High-Resolution TOF-SIMS Study of Varying Chain Length Self-Assembled Monolayer Surfaces

A high-resolution time-of-flight secondary ionization mass spectrometer (TOF-SIMS) has been used to investigate chain length effects in hydrocarbon self-assembled monolayer (SAM) surfaces on gold substrates. A wide range of n-alkanethiols was used to make homogeneous SAM surfaces, which included both odd and even hydrocarbon chain length thiols. Variations in coverage, extent of oxidation, and high-mass cluster formation as a function of hydrocarbon chain length of the alkanethiol SAM surfaces were investigated. Long−short chain length effects were observed for the relative coverage of the SAM surfaces, which directly influences the extent of oxidation for the thin films. The formation of gold−sulfur and gold−adsorbate cluster ions was also observed, since the mass range of the TOF-SIMS made it possible to monitor all of the cluster ions that were formed following the high-energy ion/surface interactions.