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<p class="MsoNormal" align="center" style="text-align:center;line-height:150%"><b><span style="font-family:"Times New Roman"">PhD Defense Student:
</span></b><span style="font-family:"Times New Roman"">Milad Yarali<b><o:p></o:p></b></span></p>
<p class="MsoNormal" align="center" style="text-align:center;line-height:150%"><b><span style="font-family:"Times New Roman"">Date:
</span></b><span style="font-family:"Times New Roman"">Friday, December 1, 2017<b><o:p></o:p></b></span></p>
<p class="MsoNormal" align="center" style="text-align:center;line-height:150%"><b><span style="font-family:"Times New Roman"">Time:
</span></b><span style="font-family:"Times New Roman"">9:30 AM<b><o:p></o:p></b></span></p>
<p class="MsoNormal" align="center" style="text-align:center;line-height:150%"><b><span style="font-family:"Times New Roman"">Location:
</span></b><span style="font-family:"Times New Roman"">College of Social Work, Room SW 229<b><o:p></o:p></b></span></p>
<p class="MsoNormal" align="center" style="text-align:center;line-height:150%"><b><span style="font-family:"Times New Roman"">Dissertation Chair:
</span></b><span style="font-family:"Times New Roman"">Dr. Anastassios Mavrokefalos<b><o:p></o:p></b></span></p>
<p class="MsoNormal" align="center" style="text-align:center;line-height:150%"><b><span style="font-family:"Times New Roman"">Title:<o:p></o:p></span></b></p>
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<b><span style="font-family:"Times New Roman"">Thermal and Thermoelectric Transport Measurements of Silicon Nanomembranes, Transition Metal Dichalcogenides, and Carbon Nanotube Networks<o:p></o:p></span></b></p>
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<span style="font-family:"Times New Roman"">Deep understanding and manipulating of energy transport characteristics in nanoscale systems<sup>
</sup>is of fundamental importance in realizing high-performance solid-state devices. As dimension of these devices progressively shrink, the size effect of nanostructures, their interfacial scattering and interactions with the surrounding environment are increasingly
dominating the electron and phonon transport properties. The objective of the work presented in this dissertation is to further the current understanding of interplay between structure and thermal and thermoelectric properties in nanofilm materials through
experimental investigations. This objective is accomplished by utilizing a micro-fabricated device to preform coupled electrical-thermal-structural characterizations on the same individual nanofilm suspended between two resistance thermometers.
<o:p></o:p></span></p>
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<span style="font-family:"Times New Roman"">First, an approach was developed to manage thermal conductivity (<i>ê</i>) of Si thin-film based nanoarchitectures through the formation of radial and planar Si/SiO<sub>x</sub> hybrid nanomembrane superlattices (HNMSLs).
For the 24 nm thick one-winding tube at room temperature </span><i><span style="font-family: Symbol;">k</span></i><i><span style="font-family: 'Times New Roman';">
</span></i><span style="font-family: 'Times New Roman';">= 7.64 W m<sup>-1 </sup>
K<sup>-1</sup> which is 20 times smaller than the value of </span><span style="font-family:"Times New Roman"">bulk single-crystalline silicon. Interestingly, a continuous reduction in
</span><i><span style="font-family:Symbol;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman";mso-bidi-font-family:
"Times New Roman";mso-char-type:symbol;mso-symbol-font-family:Symbol">k</span></i><span style="font-family:"Times New Roman"">
with increasing number of windings was observed. Meanwhile, the planar Si/SiO<sub>x</sub> HNMSL shows
</span><i><span style="font-family: Symbol;">k</span></i><i><span style="font-family: 'Times New Roman';">
</span></i><span style="font-family: 'Times New Roman';">= 5.3 W m<sup>-1 </sup>K<sup>-1</sup>, being
</span><span style="font-family:"Times New Roman"">the smallest in-plane thermal conductivity among all the reported values for Si-based superlattices.
<o:p></o:p></span></p>
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<span style="font-family:"Times New Roman"">Next, the effect of metal doping and intrinsic structural defects on
<i>ê</i> of monolayer undoped MoS<sub>2</sub> and MoSe<sub>2</sub>, and doped Mo<sub>0.82</sub>W<sub>0.18</sub>Se<sub>2</sub> grown by chemical vapor deposition were investigated. The results show the grain boundaries and vacancies are responsible for over
2 times reduction in the room temperature <i>ê</i> in our samples compared to their exfoliated counterpart, while
<i>ê</i> </span><span style="font-family:"Times New Roman";mso-fareast-font-family:
"MS MinNew Roman"">remains intact upon isoelectronic substitution of
</span><span style="font-family: 'Times New Roman';">W for Mo atoms.</span><span style="font-family:"Times New Roman""> Also, boundary scattering dominates over defects and phonon-phonon scattering at low temperatures.<o:p></o:p></span></p>
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<span style="font-family:"Times New Roman""> Lastly, the effect of physisorbed vs chemisorbed oxygen on transport properties of aligned single walled carbon nanotubes (SWCNT) nanofilm was investigated. The physisorbed oxygen molecules on the SWCNTs
surface make them initially p-type with metallic behavior. Vacuum annealing leads to desorb these molecules resulting in transition to n-type with semiconducting behavior while
<i>ê</i> remains intact. On the other hand, SWCNTs with chemisorbed oxygen molecules exhibit purely p-type metallic behavior with lower
<i>ê</i>.<o:p></o:p></span></p>
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