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

• Published in: IEEE transactions on plasma science Vol. 50; no. 9; pp. 2864 - 2869
• Main Authors: Singh, A. K., Shukla, S. K., Rawat, V. S., Singh, T. P., Manna, S., Barik, R. K.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-09-2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Cathodes; Chemicals; Current density; Doping; Electrical resistivity; Emission; Emitters; Emitters (electron); Field emitters; Graphene; graphene oxide (GO); Nanoparticles; reduced graphene oxide (rGO); Surface treatment; Thermal reduction; Tungsten; vacuum electron devices (VEDs); Vacuum technology; X-ray scattering
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2022.3198790

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 <inline-formula> <tex-math notation="LaTeX">\times4 </tex-math></inline-formula> mm) were developed using modified hummers method followed by hydrothermal technique and thermal reduction. The <inline-formula> <tex-math notation="LaTeX">I-V </tex-math></inline-formula> 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/<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>. Further improvement in the current density was achieved by doping tungsten (<inline-formula> <tex-math notation="LaTeX">W </tex-math></inline-formula>) into rGO film using dc sputtering followed by thermal annealing. The average resistivity of the film was found to be very low <inline-formula> <tex-math notation="LaTeX">\sim 15\,\,\times \,\,10^{-7}\,\,\Omega </tex-math></inline-formula>-m, due to the uniform doping of <inline-formula> <tex-math notation="LaTeX">W </tex-math></inline-formula> nanoparticles into the film. The emission characterization result showed that this <inline-formula> <tex-math notation="LaTeX">W </tex-math></inline-formula>-rGO film could deliver a maximum current density in excess of 1500 A/cm2 at 4 V/<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>, which makes it a potential candidate for use in THz-VEDs applications.