Field emission and electron energy distributions from point-type triangular-shaped emitters made of thin graphene films

摘要

We report on fabrication and detailed characterization of point-type graphene emitters, which can be further used as electron sources in modern vacuum devices. Two-dimensional free-standing and triangular-shaped field emitters with the tip angles of 30°, 60°, and 90° and a height of ～1 mm were made of thin graphene films of varying thicknesses (2.5-μm and 8-μm). The field emission properties of these emitters were systematically investigated by different measurement techniques. Wider and thicker graphene film emitters exhibited better stability and provided higher emission currents (up to ～100-420 μA). The short-term current fluctuations stayed within 8%-14%. The graphene film emitter with a tip angle of 90° and 8-μm thick yielded a high field emission current of up to 2.2 mA at 9 V/μm. All emitters reproducible showed a non-linear Fowler-Nordheim behavior, which was correlated with the electron energy spectroscopy results. High-resolved energy spectra showed that up to three discrete peaks can be observed from the graphene edges at currents of ＜1 μA. The integral energy distributions of electrons at higher currents showed single broad emission spectra with a width of up to 1-2 eV. Additionally, graphene point emitters were characterized in various vacuum environments (Xe, Ar, N_2, H_2, O_2, and air), different pressure levels (2 × 10~(-4) Pa, 2 × 10~(-3) Pa, and 2 × 10~(-2) Pa), and at various distances between the anode and the graphene emitter tip. The results showed that graphene emitters can operate in non-ultrahigh vacuum conditions, and further optimization of the vacuum gap could result in a lower turn-on voltage.