Measurement of thermionic electron emission from modified graphene petals
Abstract
Crystalline carbon nanomaterials such as nanotubes, nanofibers, and graphite have been studied widely as electron emitters. In order to interpret the electron emission characteristics of these samples, it is necessary to quantify the work function of the structure, which depends on the constituent materials as well as the atomic structure. In this study, thermionic electron emission from carbon nanosheet extensions grown on graphite pitch fibers and highly oriented pyrolytic graphite (HOPG) is measured using a hemispherical energy analyzer. The petal-like structures are synthesized by microwave plasma chemical vapor deposition (MPCVD) and consist of 5-25 layers of graphene. Samples prepared by this method are of particular interest because the maintenance of crystallinity at the graphite-graphene boundary is conducive to improved thermal and electrical transport. Methods for modifying the aforementioned structures via electrochemical deposition of Pd nanoparticles and intercalation with potassium are developed with the intent of decreasing work function and increasing emission current. Emission from these altered structures is measured and compared to data for the unaltered samples. K-intercalation appears to be a promising route to reducing work function of petal structures grown on HOPG. In the most extreme case, a work function shift from 4.27 eV to 1.66 eV was observed after intercalation. Additionally, illumination of the sample with a light source has been used to increase the emission intensity by up to 2 orders of magnitude. The role of Pd-decoration of defects in the inhibition of K-intercalation is also investigated, and preliminary results suggest this defect blocking is effective in controlling K uptake during intercalation.
Degree
M.S.E.
Advisors
Fisher, Purdue University.
Subject Area
Mechanical engineering|Nanotechnology
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