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

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 degrees, 60 degrees, and 90 degrees and a height of similar to 1mm were made of thin graphene films of varying thicknesses (2.5-mu m and 8-mu m). 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 similar to 100-420 mu A). The short-term current fluctuations stayed within 8%-14%. The graphene film emitter with a tip angle of 90 degrees and 8-mu m thick yielded a high field emission current of up to 2.2mA at 9V/mu m. 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 <1A. The integral energy distributions of electrons at higher currents showed single broad emission spectra with a width of up to 1-2eV. Additionally, graphene point emitters were characterized in various vacuum environments (Xe, Ar, N-2, H-2, O-2, and air), different pressure levels (2x10(-4)Pa, 2x10(-3)Pa, and 2x10(-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.