Dynamics of the Interaction of Vapor-Deposited Copper with Alkanethiolate Monolayers:  Bond Insertion, Complexation, and Penetration Pathways

Abstract

We have investigated the interaction of vapor-deposited copper with -CH3, -OH, -OCH3, -COOH, and -CO2CH3 terminated alkanethiolate self-assembled monolayers (SAMs) adsorbed on polycrystalline Au using time-of-flight secondary ion mass spectrometry and density functional theory calculations. For -OH, -COOH, and -CO2CH3 terminated SAMs measurements indicate that for all copper coverages there is a competition between Cu atom bond insertion into C-O bonds, stabilization at the SAM/vacuum interface, and penetration to the Au/S interface. In contrast, on a -OCH3 terminated SAM Cu only weakly interacts with the methoxy group and penetrates to the Au substrate, while for a -CH3 terminated SAM deposited copper only penetrates to the Au/S interface. The insertion of copper into C-O terminal group bonds is an activated process. We estimate that the barriers for Cu insertion are 55 +/- 5 kJ mol(-1) for the ester, 50 +/- 5 kJ mol(-1) for the acid, and 55 +/- 5 kJ mol(-1) for the hydroxyl terminated SAMs. The activation barrier for the copper insertion is much higher for the -OCH3 SAM. Copper atoms with energies lower than the activation barrier partition between complexation (weak interaction) with the terminal groups and penetration through the monolayer to the Au/S interface. Weakly stabilized copper atoms at the SAM/vacuum interface slowly penetrate through the monolayer. In contrast to the case of Al deposition, C-O bond insertion is favored over C=O, C-H, and C-C bond insertion.

Understanding the Mechanism of Solvent‐Mediated Adhesion of Vacuum Deposited Au and Pt Thin Films onto PMMA Substrates

“…[ 16 ] The results of these studies suggest that the actual surface chemistry of the initial nucleation stages of metal fi lm growth on an organic surface depends critically on the specifi c metal and the surface functional groups present.…”

Electrodeposition of gold templated by patterned thiol monolayers

“…This bears some analogy to metal evaporation onto SAMs where the neutral species impinge on the outer surface of the SAM and then penetrate through to the substrate. Both Au and Cu have been found to penetrate SAMs with chemically inert terminal groups such as CH 3 and no explicit differences in their penetration behaviour has been reported [58,71,72].…”

“…As part of our efforts to widen the knowledge base and the scope of the deposition/lift-off scheme we studied the Au deposition on both binary SAMs and e-beam patterned SAMs. From evaporation experiments it is well known that the propensity to penetrate SAM depends on the type of metal as well as A c c e p t e d M a n u s c r i p t 4 the structure and terminal group of the SAM [58][59][60]. Therefore, it was of interest to see to what extent differences between metals exist.…”

Issues and Challenges in Vapor-Deposited Top Metal Contacts for Molecule-Based Electronic Devices

“…There have been a number of studies with Cu and Ag deposition on SAMs with varied terminal groups including -COOH, -COOCH 3 , -OCH 3 , -OH, -CN, and -SH [23][24][25][26][27][50][51][52]. While interactions with Ag appear minimal, Cu can interact with O-containing functionality, e.g., -COOH interactions can lead to formation of inorganic phases such as CuO, Cu 2 O, and Cu(OH) 2 [23-27, 52, 53] and interaction between Cu and COOCH 3 can result in formation of carboxylate [23][24][25][26][27]52].…”