Modeling and Fabrication of Piezoelectric Nanomaterial Devices for Sensing and Energy Harvesting.

Abstract

Piezoelectric nanomaterials are the basis for many devices including sensors and energy harvesters, but more work is needed to realize the advantages of emerging materials and new designs. Barriers to the continued development of these devices include a limited understanding of piezoelectric behavior in emerging nanomaterials, and the limitations of current fabrication techniques. This thesis seeks to overcome these barriers, and fabricate new piezoelectric nanomaterial devices by 1) developing finite element models to explore piezoelectricity in an emerging nanomaterial, and 2) expanding a current fabrication technique to new substrates. Diphenylalanine (FF) peptide is an emerging bio-inspired piezoelectric material. However, limited information is available to predict its piezoelectric performance compared to conventional materials. In addition to piezoelectricity, nanomaterials such as zinc oxide (ZnO) may have semiconducting properties, making them suitable for highly sensitive devices enabled by the piezotronic effect. Chemical vapor deposition (CVD) can produce ultra-long ZnO nanowires, but the high-temperature process is incompatible with flexible polymer substrates, limiting device design. Finite element models were designed to predict piezoelectric potential in FF peptide. A model of a flexible FF peptide nanogenerator was created, and the nanogenerator was fabricated for mechanical energy harvesting. Next, a finite element model was created to investigate a piezotronic, ZnO nanowire-based force sensor for haptics and prosthetics applications. The use of ZnO nanowires grown by CVD was expanded to soft polymer substrates by a mechanical transfer process, to create a piezotronic strain sensor. Lastly, an apparatus for using low-temperature growth substrates inside of a high-temperature CVD furnace was designed and fabricated. Results of finite element models successfully predicted the piezoelectric behavior of a fabricated FF peptide nanogenerator, and suggest that a proposed tactile sensor could exceed the sensitivity of human mechanoreceptors. A mechanical transfer process was used to expand CVD to low-temperature substrates and realize a stretchable piezotronic strain sensor. An apparatus for cooling substrates inside a high-temperature CVD furnace was demonstrated for the synthesis of MoS2 on a low-temperature substrate. Finite element modeling and the expansion of current fabrication techniques can enable new piezoelectric nanomaterial devices for sustainable energy and human health.