Abstract
Electron emission mechanism from an interface of solid-vacuum or solid-solid, based on di?erent excitations of heat, light and electric ?eld, is classi?ed into thermionic emission, photoemission and ?eld emission. These electron emission processes can ?nd widespread applications, such as medical x-ray machines, energy converter, photodetector, ?eld emission displays and scanning electron microscopy and so on. The fundamental physics characteristics of electron emission across the material interface determine the performance of these devices applications. Graphene is regarded as a wonderful material, which shows lots of exceptional properties. It can be used to contact with other materials as a semimetal, in particular semiconductors, to enhance the performance of relevant devices merely based on metal-semiconductor contact. Therefore, a comprehensive understanding of physics in graphene based interface is crucially important to further improve the performance of devices, like thermionic energy converter and photodetector. In this dissertation, i aim at o?ering new perspectives on electron emission physics at graphene-based interface, which has been neglected in prior studies. With these novel physics, i evaluated the performance of thermionic energy converter and photodetector based on electron emission physics at the graphene interface. Thermionic energy converter based on thermionic emission is a promising alternative to thermoelectric counterpart, with its features in having higher conversion e?ciency. The high work function of cathode used however leads to failure of energy harvesting at lower temperature. I showed that the use of graphene enables lower-temperature operation of vacuum type thermionic converter with e?ciency of 45%at 900 K, and that graphene-based van der Waals heterostructure energy converter has an e?ciency of above 8 % with cathode temperature at 400 K, making the recycling of low-grade waste heat possible and practical. The improved performance of thermionic energy converter bene?ts from unique thermionic emission mechanism across graphene-based interface, which is proved to be completely di?erent from conventional Richardson’s law originally developed for bulk metals. Such a distinctive thermionic emission from graphene also leads to a new electrical transport picture