Piezoelectric Nanowires Research Articles

Characterization and performance analysis of piezoelectric ZnO nanowire for low-frequency energy harvesting applications

Characterization and performance analysis of piezoelectric ZnO nanowire for low-frequency energy harvesting applications

Analysis of static extension of piezoelectric semiconductor nanowires considering non-uniform strain and flexoelectric effects

Piezoelectric semiconductor (PSC) nanowires have a great potential to be the basic element of the next generation of micro and nano electro-mechanical systems. A lack of understanding of their electromechanical coupling behaviors can be a major obstacle to using PSC nanowires. In this paper, a one-dimensional model is proposed to investigate the electromechanical coupling behavior of PSC nanowires under static extension. In the present model, effects of piezoelectricity and flexoelectricity are considered simultaneously. Closed-form expressions for the distributions of electron concentrations and electromechanical fields are obtained. The effects of applied distributed traction force, flexoelectric effect and initial carrier concentration have been discussed. Results show that the distributions of electromechanical fields predicted by the present model are different from those of the classical model (which only considers piezoelectric effect). For example, the applied uniform distributed traction force breaks the symmetrical distributions of electromechanical fields, resulting in the redistribution of electron concentrations. However, flexoelectricity shows a significant weakening effect on the values of relevant electromechanical fields. This research offers a new method to tune the electromechanical coupling characteristics of piezoelectric semiconductor materials.

Fabrication of Piezoelectric ZnO Nanowires Energy Harvester on Flexible Substrate Coated with Various Seed Layer Structures.

Flexible piezoelectric nanogenerators (PENGs) are very attractive for mechanical energy harvesting due to their high potential for realizing self-powered sensors and low-power electronics. In this paper, a PENG that is based on zinc oxide (ZnO) nanowires (NWs) is fabricated on flexible and transparent Polydimethylsiloxane (PDMS) substrate. The ZnO NWs were deposited on two different seed layer structures, i.e., gold (Au)/ZnO and tin-doped indium-oxide (ITO)/ZnO, using hydrothermal synthesis. Along with the structural and morphological analyses of ZnO NWs, the electrical characterization was also investigated for ZnO NWs-based flexible PENGs. In order to evaluate the suitability of the PENG device structure, the electrical output performance was studied. By applying a periodic mechanical force of 3 N, the ZnO NWs-based flexible PENG generated a maximum root mean square (RMS) voltage and average power of 2.7 V and 64 nW, respectively. Moreover, the comparison between the fabricated device performances shows that a higher electrical output can be obtained when ITO/ZnO seed layer structure is adopted. The proposed ZnO NWs-based PENG structure can provide a flexible and cost-effective device for supplying portable electronics.

Zinc oxide nanowires‐based flexible pressure sensor

Embedding piezoelectric nanowires within a soft elastomer material should provide a superior pressure sensing transducer, exploiting the piezoelectric properties of the nanowire material while maintaining flexibility. Here, a flexible sensor has been fabricated on a Kapton substrate and has incorporated a layer of polydimethylsiloxane with embedded zinc oxide nanowires as the pressure sensing mechanism. In response to applied compressive pressure up to 127 kPa, the device has generated a voltage, between electrodes on either side of the nanowire/polydimethylsiloxane layer, with a sensitivity of 23.6 mV/kPa, which is 100 times greater than previously reported zinc oxide nanostructure-based flexible sensors.

Nonlinear vibration analysis of nanowire resonators for ultra-high resolution mass sensing

Nanoscale systems fabricated with low-dimensional nanostructures such as carbon nanotubes, nanowires, quantum dots, and more recently graphene sheets, have fascinated researchers from different fields due to their extraordinary and unique physical properties. For example, the remarkable mechanical properties of nanowires empower them to have a very high resonant frequency up to the order of giga to terahertz. In this paper, we originally propose a nonlinear model for the vibrations of piezoelectric nanowire resonators with added mass considering thermal variation, electromagnetic field, surface effects, external excitation, and nonlinear foundation. The mathematical model for such nanowires is formulated by applying the Euler–Bernoulli beam theory in conjunction with the nonlocal differential constitutive relations of Eringen type. In order to analyze the obtained nonlinear partial differential equation (PDE), we first use the Galerkin method in combination with a perturbation technique to obtain the primary and super-harmonic resonances. After finding the resonance cases, a parametric sensitivity analysis is carried out to investigate the effects of key parameters on the sensitivity of the nanowire resonators in mass sensing. Our main hypothesis is that tiny particles attached to the surface of the nanowire resonator would result in a detectable shift in the value of the jump frequency. The sensitivity analysis shows that the nanowire resonator is capable of detecting added mass in the order of zeptogram. In addition, we have developed a system identification technique based on the proposed mathematical model for the detection of tiny mass rested on the nanowire resonator that we have analyzed. Furthermore, a molecular dynamic simulation study has been presented to qualitatively verify the hypothesis of frequency shift due to the added mass. The results demonstrate a high potential of nanowire resonators in detecting tiny bio-particles such as DNA, RNA, proteins, viruses, and bacteria.

