Piezoelectric Nanostructures Research Articles

Flexible inorganic piezoelectric functional films and their applications

Piezoelectric materials play an increasingly important role in energy harvesters, sensors, and actuators. Flexible and thin piezoelectric films have been demonstrated to provide advanced functionalities and improved performances. However, the research on flexible inorganic piezoelectric thin films has rarely been systematically summarized. Here, we summarize the recent advances in the flexible inorganic piezoelectric thin films, focusing on their structural designs, fabrication techniques, and applications in various practical scenarios. Specifically, different fabrication techniques suitable for diverse inorganic piezoelectric nanostructures are reviewed, including sol–gel, hydrothermal, electrospinning, and other techniques, and the integration process with flexible substrates is further discussed. Biomedical and industrial applications of the flexible piezoelectric thin films are emphasized. Finally, some existing challenges and future perspectives are discussed.

Fe-metal organic framework converts mechanical energy with piezoelectric polarization to remove carbamazepine in water: Efficiency, pathway and mechanism

Piezocatalysis is a new technique that directly transforms mechanical energy into chemical energy. Although this approach can potentially be used to replace traditional water treatment methods, the structural tailorability and limited surface area of conventional inorganic piezoelectric materials restrict their catalytic efficiency. Herein, we employed a piezoelectric material made of an organic Fe-metal organic framework (MOFs) to purify water via piezocatalysis. We analyzed the physicochemical properties of MIL-100(Fe), including its piezoelectricity, bandgap structure, and charge separation efficiency. Carbamazepine (CBZ) was used as a representative aqueous drug pollutant, and MIL-100(Fe) removed 92 % of CBZ in 30 min via applying ultrasonication (US), which was 5.1 and 11.5 times higher than either the individual MIL-100(Fe) or US. The mechanical US stresses generated a built-in electric field in MIL-100(Fe) to promoted free charge migration, and also modulated the band structure of the sample. This promoted the production of reactive oxygen species. In this work, shows that porous piezoelectric nanostructures based on MOFs can convert mechanical energy into chemical energy to drive chemical oxidation processes.

Modified Stranski-Krastanov Growth of Amino Acid Arrays toward Piezoelectric Energy Harvesting.

Biomolecule-based piezoelectric nanostructures emerged as a new class of energy-converse materials, and designing tailored piezoelectric amino acid arrays is essential to achieve efficient electrical-mechanical coupling and fulfill their application potential. However, the controlled growth of amino acid nanostructures is still challenging due to the limited understanding of their growth mechanism. Herein, we base on the Stranski-Krastanov (S-K) growth mode and propose a mechanism for the growth of ordered amino acid array structures via physical vapor deposition. The growth of vertical valine sheet arrays is examined by changing the substrate temperature, chamber pressure, and source-substrate distance, and a "layer-plus-sheet" growth process is revealed. The modified S-K growth mode is applied to fabricate other amino acid nanostructures like leucine and isoleucine. The growth mode not only explains the formation of uniform and controllable morphology of amino acid structures but also leads to the significant enhancement of their piezoelectric properties. The maximal effective piezoelectric constant of valine sheets is 11.4 pm V-1, which approaches its highest predicted value. The output voltage of the valine array-based nanogenerator is ∼4.6 times the output voltage of the valine powder-based nanogenerator. This work provides new insights into the growth mechanism of ordered piezoelectric amino acid arrays, making them promising candidates for applications in wearable or implantable electronic devices.

Control of the Biodegradability of Piezoelectric Peptide Nanotubes Integrated with Hydrophobic Porphyrin.

Diphenylalanine (FF) is a piezoelectric material that is widely known for its high piezoelectric constant, self-assembly characteristics, and ease of manufacture. Because of its biocompatible nature, it is useful for implantable applications. However, its use in real applications is challenging because it degrades too easily in the body due to its solubility in water (0.76 g/mL). Upon incorporation of hydrophobic and biocompatible porphyrins into the FF, the degradability of the piezoelectric FF and their piezoelectric nanogenerators (PENGs) is controlled. Porphyrin-incorporated FFs are also formed as piezoelectric nanostructures well aligned on the substrate through self-assembly, and their piezoelectric properties are comparable to those of FF. The FF-based PENG degrades in only 5 min, whereas the FF-porphyrin-based PENG produces a stable output for >15 min in phosphate-buffered saline. This strategy for realizing biodegradable functional materials and devices with tunable degradation rates in the body can be applied to many implantable electronics.

