Diamond-based electron emission:Structure, properties and mechanisms

Diamond has an ultrawide bandgap with excellent physical properties, such as high critical electric field, excellent thermal conductivity, high carrier mobility, etc. Diamond with a hydrogen-terminated(H-terminated) surface has a negative electron affinity(NEA) and can easily produce surface electrons from valence or trapped electrons via optical absorption,thermal heating energy or carrier transport in a PN junction. The NEA of the H-terminated surface enables surface electrons to emit with high efficiency into the vacuum without encountering additional barriers and promotes further development and application of diamond-based emitting devices. This article reviews the electron emission properties of H-terminated diamond surfaces exhibiting NEA characteristics. The electron emission is induced by different physical mechanisms.Recent advancements in electron-emitting devices based on diamond are also summarized. Finally, the current challenges and future development opportunities are discussed to further develop the relevant applications of diamond-based electronemitting devices.