Work Function: Fundamentals, Measurement, Calculation, Engineering, and Applications

The familiar work function $\mathrm{\ensuremath{\Phi}}$ (the energy barrier for an electron to move across a material's surface into the vacuum) is central to a vast array of surface and interfacial processes, and thus is fundamental to technologies ranging from vacuum and solid-state electronics to catalysis. Despite this importance, multiple issues associated with the varying vacuum level of electrons near surfaces often obscure how $\mathrm{\ensuremath{\Phi}}$ is being defined, measured, and used. This Review clarifies the definition of $\mathrm{\ensuremath{\Phi}}$ with extra care, summarizes recent approaches for calculating and predicting $\mathrm{\ensuremath{\Phi}}$, and discusses how tuning bulk electronic structure and surface dipoles can be used to engineer $\mathrm{\ensuremath{\Phi}}$.