ATOMIC-FORCE MICROSCOPY STUDIES OF CONTACT-ELECTRIFIED CHARGES ON SILICON-OXIDE FILM

Microscopic contact-electrified charges on a silicon oxide layer forme d on a p-type Si substrate were investigated in air using an atomic fo rce microscope with a biased conductive cantilever. We could successfu lly image the dissipation of the contact-electrified charges after a s ingle contact. We found that the sign of the contact-electrified charg es is reproducible and controllable by the polarity of the bias voltag e. We also found that negative charges are more easily deposited on th e silicon oxide surface than the positive charges. Furthermore, we fou nd that the charge dissipation as a function of the time after contact electrification takes two steps for the negative charges. At the firs t step the charge dissipation is nearly same for both the repulsive an d the attractive force measurements, while at the second step the diss ipation for the attractive force measurement is much faster than that for the repulsive force measurement.