Evidence of Different Charging Behavior of Conductive and Dielectric Materials in Low-Temperature Plasmas and a New Diagnostic for Low-Energy Electron Absorption.

In any physical system where a surface is hit by electrons, the sticking probability s of the electrons is a central parameter governing, for example, the charging of the surface. For dielectrics, it could previously only be measured for high energies (>100  eV), while it is well-known for metals even at energies of only a few eV. Recent theoretical investigations concerning dielectrics such as silica predict values for s significantly below 1. With precision charge measurements on microparticles in the sheath of a low-pressure plasma, a difference in charge between silica and gold-coated particles is found, challenging the long-standing assumption in dusty plasma physics that dielectric and metallic particles charge in the same way for the first time. Based on the measured charging difference, the low-energy sticking coefficient of silica is obtained, validating the theoretical predictions and offering a new diagnostic for the otherwise quasi-inaccessible low-energy electron sticking of dielectric materials.