Advanced Nanoelectromechanical Systems for Next Generation Energy Harvesting

The ever-increasing desire to produce portable, mobile and self-powered wireless micro-/nano systems (MNSs) with extended lifetimes has lead to the significant advancement in the area of mechanical energy harvesting over the last few years and it has been possible not only because has nanotechnology evolved as a powerful tool for the manipulation of matter on an atomic, molecular, and supramolecular scale, but also different micro-/nano fabrication techniques have enabled researchers and scientists to create, visualize, analyse and manipulate nano-structures, as well as to probe their nano-chemistry, nano-mechanics and other properties within the systems. The dissertation first discusses briefly about energy harvesting technologies for self-powered MNSs, for example a wireless aircraft structural health monitoring (SHM) system, with a particular focus on piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG) as they are the most promising approaches for converting ambient tiny mechanical energy into electrical energy efficiently and effectively and then it analyzes the theoretical and experimental methodologies for efficient energy harvesting using PENG, TENG and hybrid devices. The piezoelectric property intertwined with the semiconducting behaviour of different ZnO nanostructures has made them ideal candidate for piezoelectric energy harvesting, also intensive and state-of-the-art research has been going on to enhance the performance of the PENG devices based on 1D and 2D ZnO nanostructures. In this work, a high performance and consolidated PENG device based on the integration of ZnO nanowires and nanoplates on the same substrate has been demonstrated, that produces an output electrical power of 8.4 µW/cm2 at the matched load of 10MΩ that manifests their ability for powering up different MNSs. Since hybrid nanogenerators (HNG) integrate different types of harvesters in a single unit, where several energy sources can be leveraged either simultaneously or individually, in the next part of this work, a HNG device integrating PENG and TENG components has been designed, fabricated and characterized where PENG and TENG parts mutually enhance the performance of each other resulting an instantaneous peak power density of 1.864mW/cm2 and subsequently the device has been used to charge several commercial capacitors to corroborate their potential for aircraft SHM applications. Moreover, the hybrid device exhibits strong potential for wearable electronics as it can harvest energy from human walking and normal hand movements. However, successful implementation of self-powered electronics, such as a wireless aircraft SHM depends not only on the performance of individual parts but also on components integration within the system, where each device/system node within the network consists of a low-power microcontroller unit, high-performance data-processing/storage units, a wireless signal transceiver, ultrasensitive sensors based on a micro-/nano electro-mechanical system, and most importantly the embedded powering units. This dissertation aims to deepen the understanding of the different energy harvesting methods utilizing the knowledge of nanoscale phenomena and nanofabrication tools along with the associated prospects and challenges and thus, this research in the field of energy harvesting using advanced nano electro-mechanical systems could have a substantial impact on many areas, ranging from the fundamental study of new nanomaterial properties and different effects in nanostructures to diverse applications

Micro-scale to nano-scale generators for energy harvesting:Self powered piezoelectric, triboelectric and hybrid devices

This comprehensive review focuses on recent advances in energy harvesting of micro-scale and nano-scale generators based on piezoelectric and triboelectric effects. The development of flexible and hybrid devices for a variety of energy harvesting applications are systematically reviewed. A fundamental understanding of the important parameters that determine the performance of piezoelectric, triboelectric and hybrid devices are summarized. Current research directions being explored and the emerging factors to improve harvester functionality and advance progress in achieving high performance and durable energy conversion are provided. Investigations with regard to integrating flexible matrices and optimizing the composition of the piezoelectric and triboelectric materials are examined to enhance device performance and improve cost-effectiveness for the commercial arena. Finally, future research trends, emerging device structures and novel materials in view of imminent developments and harvesting applications are presented.</p

Piezoelectric Energy Harvester Technologies: Synthesis, Mechanisms, and Multifunctional Applications.

Piezoelectric energy harvesters have gained significant attention in recent years due to their ability to convert ambient mechanical vibrations into electrical energy, which opens up new possibilities for environmental monitoring, asset tracking, portable technologies and powering remote "Internet of Things (IoT)" nodes and sensors. This review explores various aspects of piezoelectric energy harvesters, discussing the structural designs and fabrication techniques including inorganic-based energy harvesters (i.e., piezoelectric ceramics and ZnO nanostructures) and organic-based energy harvesters (i.e., polyvinylidene difluoride (PVDF) and its copolymers). The factors affecting the performance and several strategies to improve the efficiency of devices have been also explored. In addition, this review also demonstrated the progress in flexible energy harvesters with integration of flexibility and stretchability for next-generation wearable technologies used for body motion and health monitoring devices. The applications of the above devices to harvest various forms of mechanical energy are explored, as well as the discussion on perspectives and challenges in this field

Plasma engineering of microstructured piezo – Triboelectric hybrid nanogenerators for wide bandwidth vibration energy harvesting

