Study of electrostatic properties of dielectric surfaces and powders using scanning probe microscopy

This paper encompasses a study on the surface electrical properties of insulating materials used in industry, using an atomic force microscope (AFM). This instrument is capable of resolving the topographic and electrostatic characteristics of various samples, including single particles in finely powdered materials, with sub-micron spatial resolution. Factors which were investigated include topography and the distribution of electrostatic potential on surfaces as well as the time-dependent dynamics of charge decay on substrates and particles. The samples of polymer materials (standard Acetal and polybutylteraphtalate (PBT)) and lactose particles plated on conducting substrate (p-doped silicons) were studied by simultaneously obtaining topography and surface potential related images using two pass scanning technique. The topographical features (first pass) of the scanned surfaces were acquired using intermittent contact technique. This can affect the surface potential distribution which was subsequently obtained during the second noncontact pass. It was noticed however, that after the samples were charged using corona discharges (positive and negative polarity) it was possible to obtain topographical images in a pure noncontact mode with less disturbance to the original charge distribution present on the surface. The experimental evidence provided qualitative information on how the surface charge density is related to the sample topography. The tests were also successfully conducted to gain understanding on charge migration on surfaces by measuring the decay rate of surface potential.