The Significance of Surface Roughness in Electron Yield Data

This study investigates the relationship between surface roughness and electron yield and our understanding of how surface roughness can significantly modify the yield of emitted electrons from a smooth surface. Electron yield is the ratio of the number of electrons emitted from materials to incoming electrons. Surface roughness, even small variations at the micron scale of incident electron penetration depths, can have a substantial impact on electron yield. We characterize roughness and morphology of various samples with intentionally modified surface features on polished materials created by scratching, grit blasting, and embedding particulates. Electron yields of these roughened samples were compared to those of smooth surfaces of the same material. We consider changes in electron yield in terms of changes on the microscopic level. A simple geometric model of the effects of roughness on electron yield has been developed by approximating the surface as a series of periodic rectangular, triangular, and saw-tooth wells. These models showed clear differences in suppression of electron yield, which we compare to measured electron yield curves as a function of incident energy. We discuss extensions for hemispherical and sinusoidal features and 2D periodic surface structures.