Synthesis, characterization and integration of piezoelectric zinc oxide nanowires

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Aguilar, Carlos Andres

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An automatic implantable cardiac defibrillator (AICD) is a device that is implanted in the chest to constantly monitor and, if necessary, correct episodes of arrhythmia. While the longevity of the average AICD patient has increased to 10 years after implantation, only 5% of implants functioned for seven years, and this mismatch poses a significant and ever growing clinical and economic burden. Moreover, there are now efforts to “piggyback” devices on AICDs and BVPs for additional functionality, all of which require more power. An innovative approach towards generating power for AICDs is to harness the energy of the heart by embedding energy generators in AICD leads. The cardiovascular system as a source generator is appealing due to its ability to continuously deliver mechanical energy as long as the patient is alive. Herein a device incorporating nanostructured piezoelectrics was developed as a means to harvest the energy of heart. The generator system integrates inorganic piezoelectric nanomaterials, including aligned arrays of nanowires of crystalline zinc oxide (ZnO), with elastomeric substrates. The design combines several innovative structural configurations including a “wavy” flexible electrode and a layout where the nanowires are near or on the neutral mechanical plane. A wet synthetic strategy to reliably prepare piezoelectric ZnO nanostructures directly onto the devices was also developed and optimized to produce nanowires with high densities, large aspect ratios and high orientation. The elastomeric support permits direct integration within AICD leads and is small and flexible enough to not add resistance in systole. The flexible devices were integrated into a testbed mimicking the input a failing right ventricle and the results demonstrate progress towards energy harvesting from the cardiovascular system. A model was developed to gain insight as to how to structure the nanowire array within the latitude of the synthesis to boost the energy production. To further improve the output, the nanowires were passivated with dipolar molecules to change their resistivities and the barrier height of the Schottky contact. A novel low photon energy photoelectron spectroscopy tool was developed to measure the effects of the molecules on the individual nanowire properties. This concept of using nanostructured piezoelectrics as a means to convert the energy of the body may in the coming years represent a paradigm shift from battery dependant AICD modules to completely autonomous functional systems.