Publications

Dual-Mode Elecromechanical Resonance of Nanobelts Observed by In-situ TEM

Journal Article Dual-Mode Elecromechanical Resonance of Nanobelts Observed by In-situ TEM Get access Z L Wang, Z L Wang School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 + e-mail: zhong.wang@mse.gatech.edu Search for other works by this author on: Oxford Academic Google Scholar X D Bai, X D Bai School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245International Center for Quantum Structures and State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China Search for other works by this author on: Oxford Academic Google Scholar P X Gao, P X Gao School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 Search for other works by this author on: Oxford Academic Google Scholar E G Wang E G Wang International Center for Quantum Structures and State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 9, Issue S02, 1 August 2003, Pages 338–339, https://doi.org/10.1017/S143192760344169X Published: 19 July 2003

Piezoelectric potential in vertically aligned nanowires for high output nanogenerators

In this work we analyze the coupled piezoelectric and semiconductive behavior of vertically aligned ZnO nanowires under uniform compression. The screening effect on the piezoelectric field caused by the free carriers in vertically compressed zinc oxide nanowires (NWs) has been computed by means of both analytical considerations and finite element calculations. We predict that, for typical geometries and donor concentrations, the length of the NW does not significantly influence the maximum output piezopotential because the potential mainly drops across the tip, so that relatively short NWs can be sufficient for high-efficiency nanogenerators, which is an important result for wet-chemistry fabrication of low-cost, CMOS- or MEMS-compatible nanogenerators. Furthermore, simulations reveal that the dielectric surrounding the NW influences the output piezopotential, especially for low donor concentrations. Other parameters such as the applied force, the sectional area and the donor concentration have been varied in order to understand their effects on the output voltage of the nanogenerator.

Contact‐electro‐catalysis for Direct Synthesis of H₂O₂ under Ambient Conditions

Abstract Hydrogen peroxide (H 2 O 2 ) is an indispensable basic reagent in various industries, such as textile bleach, chemical synthesis, and environmental protection. However, it is challenging to prepare H 2 O 2 in a green, safe, simple and efficient way under ambient conditions. Here, we found that H 2 O 2 could be synthesized using a catalytic pathway only by contact charging a two‐phase interface at room temperature and normal pressure. Particularly, under the action of mechanical force, electron transfer occurs during physical contact between polytetrafluoroethylene particles and deionized water/O 2 interfaces, inducing the generation of reactive free radicals (⋅OH and ⋅O 2 − ), and the free radicals could react to form H 2 O 2 , yielding as high as 313 μmol L −1 h −1 . In addition, the new reaction device could show long‐term stable H 2 O 2 production. This work provides a novel method for the efficient preparation of H 2 O 2 , which may also stimulate further explorations on contact‐electrification‐induced chemistry process.

Environmental life cycle assessment and techno-economic analysis of triboelectric nanogenerators

Life cycle assessment within a techno-economic framework is carried out for triboelectric nanogenerators in the context of other technologies.

Three-Dimensional Hexagonal Close-Packed Superlattices of Passivated Ag Nanocrystals

Abstract Silver nanocrystals passivated by dodecanethiol self-assembled monolayers were produced using an aerosol technique described in detail elsewhere [1]. Self-assembling passivated nanocrystal-superlattices (NCS's) involve self-organization into monolayers, thin films, and superlattices of size-selected nanoclusters encapsulated in a protective compact coating [2,3,4,5,6,7]. We report the preparation and structure characterization of three-dimensional (3-D) hexagonal close-packed Ag nanocrystal supercrystals from Ag nanocrystals of ˜4.5 nm in diameters. The crystallography of the superlattice and atomic core lattices were determined using transmission electron microscopy (TEM) and high-resolution TEM. SEM was used to image the nanocrystal superlattices formed on an amorphous carbon film of an TEM specimen grid (fig. la). The superlattice films show well shaped, sharply faceted, triangular shaped sheets. Figure lb depicts numerous Ag nanocrystal aggregates uniformly distributed over the imaging region. Inset in this figure is an enlargement of the boxed region at the edge of a supercrystal typifying the ordered nanocrystal packing.

