Photo- and thermionic emission from potassium-intercalated carbon nanotube arrays

Carbon nanotubes CNTs are promising candidates to create new thermionicand photoemission materials. Intercalation of CNTs with alkali metals, such as potassium, greatly reduces their work functions, and the low electron scattering rates of small-diameter CNTs offer the possibility of efficient photoemission. This work uses a Nd:YAG YAG denotes yttrium aluminum garnet laser to irradiate singleand multiwalled CNTs intercalated with potassium, and the resultant energy distributions of photoand thermionic emitted electrons are measured using a hemispherical electron energy analyzer over a wide range of temperatures. For both singleand multiwalled CNTs intercalated with potassium, the authors observe a temperature dependent work function that has a minimum of approximately 2.0 eV at approximately 600 K. At temperatures above 600 K, the measured work function values increase with temperature presumably due to deintercalation of potassium atoms. Laser illumination causes the magnitudes of collected electron energy distributions to increase substantially but in many cases has little effect on their shape. Simple theoretical models are also developed that relate the photoand thermionic emission processes and indicate that large numbers of photoexcited electrons partially thermalize i.e., undergo one or more scattering events before escaping from the emitter surface. © 2010 American Vacuum Society. DOI: 10.1116/1.3368466