Showing papers by "Sheng Xu published in 2010"
TL;DR: This work demonstrates the vertical and lateral integration of ZnO nanowires into arrays that are capable of producing sufficient power to operate real devices and uses the vertically integrated nanogenerator to power a nanowire pH sensor and a Nanowire UV sensor, thus demonstrating a self-powered system composed entirely of nanowiring.
Abstract: The lateral and vertical integration of ZnO piezoelectric nanowires allows for voltage and power outputs sufficient to power nanowire-based sensors.
1,465 citations
TL;DR: The results show that a nanogenerator can be used to power flexible displays by means of mechanical agitations for future touchable display technologies.
Abstract: The piezoelectric generation of perovskite BaTiO3 thin films on a flexible substrate has been applied to convert mechanical energy to electrical energy for the first time. Ferroelectric BaTiO3 thin films were deposited by radio frequency magnetron sputtering on a Pt/Ti/SiO2/(100) Si substrate and poled under an electric field of 100 kV/cm. The metal-insulator (BaTiO3)-metal-structured ribbons were successfully transferred onto a flexible substrate and connected by interdigitated electrodes. When periodically deformed by a bending stage, a flexible BaTiO3 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.
690 citations
TL;DR: 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 are demonstrated and demonstrated.
Abstract: 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.
468 citations
TL;DR: The results show that the piezo-phototronic effect can enhance the detection sensitivity more than 5-fold for pW levels of light detection.
Abstract: We demonstrate the piezoelectric effect on the responsivity of a metalsemiconductormetal 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 a0.36% 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.
441 citations
22 Nov 2010
TL;DR: In this article, the authors present a review of piezotronic, piezophotonic and pieozo-phototronic devices based on laterally-bonded nanowires on a polymer substrate.
Abstract: Relying on the piezopotential created in ZnO under straining, nanogenerators, piezotronics and piezo-phototronics developed based on laterally bonded nanowires on a polymer substrate have been reviewed. The principle of the nanogenerator is a transient flow of electrons in external load as driven by the piezopotential created by dynamic straining. By integrating the contribution made by millions of nanowires, the output voltage has been raised to 1.2 V. Consequently, self-powered nanodevices have been demonstrated. This is an important platform technology for the future sensor network and the internet of things. Alternatively, the piezopotential can act as a gate voltage that can tune/gate the transport process of the charge carriers in the nanowire, which is a gate-electrode free field effect transistor (FET). The device fabricated based on this principle is called the piezotronic device. Piezo-phototronic effect is about the tuning and controlling of electro-optical processes by strain induced piezopotential. The piezotronic, piezophotonic and pieozo-phototronic devices are focused on low frequency applications in areas involving mechanical actions, such as MEMS/NEMS, nanorobotics, sensors, actuators and triggers.
223 citations
TL;DR: The capability of controlling the spatial distribution of the blue/near-UV LEDs composed of position controlled arrays of n-ZnO nanowires on a p-GaN thin fi lm substrate is demonstrated.
Abstract: [∗] S. Xu , C. Xu , Y. Liu , Y. F. Hu , R. S. Yang , Q. Yang , Prof. Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, Georgia, 30332–0245 (USA) E-mail: zlwang@gatech.edu J. H. Ryou , H. J. Kim , Z. Lochner , S. Choi , Prof. R. Dupuis School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, Georgia, 30332–0245 (USA) ZnO-based light emitting diodes (LEDs) have been considered as a potential candidate for the next generation of blue/ near-UV light sources, [ 1 ] due to a direct wide bandgap energy of 3.37 eV, a large exciton binding energy of 60 meV at room temperature, and several other manufacturing advantages of ZnO. [ 2 ] While the pursuit of stable and reproducible p-ZnO is still undergoing, [ 3,4 ] heterojunctions of n-ZnO and p-GaN are employed as an alternative approach in this regard by considering the similar crystallographic and electronic properties of ZnO and GaN. [ 5–7 ] Compared with the thin fi lm/thin fi lm LEDs, [ 5,6 , 8 ] which may suffer from the total internal refl ection, n-ZnO nanowire/p-GaN thin fi lm heterostructures are utilized in order to increase the extraction effi ciency of the LEDs by virtue of the waveguiding properties of the nanowires. [ 9–11 ] But in all of these cases, the n-ZnO nanowires are randomly distributed on the substrate, which largely limits their applications in high performance optoelectronic devices. Here in this work, we demonstrate the capability of controlling the spatial distribution of the blue/near-UV LEDs composed of position controlled arrays of n-ZnO nanowires on a p-GaN thin fi lm substrate. The device was fabricated by a conjunction of low temperature wet chemical methods and electron beam lithography (EBL). The EBL could be replaced by other more convenient patterning techniques, such as photolithography and nanosphere lithography, rendering our technique low cost and capable of scaling up easily. Under forward bias, each single nanowire is a light emitter. By Gaussian deconvolution of the emission spectrum, the origins of the blue/nearUV emission are assigned particularly to three distinct electronhole recombination processes. By virtue of the nanowire/thin fi lm heterostructures, these LEDs give an external quantum effi ciency of 2.5%. This approach has great potential applications in high resolution electronic display, optical interconnect, and high density data storage. The design of the LED is shown in Figure 1a . Ordered ZnO nanowire arrays were grown on p-GaN (Figure 1 b–d), [ 12–14 ]
220 citations
TL;DR: This work presents a new approach to fabricate three-dimensional (3D) dye-sensitized solar cells (DSSCs) by integrating planar optical waveguide and nanowires (NWs) that can be expanded to organic- and inorganic-based solar cells.
