Penetration of Deposited Ag Overlayers Through Alkanethiol Self-Assembled Monolayers on Gold

We present XPS and ISS characterization of octadecanethiol (ODT, HS(CH2)17CH3), mercaptoundecanoic acid (MUA, HS(CH2)10COOH), and mercaptohexadecanoic acid (MHA, HS(CH2)15COOH) SAMs before and after depositing up to 1.0 nm Ag at ca. 10-7 torr. The SAMs were prepared by self-assembly onto gold films on <100> silicon substrates. XPS spectra indicate that no strong interaction occurs between thedeposited Ag and the COOH organic functional group (OFG) of MUA or MHA. The Ag interaction with ODT is weak. ISS compositional depth profiles (CDPs) for Ag on MHA and MUA and ODT taken over a temperature range of 113 to 293 K indicate that Ag remains on the surface of MUA for up to 1 h after deposition, whereas Ag penetrates ODT in less than 5 min at 295 K. The rate of Ag penetration is slowerthrough ODT, MUA and MHA at temperatures below 295 K until Ag resides completely on the SAM surface between 150 and 200 K.