Universal field-emission model for carbon nanotubes on a metal tip

Electron-field-emission properties have been investigated systematically for carbon nanotubes (CNTs) fabricated on a metal tip. With a vacuum gap of 0.7 mm, the threshold field is as low as 0.7 V/μm and the current density approaches 10 mA/cm2 at an electronic field of 1.0 V/μm. The emission current is quite stable with very low fluctuation. The emission behavior is in excellent agreement with Fowler–Nordheim theory and no current saturation is found even with an emission current reaching 1 A/cm2. A universal relationship 1/β=d2/d+1/β0 between the field amplification factor β and the vacuum gap d is developed within a two-region field-emission model. This relationship provides the basis for a microscopic understanding of CNT emitters and is applicable to other systems as well.