Fabrication of <1 1 0> oriented tungsten nano-tips by field-assisted water etching

We report the field-assisted H2O etching that enabled us to fabricate nano-tips from polycrystalline <1 1 0> oriented tungsten wires at room temperature. We optimized the sharpening procedure in order to obtain field emissions (FEs) with high collimation. The typical tip apex was composed of a large base and a nano-protrusion with a radius of curvature less than 3.5 A. The narrowest opening angle (full width at half maximum) of the FE was 4.3o at 150 pA. We prepared two types of tips using two different applied bias voltages during the H2O etching. The electron microscope images and the analysis of Fowler-Nordheim (FN) plots revealed that the sizes of the individual bases depended on the fixed bias voltages during the H2O etching and affected their FE properties. In addition, we could confirm that the FE current from the nano-tip was more stable than that of the normal tip.