Reactive ion–surface collisions: Application of ionized acetone‐d6, DMSO‐d6 and pyridine‐d5 as probes for the characterization of self‐assembled monolayer films on gold

Abstract

AbstractLow‐energy collisions of ionized acetone‐d6, DMSO‐d6 and pyridine‐d5 with alkanethiolate self‐assembled monolayer (SAM) surfaces prepared on gold were investigated. These experiments can be used to monitor routinely the condition of the surfaces and to determine whether a surface is acceptable for a given application. In addition to the surface‐induced dissociation of the molecular ions, intense peaks corresponding to the addition of H (or D) to the ionized molecules are observed in the ion–surface collision spectra. The relative abundance of the [M + H(D)]+ reaction products was found to be dependent on several variables, including (i) the chemical composition of the monolayers (alkanethiolate, perdeuteroalkanethiolate, fluorinated alkanethiolate), (ii) the chain length of the alkanethiolate monolayers, (iii) the time for which the vapor‐deposited Au surfaces are exposed to the thiol solution during surface preparation and (iv) the degree of deliberate damage of the SAM film (70 eV Ar+˙ beam bombardment). The variation in [M + H(D)]+ abundance with induced surface changes illustrates the utility of these adduct ions for the characterization of the quality of the monolayers. The general trend observed is an increase in the [M + H]+ peak with the increased presence of hydrocarbon adsorbates, which in turn is believed to be directly related to increased disorder (inherent or induced) of the monolayer film. The increase in [M + H]+ is seen with a decrease in chain length, with shorter monolayer preparation times, and with an increase in surface damage. In general, a fluorinated surface that has been intentionally damaged by an Ar+˙ beam retains its highenergy deposition characteristics and is appropriate for use as a collision target for many types of projectiles.