The influence of surface conditioning on the thermionic electron emission from polycrystalline diamond films

Abstract

AbstractThermionic electron emission (TEE) properties of as deposited, bare surface, in situ hydrogen‐terminated and in situ oxygen‐terminated polycrystalline diamond (Poly‐Di) films surfaces are reported. Continuous Poly‐Di films of a thickness of ∼200 nm grown on B‐doped Si substrates by hot‐filament chemical vapor deposition (HF CVD) were used. The TEE measurements were carried out in the 500–650 °C temperature range by recording the energy spectra of the electrons emitted using a hemispherical energy analyzer under ultra‐high vacuum (UHV) conditions. As‐deposited Poly‐Di surfaces may exhibit variations in their TEE properties depending on history and surface conditioning, thus indicating the need to control the diamond surface chemistry to obtain reproduceable TEE properties. Annealing to 1000 °C results in significant decrease of the TEE intensities, related to thermal desorption of hydrogen and creation of a bare surface. in situ annealing to 1000 °C followed by in situ hydrogenation of the Poly‐Di film surface results in significant enhancement of the TEE. Several cycles of the last procedure show that the TEE of hydrogen‐terminated Poly‐Di surface can be restored, whereas minor decrease in TEE intensity can be associated with slow surface degradation of the Poly‐Di surface following this conditioning. It is suggested that the TEE from hydrogen‐terminated Poly‐Di film may involve two mechanisms. Oxygenation of the bare Poly‐Di film results in low TEE intensities, very similar to those obtained from the bare Poly‐Di film surface, indicating that the TEE process from Poly‐Di film is somehow insensitive to the difference in the surface potential induced by oxygenation and bare surface conditionings.