Zhong Lin Wang

Georgia Institute of Technology, Atlanta, Georgia, United States

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Publications (604)6000.8 Total impact

  • Morten Willatzen · Zhong Lin Wang
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    ABSTRACT: A unified treatment of coupled optical and acoustic phonons in piezoelectric cubic materials is presented whereby the lattice displacement vector and the internal ionic displacement vector are found simultaneously. It is shown that phonon couplings exist in pairs only; either between the electric potential and the lattice displacement coordinate perpendicular to the phonon wave vector or between the two other lattice displacement components. The former leads to coupled acousto-optical phonons by virtue of the piezoelectric effect. We then establish three new conjectures that entirely stem from piezoelectricity in a cubic structured material slab. First, it is shown that isolated optical phonon modes generally cannot exist in piezoelectric cubic slabs. Second, we prove that confined acousto-optical phonon modes only exist for a discrete set of in-plane wave numbers in piezoelectric cubic slabs. Third, it is shown that coupled acousto-optical phonons do not exist at the longitudinal-optical (LO) phonon frequency where the dielectric constant vanishes.
    No preview · Article · Dec 2015 · Physical Review B
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    ABSTRACT: Visible light communication (VLC) simultaneously provides illumination and communication via light emitting diodes (LEDs). Keeping a low bit error rate is essential to communication quality, and holding a stable brightness level is pivotal for illumination function. For the first time, a piezo-phototronic effect controlled visible light communication (PVLC) system based on InGaN/GaN multiquantum wells nanopillars is demonstrated, in which the information is coded by mechanical straining. This approach of force coding is also instrumental to avoid LED blinks, which has less impact on illumination and is much safer to eyes than electrical on/off VLC. The two-channel transmission mode of the system here shows great superiority in error self-validation and error self-elimination in comparison to VLC. This two-channel PVLC system provides a suitable way to carry out noncontact, reliable communication under complex circumstances.
    Full-text · Article · Oct 2015 · Small
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    ABSTRACT: One-dimensional (1D) carbon nanotubes (CNTs) and 2D single-atomic layer graphene have superior thermal, electrical, and mechanical properties. However, these nanomaterials exhibit poor out-of-plane properties due to the weak van der Waals interaction in the transverse direction between graphitic layers. Recent theoretical studies indicate that rationally designed 3D architectures could have desirable out-of-plane properties while maintaining in-plane properties by growing CNTs and graphene into 3D architectures with a seamless nodal junction. However, the experimental realization of seamlessly-bonded architectures remains a challenge. We developed a strategy of creating 3D graphene-CNT hollow fibers with radially aligned CNTs (RACNTs) seamlessly sheathed by a cylindrical graphene layer through a one-step chemical vapor deposition using an anodized aluminum wire template. By controlling the aluminum wire diameter and anodization time, the length of the RACNTs and diameter of the graphene hollow fiber can be tuned, enabling efficient energy conversion and storage. These fibers, with a controllable surface area, meso-/micropores, and superior electrical properties, are excellent electrode materials for all-solid-state wire-shaped supercapacitors with poly(vinyl alcohol)/H2SO4 as the electrolyte and binder, exhibiting a surface-specific capacitance of 89.4 mF/cm(2) and length-specific capacitance up to 23.9 mF/cm, - one to four times the corresponding record-high capacities reported for other fiber-like supercapacitors. Dye-sensitized solar cells, fabricated using the fiber as a counter electrode, showed a power conversion efficiency of 6.8% and outperformed their counterparts with an expensive Pt wire counter electrode by a factor of 2.5. These novel fiber-shaped graphene-RACNT energy conversion and storage devices are so flexible they can be woven into fabrics as power sources.
    Preview · Article · Sep 2015 · Science Advances
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    ABSTRACT: The triboelectric nanogenerator (TENG) is a promising mechanical energy harvesting technology, but its pulsed output and the instability of input energy sources make associated energy-storage devices necessary for real applications. In this work, feasible and efficient charging of Li-ion batteries by a rotating TENG with pulsed output current is demonstrated. In-depth discussions are made on how to maximize the power-storage efficiency by achieving an impedance match between the TENG and a battery with appropriate design of transformers. With a transformer coil ratio of 36.7, ≈72.4% of the power generated by the TENG at 250 rpm can be stored in an LiFePO4–Li4Ti5O12 battery. Moreover, a 1 h charging of an LiCoO2–C battery by the TENG at 600 rpm delivers a discharge capacity of 130 mAh, capable of powering many smart electronics. Considering the readily scale-up capability of the TENG, promising applications in personal electronics can be anticipated in the near future.
