Photon-stimulated desorption and fragmentation processes: formic acid on Si(111)7×7

Abstract

Abstract A photon-stimulated desorption (PSD) process consists of the production of ions and neutrals upon irradiation with light of proper wavelength. Here, we present a short review on the PSD mechanisms and the parameters influencing it, such as the adsorbate–substrate coupling, the light polarization, the surface orientation, the temperature, the mass of the leaving fragments as well as the co-adsorption effects. Furthermore, as an example, we will present a PSD investigation of formic acid on Si(1 1 1)7×7 in the energy ranges including the C 1s and the O 1s thresholds. D + , C + , CD + , O + , CO + , DCO + ions are produced in both energy ranges. The excitation in the C 1s energy range offers a less efficient substrate-mediated quenching with respect to the excitation in the O 1s one, with a consequent more structured photoexcitation spectrum. In the energy range including the O 1s the transitions to π * (CO) and σ * (C–D) levels produce selectively either D + or CDO + . O + is produced both by a transition to a π * (CO) level on through a shake-off process, and the remaining fragments are generally produced through secondary electrons.