Effects of focus change on the fabrication of tungsten nanowire by electron-beam-induced deposition

The effects of focus change on the electron-beam-induced deposition (EBID) of tungsten nanowire in a scanning transmission electron microscope (STEM), were systematically investigated. By focusing the electron beam on the surface of carbon film, smooth tungsten nanowires were fabricated. The lateral size of the nanowire first decreased with the increase of beam scan speed, then became constant at about 7 nm when the scan speed was higher than 10 nm s(-1). During the deposition of nanowire on carbon film, both overfocus and underfocus changes resulted in a conical profile with a central core line, whose deposition strongly depends on the electron dose. Broken wires can be fabricated by controlling the focus. For the deposition of self-supporting wire out of carbon film, the influence of focus change depended on the morphology of the deposited wire. Overfocus change can be used to keep the upward feature of the wire, while underfocus change is useful for the downward feature.