Browsing by Subject "Nonthermal Plasma"

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    Enhancing the Figure of Merit, ZT, of Silicon Germanium Nanocrystal Films by Synthesizing Dense Films using Nonthermal Plasma and Post Processing
    (2018-05) Mishra, Sadhana
    A thermoelectric material’s dimensionless figure of merit (ZT) determines the efficiency of conversion of heat into electricity of a thermoelectric generator (TEG). Increase in ZT, increases the efficiency of a thermoelectric generator. The figure of merit increases with increase in material’s electrical conductivity and Seebeck coefficient while decreases with an increase in thermal conductivity. Recently, the ZT of silicon germanium alloys have been increased by nanostructuring the bulk which lead to decrease in thermal conductivity by increase in phonon scattering due to nanoscale crystal grain sizes. Plasma synthesised doped silicon germanium nanocrystals have a narrow size distribution and are promising candidates as opposed to ball-milled nanopowder. Nanocrystals produced by plasma synthesis needs to be fabricated as thin films for microelectronic applications. Nanocrystal films synthesised, by rastering of substrates, in the nonthermal plasma reactor are very porous and hence have low electrical conductivity. To produce denser nanocrystal films, the plasma reactor was modified and post processes were introduced. Mixed-phase silicon films were produced by dual-plasma setup and these films were annealed to form fully nanoscrystalline silicon films. The mixed-phase and fully nanocrystalline silicon films were determined to have low porosity. These films were characterized for their crystallinity, thickness and the average crystal grain size. After characterization of the mixed-phase and nanocrystalline silicon films, the thermoelectric properties (Seebeck coefficient, thermal conductivity and electrical conductivity) were determined and hence the ZT. This ZT was determined with just silicon and thus low. Future work can be undertaken with mixed-phase film composed of doped silicon germanium alloy and to determine the thermoelectric properties.
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    Nanostructures, Nanoparticles, and 2D Materials from Nonthermal Plasmas
    (2021-02) Beaudette, Chad
    The bottom-up synthesis of thin films, nanostructures, and nanoparticles from nonthermal plasmas has been limited largely to both gas-phase and highly-volatile carbon precursors. This has stymied the application of nonthermal plasmas to several new types of materials as there are often no gas-phase or highly volatile precursors that exist for their synthesis. The sublimation of solid and low volatility liquid precursors are used here to expand the realm of new materials towards sulfide Van der Waals 2D materials, high surface area nitride nanostructured plasmonic materials, nitrogen-doped oxide nanoparticles, and crystalline metal aluminum nanoparticles. Plasmonic photodetectors and photocatalytic nanoparticles are demonstrated herein to show the utility of some of the as produced materials. Moreover, traditional nanoparticle reactor limitations such as metallic film deposition between the exciting electrode and the plasma are discussed and new reactors are developed to overcome such limitations. In addition, parameters such as the location of the powered electrode and the location of the gas inlets relative to one another are critical to the production of better materials and examples will be demonstrated herein.