<i>In situ</i> growth and field emission of single-crystal HfC nanotips

Nanotips exhibit a low turn-on field and high emission current density, and are considered promising candidates in future cold-field emitters. However, it is difficult to fabricate an emitter with ultra-fine curvature radius, outstanding collimation and stable interfacial adhesion. In this study, we developed an <i>in situ</i> technique that enables the fabrication of single-crystal hafnium carbide (HfC) nanotips on top of tungsten (W). The single-crystal feature and outstanding collimation of HfC nanotips were confirmed using transmission electron microscopy (TEM). <i>In situ</i> TEM investigation revealed that the HfC nanotip exhibited a typical field-emission turn-on voltage of 128 V (20 nA), and a significant current of ∼230 nA at a low extraction voltage of 149 V, when the distance between the tip and extractor is ∼50 nm. The field enhancement factor of the HfC nanotip was as high as ∼2 × 10⁷ m^-1. These exceptional properties can be attributed to the single-crystal feature, the nanometer-sized apex, the outstanding collimation and the stable interfacial adhesion of the HfC nanotip.