Observation of Real Metal Surfaces by Tribostimulated Electron Emission and Its Relationship to the Analyses by XPS and Photoemission

The characteristics of tribostimulated electron emission (called TriboEE) have been studied for real metal surfaces subjected to rubbing with polytetrafluoroethylene (PTFE). A gas-flow Geiger counter with a counter gas called Q gas was used for observing the TriboEE. Metal samples used were as follows: Ti, Zr (group 4 in the periodic table); V, Nb, Ta (group 5); Mo, W (group 6); Fe (group 8); Co (group 9); Ni, Pd, Pt (group 10); Cu, Ag, Au (group 11); Zn (group 12); Al (group 13); and Sn (group 14). For metals in the same groups of 4, 5, 6, 10, and 11 the number of electrons ejected during rubbing time (called TriboEE total count) increased with an increase in the period for the metal. For the metals in the groups of 4, 10, and 11 the surface fluorine content originating from PTFE debris attached at the surfaces increased with an increase in the period for the metal. The TriboEE total count was almost independent of the photoelectric thresholds determined in photoemission (PE) experiment throughout the metals, while the amount of ejected electrons in the PE measurement tended to decrease with increasing threshold. The surface potential (SP) was almost unchanged before and after the TriboEE measurement. Based on the relation to XPS, PE, and SP results the TriboEE was explained as being associated with the release of electrons transported to the attached PTFE debris from the metal substrate by a surface electric field.