Balasubramaniam Saravanakumar

Flexible, Hybrid Piezoelectric Film (BaTi(1–x)ZrxO3)/PVDF Nanogenerator as a Self-Powered Fluid Velocity Sensor

We demonstrate a flexible piezoelectric nanogenerator (PNG) constructed using a hybrid (or composite) film composed of highly crystalline BaTi(1-x)Zr(x)O3 (x = 0, 0.05, 0.1, 0.15, and 0.2) nanocubes (abbreviated as BTZO) synthesized using a molten-salt process embedded into a poly(vinylidene fluoride) (PVDF) matrix solution via ultrasonication. The potential of a BTZO/PVDF hybrid film is realized in fabricating eco-friendly devices, active sensors, and flexible nanogenerators to interpret its functionality. Our strategy is based on the incorporation of various Zr(4+) doping ratios into the Ti(4+) site of BaTiO3 nanocubes to enhance the performance of the PNG. The flexible nanogenerator (BTZO/PVDF) exhibits a high electrical output up to ∼11.9 V and ∼1.35 μA compared to the nanogenerator (BTO/PVDF) output of 7.99 V and 1.01 μA upon the application of cyclic pushing-releasing frequencies with a constant load (11 N). We also demonstrate another exciting application of the PNG as a self-powered sensor to measure different water velocities at an outlet pipe. The average maximum peak power of the PNG varies from 0.2 to 15.8 nW for water velocities ranging from 31.43 to 125.7 m/s during the water ON condition. This study shows the compositional dependence approach, fabrication of nanostructures for energy harvesting, and self-powered devices in the field of monitoring for remote area applications.

Piezoelectric-Driven Self-Charging Supercapacitor Power Cell

In this work, we have fabricated a piezoelectric-driven self-charging supercapacitor power cell (SCSPC) using MnO2 nanowires as positive and negative electrodes and a polyvinylidene difluoride (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 light-emitting diode glowed using serially connected SCSPC as the power source. This finding opens up the possibility of making self-powered flexible hybrid electronic devices.

Self-powered pH sensor based on a flexible organic-inorganic hybrid composite nanogenerator.

In this study, we developed an innovative, flexible, organic-inorganic hybrid composite nanogenerator, which was used to drive a self-powered microwire-based pH sensor. The hybrid composite nanogenerator was fabricated using ZnO nanowire and piezoelectric polymer poly(vinylidene fluoride), through a simple, inexpensive solution-casting technique. The fabricated hybrid composite nanogenerator delivered a maximum open-circuit voltage of 6.9 V and a short-circuit current of 0.96 μA, with an output power of 6.624 μW under uniaxial compression. This high-performance, electric poling free composite nanogenerator opens up the possibility of industrial-scale fabrication. The hybrid nanogenerator demonstrated its ability to drive five green LEDs simultaneously, without using an energy-storage device. Additionally, we constructed a self-powered pH sensor, using a ZnO microwire powered with our hybrid nanogenerator. The output voltage varied according to changes in the pH level. This study demonstrates the feasibility of using a hybrid nanogenerator as a self-powered device that can be extended for use as a biosensor for environmental monitoring and/or as a smart, wearable, vibration sensor in future applications.

Fabrication of a ZnO nanogenerator for eco-friendly biomechanical energy harvesting

We present a new device structure for effective energy harvesting from human body movement using a ZnO nanogenerator. This is the first report on both piezoelectric and triboelectric effects in the same device. The fabricated device structure consists of a double-sided ZnO nanowire array sandwiched between gold coated ZnO nanowire arrays using polydimethylsiloxane. The peak open circuit voltage (Voc) and short circuit current (Isc) were recorded as 30 V and 300 nA respectively with power density of 0.390 mW cm−2, when folding/bending the nanogenerator with the fingers. The ZnO nanogenerator was effectively utilized to harvest biomechanical energy from human body movements like stretching, folding, and pressing. The power density of fabricated nanogenerator was 9.49, 8.19 and 115 nW cm−2 by stretching, folding and pressing the fingers, respectively. The acquired output was used to drive a commercial light emitting diode. The generated output is combination of the piezoelectric effect from ZnO nanowire and the triboelectric effect from polydimethylsiloxane. This feasibility study substantiates human body movement as a source for energy harvesting. The energy generated by human activities (body movement) was sufficient to operate low power wearable electronic devices.

