The energy of electrons emitted from wearing solid surfaces

The energy of electrons emitted during the scratching of solids by a diamond stylus was measured using a retarding-potential energy analyzer in a vacuum of 10(-4)-10(-5) Pa: The solids tested were insulators, a semiconductor and a conductor. The insulators were normal sintered alumina (Al2O3); polymethylmethacrylate (PMMA) and glass, the semiconductor was n-type silicon (Si) and the metal was aluminum (Al). The energy of emitted electrons was distributed from low values to beyond 900 eV for the insulators and from low values to about 100 eV for the semiconductor, while that of metals could not be measured because the electron emission intensity was too low to be detected. The energy of the electrons emitted from metals was inferred from previous reports to be less than about 2 eV. These results lead to the conclusion that the electric field caused by tribocharging accelerates the electrons to give the energy of electrons increasing in the order of insulator>semiconductor>conductor. This is because electric resistivity is chiefly responsible for generating the surface potential-a function of both electric resistivity and dielectric constant.