Thermal-field treatment for creating single-crystal tungsten tips with ultimate sharpness

Thermal-field (TF) treatment conditions for < 111 > oriented single-crystal tungsten tips have been systematically studied using the remolding process, which employs a reversely polarized field in the treatment, in order to establish a treatment sequence for producing the nanotip that ends with a very sharp < 111 > apex at the end. As the remolding voltage is increased at a specific temperature, initially hemispherical tungsten tip evolves in shape due to the growth of low index facets such as (110), (211), and (110) crystal-planes. The tip finally takes a polyhedral shape. The treatment temperature has a significant effect in the shape evolution course. When the temperature is high enough, the (211) planes shrink as the treatment field is increased. Three (110) planes make the < 111 > apex in this case. At lower temperatures, the < 111 > apex remains formed by the (211) planes until the remolding voltage is increased to an extreme, which results in a number of microprotrusions on the tip surface. A scheme has been proposed for the creation of the nanotip with ultimate sharpness. Here, the TF treatment is first conducted at a relatively high temperature until the (211) plane collapse takes place. Then, the temperature is reduced and the increase of the remolding voltage resumed. It is possible, by periodically observing field-emission patterns, to terminate the TF treatment at the right stage where the < 111 > apex achieves the sharpest configuration. The field emission from the nanotip can provide electron beam with much better angular intensity and confinement than conventional field emitters. (c) 2008 American Vacuum Society.