Photo- and Thermionic Emission From Potassium-Intercalated Single-Walled Carbon Nanotube Arrays

Abstract

Vacuum thermionic electron emission has been considered for many years as a means to convert heat or solar energy directly into electrical power. However, an emitter material has not yet been identified that has a sufficiently low work function and that is stable at the elevated temperatures required for thermionic emission. Recent theoretical models predict that photonic and thermal excitation can combine to significantly increase overall efficiency and power generation capacity beyond that which is possible with thermionic emission alone. Carbon nanotubes (CNTs) intercalated with potassium have demonstrated work functions as low as 2.0 eV, and low electron scattering rates observed in small diameter CNTs offer the possibility of efficient photoemission. This study uses a Nd:YAG laser to irradiate potassium-intercalated single-walled CNTs (K/SWCNTs), and the resultant energy distributions of photo- and thermionic emitted electrons are measured using a hemispherical electron energy analyzer for a wide range of temperatures. We observe that the work function of K/SWCNTs is temperature dependent and has a minimum of approximately 2.0 eV at approximately 600 K. At temperatures above 600 K, the measured work function K/SWCNTs increases with temperature, presumably due to deintercalation of potassium atoms.