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UU2.01 - Electromechanical Characterization of Semiconducting Nanowires: Enhanced Properties and Novel Techniques 
April 22, 2014   1:30pm - 2:00pm

Nanostructures are expected to be the building blocks of next-generation electronic, electromechanical, and energy harvesting devices. In particular, semiconducting nanowires are envisioned as feasible alternatives for a number of applications such as interconnects, nano-optoelectronic systems, and energy storage and delivery elements for self-powered sensors. This emerging technological importance of nanowires has resulted in increased demand for accurate characterization, as only by quantifying their mechanical, thermal, electrical, physical and chemical properties, thorough understanding of their behavior will be generated. In turn, this understanding will be applied in the design and manufacturing stages, in order to optimize nanostructure synthesis, and nano-system architecture and performance. In this presentation we will summarize our recent work on the characterization of mechanical and electromechanical properties of semiconducting nanowires. As a core experimental technique, we have developed a MEMS-based nanoscale material testing system, designed to serve as a platform for in-situ electron microscopy testing of one dimensional (1-D) nanostructures. We have employed this system to identify mechanical property size effects in ZnO and GaN nanowires. Furthermore, the validity of atomistic force fields commonly used to model these semiconducting materials has been assessed by comparing to experimental findings and quantum mechanical simulations. It will be shown that force fields are accurate enough to capture elasticity size effects but that higher order theories are needed to interpret nanowire failure. In regards to electromechanical properties, we will present Density-functional-theory (DFT) first-principles simulations of ZnO and GaN nanowires that have revealed a piezoelectricity size-effect, where the d33 piezoelectric coefficient increases as the nanowire diameter decreases. We point out that experimental confirmation of the piezoelectricity-size effect, and its characterization in realistic nanowire sizes (10-100 nm) is of critical importance. To address this challenge, we present a novel AFM-based approach to characterize the piezoelectric tensor of nanowires and the results obtained with this method for GaN nanowires. The experimental results reveal that for realistic nanowire sizes (50 nm < diameter <200 nm), higher piezoelectric coefficients, up to six times the values of bulk, can be observed. We will close by presenting recent developments in MEMS in-situ electron-microscopy testing of nanowire piezoresistance. In particular, a novel device for four-point electromechanical characterization will be described. Initial results on the characterization of resistance variation with applied strain will be demonstrated for silver and silicon nanowires.

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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