The adsorption of methyl chloride (CH3Cl) and trichlorosilane (HSiCl3) on Cu(110) was studied by temperature-programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and ultraviolet photoelectron spectroscopy (UPS). Methyl chloride interacts weakly with Cu(110) at 100 K, and we estimate from TPD that the adsorption energy is only 8-10 kcal/mol. It adsorbs nondissociatively and reversibly on Cu(110) under these conditions; no evidence of thermal decomposition was observed. HREELS indicates that chemisorbed CH3C1 adopts a bonding geometry with a symmetry lower than C3v, presumably bonded to the surface through the Cl atom with the methyl group tipped over with respect to the surface normal. In contrast, HSiCl3 interacts strongly with Cu(110) at 100 K. Trichlorosilane is initially dissociatively adsorbed, but most of the HSiCl3 in the chemisorbed monolayer adsorbs molecularly and reversibly due to the strong poisoning of the Cu(110) surface by Cl adatoms. Thermal decomposition, which leaves some Si-Cl and Si-H bonds intact, occurs readily at 140-300 K. Silicon deposited on the Cu(110) surface during HSiCl3 decomposition is in a metallic bonding environment, directly bonded to the Cu. Low coverages of HSiCl3 form an H2 desorption state near 300 K that is attributed to the decomposition of an SiH surface species with an activation energy for decomposition of 18 kcal/mol. This H2 desorption state is not observed for the thermal decomposition of large coverages of HSiCl3 on Cu(110) nor for pre-chlorinated Cu(110) surfaces. On pre-chlorinated Cu(110), HSiCl3 is only weakly adsorbed with an adsorption energy of 8 kcal/mol and is adsorbed nondissociatively with complete reversibility. The importance of these results for understanding the Cu-catalyzed direct synthesis reaction between CH3Cl and Si to form methylchlorosilanes is discussed.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Materials Chemistry