Human Interactive Triboelectric Nanogenerator as a Self-Powered Smart Seat

A lightweight, flexible, cost-effective, and robust, single-electrode-based Smart Seat-Triboelectric Nanogenerator (SS-TENG) is introduced as a promising eco-friendly approach for harvesting energy from the living environment, for use in integrated self-powered systems. An effective method for harvesting biomechanical energy from human motion such as walking, running, and sitting, utilizing widely adaptable everyday contact materials (newspaper, denim, polyethylene covers, and bus cards) is demonstrated. The working mechanism of the SS-TENG is based on the generation and transfer of triboelectric charge carriers between the active layer and user-friendly contact materials. The performance of SS-TENG (52 V and 5.2 μA for a multiunit SS-TENG) is systematically studied and demonstrated in a range of applications including a self-powered passenger seat number indicator and a STOP-indicator using LEDs, using a simple logical circuit. Harvested energy is used as a direct power source to drive 60 blue and green commercially available LEDs and a monochrome LCD. This feasibility study confirms that triboelectric nanogenerators are a suitable technology for energy harvesting from human motion during transportation, which could be used to operate a variety of wireless devices, GPS systems, electronic devices, and other sensors during travel.

Gate-Tunable Photoresponse of Defective Graphene: from Ultraviolet to Visible

We report the gate-tunable photoresponse of a defective graphene over the ultraviolet (UV) and the visible light illumination, where the defect was generated by plasma irradiation. Plasma induced Dirac point shift indicates the p-doping effect. Interestingly the defective-graphene field effect transistor (defective-GFET) showed a negative shift upon UV illumination, whereas the device showed a positive shift under visible light illumination, along with the change in the photocurrent. The defective-GFET device showed a high photoresponsivity of 37 mA W(-1) under visible light, that is ∼3 times higher than that of the pristine graphene device. Photoinduced molecular desorption causes the UV light responsivity to 18 mA W(-1). This study shows that the tunable photodetector with high responsivity is feasible by introducing an artificial defect on graphene surface.

A microcrystalline cellulose ingrained polydimethylsiloxane triboelectric nanogenerator as a self-powered locomotion detector

Scavenging of ambient dissipated mechanical energy addresses the limitations of conventional batteries by providing an auxiliary voltaic power source, and thus has significant potential for self-powered and wearable electronics. Here, we demonstrate a cellulose/polydimethylsiloxane (PDMS) triboelectric nanogenerator (C-TENG) based on the contact and separation mode between a cellulose/PDMS composite film and an aluminium electrode. The device fabricated with a composite film of 5 wt% generates an open circuit voltage of 28 V and a short circuit current of 2.8 μA with an instantaneous peak power of 576 μW at a mechanical force of 32.16 N. The C-TENG was systematically studied and demonstrated to be a feasible power source that can commute instantaneous operation of LEDs and act as a self-powered locomotion detector for security applications. The C-TENG can also be used as a wearable power source with an in-built lithium ion battery charging circuit during a range of human motions.

Defect-induced metallic-to-semiconducting transition in multilayer graphene

We investigate the electrical transport properties of multilayer graphene (MLG) following irradiation with Ar plasma. The plasma induces defects, including vacancies, voids, and nanoholes, which altered the resistance of the MLG. The resulting defect-rich MLG device exhibits an asymmetric ambipolar behavior, with a strong p-doping effect, which considerably deteriorates the electron conductivity, implies defect generation on the MLG surface. The pristine MLG was metallic; however, the resulting defect-rich MLG following plasma treatment exhibited a semiconductor-like temperature dependence of the resistance. Thus, MLG with morphological disorder exhibits a metallic-to-semiconductor transition in the resistance as a function of temperature.

Self-Induced Gate Dielectric for Graphene Field-Effect Transistor

We report the electronic characteristics of an avant-garde graphene-field-effect transistor (G-FETs) based on ZnO microwire as top-gate electrode with self-induced dielectric layer. Surface-adsorbed oxygen is wrapped up the ZnO microwire to provide high electrostatic gate-channel capacitance. This nonconventional device structure yields an on-current of 175 μA, on/off current ratio of 55, and a device mobility exceeding 1630 cm(2)/(V s) for holes and 1240 cm(2)/(V s) for electrons at room temperature. Self-induced gate dielectric process prevents G-FETs from impurity doping and defect formation in graphene lattice and facilitates the lithographic process. Performance degradation of G-FETs can be overcome by this avant-garde device structure.