Transfer of electrons on scratched iron surfaces: Photoelectron emission and X-ray photoelectron spectroscopy studies

Abstract

Abstract:We report the activation energy, ΔE 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 ΔE a using Y, called Y GC , at seven temperatures up to 353 °C , for the same Y glow curve, was proposed. The ΔE 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 ΔE 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. ΔE aUp1 was in the 0.212-0.035 eV range, depending on the environment in which scratching was performed; ΔE 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 ΔE aDown1 , ΔE aUp2 , and ΔE 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 ΔE aUp1 and ΔE aUp2 , respectively. ΔE 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.

Thermal Analysis of Photoelectron Emission (PE) and X-ray Photoelectron Spectroscopy (XPS) Data for Iron Surfaces Scratched in Air, Water, and Liquid Organics

“…The intensity of TAPE was measured in two experimental methods: (1) during a temperature scan under light irradiation at a fixed wavelength, and (2) during a wavelength scan at a fixed temperature. The PE results from the scratched samples during the temperature scan were reported previously [5,6]. Here, we briefly describe the operation conditions used in the temperature scan.…”

“…The TAPE measurement apparatus was shown in detail previously [5,13]. We briefly describe the measurement apparatus and its operation procedure.…”

“…We developed a non-vacuum-based method to examine the influence of temperature and incident light wavelengths (photon energies) on PE from real iron surfaces. In the present study, for sample surfaces scratched in the environments such as air, water, and liquid organics, the PE results obtained from the PE measurement, carried out in two ways as a function of temperature and light wavelength, were reexamined in more detail in relation to the X-ray photoelectron spectroscopy (XPS) results.In the first case, for real iron surfaces scratched in air, water, and liquid organic environments, we outlined the results of PE previously reported, often called thermally assisted photoelectron emission (TAPE) [5], as well as the results of XPS. The experiments were carried out to examine the influence of the interaction between mechanical deformed metal surfaces and the environments on the PE behavior of the surfaces.…”

“…The PE glow curve obtained in the Up1 scan was found to be strongly affected by the environment in which scratching was performed, while those obtained in the following three scans took a similar trend and were almost independent of the environment. For the above-scratched iron samples, we obtained the activation energies from the glow curves of PE quantum yield (emitted electrons per incident photon), Y, during four temperature scans under 210-nm-wavelength light irradiation and reported their relationship with the acid-base interaction between molecules of the liquid environments and Fe-OH on the surface [5]. The Arrhenius activation energy was obtained using an Arrhenius type Equation (1), for Y GC values at seven temperatures selected in the glow curves.where Y GC is the quantum yield, ∆E a is the activation energy, Y 0 is the pre-exponential factor, k B is Boltzmann's constant, and T is the temperature in Kelvin.…”

“…In the first case, for real iron surfaces scratched in air, water, and liquid organic environments, we outlined the results of PE previously reported, often called thermally assisted photoelectron emission (TAPE) [5], as well as the results of XPS. The experiments were carried out to examine the influence of the interaction between mechanical deformed metal surfaces and the environments on the PE behavior of the surfaces.…”