J. Phys. Chem. 1991,95,4453-4463
4453
A Reexamination of the Chemisorption of Trimethylaluminum on Silica M. E. Bartram,* T. A. Michalske, and J. W. Rogers, Jr.+ Sandia National Laboratory, Albuquerque, New Mexico 87185 (Received: May 8, 1990; In Final Form: March 13, 1991)
Fourier transform infrared spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy have been used to study the chemisorption and decomposition of trimethylaluminum (TMA) on silica under high vacuum. By annealing a series of silica substrates from 425 to 1573 K prior to TMA exposures at 300 K,we have examined the distributions of chemisorption products as a function of the relative concentrationsof isolated hydroxyls (OHi),hydrogen-bonded hydroxyls (OHH), and siloxane bridges. The observed variation in the Si-methyl to AI-methyl population ratios supports a new chemisorption model in which a monomethylaluminum surface complex and methyl groups bonded to silicon are proposed as the majority species on the surface at 300 K. Although the initial reactive sticking probability for TMA on the silica substrates is