A Self‐Powered Triboelectric Nanosensor for Mercury Ion Detection

Moving to mercury: The first triboelectric effect-based sensor for the detection of Hg2+ ions by using Au nanoparticles (see picture; red) as electrical performance enhancer and recognition element has been successfully demonstrated. This self-powered and stand-alone triboelectric nanosensor has the advantages of simplicity, low cost, high selectivity, and sensitivity. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Triboelectric Sensor for Self-Powered Tracking of Object Motion inside Tubing

We report a self-powered, single-electrode-based triboelectric sensor (SE-TES) array for detecting object motion inside of a plastic tube. This innovative, cost-effective, simple-designed SE-TES consists of thin-film-based ring-shaped Cu electrodes and a polytetrafluoroethylene (PTFE) tube. On the basis of the coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical motion of an object (such as a ball) passing through the electrodes. An array of Cu electrodes linearly aligned along the tube enables the detection of location and speed of the moving steel ball inside. The signal-to-noise ratio of this fabricated device reached 5.3 × 103. Furthermore, we demonstrated real-time monitoring and mapping of the motion characteristics of the steel ball inside the tube by using a seven-unit array of electrode channels arranged along the tube. Triggered by the output current signal, LED bulbs were utilized as real-time indicators of the position of a rolling ball. In addition, the SE-TES also shows the capability of detecting blockage in a water pipe. This work demonstrates potentially widespread applications of the triboelectric sensor in a self-powered tracking system, blockage detection, flow control, and logistics monitoring.

Tribovoltaic nanogenerators based on n-n and p-p semiconductor homojunctions

Theoretical analysis of triboelectric nanogenerators: Charge mechanisms, energy conversion, and multifunctional applications

Triboelectrification Based Motion Sensor for Human-Machine Interfacing

We present triboelectrification based, flexible, reusable, and skin-friendly dry biopotential electrode arrays as motion sensors for tracking muscle motion and human–machine interfacing (HMI). The independently addressable, self-powered sensor arrays have been utilized to record the electric output signals as a mapping figure to accurately identify the degrees of freedom as well as directions and magnitude of muscle motions. A fast Fourier transform (FFT) technique was employed to analyse the frequency spectra of the obtained electric signals and thus to determine the motion angular velocities. Moreover, the motion sensor arrays produced a short-circuit current density up to 10.71 mA/m2, and an open-circuit voltage as high as 42.6 V with a remarkable signal-to-noise ratio up to 1000, which enables the devices as sensors to accurately record and transform the motions of the human joints, such as elbow, knee, heel, and even fingers, and thus renders it a superior and unique invention in the field of HMI.

Anisotropic Third-Order Optical Nonlinearity of a single ZnO Micro/Nanowire

We report a systematic study about the anisotropic third-order optical nonlinearity of a single ZnO micro/nanowire by using the Z-scan method with a femtosecond laser. The two-photon absorption coefficient and nonlinear refraction index, which are measured as a function of polarization angle and sample orientation angle, exhibit oscillation curves with a period of π/2, indicating a highly polarized optical nonlinearity of the ZnO micro/nanowire. Further studies show that the polarized optical nonlinearity of the ZnO micro/nanowire is highly size-dependent. The results indicate that ZnO nanowire has great potential in applications of nanolasers, all-optical switching and polarization-sensitive photodetectors.

A standard for normalizing the outputs of triboelectric nanogenerators in various modes

By the proposed standard of normalizing the output performance for triboelectric nanogenerators in various modes, it is proved that the order of influencing factors is contact area > film thickness > applied force > displacement distance.

