DENSITY SATURATION OF DENSELY CONTACT-ELECTRIFIED NEGATIVE CHARGES ONA THIN SILICON-OXIDE SAMPLE DUE TO THE COULOMB REPULSIVE FORCE

To compare the mechanism of the contact electrification on a thin sili con oxide sample in air with that in vacuum, the contact voltage V-C a nd contact time t(0) dependences of the peak value and the full width at half maximum (FWHM) of the electrostatic force distributions induce d by the deposited negative charges just after the contact electrifica tion were measured. In air, the peak value of the electrostatic force was found to saturate with increase in both V-C and t(0). Also, the FW HM was found to increase monotonically with increase in both V-C and t (0). These results suggest that density saturation of the deposited ne gative charges occurs and that the saturated charge density is indepen dent of both V-C and t(0). Further, the deposited negative charges dif fuse owing to the Coulomb repulsive force between the deposited negati ve charges. On the other hand, in vacuum, the peak value of the electr ostatic force was found to saturate with increase in t(0), whereas it increases monotonically with increase in V-C. Also, the FWHM of the el ectrostatic force was found to be nearly independent of both V-C and t (0). Thus deposited negative charges do not diffuse even during contac t electrification and the incessant deposition seems to be inhibited b y the Coulomb repulsive force at the charge density where the Coulomb repulsive force due to the deposited negative charges equilibrates wit h the force for the contact electrification due to V-C.