Dr. Robert W. Cohn
Department of Electrical & Computer Engineering
University of Louisville
Louisville, KY 40292
Phone: 502-852-7077
Email: rwcohn@louisville.edu
A scanning electron microscope and a nanomanipulator system that has four independently movable probe is being modified to perform electron emission studies from nanomaterials, including pure and low work function material decorated nanotubes, monolayer graphene, nanowires and UofL's novel tapered nanopipettes. The nanomanipulator is being outfitted with hot and cold stages to enable the study field emission, thermal-field emission and thermionic emission, both in two terminal (diode) and three terminal (triode) measurements. The nanomanipulator provides the ability to study emission from single, high aspect ratio nanostructures which will be used to quantify the effects of material work function, geometric relationships between the anode-cathode-gate. An especially interesting aspect of the study is the ability to probe graphene edges cut at various orientations to the graphene lattice, which is expected to produce variations in emission characteristics. Overall these studies are intended to characterize individual emitters with the goal of finding conditions at which freely available waste heat can be converted to electrical energy in excess of the amount of electrical power consumed. In addition to experimental measurements, available published models on field and thermionic emission will be coded and used to help design the preferred measurement geometry and material selection. This software tool will also be used to enable a fair comparison of our results with published reports.
This study is closely linked to two other studies: One is the Sumanasekera group's measurements of emission and electron energy spectra from carpets of the same nanomaterials,that we are studying as single, isolated materials in the SEM.
The other is P. Menguc's group's models of radiant energy transfer, which can reduce the thermal difference between anode and cathode. The thermal transfer can be especially profound where there can be enhanced transfer due to evanescent enhancement (similar to tunneling) across the small gap between the anode and cathode. We will discuss with the Menguc group, possibilities for introducing hot mirrors--perhaps in the form of graphene sheet gates, into the system.
mehanna@engr.uky.edu