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R8.01 - Piezotronic Effect in Electrochemical Processes and Soar Energy Conversion 
April 24, 2014   1:30pm - 2:00pm

The piezotronic effect describes the coupling of piezoelectric polarization and the intrinsic electric field in a space charge region for the purpose of tuning charge transport behaviors of semiconductor materials and devices. The piezotronic effect has a significant influence on the heterostructure’s electronic properties by precise modification of the interfacial energetics via mechanical strain. The merit of this approach is that it allows for a device to be composed of materials which are still individually optimized for their specific bulk electronic properties while allowing the independent optimization of their heterointerface. We first discuss barrier-height engineering of a heterogeneous semiconductor interface manifested by a PEC half-cell, where the influence of the remnant piezoelectric polarization on the photocurrent of water splitting was studied as a function of strain applied to the anode. The direct interaction between piezoelectric polarization and electrochemical processes is denoted as piezocatalysis effect. This provides a direct pathway for mechanical to chemical energy conversion. By straining a piezoelectric ferroelectric PMN-PT beam in water, we experimentally demonstrated that piezoelectric potential can raise the energy of electrons at the surface of piezoelectric material (or electrode) to such a level that is sufficient to drive proton reduction reactions within its immediate vicinity. The piezocatalytic efficiency (~0.2% - ~2.4%) was found to depend sensitively upon the length of straining state, consistent with the limitations imposed by electrochemical reaction kinetics in the DI water environment. The piezotronic effect has also been applied to the ZnO/PbS quantum dot (QD) heterojunction for engineering the interfacial band structure and depletion region. This method escalated the solar energy efficiency by 30% when a relatively small strain -0.25% was applied to the QDSC under low-intensity illumination. The enhancement of short circuit current and efficiency was mostly due to the expansion of depletion region in PbS, as a result of piezoelectric polarization-induced charge redistribution at the ZnO/PbS interface. These initial investigations of the piezotronic effect open a new route toward efficient and effective energy harvesting and conversion, particular in the flexible systems where strain could be significant.

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis