Date of Award

Fall 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical/Computer Engineering

Committee Director

Helmut Baumgart

Committee Member

Gon Namkoong

Committee Member

Qiliang Li

Committee Member

Christopher Bailey

Abstract

Thermoelectrics is a green renewable energy technology that plays an important role in power generation due to its potential in generating electricity out of waste heat. The main challenge for the development of thermoelectrics is its low conversion efficiency. One key strategy to improve conversion efficiency is focused on reducing the thermal conductivity of thermoelectric materials. In this thesis, the novel phononic engineering concept was implemented by conformal ALD deposition of PbTe, PbSe thermoelectric films, and PbTe/PbSe nanolaminates on patterned silicon substrates in order to improve the thermoelectric performance of the thermoelectric films. The silicon substrates were lithographically patterned with a mask into porous templates with a regular or staggered pore arrangement and alternatively into stripe and trench patterns. The effect of nano-patterning on the Seebeck coefficient, electrical conductivity, and thermal conductivity of the thermoelectric films was studied experimentally. The results indicate that usage of porous Si templates simultaneously enhances the Seebeck coefficient and reduces thermal conductivity. A ZT enhancement was acheieved in porous ALD PbTe/PbSe nanolaminates by a factor of up to three at a temperature of 500 K. Therefore, the novel concept and engineering approach of phonon engineering has been successfully rendered. For the case of stripe patterning nano-structures, the simulation results indicate a ZT enhancement was expected in the structures with a mesa stripe width of less than 2 µm and a trench depth larger than 500 nm. For in-plane ZT characterization, a lab-on-a-chip based platform was applied to measure the in-plane Seebeck coefficient, electrical conductivity and thermal conductivity quasi-simultaneously. All of the ALD PbTe and PbSe thin film samples exhibit super low in-plane thermal conductivity κ, which is attributed to grain boundary scattering occurring in polycrystalline ALD PbTe and PbSe films. In addition, we extended our investigation to the thermoelectric properties of hybrid Surface Anchored Metal-Organic-Framework (SURMOF) thin films. TCNQ loaded MOF films exhibit a higher Seebeck coefficient and super low thermal conductivity κ in the temperature range of 290 ~ 350 K, which render MOF films a promising thermoelectric material for thermoelectric applications around room temperature and a potentially inexpensive alternative hybrid organic-inorganic thermoelectric materials.

DOI

10.25777/72dn-tm86

ISBN

9780355778229

ORCID

0000-0003-4724-0426

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