RESUMO
Thermionic emission relies on the low work function and negative electron affinity of the, often functionalized, surface of the emitting material. However, there is little understanding of the interplay between thermionic emission and temperature-driven dynamic surface transformation processes as these are not represented on the traditional Richardson-Dushman equation for thermionic emission. Here, we show a new model for thermionic emission that can reproduce the effect of dynamic surface changes on the electron emission and correlate the components of the thermionic emission with specific surface reconstruction phases on the surface of the emitter. We use hydrogenated <100> single-crystal and polycrystalline diamonds as thermionic emitters to validate our model, which shows excellent agreement with the experimental data and could be applicable to other emitting materials. Furthermore, we find that tailoring the coverage of specific structures of the C(100)-(2 × 1):H surface reconstruction could increase the thermionic emission of diamond by several orders of magnitude.
RESUMO
Thermionic emitting materials are relevant for several technological applications like electron guns, X-ray sources, or thermionic energy converters. As new materials and surface functionalisations that enable thermionic emission are developed, it is essential to be able to test them in a repeatable and reliable manner. Here, we present a CO2 laser-heated system for thermionic tests that can be used to test the thermionic emission current of different materials regardless of the optical properties or form factor. Our system can reach sample temperatures of T ≈ 1000 °C and can follow pre-programmed heating profiles. Additionally, a double thermo-electrical decoupling provides a very low electrical noise environment while keeping the sample heat loss to a minimum. Experimental data on sample temperature and thermionic current from a hydrogen terminated single crystal diamond are presented and discussed.