Shaping of tungsten field emission cathode. Observations by means of scanning field emission microscope (SFEM)

The paper describes a procedure of shaping of the surface of tungsten field emitters, which produces tips with decreased both extraction voltage and the emitting area in comparison with analogous factors for tungsten tips cleaned by the standard flash heating up to 2300 K. It has been shown, that for prepared in the proposed way tips, field emission occurs mainly from a few spots, which we have found as related to 〈111〉 and 〈100〉 directions of tungsten crystal. Scanning field emission microscopy (SFEM) was proposed as the method testing quality of field emitters.