Single crystal HfC was evaluated as a cold field emission (T=300 K, < 1 x 10(-9) Torr) electron source for high-resolution scanning electron microscopy/transmission electron microscopy applications and it is shown to be an excellent candidate for this use. Single crystal HfC was produced and fabricated into a cold field emitter. Angular intensity and reduced brightness were determined from experimental I(V) data. A software program was written to calculate from first principles the full width at half maximum of the emitted electron total energy distribution over a range of geometrical and tunneling parameters, including a component for space charge effects. Experimental energy distribution data are in good agreement with the modeling results. The reduced brightness, energy distribution, and emission stability of HfC are compared with commercially available sources. HfC produced a higher brightness and a lower energy spread than a W cold field source or a ZrO/W Schottky emitter. HfC maintains its emission level for 1 h in moderate UHV condition, which shows a dramatic improvement over the long-term stability of W. This stability combined with a durability that allows for frequent flash cleaning without degradation of the emitter end form makes HfC a highly promising cold field emission source. (c) 2008 American Vacuum Society.