Abstract
Low work function materials are desirable in many applications such as electron emission and photocatalysis. We have studied low energy electron emission from low work function hydrogen terminated diamond surfaces via electron spectroscopy to gain insight into the mechanisms involved during electron excitation and emission. Electron emission was found to be dominated by electrons within the band gap energy region, allowed due to the negative electron affinity diamond surface, while sub-bandgap illumination was able to significantly increase emission current. Substantial upward surface band bending greater than 2 eV was observed for the diamond samples, which affect electron accumulation at the surfaces. Intra-bandgap states are shown to strongly influence electron emission behavior, which can have great implications for various energy conversion devices.
Highlights
Thermionic emission involves the removal of electrons from within a material after absorbing energies greater than the work function (WF), sharing similarities to that of secondary electron emission or photoemission, but using thermal energy to overcome the surface potential barrier[1]
While WF variations commonly exist between different surface orientations[14], their contributions are insignificant for the studies done here
It should be noted that for other electron emission mechanisms such as field emission, the diamond surface morphology and grain boundaries can play a crucial role[15,16], the Raman spectra for the two samples are shown in Fig. S2 for reference
Summary
Thermionic emission involves the removal of electrons from within a material after absorbing energies greater than the work function (WF), sharing similarities to that of secondary electron emission or photoemission, but using thermal energy to overcome the surface potential barrier[1]. This simplicity in generating free electrons allows it to form the basis of a variety of devices such as electron guns, X-ray sources, magnetrons and energy converters[2] [e] [6]. Thermionic emission current is dependent on the density of states (DOS), temperature and WF of the material, and can be approximated for bulk metals using the Richardson-Dushman equation[1].
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