Selective terminal function modification of SAMs driven by low-energy electrons (0–15 eV)

Abstract

Low-energy electron induced degradation of a model self-assembled monolayer (SAM) of acid terminated alkanethiol was studied under ultra-high vacuum (UHV) conditions at room and low (∼40 K) temperatures. Low-energy electron induced chemical modifications of 11-mercaptoundecanoic acid (MUA, HS–(CH₂)₁₀–COOH) SAMs deposited on gold were probed in situ as a function of the irradiation energy (<11 eV) by combining two complementary techniques: High Resolution Electron Energy Loss Spectroscopy (HREELS), a surface sensitive vibrational spectroscopy technique, and Electron Stimulated Desorption (ESD) analysis of neutral fragments. The SAM's terminal functions were observed to be selectively damaged at around 1 eV by a resonant electron attachment mechanism, observed to decay by CO, CO₂ and H₂O formation and desorption. CO₂ and H₂O were also directly identified at low temperature by vibrational analysis of the irradiated SAMs. At higher irradiation energy, both terminal functions and spacer alkyl chains are damaged upon electron irradiation, by resonant and non-resonant processes.