Vibration and Buckling Analysis of Piezoelectric Nanowires Based on Surface Energy Density

In this paper, the influences of surface effects on free transverse vibration and buckling of piezoelectric nanowires are investigated by surface energy density elasticity theory. Analytical relations are given for the natural frequencies of nanowires by taking into account the effects of surface energy density and surface relaxation parameter. By implementing this theory with consideration of surface effects under clamped–clamped boundary conditions, the natural frequencies of nanowires are calculated. It is shown that the natural frequency depends on both the surface effects and piezoelectricity. A closed-form solution is also obtained to calculate the critical buckling voltage. This study is expected to provide useful insights for the design of piezoelectric nanowire-based nanodevices.

Phase transformation and its effect on the piezopotential in a bent zinc oxide nanowire

Most piezotronic nanodevices rely on the piezopotential generated by the bending of their component piezoelectric nanowires (NWs). The mechanical behaviours and piezopotential properties of zinc oxide (ZnO) NWs under lateral bending are investigated in this paper by using a multiscale modelling technique combining first-principles calculations, molecular dynamics simulations and finite-element calculations. Two phase transformation processes are successively found in ZnO NWs by increasing the bending force. As a result, the inner and outer surfaces of bent ZnO NWs transform from the parent wurtzite (WZ) structure to a hexagonal (HX) structure and a body-centred-tetragonal (BCT-4) structure, respectively. Different material properties are found among the WZ, BCT-4, and HX structures, which result in a significant change in the piezopotential distribution in bent ZnO NWs after the phase transformation. Meanwhile, the piezopotential generated in bent ZnO NWs can be enhanced by an order of magnitude due to the phase transformation. Moreover, a significant increase in the electronic band gap is found in the transformed HX structure, which implies that the phase transformation may also affect the piezopotential in bent ZnO NWs by modifying their semiconducting properties especially when the doping level of NWs is large.

Recent Progress in Hybridized Nanogenerators for Energy Scavenging.

SummaryAs the world's demand for alternative energy increases, the development of green energy harvesters becomes ever more important. As a result, the creation of triboelectric (TENG), piezoelectric (PENG), and pyroelectric nanogenerators, electromagnetic generators (EMG), solar cells, and electrochemical cells is attracting interest in an effort to convert mechanical, thermal, magnetic, solar, and chemical energy into electricity. In order to take advantage of the ambient energies from our surrounding environment, the design of hybridized generator units that can simultaneously scavenge energy in a variety of forms continues to develop. These systems are being considered to satisfy the energy needs of a range of electronic devices and adapt to a variety of working environments. This review demonstrates the latest progress in hybridized nanogenerators in accordance with their structure, operating principle, and applications. These studies demonstrate new approaches to developing hybrid techniques and novel assemblies for efficiently harvesting environmental energy from a number of sources.

Hydrogenic impurity-related optical properties in a piezoelectric core–shell nanowire

The impurity-associated optical transitions in a piezoelectric core–shell nanowire were studied using the density matrix formalism. In the calculations, four electron states were considered using a finite-difference algorithm combined with a variational approach. An obvious blueshift in the optical spectrum, especially for the transition from the free electron to impurity-bound ground states, was predicted to result from the intrinsic Stark effect induced by the piezoelectric field. The effects of the optical transition between impurity-bound states on the absorption coefficient and the refractive index of wurtzite nanowires were enhanced as the piezoelectric polarization becomes stronger. The findings are helpful for guiding further experiments on the linear and nonlinear optical properties of piezoelectric nanowires.

