Thermal and thermoelectric transport measurements of one-dimensional nanostructures
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This dissertation presents thermal and thermoelectric transport measurements of onedimensional nanostructures including bismuth telluride (BixTe1-x) nanowires and singlewalled carbon nanotubes (SWCNT). Theoretical calculations have predicted that BixTe1-x nanowires may have enhanced thermoelectric figure of merit defined as ZT = (S2 σ/κ)T, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. Our measurements showed that the σ of BixTe1-x nanowires was very close to, and the κ was largely reduced compared to the bulk values at 300 K. For a BixTe1-x nanowire with x ≈ 0.46, the room temperature S of 260 µV/K was 60% higher than that of its bulk counterpart, while small negative S was measured for four nanowires with x ≈ 0.54. High ZT can be expected for BixTe1-x nanowires with optimized x. The unique electron transport and heat dissipation mechanisms in current – carrying metallic and semiconducting SWCNTs were studied with the use of Scanning Probe Microscopy (SPM) methods including Electrostatic Force Microscopy (EFM), Scanning Gate Microscopy (SGM) and Scanning Thermal Microscopy (SThM). For several metallic SWCNTs with low-bias resistance above 40 x 103 Ω, the electrical potential profile along the SWCNTs was linear at a voltage bias of 0.1 V, suggesting that the electron mean free path was shorter than the length of the nanotube at the low bias. Heat dissipation along these metallic SWCNTs was uniform at voltage biases above 0.22 V. For several semiconducting SWCNTs with low-bias resistance as low as 20 x 103 Ω, large conduction barriers were induced by SGM probes at locations where defects existed, and the heat dissipation was uniform at voltage biases above 0.12 V. This observation suggests diffusive and dissipative heat dissipation in semiconducting SWCNTs. A large tip-sample thermal contact resistance has made it challenging to obtain the actual temperature rise of the sample surface using the SThM method. We have developed a nanocontact thermometry technique that can potentially be employed for quantitatively mapping surface temperature profiles of nanoelectronics with spatial resolution below 20 nm. This method was tested with metal interconnect structures.