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Research Letter

Fabrication, microstructure, and enhanced thermionic electron emission properties of vertically aligned nitrogen-doped nanocrystalline diamond nanorods Kamatchi Jothiramalingam Sankaran, Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium; IMOMEC, IMEC vzw, 3590 Diepenbeek, Belgium Sujit Deshmukh, Department of Physics, School of Natural Sciences, Shiv Nadar University, NH-91, Tehsil Dadri, Gautam Buddha Nagar, Uttar Pradesh 201314, India Svetlana Korneychuk, Electron Microscopy for Materials Science (EMAT), University of Antwerp, 2020 Antwerp, Belgium Chien-Jui Yeh, Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan, Republic of China Joseph Palathinkal Thomas, WATLab and Department of Chemistry, University of Waterloo, Waterloo, N2L3G1 Ontario, Canada Sien Drijkoningen, Paulius Pobedinskas, and Marlies K. Van Bael, Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium; IMOMEC, IMEC vzw, 3590 Diepenbeek, Belgium Johan Verbeeck, Electron Microscopy for Materials Science (EMAT), University of Antwerp, 2020 Antwerp, Belgium Keh-Chyang Leou, Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan, Republic of China Kam-Tong Leung, WATLab and Department of Chemistry, University of Waterloo, Waterloo, N2L3G1 Ontario, Canada Susanta Sinha Roy, Department of Physics, School of Natural Sciences, Shiv Nadar University, NH-91, Tehsil Dadri, Gautam Buddha Nagar, Uttar Pradesh 201314, India I-Nan Lin, Department of Physics, Tamkang University, 251 Tamsui, Taiwan Ken Haenen, Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium; IMOMEC, IMEC vzw, 3590 Diepenbeek, Belgium Address all correspondence to Kamatchi Jothiramalingam Sankaran and Ken Haenen at [email protected] and ken.haenen@ uhasselt.be (Received 21 June 2018; accepted 26 July 2018)

Abstract Vertically aligned nitrogen-doped nanocrystalline diamond nanorods are fabricated from nitrogen-doped nanocrystalline diamond films using reactive ion etching in oxygen plasma. These nanorods show enhanced thermionic electron emission (TEE) characteristics, viz., a high current density of 12.0 mA/cm2 and a work function value of 4.5 eV with an applied voltage of 3 V at 923 K. The enhanced TEE characteristics of these nanorods are ascribed to the induction of nanographitic phases at the grain boundaries and the field penetration effect through the local field enhancement from nanorods owing to a high aspect ratio and an excellent field enhancement factor.

Introduction The conversion of thermal waste energy into electrical energy makes thermionic electron emission (TEE) a promising renewable energy source. Contrary to the field electron emission behavior, in which the emitted electrons are extracted from the materials due to band bending induced by an external applied field, TEE implies the heat-induced emission of charge carriers over a surface-potential barrier typically into vacuum spa