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

Featured Application This work describes the results of Arrhenius plot analysis of photoelectron emission (PE) and X-ray photoelectron spectroscopy (XPS) data for scratched iron surfaces. The data were obtained as a function of three variables of temperature, photon energy, and scratching environments. This study is considered to contribute to better understanding of electron transfer occurring across the real metal surfaces in the fields such as tribology, adhesion, catalysis, corrosion, and so on. Abstract Little is known about the temperature dependence of electron transfer occurring at real metal surfaces. For iron surfaces scratched in seven environments, we report Arrhenius activation energies obtained from the data of photoelectron emission (PE) and X-ray photoelectron spectroscopy (XPS). The environments were air, benzene, cyclohexane, water, methanol, ethanol, and acetone. PE was measured using a modified Geiger counter during repeated temperature scans in the 25-339 degrees C range under 210-nm-wavelength light irradiation and during light wavelength scans in the range 300 to 200 nm at 25, 200, and 339 degrees C. The standard XPS measurement of Fe 2p, Fe 3p, O 1s, and C 1s spectra was conducted after wavelength scan. The total number of electrons counted in the XPS measurement of the core spectra, which was called XPS intensity, strongly depended on the environments. The PE quantum yields during the temperature scan increased with temperature, and its activation energies (Delta E-aUp1) strongly depended on the environment, being in the range of 0.212 to 0.035 eV. The electron photoemission probability (alpha A) obtained from the PE during the wavelength scan increased with temperature, and its activation energies (Delta E-alpha A) were almost independent of the environments, being in the range of 0.113-0.074 eV. The environment dependence of the PE behavior obtained from temperature and wavelength scans was closely related to that of the XPS characteristics, in particular, the XPS intensities of O 1s and the O2- component of the O 1s spectrum, the acid-base interaction between the environment molecule and Fe-OH, and the growth of non-stoichiometric FexO. Furthermore, the origin of the alpha A was attributed to the escape depth of hot electrons across the overlayer.