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UV response of ZnO nanowire nanosensor has been studied under ambient condition. By utilizing Schottky contact instead of Ohmic contact in device fabrication, the UV sensitivity of the nanosensor has been improved by four orders of magnitude, and the reset time has been drastically reduced from ϳ417 to ϳ0.8 s. By further surface functionalization with function polymers, the reset time has been reduced to ϳ20 ms even without correcting the electronic response of the measurement system. These results demonstrate an effective approach for building high response and fast reset UV detectors. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3133358͔ Ultraviolet ͑UV͒ photon detectors have a wide range of applications from environmental monitoring, missile launching detection, space research, high temperature flame detection to optical communications.1 For these applications, fast response time, fast reset time, high selectivity, high responsivity, and good signal-to-noise ratio are commonly desired characteristics.2 For UV photon detector based on polycrystalline ZnO thin film, a slow response time ranging from a few minutes to several hours is commonly observed.3,4 Due to large surface-to-volume ratio and reduced dimensionality of the active area, ZnO nanostructures are expected to have high photon conductance.5 Kind et al. 6 reported the photon response of a single ZnO nanowire ͑NW͒ under UV illumination, which has also been studied by other groups.7-9 Most of the studies have been focused on the mechanism investigation 10,11 and improving the sensitivity. 9,12 For example, Lao et al. 9 have improved the sensitivity of the ZnO NW UV nanosensor ͑NS͒ for five orders of magnitude by functionalizing the surface of ZnO nanobelts using polymers that have a high absorption at the UV range. However, little attention has been paid on improving the response and recovery time 13 especially the reset time ͑defined as the time need to recovery to 1 / e ͑37%͒ of the maximum photocurrent͒.In this letter, we demonstrate effective ways for improving both the sensitivity and reset time of ZnO NW NSs. By fabricating Schottky type ͑ST͒ devices instead of Ohmic type ͑OT͒ devices, the UV sensitivity of ZnO NW NS has been improved for four orders of magnitude, and the reset time has been decreased from ϳ417 to ϳ0.8 s. By further surface coating with positive charged poly͑diallydimethylammonium chloride͒ ͑PDADMAC͒ and negative charged poly͑sodium 4-styrenesulfonate͒ ͑PSS͒, the reset time has been decreased to ϳ20 ms even without correcting the electronic response of the measurement system. The ZnO NWs for the NS fabrication were synthesized by thermal evaporation of ZnO powders without using any catalyst.14 UV response of our devices was characterized by a portable UV lamp ͑Spectroline, Model ENF-280C, 365 nm͒. The photon-response spectrum measurement was carried out in a PTI QuantaMaster Luminescence ͑QM 3PH͒ system. All of the measurements were carried out at room temperature in ambient condition.We first studied the performance of...

Harvesting thermoelectric energy mainly relies on the Seebeck effect that utilizes a temperature difference between two ends of the device for driving the diffusion of charge carriers. However, in an environment that the temperature is spatially uniform without a gradient, the pyroelectric effect has to be the choice, which is based on the spontaneous polarization in certain anisotropic solids due to a time-dependent temperature variation. Using this effect, we experimentally demonstrate the first application of pyroelectric ZnO nanowire arrays for converting heat energy into electricity. The coupling of the pyroelectric and semiconducting properties in ZnO creates a polarization electric field and charge separation along the ZnO nanowire as a result of the time-dependent change in temperature. The fabricated nanogenerator has a good stability, and the characteristic coefficient of heat flow conversion into electricity is estimated to be ∼0.05−0.08 Vm 2 /W. Our study has the potential of using pyroelectric nanowires to convert wasted energy into electricity for powering nanodevices. KEYWORDS: ZnO nanowires, pyroelectric effect, nanogenerators, Schottky contact, Seebeck effect W asted heat is a rich source of energy that could be harvested. In 2010, for example, more than 50% of the energy generated from all sources in the U.S. was lost mainly in the form of wasted heat, 1 which presents us with a great opportunity to harvest this type of energy using nanotechnology. Harvesting thermoelectric energy mainly relies on the Seebeck effect that utilizes a temperature difference between the two ends of the device for driving the diffusion of charge carriers. 2,3 The presence of a temperature gradient is a must for the conventional thermoelectric cell. However, in an environment that the temperature is spatially uniform without a gradient, such as in outdoor in our daily life, the Seebeck effect is hardly useful for harvesting thermal energy arising from a time-dependent temperature fluctuation. In this case, the pyroelectric effect is the choice, which is about the spontaneous polarization in certain anisotropic solids as a result of temperature fluctuation, 4 but there are few studies about using pyroelectric effect for harvesting thermal energy. 5 Recently, piezoelectric ZnO nanowires have been effectively used to harvest small-scale mechanical energy. 6−9 The core of the piezoelectric nanogenerator (NG) is to utilize the piezoelectric potential (piezopotential) in the nanowires created by mechanical straining to drive the flow of electrons in the external load. Piezopotential can be generated by either strain or by temperature due to the anisotropic physical properties of ZnO. Here, we demonstrate the first application of converting heat energy into electricity by means of pyroelectric ZnO nanowire arrays. By using the coupling of the pyroelectric and semiconducting properties in ZnO, a polarization electric field and charge separation can be created along the ZnO nanowire as a result of the time-dependent...

