Chemical Effects of Methyl and Methyl Ester Groups on the Nucleation and Growth of Vapor-Deposited Aluminum Films

The interaction of vapor deposited Al atoms with self-assembled monolayers (SAMs) of HS(CH sub 2) sub (15) CH sub 3 and HS(CH sub 2) sub (15) CO sub 2 CH sub 3 chemisorbed at Au(111) surfaces was studied using X-ray photoelectron spectroscopy, infrared spectroscopy, time-of-flight secondary mass spectrometry and spectroscopic ellipsometry. For the CH sub 3-terminated SAM, no reaction with C-H or C-C bonds was observed. For total Al doses up to ~12 atoms/nm sup 2, penetration to the Au-S interface occurs with no disruption of the average chain conformation and tilt, indicating formation of a highly uniform ~1:1 Al adlayer on the Au. Subsequently, penetration ceases and a metallic overlayer begins to form at the SAM-vacuum interface. These results are explained in terms of an initial dynamic hopping of the -S headgroups on the Au lattice, which opens transient diffusion channels to the Au-S interface, and the closing of these channels upon completion of the adlayer.