Many-body and low-dimensional phenomena in electron emission from efficient photocathodes

A brief survey is presented, in the historical context, of the development of physical views on the mechanisms of photoelectron emission from effectiv e photocathodes. Particular emphasis is placed On the impact of many-body e xcitations, such as excitons in semiconductors and electronic excitations i n metal particles and at metal surfaces, on the efficiency of antimony-cesi um, silver-oxygen-cesium and magnesium-barium photocathodes. We give exampl es how the quasi-two-dimensional photoelectron emission from subsurface lay ers of atomic thickness can be exploited to tune the photoemitter propertie s to the incident light and to enhance the photoelectric yield.