Chemisorption Properties and Structural Evolution of Pt−Si Intermetallic Thin Films Prepared by the Activated Adsorption of SiH₄ on Pt(111)

Abstract

The reaction of a silicon adlayer deposited on Pt(111) by chemical vapor deposition (CVD) using silane (SiH 4 ) 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) R 19.1° and (√19 × √19) R 23.4° 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.