1D semiconductor nanowires for energy conversion, harvesting and storage applications

Abstract The accomplishment of 1D semiconductor nanowires (SN) in the field of energy has attracted intense interest in recent years due to their advantageous properties (e.g., large surface area, unique surface chemistry, and tunable transport properties). Considerable efforts were devoted to explore 1D-SN building blocks as the harvesting channel/unit (e.g., in thermal, chemical, mechanical, and solar energy applications) and as the storage media (for electrochemical energy). A wide bandgap tuning of SN in the range of 0.39 eV (in case of InAs nanowires) to 4.66 eV (in case of β-Ga2O3 nanowires) due to quantum size effect makes them a suitable candidate for optoelectronic applications. This review focuses on 1D-SN wherein the travel of electron and photon is confined in two directions but in one dimension. The SN emerged as promising nanostructures for developing electronic devices of high carrier-mobilities (e.g., >12000 cm2V−1s−1 for holes and 3000 cm2V−1s−1 for electrons in case of Ge nanowires). A list of efficient fabrication strategies (e.g., vapor-liquid-solid [VLS], hard-template approaches, and solution-phase) are discussed along with ultrafast electron transport dynamics of SN and piezoelectric nanowires. The control on electrons, photons, and phonons transport makes 1D-SN ideal for solid-state energy conversion, harvesting, and storage applications. State-of-the-art 1D-SN energy nano-systems have been demonstrated to yield diverse outcomes of high significance including single-nanowire and array-based photovoltaic cells (InP nanowires with a maximum power conversion efficiency up to 17.8%), nanogenerators (SiGe nanowires with a maximum power output of 7.1 μW/cm2), supercapacitors (core-shell hierarchical CoS@MoS2 nanowire array with an energy density of 95.7 Wh kg−1 at power density of 711.2 W kg−1), and lithium-air batteries (3D freestanding hierarchical CuCo2O4 nanowires@Ni foam with an excellent specific capacity of 13654 mAh g−1 at 0.1 mA cm−2). This review will serve as a key platform to understand 1D-SN to fabricate the next-generation novel nano-systems for developing efficient energy devices of high performance.

High-Performance Strain Sensors Based on Vertically Aligned Piezoelectric Zinc Oxide Nanowire Array/Graphene Nanohybrids

A nanohybrid piezoelectric strain sensor was fabricated by growing vertically aligned (0001)-oriented crystalline zinc oxide nanowires directly on graphene (ZnO-VANWs/Gr) using a facile seedless hy...

Flexoelectric effect on electric potential in piezoelectric graphene-based composite nanowire: Analytical and numerical modelling

In this work, an analytical model was developed to study the distribution of electric potential in a graphene reinforced nanocomposite (GRNC) nanowire. The electromechanical responses such as electric potential and deflection of cylindrical GRNC cantilevered nanowire were investigated. Moreover, the conservative fully coupled finite element (FE) models were developed to validate the analytical predictions. Analytical solution shows that the piezoelectric potential in the GRNC nanowire depends on the transverse force, but it is not a function of the force acting along its axial direction. The electric potential in the tensile and compressive sections of nanowire is antisymmetric along its cross-section, making it as a “parallel plate capacitor” for nanopiezotronics applications such as nanogenerator and piezoelectric field effect transistor due to potential drop across the nanowire which assists as the gate voltage. The predictions of potential distributions across the GRNC nanowire considering piezoelectricity show better agreement with FE predictions. Outcomes of the current work reveal that the flexoelectric effect on the electromechanical behavior of GRNC nanowire is noteworthy and cannot be ignored.

Enhanced-sensitivity and highly flexible stress/strain sensor based on PZT nanowires-modified graphene with wide range carrier mobility

