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

The work function, which is the energy barrier for an electron escaping from the surface of a material, is a fundamental material surface property with many applications spanning energy harvesting, heteroge-neous catalysis, vacuum electronics, and solid-state electronics. In this review, we define different aspects of the work function through an electrostatic potential treatment. We discuss in detail the role of electric fields, especially the heterogeneous surface patch field, in order to clarify potential points of confusion about work-function measurement and interpretation. We review standard experimental approaches to measure work function and the use of density-functional theory as a computational tool to predict work function. We then discuss the influence of materials chemistry and structure on work-function trends. We also discuss the role of work function in various applications, including a particular focus on relative elec-tron energy-level alignment. Finally, we discuss two common approaches for engineering work-function values for specific applications: tuning the Fermi level and tuning the surface dipole. This review provides guidance for researchers interested in the intersection of work function, surface characterization, surface and interface physics and chemistry, and materials and device design for a wide array of technologically relevant applications.