Experimental and Simulation Investigation of the Nanoscale Charge Diffusion Process on a Dielectric Surface: Effects of Relative Humidity

Abstract

Electrostatic charge generation and diffusion on the nanoscale were studied by atomic force microscopy and Kelvin probe microscopy. The charge diffusion coefficients were obtained by matching experimental results with numerical solutions of the diffusion equation. The results found that the relative humidity variations could significantly alter both the charge generation and diffusion processes. For the charge generation, the increase in relative humidity led to a decrease in transferred charge amount between the contact surfaces owing to the presence of the absorbed water film on the tip–sample interface. For the charge diffusion, the increase in relative humidity could accelerate the charge diffusion process laterally, and the diffusion coefficient of higher relative humidity was 3–5 orders of magnitude larger than those under dry air and N2. It was proved that the charge diffusion process for the positive charge was not necessarily faster than that for the negative one. In addition, the contribution from atmospheric water molecules to the surface charge diffusion was distinguished from that of absorbed water films by calculating the net loss of surface charge, and this effect was found to be more obvious under higher relative humidity. The dominant mechanism for the charge diffusion was discussed, and we argued that the relative humidity could be the main reason, and probably the only reason, for the charge diffusion and decay on the dielectric surfaces.