We introduce herein the advanced application of low-pressure plasma procedures for the development of piezo and triboelectric mode I hybrid nanogenerators. Thus, plasma assisted deposition and functionalization methods are presented as key enabling technologies for the nanoscale design of ZnO polycrystalline shells, the formation of conducting metallic cores in core@shell nanowires, and for the solventless surface modification of polymeric coatings and matrixes. We show how the perfluorinated chains grafting of polydimethylsiloxane (PDMS) provides a reliable approach to increase the hydrophobicity and surface charges at the same time that keeping the PDMS mechanical properties. In this way, we produce efficient Ag/ZnO convoluted piezoelectric nanogenerators supported on flexible substrates and embedded in PDMS compatible with a contact–separation triboelectric architecture. Factors like crystalline texture, ZnO thickness, nanowires aspect ratio, and surface chemical modification of the PDMS are explored to optimize the power output of the nanogenerators aimed for harvesting from low-frequency vibrations. Just by manual triggering, the hybrid device can charge a capacitor to switch on an array of color LEDs. Outstandingly, this simple three-layer architecture allows for harvesting vibration energy in a wide bandwidth, thus, we show the performance characteristics for frequencies between 1 Hz and 50 Hz and demonstrate the successful activation of the system up to ca. 800 Hz.EMERGIA Junta de Andalucía programUniversity of Seville the VI PPIT-USICMS and the CITIUS from the University of Sevill

Hybrid cell for harvesting multiple-type energies

An abundance of energy in our environment exists in the form of light, thermal, mechanical (e.g., vibration, sonic waves, wind, and hydraulic), magnetic, chemical, and biological. Harvesting these forms of energy is of critical importance for solving long-term energy needs and the sustainable development of the planet. However, conversion cells for harvesting solar energy and mechanical energy are usually independent entities that are designed and built following distinct physical principles. The effective and complementary use of such energy resources whenever and wherever one or all of them are available demands the development of innovative approaches for the conjunctional harvesting of multiple types of energy using an integrated structure/material. By combining solar and mechanical energy-harvesting modules into a single package for higher energy conversion efficiency and a more effective energy recovery process, the research has designed and demonstrated a hybrid cell for harvesting solar and mechanical energy. The results of the research show that we can fully utilize the energy available from our living environment by developing a technology that harvests multiple forms of both solar and mechanical energy 24 hours a day. As the proposed research represents a breakthrough in the innovation of energy harvesting, it should pave the way toward building a new field called "multi-type hybrid" energy harvesting.PhDCommittee Chair: Zhong Lin Wang; Committee Member: Christopher Summers; Committee Member: Gee-Kung Chang; Committee Member: Jud Ready; Committee Member: Zhiqun Li

Polarity in ZnO nanowires: A critical issue for piezotronic and piezoelectric devices

The polar and piezoelectric nature of the wurtzite structure of ZnO nanowires with a high aspect ratio at nanoscale dimensions is of high interest for piezotronic and piezoelectric devices, but a number of issues related to polarity are still open and deserve a particular attention. In this context, chemical bath deposition offers a unique opportunity to select the O- or Zn-polarity of the resultant nanowires and is further compatible with the fabrication processes of flexible devices. The control and use of the polarity in ZnO nanowires grown by chemical bath deposition opens a new way to greatly enhance the performance of the related piezotronic and piezoelectric devices. However, polarity as an additional tunable parameter should be considered with care because it has a strong influence on many processes and properties. The present review is intended to report the most important consequences related to the polarity in ZnO nanowires for piezotronic and piezoelectric devices. After introducing the basic principles involving crystal polarity in ZnO, a special emphasis is placed on the effects of polarity on the nucleation and growth mechanisms of ZnO nanowires using chemical bath deposition, defect incorporation and doping, electrical contacts and device properties

Three Dimensional Nanowire Array Piezo-phototronic and Piezo-photo-magnetotronic Sensors

Piezotronic and piezo-phototronic is a burgeoning field of study which emerges from the coupling of intrinsic materials properties exhibited by non-centrosymmetric semiconductors. In the past decade research efforts were mainly focused on the wurtzite family of 1D nanostructures, with major emphasis on ZnO nanowire nanogenerators, MS piezotronic transistors, LEDs and photodetectors mainly integrated on single nanowires. In view of previously known advantages of charge carrier separation in radial heterojunctions, particularly in type-II core/shell nanowires, it can be anticipated that the performance of photosensing devices can be largely enhanced by piezo-phototronic effect. Moreover, the performance metrics can be further improved in an array of nanowires where geometrical feature enabled multiple reflection can efficiently trap incident illumination. The crux of this dissertation lies in the development of 3D type-II core/shell nanowire array based piezo-phototronic device and also to investigate the effect of magnetic field on ZnO nanowire arrays based piezotronic and piezo-phototronic device for new class of sensors. In this regard, prototype piezo-phototronic broadband photodetectors integrated on two material systems, namely type-II CdSe/ZnTe 3D core/shell nanowire arrays and fully wide band gap type-II ZnO/ZnS 3D core/shell nanowire arrays have been developed where the photodetection performance of each device exhibits high sensitivity, fast response and large responsivity. The application of piezo-phototronic effect further improves the device performance by three to four orders of magnitude change numerically calculated from absolute responsivities at multiple wavelengths. A 3D ZnO nanowire array based new class of piezo-photo-magnetotronic sensor is also developed for detection of pressure, illumination and magnetic field suggesting multiple functionality of a single device where more than one effect can be coupled together to exhibit piezo-magnetotronic or piezo-photo-magnetotronic type of device behavior