Flexoelectric-boosted piezoelectricity of BaTiO3@SrTiO3 core-shell nanostructure determined by multiscale simulations for flexible energy harvesters

Achieving lead-free piezoelectric nanoparticles with excellent electromechanical responses is in great demand for fabricating nanoscale electronic devices. Recently, the coupling effect of combining flexoelectricity and piezoelectricity has attracted attention as a promising approach to control electromechanical properties. However, the implication of the coupling for the nanoparticles in this regard has been challenging due to its difficulty in controlling and observing the internal strain gradient. In this study, we demonstrate the flexoelectric-boosted electromechanical properties of piezoelectric nanoparticles using an induced built-in strain gradient in heterogeneous core-shell nanostructure. The composition-graded core-shell structure of BaTiO3@SrTiO3 nanoparticles enables a significant increment of the effective piezoelectric charge coefficient via the chemical heterogeneities-induced lattice strain gradient. Through the combinations of ab-initio calculation and multiphysics simulations, the origin of the strain distribution over nanoparticles is theoretically interpreted with accompanying phase balance and diffusion criteria. In addition, our designed core-shell nanoparticles-based energy harvesting devices generate highly efficient and flexoelectric-boosted piezoelectric output signals. Individual core-shell nanoparticles and related elastomeric nanocomposites reported in this work represent state-of-the-art electromechanical properties compared to previously reported piezoelectric nanoparticles and composites. This study provides a new source of inspiration for achieving high-performance lead-free piezoelectric nanostructures, paving the way for developing nano-electromechanical applications.

Size effect in piezoelectric semiconductor nanostructures

A gradient theory is applied to the mechanical constitutive equations for piezoelectric semiconductor nanostructures. This is achieved by considering the strain gradients in the constitutive equation with high-order stresses and electric displacements in advanced continuum model. The C1 continuous interpolations of displacements or a mixed formulation is required in the finite element method (FEM) due to the presence of the second-order derivative on the elastic displacements. A mixed FEM is then developed from the principle of virtual work. Numerical examples clearly show the significant effect of flexoelectricity on the induced electric potential and electric current in the piezoelectric semiconductor nanostructures.

Direct Visualization of Gigahertz Acoustic Wave Propagation in Suspended Phononic Circuits

We report direct visualization of gigahertz-frequency Lamb waves propagation in aluminum nitride phononic circuits by transmission-mode microwave impedance microscopy (TMIM). Consistent with the finite-element modeling, the acoustic eigenmodes in both a horn-shaped coupler and a sub-wavelength waveguide are revealed in the TMIM images. Using fast Fourier transform filtering, we quantitatively analyze the acoustic loss of individual Lamb modes along the waveguide and the power coupling coefficient between the waveguide and the parabolic couplers. Our work provides insightful information on the propagation, mode conversion, and attenuation of acoustic waves in piezoelectric nanostructures, which is highly desirable for designing and optimizing phononic devices for microwave signal processing and quantum information transduction.

НАНОРЕЛЕ И ЛОГИЧЕСКИЕ ЭЛЕМЕНТЫ НА ОСНОВЕ ГРАФЕНА И ГЕКСАГОНАЛЬНОГО НИТРИДА БОРА

Recently, the problem of creating new types of storage devices having non-volatile memory and commensurate in speed and number of rewriting cycles with operational storage is getting more relevant. However, microminiaturization of most known devices of this kind appears to have already reached scaling limits. In this regard, many computer developers have become involved in the development of low-power processors based on nanoelectromechanical relay elements. The article proposes nanorelay and logical elements based on graphene and hexagonal boron nitride having piezoelectric properties. It describes their design features, working principles and expected characteristics are described. It is noted that for the successful practical implementation of the proposed idea it is advisable to carry out additional works on synthesis of new two-dimensional piezoelectric and electroconductive nanostructures, which allow to reduce control voltage and the distance between relay contacts even in the off state.