The triboelectric nanogenerator (TENG) is a powerful approach toward new energy technology, especially for portable electronics. A theoretical model for the sliding-mode TENG is presented in this work. The finite element method was utilized to characterize the distributions of electric potential, electric field, and charges on the metal electrodes of the TENG. Based on the FEM calculation, the semi-analytical results from the interpolation method and the analytical V-Q-x relationship are built to study the sliding-mode TENG. The analytical V-Q-x equation is validated through comparison with the semi-analytical results. Furthermore, based on the analytical V-Q-x equation, dynamic output performance of sliding-mode TENG is calculated with arbitrary load resistance, and good agreement with experimental data is achieved. The theory presented here is a milestone work for in-depth understanding of the working mechanism of the sliding-mode TENG, and provides a theoretical basis for further enhancement of the sliding-mode TENG for both energy scavenging and self-powered sensor applications.

Single‐electrode triboelectric nanogenerators (SETENGs) significantly expand the application of triboelectric nanogenerators in various circumstances, such as touch‐pad technologies. In this work, a theoretical model of SETENGs is presented with in‐depth interpretation and analysis of their working principle. Electrostatic shield effect from the primary electrode is the main consideration in the design of such SETENGs. On the basis of this analysis, the impacts of two important structural parameters, that is, the electrode gap distance and the area size, on the output performance are theoretically investigated. An optimized electrode gap distance and an optimized area size are observed to provide a maximum transit output power. Parallel connection of multiple SETENGs with micro‐scale size and relatively larger spacing should be utilized as the scaling‐up strategy. The discussion of the basic working principle and the influence of structural parameters on the whole performance of the device can serve as an important guidance for rational design of the device structure towards the optimum output in specific applications.

We have fabricated ballistic n-type carbon nanotube (CNT)-based field-effect transistors (FETs) by contacting semiconducting single wall CNTs using Sc. Together with the demonstrated ballistic p-type CNT FETs using Pd contacts, our work closes the gap for doping-free fabrication of CNT-based ballistic complementary metal-oxide semiconductor (CMOS) devices and circuits. We demonstrated the feasibility of this dopingfree CMOS technology by fabricating a simple CMOS inverter on a SiO 2 /Si substrate using the back-gate geometry, but in principle much more complicated CMOS circuits may be integrated on a CNT on any suitable insulator substrate using the top-gate geometry and high-K dielectrics. This CNT-based CMOS technology only requires the patterning of arrays of parallel semiconducting CNTs with moderately narrow diameter range, for example, 1.6−2.4 nm, which is within the reach of current nanotechnology. This may lead to the integration of CNT-based CMOS devices with increasing complexity and possibly find its way into the computers brain: the logic circuit.

ABSTRACT:We introduce an innovative design of a disk triboelectric nanogenerator (TENG) with segmental structures for harvesting rotational mechanical energy. Based on a cyclic in-plane charge separation between the segments that have distinct triboelectric polarities, the disk TENG generates electricity with unique characteristics, which have been studied by conjunction of experimental results with finite element calculations. The role played by the segmentation number is studied for maximizing output. A distinct relationship between the rotation speed and the electrical output has been thoroughly investigated, which not only shows power enhancement at high speed but also illuminates its potential application as a selfpowered angular speed sensor. Owing to the nonintermittent and ultrafast rotation-induced charge transfer, the disk TENG has been demonstrated as an efficient power source for instantaneously or even continuously driving electronic devices and/or charging an energy storage unit. This work presents a novel working mode of TENGs and opens up many potential applications of nanogenerators for harvesting even large-scale energy. KEYWORDS: Triboelectric nanogenerator, in-plane charge separation, self-powered system, angular speed sensor S cavenging mechanical energy from ambient environment has attracted increasing interest not only for achieving selfpowered systems, but also for large-scale energy needs. 1−4Various approaches for harvesting mechanical energy have been developed that are based on piezoelectrics, 5−9 electromagnetics, 10,11 and electrostatics, 12,13 and so forth. The recently invented triboelectric nanogenerator (TENG) 14−20 provides an effective approach to convert mechanical energy into electricity, based on the coupling between triboelectrification 21−23 and electrostatic induction. The output performance of the TENG highly relies on the effectiveness of the charge separation process. 17,19 In previous works, the separation of triboelectric charges was along the normal direction in reference to the triboelectric-charged surfaces (tribo-surfaces), which was accomplished relying on the resilience of the device structure when the external force was withdrawn. However, such approaches might lead to high processing cost and difficulty for fully packaging the TENG device. Moreover, the vertical separation based TENG may only work for low-frequency mechanical triggering, such as impact and deformation. Recently, we have introduced a contact-sliding based approach for TENG, 24,25 in which the two tribo-surfaces are in contact. A time-dependent change in their contact area results in a lateral polarization of the triboelectric charges (tribo-charges) parallel to the tribo-surfaces, which can also give high power output.Here in this work, we developed a segmentally patterned disk-shaped TENG, in which a periodic overlapping and separation process of the two groups of sectors on the two concentric and closely contacted disks is achieved by relative rotation. This design not only introduces th...

We demonstrate the first self-powered system driven by a nanogenerator (NG) that works wirelessly and independently for long-distance data transmission. The NG was made of a free cantilever beam that consisted of a five-layer structure: a flexible polymer substrate, ZnO nanowire textured films on its top and bottom surfaces, and electrodes on the surfaces. When it was strained to 0.12% at a strain rate of 3.56% S(-1), the measured output voltage reached 10 V, and the output current exceeded 0.6 μA (corresponding power density 10 mW/cm(3)). A system was built up by integrating a NG, rectification circuit, capacitor for energy storage, sensor, and RF data transmitter. Wireless signals sent out by the system were detected by a commercial radio at a distance of 5-10 m. This study proves the feasibility of using ZnO nanowire NGs for building self-powered systems, and its potential application in wireless biosensing, environmental/infrastructure monitoring, sensor networks, personal electronics, and even national security.