Thermionic electron emitters are a key component in applications ranging from travelling wave tubes for communications, space propulsion and direct energy conversion. As the conventional approach based on metallic emitters requires high operating temperatures the negative electron affinity (NEA) characteristic of diamond surfaces in conjunction with suitable donors would allow an electronic structure corresponding to a low effective work function. We have thus prepared phosphorus-doped polycrystalline diamond films on metallic substrates by plasma assisted chemical vapor deposition where an NEA surface characteristics was induced by exposure of the film surface to a hydrogen plasma. Thermionic electron emission measurements in an UHV environment were conducted with respect to the Richardson-Dushman relation observing an emission current at temperatures < 375 ºC. Measurements were terminated at 765 ºC without significant reduction in the electron emission current indicating a stable hydrogen passivation of the diamond surface. A fit of the emission data to the Richardson equation allowed for the extraction of emission parameters where the value of the materials work function was

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The formation and properties of (110)-textured P-doped microcrystalline CVD diamond were studied. Based on several microscopy techniques, with a special emphasis on electron backscattered diffraction, a detailed determination of the grain orientations with respect to the exact [110] axis is given. The different orientations present in the film, in combination with low phosphine concentrations in the gas phase, lead to a variation in P incorporation that can vary over three orders of magnitude, as determined with cathodoluminescence mapping. The role of the surface morphology in the observation of these large incorporation differences is explained. Hall measurements confirm that the films are n-type conductive with a thermal activation energy of 0.56 eV. Based on B-doped substrates, pn junctions were created, showing a rectification ratio of nearly 10(4) at ± 25 V.