Toward Quantitative Measurements of Piezoelectricity in III-N Semiconductor Nanowires

Piezoelectric semiconductor III-nitride nanostructures have received increasing interest as an alternative material for energy harvesters, sensors, and self-sustainable electronics, demanding furth...

Fundamental Definitions for Axially-Strained Piezo-Semiconductive Nanostructures.

Piezoelectric nanotransducers may offer key advantages in comparison with conventional piezoelectrics, including more choices for types of mechanical input, positions of the contacts, dimensionalities and shapes. However, since most piezoelectric nanostructures are also semiconductive, modeling becomes significantly more intricate and, therefore, the effects of free charges have been considered only in a few studies. Moreover, the available reports are complicated by the absence of proper nomenclature and figures of merit. Besides, some of the previous analyses are incomplete. For instance, the local piezopotential and free charges within axially strained conical piezo-semiconductive nanowires have only been systematically investigated for very low doping (1016 cm−3) and under compression. Here we give the definitions for the enhancement, depletion, base and tip piezopotentials, their characteristic lengths and both the tip-to-base and the depletion-to-enhancement piezopotential-ratios. As an example, we use these definitions for analyzing the local piezopotential and free charges in n-type ZnO truncated conical nanostructures with different doping levels (intrinsic, 1016 cm−3, 1017 cm−3) for both axial compression and traction. The definitions and concepts presented here may offer insight for designing high performance piezosemiconductive nanotransducers.

On the local/nonlocal piezoelectric nanobeams: Vibration, buckling, and energy harvesting

Based on a paradox-free nonlocal theory—two-phase local/nonlocal elasticity—vibration, buckling, and energy harvesting of piezoelectric nanobeams are investigated for the first time. By the means of the differential form of two-phase elasticity and Hamilton's principle, governing equations and boundary conditions are obtained. The exact solution as well as a numerical solution, Generalized Differential Quadrature Method (GDQM), are presented to extract results. Also, for the sake of obtaining equations for the forced vibration and energy harvesting analysis, the Galerkin method is utilized to discretize the governing equation. Given the fact that the differential nonlocal elasticity is not able to apply the size dependency on uniform loads, for the first time, the size-dependent piezoelectric load is taken into account through the two-phase elasticity. Also, vibration and energy harvesting of a clamped free nanobeam – which is a really good case for harvesting energy and cannot be accurately studied by differential nonlocal – are investigated employing the two-phase elasticity. To validate the present formulation and solution procedures, several comparison studies are conducted. Comparison between the common differential nonlocal elasticity and two-phase theory reveals that differential nonlocal elasticity is incompetent to yield reliable results for studying the vibration and energy harvesting of piezoelectric-based materials. Therefore, to study the mechanics of piezoelectric nano structures, other nonlocal theories such as two-phase local/nonlocal elasticity should be used. This paper can be a useful basis to investigate the vibration, buckling, and energy harvesting of nano piezoelectric devices and to improve their design.

Non-linear nanoscale piezoresponse of single ZnO nanowires affected by piezotronic effect

Zinc oxide (ZnO) nanowires (NWs) as semiconductor piezoelectric nanostructures have emerged as material of interest for applications in energy harvesting, photonics, sensing, biomedical science, actuators or spintronics. The expression for the piezoelectric properties in semiconductor materials is concealed by the screening effect of the available carriers and the piezotronic effect, leading to complex nanoscale piezoresponse signals. Here, we have developed a metal–semiconductor–metal model to simulate the piezoresponse of single ZnO NWs, demonstrating that the apparent non-linearity in the piezoelectric coefficient arises from the asymmetry created by the forward and reversed biased Schottky barriers at the semiconductor–metal junctions. By directly measuring the experimental I–V characteristics of ZnO NWs with conductive atomic force microscope together with the piezoelectric vertical coefficient by piezoresponse force microscopy, and comparing them with the numerical calculations for our model, effective piezoelectric coefficients in the range d 33eff ∼ 8.6 pm V−1–12.3 pm V−1 have been extracted for ZnO NWs. We have further demonstrated via simulations the dependence between the effective piezoelectric coefficient d 33eff and the geometry and physical dimensions of the NW (radius to length ratio), revealing that the higher d 33eff is obtained for thin and long NWs due to the tensor nature proportionality between electric fields and deformation in NW geometries. Moreover, the non-linearity of the piezoresponse also leads to multiharmonic electromechanical response observed at the second and higher harmonics that indeed is not restricted to piezoelectric semiconductor materials but can be generalized to any type of asymmetric voltage drops on a piezoelectric structure as well as leaky wide band-gap semiconductor ferroelectrics.

