CORRECTIONS TO QUANTUM EFFICIENCY PREDICTIONS FOR LOW WORK FUNCTION ELECTRON SOURCES

The Three-Step Model of Spicer, or the analogous Moments-based models, can be used to predict photoemission from metals and cesiated metals. In either, it is a convenient approximation to neglect electrons that have undergone scattering. Using Monte Carlo to follow scattered electrons, we assess the utility of the approximation particularly for low work function (cesiated) surfaces. MOTIVATION For metals, scattering is electron-electron or acoustic phonon: the former reduces the energy of photoexcited electron and changes its direction, whereas the later changes direction (energy loss is negligible). However, particularly when the work function is low, a scattered electron may retain enough energy to still be emitted. In the present work, we seek to quantify the impact on QE predictions from having neglected scattered electrons, and to do so, we make use of Monte Carlo simulations of transport and emission of photoexcited electrons. By “Fatal Approximation” the following assumptions are made: photoexcited electrons will contribute to QE if their energy after photoexcitation exceeds surface barrier height (EF + Φ), their energy component directed into surface barrier is greater than surface barrier height, and they do not suffer a scattering event on way to surface. By “Non-Fatal Approximation” it is meant that if electrons do suffer a scattering event then either the photoexcited electron’s post-scattering energy is not brought below barrier height or the collisionally excited electron’s energy is brought above barrier height, as indicated in Figure 1.