Mechanical Effects of Galvanic Corrosion on Structural Polysilicon

The mechanical properties of miniaturized materials depend strongly on their structure, which can be altered by wet chemistry methods common in microsystems postprocessing.In a comprehensive and systematic study, we examine the dissolution of silicon when immersed in various hydrofluoric acid (HF)-based chemistries.Specifically, the frequency of mechanical resonance f R of microcantilever beams is used as a vehicle to examine the corrosion of polycrystalline silicon (polySi).A decrease in f R that occurs as a function of immersion time in HF was measured for microcantilevers as well as "comb drives" in contact with a noble metal (gold).Time-dependent variation was also observed in the modulus and hardness measured during indentation testing, sometimes with pronounced difference for specimens contacted to gold.Secondary sources of influence, such as in-plane-oriented residual strain (which remained unchanged), through-thickness-oriented residual strain gradient (increased away from the substrate), and electrical resistance (greatly increased) are examined, but were found not to significantly contribute to the decrease in fR of the microcantilevers.Morphological characterization identified attack on the surface along with grain delineation for the polySi, with the formation of a nanoscale porous layer at the near surface.The damage to the microcantilevers can be modeled by approximating the beams as a laminated composite structure.Such analysis suggests that damage, induced as the result of galvanic corrosion, results from the decreased stiffness of the near surface porous silicon (PS) layer as well as a change in the effective thickness of the beams.Last, corrosion damage is compared between eight representative HF-based chemistries.The measurements here suggest that the fabrication and postprocessing of microsystems components are important, because they can greatly influence the material properties, design, performance, lifetime, tribology, manufacture, and required operating environment of microscale and nanoscale devices.

La(OH)₃ and La₂O₃ Nanobelts—Synthesis and Physical Properties

A facile composite-hydroxide-mediated synthesis method is adopted to prepare ultralong, single-crystalline, hexagonal structured La(OH)3 nanobelts. The detectable conductive behavior of a single La(OH)3 nanobelt promises their potential application in sensors. La2O3 nanobelts can be obtained by calcination of the La(OH)3 nanobelts. Both types of nanobelts fluoresce with purple light under UV excitation, which may be used in biological labeling.

Quantum-enhanced sensing of axion dark matter with a transmon-based single microwave photon counter

We report an axion dark matter search with a haloscope equipped with a microwave photon counter. The haloscope is a tunable high quality factor 3-dimensional microwave cavity placed in a magnetic field. The photon counter, operated cyclically, maps an incoming microwave photon onto the state of a superconducting transmon qubit. The measurement protocol continuously monitors the power emitted by the haloscope cavity as well as the dark count background, and enables tuning of the cavity frequency to probe different axion masses. With this apparatus we enhance by a factor 20 the search speed that can be reached with quantum-limited linear amplifiers, and set a new standard for probing the existence of axions with resonant detectors.

Mechanoluminescent hybrids from a natural resource for energy‐related applications

Abstract Mechanoluminescent (ML) materials that directly convert mechanical energy into photon emission have emerged as promising candidates for various applications. Despite the recent advances in the development of both novel and conventional ML materials, the limited access to ML materials that simultaneously have the attributes of high brightness, low cost, self‐recovery, and stability, and the lack of appropriate designs for constructing ML devices represent significant challenges that remain to be addressed to boost the practical application of ML materials. Herein, ML hybrids derived from a natural source, waste eggshell, with the aforementioned attributes are demonstrated. The introduction of the eggshell not only enables the preparation of the hybrid in a simple and cost‐effective manner but also contributes to the homochromatism (red, green, or blue emission), high brightness, and robustness of the resultant ML hybrids. The significant properties of the ML hybrids, together with the proposed structural design, such as porosity or core–shell structure, could expedite a series of mechanic‐optical applications, including the self‐luminous shoes for the conversion of human motions into light and light generators that efficiently harvest water wave energy. The fascinating properties, versatile designs, and the efficient protocol of “turning waste into treasure” of the ML hybrids represent significant advances in ML materials, promising a leap to the practical applications of this flouring material family. image

Robust Low-Sidelobe Beamforming Method via Alternating Projection Technique

Tunable WSe₂–CdS mixed-dimensional van der Waals heterojunction with a piezo-phototronic effect for an enhanced flexible photodetector

A strain-tunable WSe₂–CdS mixed-dimensional vdWs heterointerface is demonstrated and the photoresponse is dramatically enhanced with the piezo-phototronic effect.