    No preview · Article · Sep 2015
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    ABSTRACT: Using the high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NW with an atomic force microscopy (AFM) tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by piezotronic effect. In contrast, the normal compressive force cannot change the electron transportation characteristics in m-plane GaN NW whose piezoelectric polarization axis turned to the transverse direction. This observation provided a solid evidence for clarifying the difference between piezotronic effect and piezoresistive effect. We further demonstrated a high sensitivity of m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in an direction.
    Full-text · Article · Aug 2015 · ACS Nano
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    ABSTRACT: Fresh water for human daily life is an important resource of the world, which could be as precious as oil in many cases. The increased needs for fresh water are becoming a major challenge to the quality of our life. Recently much attention has been paid to the seawater desalination with low energy cost. Here we report a seawater desalination (SD) and electrolysis (SE) system on the basis of the newly invented triboelectric nanogenerator (TENG). The TENG consists of radial arrays of micro-sized sectors on the contact surfaces and exhibits a high output current of 3.3 mA. 0.5 M salt solution was desalinated to form drinking water in 16 h and the desalination rate reached 98.3%. Subsequently, a totally self-powered SD and SE system driven by the kinetic energy of flowing water was presented. Using the power generated by flowing water at a rate of 40 L•min−1, the desalination rate reaches 8.2% in 3 h. Furthermore, the byproduct of concentrated salty water was splitat a hydrogen production rate of 2.6×10−5 mL•s−1. Our study demonstrates an innovative and unique approach toward a total self-powered SD and SE system. This is an important step toward self-powered environmental electrochemistry.
    No preview · Article · May 2015 · Nano Energy
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    ABSTRACT: An electric field built inside a crystal was proposed to enhance photoinduced carrier separation for improving photocatalytic property of semiconductor photocatalysts. However, a static built-in electric field can easily be saturated by the free carriers due to electrostatic screening, and the enhancement of photocatalysis, thus, is halted. To overcome this problem, here, we propose sonophotocatalysis based on a new hybrid photocatalyst, which combines ferroelectric nanocrystals (BaTiO3) and semiconductor nanoparticles (Ag2O) to form an Ag2O-BaTiO3 hybrid photocatalyst. Under periodic ultrasonic excitation, a spontaneous polarization potential of BaTiO3 nanocrystals in responding to ultrasonic wave can act as alternating built-in electric field to separate photoinduced carriers incessantly, which can significantly enhance the photocatalytic activity and cyclic performance of the Ag2O-BaTiO3 hybrid structure. The piezoelectric effect combined with photoelectric conversion realizes an ultrasonic-wave-driven piezophototronic process in the hybrid photocatalyst, which is the fundamental of sonophotocatalysis.
    Full-text · Article · Mar 2015 · Nano Letters
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    ABSTRACT: In this work, we have fabricated the piezoelectric driven Self-Charging Supercapacitor Power Cell (SCSPC) using MnO2 nanowires as positive and negative electrodes and PVDF-ZnO film as a separator (as well as a piezoelectric), which directly converts mechanical energy into electrochemical energy. Such a SCSPC consists of a nanogenerator, a supercapacitor and a power-management system, which can be directly used as a power source. The self-charging capability of SCSPC was demonstrated by mechanical deformation under human palm impact. The SCSPC can be charged to 110 mV (aluminum foil) in 300 s under palm impact. In addition, the green LED was glowed using serially connected SCSPC as the power source. This finding opens up the doors to make self-powered flexible hybrid electronic devices.
