05 March 2018
We report the activation energy, Δ E a, for the quantum yield in thermally assisted photoelectron emission (TAPE) under 210-nm-wavelength light irradiation, and the associated X-ray photoelectron spectroscopy (XPS) results. Samples were cleaned only in acetone and scratched in air, water, methanol, ethanol, acetone, benzene, and cyclohexane. Glow curves, describing the temperature dependence of photoelectron emission (PE) quantum yield (emitted electrons/photon), Y, were obtained. A simple method of determining Δ E a using Y, called Y GC, at seven temperatures up to 353 °C, for the same Y glow curve, was proposed. The Δ E a obtained using this method was almost the same as that obtained from Y for seven stationary temperatures ( Y ST). For scratched samples, the TAPE was measured over two cycles of temperature increase and subsequent decrease (Up1, Down1 and Up2, Down2 scans) in the 25–339 °C range, and Δ E a was obtained from Y GC. The Arrhenius plot was approximated by a straight line, although a convex swelling peak appeared in the Up1 scan. Δ E aUp1 was in the 0.212–0.035 eV range, depending on the environment in which scratching was performed; Δ E aUp1 for water was much higher than that for acetone. This was explained in terms of the mode of the acid–base interaction between the liquid molecules and the hydroxyl group of Fe–OH. The values of Δ E aDown1, Δ E aUp2, and Δ E aDown2 were in the 0.038–0.012 eV range. The total count of electrons emitted during the Up1 and Up2 scans was found to decrease with increasing Δ E aUp1 and Δ E aUp2, respectively. Δ E aUp2 was found to increase with increasing presence of the FeO component in the analyzed Fe oxides. The convex swelling peak was attributed to the removal of carbon materials from the scratched surface and the effect of the increased electron density of the surface hydroxyl group of FeOH under the light irradiation.