Flexible stress/strain sensors have widespread applications including healthy monitoring systems, smart robotics, and wearable devices. Graphene, a promising carbon material with several excellent properties, is widely used in flexible stress/strain sensors. Creating a graphene-based pressure sensor with improved sensitivity remains highly challenging owing to the difficulty in widening the band gap of graphene. Herein, a novel heterostructural enhanced-sensitivity stress/strain sensor composed of two-dimensional (2D) graphene and one-dimensional (1D) lead zirconate titanate (PZT) nanowires as the sensitivity material, was fabricated. The polarized charges generated by the piezoelectric nanowires under mechanical stress acted as ionized impurities to increase the scattering carriers of graphene, thereby changing its conductivity; additionally, the high piezoelectric property of nanowires provided numerous polarized charges, resulting in increased scattering carriers. Therefore, the as-fabricated device has an enhanced sensitivity of 2.95 × 10−2 kPa−1, which is higher than that of the pure graphene-based pressure sensor. In particular, the fabricated sensor can detect bending strain, such as the bending and straightening of a finger, and the angle of opening a book. Furthermore, the device can record handwritten signals that can be used as indicators of biometric information. Thus, the fabricated device provides a viable and convenient approach for application in multi-functional electronic wearable devices.

Bilaterally flexural vibrations and instabilities of moving piezoelectric nanowires with surface effect

Vibrations of piezoelectric beam-like nanostructures have been widely examined; however, their dynamic response and instabilities in the moving state accounting for surface effect have not been investigated yet thoroughly. Given the importance of the subject and potential applications of piezoelectric nanowires in moving bodies, herein, we are interested in exploring their bidirectional-transverse vibrations in the context of the surface elasticity theory of Gurtin and Murdoch. To this end, equations of motion that describe transverse vibrations of axially moving piezoelectric nanowires are obtained by employing Rayleigh’s and Timoshenko’s beam theories. Using assumed mode approach in conjunction with Galerkin method, the flexural frequencies are evaluated and the explicit expressions of divergence velocities accounting for surface energy are derived. The influences of nanowire’s length, axial velocity, surface energy, shear deformation effect, and voltage difference on the free transverse vibrations as well as divergence and flutter instabilities of the moving piezoelectric nanostructure are displayed. The present work can provide a solid basis for better understanding of vibrations of moving vertically aligned ensembles of piezoelectric nanowires. An axially moving piezoelectric nanowire.

Vibration Damping Mechanism of Fiber-Reinforced Composites with Integrated Piezoelectric Nanowires.

Here, both piezoelectric and nonpiezoelectric nanostructures are used within fiber-reinforced composites to improve the damping capabilities of the host material. This work investigates and isolates the role of both piezoelectricity and the mechanical redistribution of strain on the damping properties of fiber-reinforced composites through the integration of a nanowire interphase between the fiber and matrix. Prior works have successfully studied and reported the effectiveness of modifying the surface of the reinforcing fibers in a composite material using nanowires and other nanostructured interfaces to increase mechanical damping, however, have yet to fully investigate the mechanism dictating the observed behavior. This study analyzes the effects of nonpiezoelectric nanowire interfaces in comparison to piezoelectric nanowire interfaces of the same microscale morphology. The damping properties of carbon fiber-reinforced composites containing both sets of nanowires are investigated via dynamic mechanical analysis over a range of temperatures as well as modal analysis at the first resonant frequency. The results conclusively indicate that a combination of both mechanical and piezoelectric effects contributes to the significant increase in damping properties of fiber-reinforced composites and quantifies the individual contributions.

A review on piezoelectric fibers and nanowires for energy harvesting

Recent advances in self-powered electronic devices have urged the development of energy-harvesting technology. Batteries are gradually unable to satisfy the practical requirements for powering the different types of microelectronic devices owing to their drawbacks such as occupying a significant percentage and weight of portable products, the need to replace or recharge them, constructing an important environmental impact, and the probable seepage of electrolyte solutions. Various technologies for converting renewable energies into electricity have been reported. Particularly, energy harvesters based on piezoelectricity to convert mechanical energy into usable electricity have received considerable attention. Electrospun fibers from piezoelectric polymers and inorganic nanowires as emerging piezoelectric materials have shown great potential for energy-harvesting applications. This review paper summarizes energy-harvesting technology based on piezoelectric polymeric fibers, inorganic piezoelectric fibers, and inorganic nanowires. A comprehensive overview of fundamentals of piezoelectric effect, types of piezoelectric materials, energy harvesting from fibers, energy harvesting from inorganic nanowires, and energy harvesting from polymeric/inorganic fibers and nanowires composites are discussed.