High-quality PMMA/ZnO NWs piezoelectric coating on rigid and flexible metallic substrates

This paper reports the comparative study of piezoelectric nanostructures deposited on metallic flexible substrate versus rigid substrates as a new architecture for energy harvesters. Rigid metallic substrates are multi-layered types of Pt/Ti/SiO2/Si or Au/Ti/SiO2/Si while Ti foil is a flexible metallic substrate. The active piezo-layer consisted of a vertical ZnO nanowires (ZnO NWs) array grown by the hydrothermal method at low temperature, on a previously deposited crystalline seed (nucleation) sol-gel layer and covered with a layer of polymethylmethacrylate (PMMA). The new obtained nanostructures have been characterized in different stages of preparation by X-Ray Diffraction, Scanning and Transmission Electron Microscopy, Atomic Force Microscopy, Spectroscopic Ellipsometry. The piezoelectric performance of PMMA/(ZnO NWs)/Ti structures was evaluated by measuring the d33 coefficient. Results show that ZnO nanowires have successfully grown on the flexible substrates with a piezoelectric coefficient four times greater than on rigid substrates. By improving vertical integration of ZnO NWs on flexible metallic substrate, PMMA/(ZnO NWs)/Ti affordable nanostructures open the way towards integration in wireless or defence technologies and in wearable or implantable biomedical systems as efficient harvester.

On the statics and dynamics of an electro-thermo-mechanically porous GPLRC nanoshell conveying fluid flow

Due to wide-ranging applications of piezoelectric nanostructures as the next generation of smart devices, this article analyzes size-dependent buckling and free vibration performance of fluid-conveying functionally graded-graphene nanoplatelets reinforced composite (FG-GPLRC) porous cylindrical nanoshell embedded in piezoelectric layer and subjected to the temperature gradient and a uniform electrical field based on modified couple stress theory incorporated into first-order shear deformation theory. Classical continuum theories are unable to capture the size effects on small-scale structures; thus, it is required to employ a nonclassical theory. To accomplish this purpose, modified couple stress theory is utilized to present a size-dependent shell model in which its displacement field is formulated by first-order shear deformation theory. The mechanical properties of the GPLRC layer are estimated based on modified Halpin-Tsai micromechanics and the rule of mixtures. Hamilton’s principle is employed to develop governing equations of motion and boundary conditions. Eventually, an analytical solution is prepared based on the Navier method to obtain critical voltage, critical buckling load, and natural frequency in the case of simply supported nanoshell, whereas, for other boundary conditions, the differential quadrature method is employed to solve the problem semi-analytically. The numerical illustration reveals that graphene reinforcement and porosity affect free vibration and buckling behavior of the nanoshell significantly. Moreover, it is concluded that the effect of fluid flow on vibration behavior nanoshell is more noticeable.

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.

A comprehensive review on the modeling of smart piezoelectric nanostructures

In this paper, a comprehensive review of nanostructures that exhibit piezoelectric behavior on all mechanical, buckling, vibrational, thermal and electrical properties is presented. It is firstly explained vast application of materials with their piezoelectric property and also introduction of other properties. Initially, more application of material which have piezoelectric property is introduced. Zinc oxide (ZnO), boron nitride (BN) and gallium nitride (GaN) respectively, are more application of piezoelectric materials. The nonlocal elasticity theory and piezoelectric constitutive relations are demonstrated to evaluate problems and analyses. Three different approaches consisting of atomistic modeling, continuum modeling and nano-scale continuum modeling in the investigation atomistic simulation of piezoelectric nanostructures are explained. Focusing on piezoelectric behavior, investigation of analyses is performed on fields of surface and small scale effects, buckling, vibration and wave propagation. Different investigations are available in literature focusing on the synthesis, applications and mechanical behaviors of piezoelectric nanostructures. In the study of vibration behavior, researches are studied on fields of linear and nonlinear, longitudinal and transverse, free and forced vibrations. This paper is intended to provide an introduction of the development of the piezoelectric nanostructures. The key issue is a very good understanding of mechanical and electrical behaviors and characteristics of piezoelectric structures to employ in electromechanical systems.

