Thermoelectric metal nanostructures: Disorder, plasmons, and photodetection

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Abstract:Nontechnical:The flow of heat and electric charge are coupled together, and these thermoelectric effects underpin diverse critical technologies, including thermostats, electrically driven refrigerators, and photodetectors. Thermoelectric properties can be engineered by structuring materials on the nanoscale. Using a scanning laser as a moveable heat source, the PI's group has revealed unexpected thermoelectric effects even in nominally simple metal structures. Specifically, grain boundaries and surface chemistry can modify thermoelectric response, and greatly enhanced photo-voltages are possible in structures where electrons have to "tunnel" across a nanoscale gap between metal electrodes. This project will confirm the mechanisms behind these surprising features, and build upon this knowledge to create and characterize prototypes of new photodetectors based on metal optical antennas. While not as sensitive as semiconductor-based photodetectors, metal optical antenna systems are geometrically tunable, have different noise processes, and can be simpler to fabricate. Results will be disseminated via publications, presentations at conferences, and popular writings by the PI on his blog. This project will provide training and professional development to graduate students and undergraduate researchers, aiding in the creation of the next generation of a technologically skilled and innovative workforce. The PI will also work with K12 teachers and undergraduates from other institutions through ongoing Rice programs. Through his blog and writings in collaboration with the Houston Chronicle, the PI will continue to popularize nanoscale science and engineering in general, and this project's research outcomes in particular.Technical:Nanostructured thermoelectric devices have enormous potential as technologies and as tools to acquire the basic scientific and engineering knowledge necessary to control and optimize the flow of energy at the nanoscale. By coupling electronic transport measurements and illumination via a scanning laser microscope, the PI's group has found unexpected photothermoelectric effects in nominally simple metal nanostructures. Metal nanowires demonstrate previously unreported inhomogeneities in Seebeck response, indicating that grain boundaries and surface chemistry can be tools for engineering thermoelectric response. Nanoscale tunneling gaps between metallic electrodes show greatly enhanced photovoltages compared to nontunneling structures, with material and polarization dependences that are consistent with plasmon-enhanced hot electron tunneling as the mechanism. The intellectual merit of this project lies in its three specific research goals: quantifying and engineering photothermoelectric effects in metal nanostructures through control of surface conditions (via self-assembled monolayers) and grain structure; understanding and optimizing greatly enhanced thermoelectric effects in nanogaps; and demonstrating photodetectors based on these enhanced photothermoelectric effects, looking at sensitivity and noise properties. The PI's team of graduate and undergraduate students will collaborate with theorists in modeling the optoelectronic and thermal transport processes at work in these structures, providing critical feedback for optimization of response. Results will be disseminated broadly through publications, presentations at conferences, and when appropriate the PI's blog. This project will provide training and professional development to graduate students and undergraduate researchers, aiding in the creation of the next generation of a technologically skilled and innovative workforce. The PI will also work with K12 teachers and undergraduates from other institutions through ongoing Rice programs. Through his blog and writings in collaboration with the Houston Chronicle, the PI will continue to popularize nanoscale science and engineering in general, and this project's research outcomes in particular.