Nitride metal - semiconductor superlattices for solid state thermionic energy conversion
Abstract
With the current energy crisis, efficiency of thermal systems is becoming ever more important. Furthermore, as the cost of energy goes up, methods to increase efficiencies of these systems become more and more cost-effective. Waste heat from engines and power plants is a readily available source of energy that, for the most part, is not being used. Using this waste heat therefore represents the easiest method for energy recovery and generation and can result in a higher overall system efficiency. The research is focused on the direct conversion of waste heat (and in some niche applications, non-waste heat) into electricity. The method for conversion, however, differs from that of standard thermoelectric generators. Thermoelectrics tend to be homogenous materials, typically semiconductors. In contrast, the non-homogenous solid state thermionic emission device uses a layered structure of metals and semiconductors with nanometer-scale layer thicknesses. By using this structure, thermal conductivity is greatly reduced as compared to the constituent materials by means of interface scattering. In addition, if ballistic transport across the semiconductor layer can be realized, the energy in the electrons is preserved, resulting in an increased Seebeck Coecient. By these methods, the figure of merit of our devices (ZT) has been shown in theory to be much higher than currently reported devices at the temperature of interest (900 K). To this end, superlattices of ZrN/ScN and HfN/ScN have been grown via reactive D.C. magnetron sputtering. Characterization of the grown lms has been carried out using X-ray diffraction, SEM and TEM. In addition, the initial development of testing structures has been carried out. The creation of these structures using photolithography as well as wet and dry etching techniques is in the preliminary stages.
Degree
Ph.D.
Advisors
Sands, Purdue University.
Subject Area
Electrical engineering|Materials science
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