A Study on the Selective Organometallic Vapor Deposition of Palladium onto Self-assembled Monolayers of 4,4‘-Biphenyldithiol, 4-Biphenylthiol, and 11-Mercaptoundecanol on Polycrystalline Silver

Abstract

The selective organometallic vapor deposition of palladium onto self-assembled monolayers using cyclopentadienyl-allyl-palladium (Cp(allyl)Pd) as the palladium source was investigated by X-ray photoelectron spectroscopy (XPS). It was found that the deposition onto SAMs formed of 4,4‘-biphenyldithiol (BDT) on polycrystalline silver substrates proceeds in two successive steps. During the first step, a monolayer of a Pd(II) species is formed selectively on a BDT-SAM whereas no deposition can be observed on a 4-biphenylthiol-SAM (BT). Upon extension of the deposition time, unselective deposition of Pd(0) on the surface of both the Pd(II)-coated BDT-SAM and BT-SAM takes place in a second step. To deposit Pd(0) while maintaining the selectivity of the process, a different approach has been chosen: Trimethylamine alane (TMAA) was deposited selectively on an hydroxy-terminated SAM obtained by self-assembly of 11-mercaptoundecanol on a silver substrate. The resulting surface, which possesses highly reactive Al−H bonds, was exposed to the vapor of Cp(allyl)Pd at room temperature and the deposition of Pd(0) was observed. On a dodecanethiol-SAM, which has been subjected to the same procedure, neither aluminum nor palladium could be detected, proving the selectivity of both the adsorption of TMAA and the deposition of palladium.