Abstract: We present a new approach to fabricate three-dimensional (3D) dye-sensitized solar cells (DSSCs) by integrating planar optical waveguide and nanowires (NWs). The ZnO NWs are grown normally to the quartz slide. The 3D cell is constructed by alternatively stacking a slide and a planar electrode. The slide serves as a planar waveguide for light propagation. The 3D structure effectively increases the light absorbing surface area due to internal multiple reflections without increasing electron path length to the collecting electrode, resulting in a significant improvement in energy conversion efficiency by a factor of 5.8 on average compared to the planar illumination case. Our approach demonstrates a new methodology for building large scale and high-efficient 3D solar cells that can be expanded to organic- and inorganic-based solar cells.
100 citations
TL;DR: In this paper, a site controllable ZnO nanowire array was synthesized and replicated via hydrothermal method on general flexible substrates, and the replication was demonstrated for three generations.
Abstract: Vertically aligned and site controllable ZnO nanowire arrays have been synthesized and replicated via hydrothermal method on general flexible substrates. The replication was demonstrated for three generations. The morphology and density of the nanowire arrays could be optimized in the original generation by adjusting the chemical reaction parameters. The pattern of the original generation was inherited by the succeeding generations by a new transferring method. The growth mechanism of the replicated nanowire arrays was investigated with the help of inductively coupled plasma (ICP) etching and AFM tip scanning. The robustness of the ZnO nanowire arrays was obviously improved compared with the seedless ZnO nanowires grown on Au (111) surface, according to the excellent morphology preservation after ultrasonic wave treatment.
75 citations
TL;DR: In this paper, a mask polymer layer is applied to a selected crystal surface of a seed crystal, and a plurality of spaced apart elongated openings is defined through the mask polymer layers, thereby exposing a corresponding plurality of portions of the crystal surface.
Abstract: In a method of making a monolithic elongated nanowire, a mask polymer layer is applied to a selected crystal surface of a seed crystal. A plurality of spaced apart elongated openings is defined through the mask polymer layer, thereby exposing a corresponding plurality of portions of the crystal surface. The openings are disposed so as to be aligned with and parallel to a selected crystal axis of the seed crystal. The portions of the crystal surface are subjected to a chemical nutrient environment that causes crystalline material to grow from the plurality of portions for at least a period of time so that monocrystalline members grow from the elongated openings and until the monocrystalline members laterally expand so that each monocrystalline member grows into and merges with an adjacent one of the monocrystalline members, thereby forming a monolithic elongated nanowire.
39 citations
TL;DR: In this paper, a new method is demonstrated that uses sideways pulsed laser deposition to deliberately bend nanowires into a desired shape after growth and fabricate arc-shaped composite nanowire arrays of a wide range of nanomaterials.
Abstract: Here, a new method is demonstrated that uses sideways pulsed laser deposition to deliberately bend nanowires into a desired shape after growth and fabricate arc-shaped composite nanowire arrays of a wide range of nanomaterials. The starting nanowires can be ZnO, but the materials to be deposited can be metallic, semiconductor, or ceramic depending on the application. This method provides a general approach for rational fabrication of a wide range of side-by-side or "core-shell" nanowire arrays with controllable degree of bending and internal strain. Considering the ZnO is a piezoelectric and semiconductive material, its electrical properties change when deformed. This technique has potential applications in tunable electronics, optoelectronics, and piezotronics.
29 citations
01 Jan 2010
TL;DR: In this article, the authors provide an overview of zinc oxide (ZnO) nanowire synthesis strategies pertinent to flexible organic substrates. But their focus was on the fundamental mechanism of the piezoelectricity and nanogenerators.
Abstract: Publisher Summary This chapter provides an overview of zinc oxide (ZnO) nanowire synthesis strategies pertinent to flexible organic substrates. The different strategies have been used to grow ZnO nanowire arrays on flat flexible substrates, such as polyimide and polystyrene, and curved flexible substrates, such as microfibers. By using electron beam lithography (EBL) or photolithography, a patterned growth of ZnO nanowire arrays could also be achieved on both flat substrates and microfibers. Furthermore, based on vertically aligned ZnO nanowire arrays on the flexible substrates, innovative nanotechnology-enabled methods for converting mechanical energy into electrical energy have been demonstrated, with the aim of building self-powered nanosystems. The focus was on the fundamental mechanism of the piezoelectricity and nanogenerators. The core of the nanogenerator is based on coupling the piezoelectric and semiconducting properties of ZnO nanowires and the presence of a Schottky barrier at the metal–semiconductor interface.