The harvesting of mechanical energy from ambient sources could power electrical devices without the need for batteries. However, although the efficiency and durability of harvesting materials such as piezoelectric nanowires have steadily improved, the voltage and power produced by a single nanowire are insufficient for real devices. The integration of large numbers of nanowire energy harvesters into a single power source is therefore necessary, requiring alignment of the nanowires as well as synchronization of their charging and discharging processes. Here, we demonstrate the vertical and lateral integration of ZnO nanowires into arrays that are capable of producing sufficient power to operate real devices. A lateral integration of 700 rows of ZnO nanowires produces a peak voltage of 1.26 V at a low strain of 0.19%, which is potentially sufficient to recharge an AA battery. In a separate device, a vertical integration of three layers of ZnO nanowire arrays produces a peak power density of 2.7 mW cm(-3). We use the vertically integrated nanogenerator to power a nanowire pH sensor and a nanowire UV sensor, thus demonstrating a self-powered system composed entirely of nanowires.

One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, positioncontrolled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

The piezoelectric generation of perovskite BaTiO 3 thin films on a flexible substrate has been applied to convert mechanical energy to electrical energy for the first time. Ferroelectric BaTiO 3 thin films were deposited by radio frequency magnetron sputtering on a Pt/Ti/SiO 2 /(100) Si substrate and poled under an electric field of 100 kV/cm. The metal-insulator (BaTiO 3 )-metal-structured ribbons were successfully transferred onto a flexible substrate and connected by interdigitated electrodes. When periodically deformed by a bending stage, a flexible BaTiO 3 nanogenerator can generate an output voltage of up to 1.0 V. The fabricated nanogenerator produced an output current density of 0.19 µA/cm 2 and a power density of ∼7 mW/cm 3 . The results show that a nanogenerator can be used to power flexible displays by means of mechanical agitations for future touchable display technologies.KEYWORDS BaTiO 3 , thin film, piezoelectric, flexible electronics, nanogenerator, energy harvesting E nergy harvesting technologies that convert existing sources of energies, such as thermal energy as well as vibrational and mechanical energy from the natural sources of wind, waves, or animal movements into electrical energy, is attracting immense interest in the scientific community. [1][2][3][4][5][6] The fabrication of nanogenerators is particularly interesting because it can even scavenge the biomechanical energy from inside the human body, such as the heart beat, blood flow, muscle stretching, or eye blinking, and turn it into electricity to power implantable biodevices. [7][8][9] One way of harvesting electrical energy from the mechanical energy of ambient vibrations is to utilize the piezoelectric properties of ferroelectric materials. Piezoelectric harvesting has been proposed and investigated by many researchers.10-14 Chen et al. 12 reported on the fabrication of a nanogenerator that involves the use of lead zirconate titanate (PbZr x Ti 1-x O 3 , PZT) nanofibers on a bulk Si substrate. The PZT nanofibers were connected to interdigitated electrodes (IDEs) and, when pressure was applied perpendicularly to the nanogenerator surface, the nanogenerator producedanoutstandingoutputvoltage.Wangandco-workers 13,14 used piezoelectric ZnO nanowires to develop a multiple lateral-nanowire-array integrated nanogenerator (LING) 13 and a high-output nanogenerator (HONG) 14 on plastic substrates. They also demonstrated the feasibility of harvesting energy from the breath and heartbeat of animals. 9 As of today, the nanogenerator has an output voltage of 2 V, and the power generated can be used to power a commercial light-emitting diode (LED).14 Recently, there have been attempts to transfer flexible perovskite materials and capacitors onto flexible substrates for the purpose of utilizing the high inherent piezo-properties of ferroelectric materials from bulk substrates. 15,16 In those attempts, perovskite thin films (PZT and BaTiO 3 ) deposited on bulk substrates were annealed at high temperatures and transferred onto plastic sub...

Harvesting energy from irregular/random mechanical actions in variable and uncontrollable environments is an effective approach for powering wireless mobile electronics to meet a wide range of applications in our daily life. Piezoelectric nanowires are robust and can be stimulated by tiny physical motions/disturbances over a range of frequencies. Here, we demonstrate the first chemical epitaxial growth of PbZr x Ti 1 − x o 3 (PZT) nanowire arrays at 230 °C and their application as high-output energy converters. The nanogenerators fabricated using a single array of PZT nanowires produce a peak output voltage of ~0.7 V, current density of 4 µA cm − 2 and an average power density of 2.8 mW cm − 3 . The alternating current output of the nanogenerator is rectified, and the harvested energy is stored and later used to light up a commercial laser diode. This work demonstrates the feasibility of using nanogenerators for powering mobile and even personal microelectronics.

We demonstrate the piezoelectric effect on the responsivity of a metal-semiconductor-metal ZnO micro-/nanowire photodetector. The responsivity of the photodetector is respectively enhanced by 530%, 190%, 9%, and 15% upon 4.1 pW, 120.0 pW, 4.1 nW, and 180.4 nW UV light illumination onto the wire by introducing a -0.36% compressive strain in the wire, which effectively tuned the Schottky barrier height at the contact by the produced local piezopotential. After a systematic study on the Schottky barrier height change with tuning of the strain and the excitation light intensity, an in-depth understanding is provided about the physical mechanism of the coupling of piezoelectric, optical, and semiconducting properties. Our results show that the piezo-phototronic effect can enhance the detection sensitivity more than 5-fold for pW levels of light detection.