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Quantum efficiency (QE) of a photoemissive surface is lowered via a sub-monolayer coating of adsorbed alkali metal: we here measure QE of cesium, potassium, and sodium on tungsten and refine theoretical predictions using a hard-sphere model to compare to experiment. We identify variation of the percent-monolayer coverage corresponding to peak QE as affected by adsorbate covalent diameter and substrate lattice constant.

Electron transport through thin film semiconductors is common to both the development of semiconductor photocathodes and to secondary emission electron sources. We discuss the modeling and numerical simulation of such transport in the presence of scattering and loss mechanisms, to enable predictive estimations of energy distributions, time response, and the nature of the distribution of the emitted electrons.

An analytical formula of the emittance of and space charge effects on a sharply curved emitter surface is given. The 3D formulation makes use of the Point Charge Model (PCM) of a unit cell emitter coupled with a trajectory analysis to follow electrons to an evaluation plane where emittance is determined. The single tip theory extended to an array predicts the emittance of a Field Emitter Array 0.2 cm on a side producing 2000 A/cm2 is 23 mm-mrad. Space charge within the unit cell on the beam is estimated from the determination of the apex radius and field enhancement factor for arbitrarily sharp emitter structures Predictions of the impact of space charge on the emitted current are made, and compared to the literature. Methods to extend theory to beam codes are discussed.