The schematic, above, illustrates a liquid metal ion source (LMIS), which appears in commercially available focused ion beam milling machines. The high voltage electrode causes a liquid metal film on a not-necessarily-sharp needle to form a self-sharpening nanoscale cusp, or Taylor cone, which serves as a high-brightness ion source. Such liquid metal asperities have been solidified for use as electron field emitters, as well [34,35]. If the liquid metal were a suitable catalyst (iron, nickel, or cobalt), it is tempting to think we could use this cone as a template for a conical graphene field emitter. In practice, the graphene film tends to form dendrites, such as those observed on iron and cobalt. A solid graphene film on a liquid metal can form structures that would not be stable on a pure liquid surface.
Considering the active research regarding the use of carbon nanotubes as field emitters[25,26], graphene dendrites may be suitable for this application if they can be made sharper than the ones produced so far. The current procedure for precipitating curved graphite uses supersaturated solutions of carbon, which yield thick graphite deposits. A modified procedure, employing a lower concentration of carbon, is likely to yield thinner graphene structures, including nanoscale cusps suitable for use as field emitters and proximal probes.