Photoinduced decomposition of PTCDA molecules and desorption of their fragments from the films formed on the GaAs(110) surface

Abstract

Photoinduced fragmentation and desorption of thin films of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) vacuum-deposited on the GaAs(110) surface were studied by time-of-flight (TOF) mass spectroscopy under ultrahigh vacuum conditions. The main effects under pulsed laser light irradiation (pulse duration 10 ns, photon energy 2.34 eV, laser fluence 0.5–7 mJ/cm2) were the fragmentation of the PTCDA molecule and desorption of the resulting fragments in vacuum, whereas no desorption of the intact PTCDA molecule was recorded. The fragments included the perylene core C20H8, its half C10H4, carbon dioxide and monooxide, and atomic oxygen. The desorbed fragments of different types have significantly different kinetic energies of translational motion in the gas phase because of the nonthermal mechanism of photofragmentation and photodesorption.