Extended Modeling of the Effects of Surface Roughness on Electron Yield*

Surface conditions—including surface morphology, composition, contamination, and oxidation—can significantly affect electron yields and consequently materials surface charging. The effects of surface roughness on electron yield are modeled in this study by considering four aspects of electron yield calculations: (i) simple 1D models of rough surface geometry, (ii) the relative fractions of smooth and and rough surfaces, (iIi) the energy-dependent angular distributions of emitted electrons from these surfaces, and (iv) the likelihood these emitted electrons can escape the rough surface. (Previous work considered the simplest of surface features, but four additional simple 1D surface profiles were considered namely hemispherical, inverted hemispherical and sawtooth features and a sinusoidal surface profile. Three different angular emission profiles were considered for: (i) isotropic emission as a baseline, (ii) a Lambertian cosine distribution for lower energy secondary electrons, () and (iii) an energy-dependent screened Rutherford model for higher energy backscattered electrons. In this initial study only normally-incident electron profiles were considered, and any emitted electron was assumed to be recaptured if it impinged on any surface. Combining the surface profiles with the emission distributions allowed calculation of a roughness which predicts the effect of the surface profile on the electron yield of a smooth surface. Results are contrasted for the expected critical escape angles and the yield suppression or roughness coefficient as a function of aspect ratio and the fraction of the rough surface for both secondary and backscattered yields.