Three Dimensional Nanowire Array Piezo-phototronic and Piezo-photo-magnetotronic Sensors

Piezotronic and piezo-phototronic is a burgeoning field of study which emerges from the coupling of intrinsic materials properties exhibited by non-centrosymmetric semiconductors. In the past decade research efforts were mainly focused on the wurtzite family of 1D nanostructures, with major emphasis on ZnO nanowire nanogenerators, MS piezotronic transistors, LEDs and photodetectors mainly integrated on single nanowires. In view of previously known advantages of charge carrier separation in radial heterojunctions, particularly in type-II core/shell nanowires, it can be anticipated that the performance of photosensing devices can be largely enhanced by piezo-phototronic effect. Moreover, the performance metrics can be further improved in an array of nanowires where geometrical feature enabled multiple reflection can efficiently trap incident illumination. The crux of this dissertation lies in the development of 3D type-II core/shell nanowire array based piezo-phototronic device and also to investigate the effect of magnetic field on ZnO nanowire arrays based piezotronic and piezo-phototronic device for new class of sensors. In this regard, prototype piezo-phototronic broadband photodetectors integrated on two material systems, namely type-II CdSe/ZnTe 3D core/shell nanowire arrays and fully wide band gap type-II ZnO/ZnS 3D core/shell nanowire arrays have been developed where the photodetection performance of each device exhibits high sensitivity, fast response and large responsivity. The application of piezo-phototronic effect further improves the device performance by three to four orders of magnitude change numerically calculated from absolute responsivities at multiple wavelengths. A 3D ZnO nanowire array based new class of piezo-photo-magnetotronic sensor is also developed for detection of pressure, illumination and magnetic field suggesting multiple functionality of a single device where more than one effect can be coupled together to exhibit piezo-magnetotronic or piezo-photo-magnetotronic type of device behavior

Piezo-Tribo Dual Effect Hybrid Nanogenerators for Health Monitoring

Over the years, nanogenerators for health monitoring have become more and more attractive as they provide a cost-effective and continuous way to successfully measure vital signs, physiological status, and environmental changes in/around a person. Using such sensors can positively affect the way healthcare workers diagnose and prevent life-threatening conditions. Recently, the dual piezo-tribological effect of hybrid nanogenerators (HBNGs) have become a subject of investigation, as they can provide a substantial amount of data, which is significant for healthcare. However, real-life exploitation of these HBNGs in health monitoring is still marginal. This review covers piezo-tribo dual-effect HBNGs that are used as sensors to measure the different movements and changes in the human body such as blood circulation, respiration, and muscle contractions. Piezo-Tribo dual-effect HBNGs are applicable within various healthcare settings as a means of powering noninvasive sensors, providing the capability of constant patient monitoring without interfering with the range of motion or comfort of the user. This review also intends to suggest future improvements in HBNGs. These include incorporating surface modification techniques, utilizing nanowires, nanoparticle technologies, and other means of chemical surface modifications. These improvements can contribute significantly in terms of the electrical output of the HBNGs and can enhance their prospects of applications in the field of health monitoring, as well as various in vitro/in vivo biomedical applications. While a promising option, improved HBNGs are still lacking. This review also discusses the technical issue which has prevented so far, the real use of these sensors

Optimization of zno nanorods concentration in a micro-structured polymeric composite for nanogenerators

The growing use of wearable devices has been stimulating research efforts in the de-velopment of energy harvesters as more portable and practical energy sources alternatives. The field of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), especially employing zinc oxide (ZnO) nanowires (NWs), has greatly flourished in recent years. Despite its modest piezoelectric coefficient, ZnO is very attractive due to its sustainable raw materials and the facility to obtain distinct morphologies, which increases its multifunctionality. The integration of ZnO nanostructures into polymeric matrices to overcome their fragility has already been proven to be fruitful, nevertheless, their concentration in the composite should be optimized to maximize the harvesters’ output, an aspect that has not been properly addressed. This work studies a composite with variable concentrations of ZnO nanorods (NRs), grown by microwave radiation assisted hydrothermal synthesis, and polydimethylsiloxane (PDMS). With a 25 wt % ZnO NRs concentration in a composite that was further micro-structured through laser engraving for output enhancement, a nanogenerator (NG) was fabricated with an output of 6 V at a pushing force of 2.3 N. The energy generated by the NG could be stored and later employed to power small electronic devices, ultimately illustrating its potential as an energy harvesting device.publishersversionpublishe