Contact Information

Dr. Gamini U. Sumanasekera
Department of Physics
University of Louisville
Louisville, KY 40291
Phone: 502-852-9019
E-mail: gamini.sumanasekera@louisville.edu

Thermionic Emission Based Energy Conversion Research

Thermionic energy conversion utilizes the electron emission from appropriate materials to transform thermal energy into electrical energy. An emitter maintained at an elevated temperature and separated from a cooler collector by a narrow vacuum gap can generate a thermionic voltage. However efficient thermionic emitters require low work function materials. This study is primarily aimed at developing novel nanostructures exhibiting low work function materials in addition to other intrinsic properties such as diminished space charge formation.

Diamond nanocrystals grown at the tips of carbon nanopipettes will be studied for efficient thermionic power conversions. Attempts will be made for selective doping of diamond nanocrystals to take advantage of the negative electron affinity in addition to the geometrical enhancement due to the conical structure of the carbon nanopipettes.

A custom made UHV system equipped with an ion-pump is employed for the characterization of the field emission and thermionic emission properties of carbon nanopipettes grown on planar substrates. The cathode (material of interest) is mounted on a ceramic heater that can be heated to temperatures above 1200 0C. The anode is mounted onto a micro manipulator for precise control of the separation between the cathode and the anode with provisions for the flow of a coolant. As a model system, ultra-long (exceeding 1 cm) multiwalled carbon nanotube forests will be studied to better understand the properties such as field enhancement factor and field screening effect. Kelvin probe technique and ultraviolet photoelectron spectroscopy will be routinely used for the determination of the work function of the cathode material subjected to various modifications and doping. Suitable spacers will be designed to maintain the constant temperatures at both electrodes. The energy distribution of the thermionically emitted electrons will be studied in situ using a hemispherical analyzer in a UHV system.