Carbon nanotube fiber field emission cathodes

Abstract

Summary form only given. Field emission (FE) cathodes made from carbon nanotube (CNT) fibers have demonstrated high emission currents, low turn-on voltages, long lifetimes and offer considerable potential for use as electron sources for vacuum electronic devices. CNT fibers were fabricated by wet-spinning of pre-made CNTs ¹ and consist of CNT fibrils held together by van der Waals forces. The fibers were 10-100 μm in diameter and their morphology was controlled by fabrication method, processing conditions, as well as purity, size, and type of the CNT starting material. Thermal and electrical conductivity was measured with the 3-omega method, and fiber density was determined with transmission electron microscopy. Wide angle x-ray diffraction was used to measure fiber alignment. Fibers with the highest density, alignment, thermal and electrical conductivity had the best field emission performance. Recent results have demonstrated a single 5 mm long fiber with a 20 μm diameter emitting 5.2 mA before failure, and 6.1 mA when treated with Boron Nitride ² . Residual gas analysis (RGA) was used to identify the species desorbed during field emission and model was developed for the transition from adsorbate-enhanced FE at low bias to FE from pure CNTs at high bias ³ . Infrared images of CNT fibers during FE have been captured with an InGaAs array camera, showing temperatures of ~600°C while emitting currents of ~4mA. Mechanisms of fiber heating during FE, to include Joule and Nottingham effects, were investigated. Calculated thermal performance based on measured thermal conductivity is presented, and comparisons between observed and calculated thermal performance are discussed.