (LEED). The chemisorption properties of each of the ordered overlayers were studied using CO as a molecular probe. Reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) studies indicated that CO was mostly limited to chemisorption at "atop" Pt sites in the √7 phase with a significant reduction of the heat of adsorption with respect to the Pt(111) surface. The √19 phase also showed a significant modification of the chemisorption properties although it is not as pronounced as that seen for the √7 structure. The relevance of these studies to intermetallic thin film growth is discussed.