    Full-text · Article · Mar 2015 · ACS Nano
  • Ning Wang · Caizhen Gao · Fei Xue · Yu Han · Tao Li · Xia Cao · Xueji Zhang · Yue Zhang · Zhong Lin Wang
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    ABSTRACT: Cytochromes P450 (CYPs) enzymes are involved in catalyzing the metabolism of various endogenous and exogenous compounds. A rapid analysis of drug metabolism reactions by CYPs is required because they can metabolize 95% of current drugs in drug development and effective therapies. Here, we describe a study of piezotronic-effect enhanced drug metabolism and sensing by utilizing a single ZnO nanowire (ZnO NW) device. Owing to the unique hydrophobic feature of a ZnO NW that provides a desirable "microenvironment" for the immobilization of biomolecules, our device can effectively stimulate the tolbutamide metabolism by decorating a ZnO NW with cytochrome P4502C9/CYPs reductase (CYP2C9/CPR) microsomes. By applying an external compressive strain to the ZnO nanowire, the piezotronic effect, which plays a primary role in tuning the transport behavior of a ZnO NW utilizing the created piezoelectric polarization charges at the local interface, can effectively enhance the performance of the device. A theoretical model is proposed using an energy band diagram to explain the experimental data. This study provides a potential approach to study drug metabolism and trace drug detection based on the piezotronic effect.
    No preview · Article · Mar 2015 · ACS Nano
  • Gang Cheng · Li Zheng · Zong‐Hong Lin · Jin Yang · Zuliang Du · Zhong Lin Wang
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    ABSTRACT: The open-circuit voltage of a triboelectric nanogenerator (TENG) increases with the tribo-charge density and the separated distance between two tribo-surfaces, which can reach several thousand volts and is much higher than the working voltage required by most electrical devices and energy storage units. Therefore, improving the effective efficiency of TENGs requires reducing the output voltage and enhancing the transferred charges. Here, a multilayered-electrode-based TENG (ME-TENG) is developed in which the output voltage can be managed by controlling the charge flow in a process of multiple (N) steps, which results in N times lower voltage but N times higher total charge transport. The ME-TENG is demonstrated to work in various modes, including multichannel, single-channel, and double-tribo-surface structures. The effects of insulator layer thickness and total layer number on the output voltage are simulated by the finite element method. The output voltage can be modulated from 14 to 102 V by changing the insulator layer number between two adjacent working electrodes, based on which the 8-bit logic representations of the characters in the ACSII code table are demonstrated. The ME-TENG provides a novel method to manage the output power and has potential applications in self-powered sensors array and human–machine interfacing with logic communications.
    No preview · Article · Mar 2015 · Advanced Energy Materials
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    ABSTRACT: A novel integrated power unit realizes both energy harvesting and energy storage by a textile triboelectric nanogenerator (TENG)-cloth and a flexible lithium-ion battery (LIB) belt, respectively. The mechanical energy of daily human motion is converted into electricity by the TENG-cloth, sustaining the energy of the LIB belt to power wearable smart electronics. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Full-text · Article · Mar 2015 · Advanced Materials
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    ABSTRACT: The search for harvesting both the mechanical and solar energies from a single hybrid system is of significant value and represents a new trend in energy harvesting technologies. This single hybrid system can utilize both the energy sources easily available from nature and most importantly it is clean and sustainable. It is a novel technique involving completely different physical principles utilized for scavenging different types of energies. This report presents studies of a hybrid power generator made a direct-current piezoelectric nanogenerator based on ZnO nanosheets and a bulk heterojunction organic solar cell based on an inverted structure. The device shows much larger electric power output compared to its two individual power output components, which facilitates more effective multi-type energies harvesting and clarifies a mechanism for realizing multi-functional energy devices.
    Full-text · Article · Mar 2015 · Nano Energy
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    Ranran Zhou · Guofeng Hu · Ruomeng Yu · Caofeng Pan · Zhong Lin Wang
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    ABSTRACT: Compared with conventional Ohmic-contact nanosensors, Schottky-contact has been introduced as a fundamentally new design for much enhanced sensitivity and improved responsive time of one-dimensional nanostructure based sensors. Here we demonstrate ZnO micro/nanowire sensors for hydrogen (H2) and nitrogen dioxide (NO2) detections at room-temperature based on a metal-semiconductor-metal (M-S-M) structure. By utilizing strain-induced piezoelectric polarization charges presented at the vicinity of local interface to modify the band structure at Schottky contact, piezotronic effect has been introduced to gate/modulate the charge carriers transport process across the M-S contact and thus hugely enhance/optimize the performances of H2/NO2 gas sensors. Upon straining, the detection sensitivity and resolution are obviously improved, together with a significant enhancement in output current by 5359% for H2 and 238.8% for NO2 detection. This work provides a promising approach to raise the sensitivity, improve the detection resolution, and generally enhance the performance of gas sensing, making it possible for fabricating room temperature of gas sensor while preserving its sensitivity.