Vertically Aligned Piezoelectric Perovskite Nanowire Array on Flexible Conducting Substrate for Energy Harvesting Applications

AbstractEnergy conversion based on vertically aligned piezoelectric nanowire (NW) arrays is of great interest because of their unusual properties originating from large surface area/high aspect ratio and excellent piezoelectric properties. Here, perovskite‐structured piezoelectric BaTiO3 NW arrays are vertically grown onto the flexible Ti substrates by a two‐step hydrothermal reaction to realize an aligned 1D nanostructures‐based flexible energy harvester. The BaTiO3 NW array‐based flexible piezoelectric energy harvester (PEH) successfully converts a maximum open‐circuit voltage of ≈15 V, a maximum short‐circuit current of ≈400 nA, and an effective power of ≈0.27 µW during repeated bending deformations. Under pressing with an external force of 49.57 N, the harvested output signals of the vertically aligned NW arrays‐based PEH are ≈20 V and ≈60 nA. Finite element analysis with multiphysics simulation supports the hypothesis of effective potential generation by the NW arrays‐based flexible PEH. These results can aid in the further development of high‐output 1D nanostructures‐based flexible PEHs.

Tailored nanocomposite energy harvesters with high piezoelectric voltage coefficient through controlled nanowire dispersion

Composites composed of piezoelectric nanomaterials dispersed in a flexible polymer have emerged as promising materials for highly durable and flexible energy harvesters and sensors. Although piezoelectric materials in their bulk form have a high electromechanical coupling coefficient and can efficiently convert mechanical energy to electrical energy, the ceramic form has low fracture toughness and thus they are limited in certain applications due to difficulty in machining and conforming to curved surfaces. Recently, additive manufacturing processes such as direct write, have been developed to incorporate piezoelectric nanowires into a polymer matrix with controlled alignment to realize printed piezoelectrics. Given the multiphase structure of a nanocomposite, it is possible to control the material structure such that the piezoelectric coupling and dielectric properties can be varied independently. In this paper, experimentally validated finite element (FE) and micromechanics models are developed for calculation and optimization of the piezoelectric voltage coefficient, g31, of a nanocomposite. It is shown that by using high aspect ratio nanowires with controlled alignment, the piezoelectric coupling can be disproportionately increased with respect to the dielectric constant which yields a g31 coefficient that can be enhanced more than seven times compared to the bulk piezoelectric material. Moreover, it is demonstrated that the use of high aspect ratio nanowires in the energy harvester resulted in significant improvement on the output electrical power of an energy harvester.

In Situ Observation of Current Generation in ZnO Nanowire Based Nanogenerators Using a CAFM Integrated into an SEM.

In this work, we monitor in situ the movement of ZnO piezoelectric nanowires by using a conductive atomic force microscope integrated into a scanning electron microscope. This setup allows seeing the bending of the nanowires and simultaneously measuring the currents generated. We conclude that the currents generated not only come from piezoelectric effect, but also from contact potential and triboelectric effect. These contributions have been ignored in all previous reports in this field, meaning that the power conversion efficiency of these devices may have been systematically overestimated. Our study helps to clarify the working mechanism of piezoelectric nanogenerators based on ZnO nanowires.

Electromechanical modeling and experimental verification of a direct write nanocomposite

Piezoelectric materials are currently among the most promising building blocks for sensing, actuation and energy harvesting systems. However, these materials are limited in certain applications due to their lack of machinability as well as their inability to conform to curved surfaces. One method to mitigate this issue is through additive manufacturing (direct printing) of piezoelectric nanocomposites, where piezoelectric nanomaterials are embedded in a polymer matrix. Although significant progress has been made in this area, filler morphology, alignment and volume fraction are critical parameters that influence the electromechanical response and have not been adequately modeled. With the advent of additive manufacturing it is now possible to realize directly printed nanocomposites with tailored microstructure. The objective of this study is to develop and experimentally validate micromechanical and finite element models that allow the study of the electroelastic properties of a directly printed nanocomposite containing piezoelectric inclusions. Furthermore, the dependence of these properties on geometrical parameters such as aspect ratio and alignment of the active phase are investigated. In particular, the core focus of this work is to demonstrate how the gradual alignment of piezoelectric nanowires in the nanocomposite from randomly oriented to purely aligned can improve electroelastic properties of a printed nanocomposite. Finally, this work provides the first experimental validation of the theoretical and FEM models through measurement of the electroelastic properties of the nanocomposites containing barium titanate nanowires in a polydimethylsiloxane (PDMS) polymer matrix.