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Virginia Tech

1. Myers, Kirby. Experiments on the Thermal, Electrical, and Plasmonic Properties of Nanostructured Materials.

Degree: PhD, Physics, 2018, Virginia Tech

Nanofabrication techniques continue to advance and are rapidly becoming the primary route to enhancement for the electrical, thermal, and optical properties of materials. The work presented in this dissertation details fabrication and characterization techniques of thin films and nanoparticles for these purposes. The four primary areas of research presented here are thermoelectric enhancement through nanostructured thin films, an alternative frequency-domain thermoreflectance method for thin film thermal conductivity measurement, thermal rectification in nanodendritic porous silicon, and plasmonic enhancement in silver nanospheroids as a reverse photolithography technique. Nanostructured thermoelectrics have been proposed to greatly increase thermopower efficiency and to bring thermoelectrics to mainstream power generation and cooling applications. In our work, thermoelectric thin films of SbTe, BiTe, and PbTe grown by atomic layer deposition and electrochemical atomic layer deposition were characterized for enhanced performance over corresponding bulk materials. Seebeck coefficient measurements were performed at temperatures ranging from 77 K to 380 K. Atomic composition was verified by energy-dispersive X-ray spectroscopy and structures were imaged by scanning electron microscopy. All thin films measured were ultimately found to have a comparable or smaller Seebeck coefficient to corresponding materials made by conventional techniques, likely due to issues with the growth process. Frequency-domain thermoreflectance offers a minimally invasive optical pump-probe technique for measuring thermal conductivity. Like time-domain thermoreflectance, the version of frequency-domain thermoreflectance demonstrated here relies on a non-zero thermo-optic coefficient in the sample, but uses moderate cost continuous wave lasers modulated at kHz or MHz frequencies rather than a more expensive ultrafast laser system. The longer timescales of these frequency ranges enables this technique to take measurements of films with thicknesses ranging from 100 nm to 10 um, complimentary to time-domain thermoreflectance. This method differentiates itself from other frequency-domain methods in that it is also capable of simultaneous independent measurements of both the in plane and out of plane values of the thermal conductivity in anisotropic samples through relative reflective magnitude, rather than phase, measurements. We validated this alternate technique by measuring the thermal conductivity of Al2O3 and soda-lime and found agreement both with literature values and with separate measurements obtained with a conventional time-domain thermoreflectance setup. Thermal rectification has the potential to enhance microcircuit performance, improve thermoelectric efficiency, and enable the creation of thermal logic circuits. Passive thermal rectification has been proposed to occur in geometrically asymmetric nanostructures when heat conduction is dominated by ballistic phonons. Here, nanodendritic structures with branch widths of ~ 10 nm and… Advisors/Committee Members: Robinson, Hans (committeechair), Arav, Nahum (committee member), Asryan, Levon Volodya (committee member), Heflin, James Randy (committee member).

Subjects/Keywords: Thermoelectrics; Thermoreflectance; Thermal Rectification; Plasmonics; Thin films; Nanospheres

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APA (6th Edition):

Myers, K. (2018). Experiments on the Thermal, Electrical, and Plasmonic Properties of Nanostructured Materials. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/83822

Chicago Manual of Style (16th Edition):

Myers, Kirby. “Experiments on the Thermal, Electrical, and Plasmonic Properties of Nanostructured Materials.” 2018. Doctoral Dissertation, Virginia Tech. Accessed December 12, 2018. http://hdl.handle.net/10919/83822.

MLA Handbook (7th Edition):

Myers, Kirby. “Experiments on the Thermal, Electrical, and Plasmonic Properties of Nanostructured Materials.” 2018. Web. 12 Dec 2018.

Vancouver:

Myers K. Experiments on the Thermal, Electrical, and Plasmonic Properties of Nanostructured Materials. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2018 Dec 12]. Available from: http://hdl.handle.net/10919/83822.

Council of Science Editors:

Myers K. Experiments on the Thermal, Electrical, and Plasmonic Properties of Nanostructured Materials. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/83822

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