While initial interest in using diamond materials for electron emission was derived from the observation of a negative electron affinity of the material, the nanoscale structure of the material has proven to be critical to obtaining field emission at an applied field of less than 2V/μm. This study presents topographic and emission site images of nanocrystalline diamond films. The results suggest that morphology variations are insufficient to explain the observed emission patterns. The thermionic properties of sulphur doped nanocrystalline diamond films and carbon nanotubes were measured and analyzed in terms of Schottky barrier lowering. The results indicated a general consistency of the field emission and thermionic emission from the same films. The potential for thermionic energy conversion based on these films is presented.