Dynamical studies of the single point contact electrification of inorganic and polymer substrates.

The tip of a scanning probe microscope can be used to make isolated single point contacts on insulating surfaces and to study the dynamics of microscopic patches of enhanced surface potential when the contacts are broken. Comparative studies of dissimilar materials (silicon dioxide, silicon nitride, sapphire and polymethylmethacrylate) reveal common features which include the possibility of inducing positive or negative electrification signals by reversing the bias voltage applied to the tip. However there are clear differences between materials in signal magnitude and decay characteristics. None of the materials exhibit simple exponential decays in surface potential, and the decay mechanisms for silicon dioxide and sapphire are clearly shown to be voltage-dependent.