Reports: DNI1048800-DNI10: Nanowire Thermoelectrics for Energy Conversion

Xuan Gao , Case Western Reserve University

The main objective of this project is to explore one-dimensional quantum confinement effects in tailoring the thermoelectric properties of semiconductor nanowires. Over the past year, the PI’s group continued to make progress towards this goal. Meanwhile, efforts were spent on several emerging directions in nanomaterial synthesis and electronic properties. Our research efforts have resulted two publications during this grant period (one in ACS Nano and the other in Advanced Functional Materials). The main progress and findings are summarized below.

Characterizing the thermoelectric power of single nanowire is not a trivial task. Sophisticated microfabrication, device calibration are needed together with the growth of high quality semiconductor nanowires and contacting them one at a time. In this regard, we have made significant progress in the past year. Upon the departure of the previous postdoc who was supported by this grant, a visiting graduate student from Chinese Academy of Sciences was assigned to take over the project. Up till now, she has successfully fabricated, and measured the thermoelectric power of two individual InAs nanowires, together with a comprehensive calibration of the micro-thermometers on device. Our results showed strong gate modulation of the thermoelectric power in InAs nanowires, indicating that the one-dimensional quantum confinement effect may indeed be at work. The results are being prepared as a manuscript and more devices are being measured right now.

Another interesting nanomaterial that we explored during this grant period is Bi2Se3 nanowires and nanoribbons. Traditionally known as a good thermoelectric material, Bi2Se3 is found to belong to a new class of quantum materials, ‘topological insulators’ in which the Dirac surface states are conductive and protected by time-reversal symmetry and the topology of the band structure. We synthesized nanowires and nanoribbons of Bi2Se3 and studied their electrical transport properties. Our experiments revealed a novel linear magneto-resistance effect in the perpendicular field configuration. We further proved that this effect has a purely two-dimensional nature and therefore it is most likely originating from the two-dimensional surface states. These results were published in ACS Nano recently. With the partial support of this grant, we also collaborated with Sankaran group at CWRU chemical engineering and achieved growing InAs nanowires in pattern areas of metal nanoparticles made by plasma electrochemical reduction. This result was published in Advanced Functional Materials.

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