Large current emission from carbon nanotubes on metal substrates by chemical-vapor deposition

Carbon nanotubes (CNTs) have attracted considerable attention due to their unique structure, remarkable properties, and their potential for a variety of applications, since their discovery by Iijima in 1991.The nanotube's high field enhancement, high aspect ratios, small tip radii of curvature and high current density make it a nearly ideal electron source for field emission. This paper discusses the production of CNTs produced by cathode self-heated CVD,so that the segment heated in growth is achieved and the temperature is controllable. Unlike the conventional method using silicon as substrates, molybdenum substrates are used. As the conductivity of silicon is not good, there are two techniques to deal with it: One is to use either p-doped or n-doped silicon as substrates. The other is to deposit metal contact layers on pristine silicon. However, using metal, like Mo, brings simplicity to the fabrication.Two kinds of catalysts are compared: sub-nanometer Fe and Al/ Fe bilayer catalyst films. In the same synthesis conditions, different catalysts are utilized to get different CNTs. Field emission characteristics of CNTs with Fe catalyst and CNTs with Al/Fe catalysts are discussed. Results show that emission properties of CNTs with Al/Fe catalysts are better. Also, results demonstrate that the emission current is determined not only by the morphology of CNTs, but also how the CNTs adhere to the electrode below. Good adhesion between CNTs and the substrate leads to easier transmission of electrons from electrodes to the bottom of CNTs. Aging process increased the field emission current of the CNT cathode.