    Full-text · Article · Feb 2015 · Nano Energy
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    Jianjun Luo · Feng Ru Fan · Tao Zhou · Wei Tang · Fei Xue · Zhong Lin Wang
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    ABSTRACT: Portable and flexible pressure sensors with highly sensitive and small size have great potential applications in areas such as wearable electronics, environmental monitoring, and medical equipment. Here, we demonstrate an integrated self-powered pressure sensing system made of a passive resistive pressure sensor and a triboelectric nanogenertor. Based on wrinkled and flexible polydimethylsiloxane films, the whole device is of sandwich structure with ultrahigh sensitivity to pressure ( ), which is more than one order of magnitude higher than all previously reported flexible pressure sensors. And our system exhibits a very low detection limit, rapid response time, and long-term stability. In addition, we built a self-powered, portable visualization system for semi-quantitative analysis of pressure, which can directly convert a pressure information to visual display.
    Preview · Article · Jan 2015 · Extreme Mechanics Letters
  • Chi Zhang · Wei Tang · Yaokun Pang · Changbao Han · Zhong Lin Wang
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    ABSTRACT: Based on a triboelectric nanogenerator (TENG) the first active micro-actuator for optical modulation driven by mechanical energy without external power or mechanical joint is presented. This demonstrates the enormous potential of TENGs for independent and sustainable self-powered micro/nano electromechanical systems, and opens up new -applications of TENGs in triboelectric-voltage-controlled devices. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Jan 2015 · Advanced Materials
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    ABSTRACT: Silk fibroin-based biodegradable composite-type nanogenerators are demonstrated with controllable lifetime for powering to the implantable devices. The 2D thin film- and 1D wire-type composites consist of the well-dispersed lead-free ferroelectric (BaTiO3, ZnSnO3, Bi0.5(Na0.82K0.18)0.5TiO3, and K0.5Na0.5Nb0.995Mn0.005O3) nanoparticles. Ag nanowires are used to enhance the dispersion of the nanoparticles and polyvinylpyrrolidone prevents Ag nanowires from connecting with each other. A maximum output voltages and current densities of 2.2 V and 0.12 µA/cm2 in the thin film, and 1.8 V and 0.1 µA/cm2 in the wire are obtained under the motion of a foot step for when 30 wt% KNN:Mn nanoparticles are well-dispersed in the solution because of the largest piezoelectric coupling figure of merit. The properties of water-soluble composite films are also controlled with the glycerol content up to two days.
    Full-text · Article · Jan 2015 · Nano Energy
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    ABSTRACT: Discovering renewable and sustainable power sources is indispensable for the development of green electronics and sensor networks. In this paper, we present the origami triboelectric nanogenerators (TENGs) using paper as the starting material, with high degree of flexibility, light weight, low cost, and recyclability. Slinky and doodlebug shape TENGs can be easily fabricated by properly folding printer papers. The as-fabricated TENGs are capable of harvesting ambient mechanical energy from various kinds of human motions, such as stretching, lifting, and twisting. The generated electric outputs have been used to directly light up commercial LEDs. In addition, the as-fabricated TENGs can also serve as self-powered pressure sensors.
    No preview · Article · Jan 2015 · ACS Nano
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    Ruomeng Yu · Wenzhuo Wu · Caofeng Pan · Zhaona Wang · Yong Ding · Zhong Lin Wang
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    ABSTRACT: Using polarization charges created at the metal-cadmium sulfide interface under strain to gate/modulate electrical transport and optoelectronic processes of charge carriers, the piezo-phototronic effect is applied to process mechanical and optical stimuli into electronic controlling signals. The cascade nanowire networks are demonstrated for achieving logic gates, binary computations, and gated D latches to store information carried by these stimuli. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Full-text · Article · Dec 2014 · Advanced Materials
  • Ken C. Pradel · Wenzhuo Wu · Yong Ding · Zhong Lin Wang
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    ABSTRACT: Emerging applications in wearable technology, pervasive computing, human-machine interfacing and implantable biomedical devices demand an appropriate power source that can sustainably operate for extended periods of time with minimal intervention1. Self-powered nanosystems, which harvest operating energy from its host (i.e. the human body), may be feasible due to their extremely low power consumption2-4. Here we report materials and designs for wearable-on-skin piezoelectric devices based on ultrathin (2 μm) solution-derived ZnO p-n homojunction films for the first time. The depletion region formed at the p-n homojunction effectively reduces internal screening of strain-induced polarization charges by free carriers in both n-ZnO and Sb-doped p-ZnO, resulting in significantly enhanced piezoelectric output compared to a single layer device. The p-n structure can be further grown on polymeric substrates conformable to a human wrist and used to convert movement of the flexor tendons into distinguishable electrical signals for gesture recognition. The ZnO homojunction piezoelectric devices may have applications in powering nanodevices, bio-probes and self-powered human-machine interfacing.
