Inelastic electron tunneling as vibrational spectroscopy of adsorbed organic molecules after 3 MeV proton irradiation at 4.2 and 293 K

Abstract

The molecular vibrations of monolayers of formic and benzoic acid adsorbed on Al-oxide were measured by inelastic electron tunneling spectroscopy at 4.2 K in situ after room temperature and low temperature irradiation with 3 MeV protons. As fundamental results of radiation damage a non-uniform reduction of the vibration modes was observed as a function of proton fluence studied up to 2.5 × 10 16 p cm −2 . Only after low temperature irradiation are some new peaks formed, which disappear after annealing at 293 K. This may be due to the fact that molecular fragments are formed which are only stable at low temperatures. Benzoic acid is found to be significantly less sensitive to radiation damage. While electron microscopy studies of organic materials indicate considerable effects of cryogenic protection, our experiments exhibit similar cross sections for molecular damage at different irradiation temperatures.