Graphene-Based High Current Density Electron Emitters for THz-VEDs

One of the critical technologies for the development of a compact high-power terahertz (THz)-VEDs is the requirement of efficient cathodes with emission density in excess of 1000 A/cm2. In view of this, it is proposed to develop graphene-based field emitters with low electrical resistivity. Average ~100-nm ultrathin free-standing reduced graphene oxide (rGO) films (4 mm $\times4$ mm) were developed using modified hummers method followed by hydrothermal technique and thermal reduction. The $I-V$ characterization of the developed film was carried out in specially designed UHV chamber in closely spaced diode (CSD) mode. The maximum current density obtained from the rGO film was ~500 A/cm2 at 4 V/ $\mu \text{m}$ . Further improvement in the current density was achieved by doping tungsten ( $W$ ) into rGO film using dc sputtering followed by thermal annealing. The average resistivity of the film was found to be very low $\sim 15\,\,\times \,\,10^{-7}\,\,\Omega $ -m, due to the uniform doping of $W$ nanoparticles into the film. The emission characterization result showed that this $W$ -rGO film could deliver a maximum current density in excess of 1500 A/cm2 at 4 V/ $\mu \text{m}$ , which makes it a potential candidate for use in THz-VEDs applications.