Penetration of deposited Au, Cu, and Ag overlayers through alkanethiol self-assembled monolayers on gold or silver

The purpose of our research is to study the interactions or processes between vacuum-deposited metals (M) and the organic functional end groups (OFGs) of self-assembled monolayers (SAMs) on Au or Ag films under controlled conditions. Meta/SAM/Au or Ag systems are models for understanding bonding at M/organic interfaces and the concomitant adhesion between the different materials. In broad terms; the M/OFGs form interacting interfaces (e.g., Cr/COOH or Cu/COOH) in which the deposit resides on top of the OFGs or weakly interacting interfaces through which the overlayer penetrates and resides at the SAM/gold interface. We present results from weakly interacting systems (Au/CH3, Cu/CH3, Cu/COOCH3, Ag/CH3, Ag/COOH) and discuss the time-temperature dependence of the disappearance of the metal from the M/SAM interface following deposition using ion scattering spectroscopy (ISS) on these systems. X-ray photoelectron spectroscopy (XPS) and ISS were used to characterize alkanethiols terminated with CH3 (C-6, -10, -12, -16, and -18 chain lengths), COOH (C-11 and C-16 chain lengths), and COOCH3 (C-16) before and after depositing up to 1.0 nm Au, Ag, or Cu at ca. 10(-7) Torr. XPS spectra indicate that no strong interaction occurs between any of the deposited metals and the organic functional groups studied, although a stronger interaction is evident for Ag on a C-16 COOH than a C-11 COOH and a weak interaction is formed between Cu and COOCH3. Although these interactions between the OFG and Cu or Ag are evident, metal penetration into these SAMs occurs. No interaction between Au, Ag, or Cu with CH3 is evident. ISS compositional depth profiles indicate penetration occurs in less than 16 h in all cases and as short as 30 s for the M/CH3 systems. The time to penetrate is in the following order: Ag, Cu and Au/CH3 (C-16) <Cu/COOCH3 <Ag/COOH (C-16).