    No preview · Article · Nov 2014 · Nano Letters
  • Simiao Niu · Zhong Lin Wang
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    ABSTRACT: Triboelectric nanogenerator (TENG) technology based on contact electrification and electrostatic induction is an emerging new mechanical energy harvesting technology with numerous advantages. The current area power density of TENGs has reached 313 W/m2 and their volume energy density has reached 490 kW/m3. In this review, we systematically analyzed the theoretical system of triboelectric nanogenerators. Starting from the physics of TENGs, we thoroughly discussed their fundamental working principle and simulation method. Then the intrinsic output characteristics, load characteristics, and optimization strategy is in-depth discussed. TENGs have inherent capacitive behavior and their governing equation is their V–Q–x relationship. There are two capacitance formed between the tribo-charged dielectric surface and the two metal electrodes, respectively. The ratio of these two capacitances changes with the position of this dielectric surface, inducing electrons to transfer between the metal electrodes under short circuit conditions. This is the core working mechanism of triboelectric generators and different TENG fundamental modes can be classified based on the changing behavior of these two capacitances. Their first-order lumped-parameter equivalent circuit model is a voltage source in series with a capacitor. Their resistive load characteristics have a “three-working-region” behavior because of the impedance match mechanism. Besides, when TENGs are utilized to charge a capacitor with a bridge rectifier in multiple motion cycles, it is equivalent to utilizing a constant DC voltage source with an internal resistance to charge. The optimization techniques for all TENG fundamental modes are also discussed in detail. The theoretical system reviewed in this work provides a theoretical basis of TENGs and can be utilized as a guideline for TENG designers to continue improving TENG output performance.
    No preview · Article · Nov 2014 · Nano Energy

Publication Stats

47k Citations
6,000.80 Total Impact Points

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  • 1997-2015
    • Georgia Institute of Technology
      • School of Materials Science and Engineering
      Atlanta, Georgia, United States
  • 2014
    • Beijing University of Aeronautics and Astronautics (Beihang University)
      • School of Biological and Medical Engineering
      Peping, Beijing, China
  • 2002-2014
    • Chinese Academy of Sciences
      • Beijing Laboratory of Electron Microscopy
      Peping, Beijing, China
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, CA, United States
    • University of Science and Technology, Beijing
      • School of Materials Science and Engineering
      Peping, Beijing, China
    • University of Washington Seattle
      • Department of Materials Science and Engineering
      Seattle, WA, United States
    • University of Akron
      Akron, Ohio, United States
    • Sandia National Laboratories
      • Electronic and Nanostructured Materials Department
      Albuquerque, New Mexico, United States
    • Nanjing University
      • Department of Physics
      Nanjing, Jiangsu Sheng, China
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, MA, United States
    • Peking University
      • Laboratory for the Physics & Chemistry of Nanodevices
      Peping, Beijing, China
    • The Hong Kong University of Science and Technology
      Chiu-lung, Kowloon City, Hong Kong
  • 2010-2012
    • Huazhong University of Science and Technology
      Wu-han-shih, Hubei, China
    • Xiamen University
      • College of Chemistry and Chemical Engineering
      Amoy, Fujian, China
    • Duke University
      Durham, North Carolina, United States
  • 2011
    • University of Rome Tor Vergata
      • Dipartimento di Ingegneria Civile e Ingegneria Informatica (DICII)
      Roma, Latium, Italy
  • 2007
    • University of Texas at Arlington
      • Department of Physics
      Arlington, Texas, United States
  • 2006
    • National Center for Nanoscience and Technology
      Peping, Beijing, China
    • National Tsing Hua University
      • Department of Materials Science and Engineering
      Hsinchu, Taiwan, Taiwan
  • 2005
    • Chongqing University
      • Department of Applied Physics
      Chongqing, Chongqing Shi, China
  • 2004
    • University of Texas at Austin
      • Department of Mechanical Engineering
      Austin, Texas, United States