Micro/Nanostructure Engineering of Epitaxial Piezoelectric α-Quartz Thin Films on Silicon.

The monolithic integration of sub-micron quartz structures on silicon substrates is a key issue for the future development of piezoelectric devices as prospective sensors with applications based on the operation in the high-frequency range. However, to date, it has not been possible to make existing quartz manufacturing methods compatible with integration on silicon and structuration by top-down lithographic techniques. Here, we report an unprecedented large-scale fabrication of ordered arrays of piezoelectric epitaxial quartz nanostructures on silicon substrates by the combination of soft-chemistry and three lithographic techniques: (i)laser interference lithography, (ii) soft nanoimprint lithography on Sr-doped SiO2 sol-gel thin films, and (iii) self-assembled SrCO3 nanoparticle reactive nanomasks. Epitaxial α-quartz nanopillars with different diameters (from 1 μm down to 50 nm) and heights (up to 2 μm) were obtained. This work demonstrates the complementarity of soft-chemistry and top-down lithographic techniques for the patterning of epitaxial quartz thin films on silicon while preserving its epitaxial crystallinity and piezoelectric properties. These results open up the opportunity to develop a cost-effective on-chip integration of nanostructured piezoelectric α-quartz MEMS with enhanced sensing properties of relevance in different fields of application.

Piezoelectric Energy Harvesting from Two-Dimensional Boron Nitride Nanoflakes.

Two-dimensional (2D) piezoelectric hexagonal boron nitride nanoflakes (h-BN NFs) were synthesized by a mechanochemical exfoliation process and transferred onto an electrode line-patterned plastic substrate to characterize the energy harvesting ability of individual NFs by external stress. A single BN NF produced alternate piezoelectric output sources of ∼50 mV and ∼30 pA when deformed by mechanical bendings. The piezoelectric voltage coefficient (g11) of a single BN NF was experimentally determined to be 2.35 × 10-3 V·m·N-1. The piezoelectric composite composed of BN NFs and an elastomer was spin-coated onto a bulk Si substrate and then transferred onto the electrode-coated plastic substrates to fabricate a BN NFs-based flexible piezoelectric energy harvester (f-PEH) which converted a piezoelectric voltage of ∼9 V, a current of ∼200 nA, and an effective output power of ∼0.3 μW. This result provides a new strategy for precisely characterizing the energy generation ability of piezoelectric nanostructures and for demonstrating f-PEH based on 2D piezomaterials.

Flexoelectric effects on wave propagation responses of piezoelectric nanobeams via nonlocal strain gradient higher order beam model

This paper is devoted to investigate the effects of the flexoelectric phenomenon on wave dispersion characteristics of piezoelectric nanobeams. Modified constitutive relations containing the flexoelectric effects are taken into account. The problem is formulated utilizing Reddy’s higher order shear deformation beam theory in conjunction with the nonlocal strain gradient theory (NSGT). Additionally, Hamilton’s principle is employed to derive the governing equations of the problem. Thereafter, considering harmonic wave dispersion, the solution of equations of motion is expressed as complex form. Applying this solution to the governing equations gives rise to the eigenvalue problem. Afterwards, the eigenvalue problem is solved analytically to achieve the wave frequencies and phase velocities of the system. Totally, the role of various involved parameters namely the flexoelectric effects and applied electric voltage on the wave dispersion curves is studied in detail. In addition, the size-dependency of the flexoelectric phenomenon on wave dispersion behavior of the nanobeam is explored. Due to the fact that adequate knowledge about wave dispersion characteristics of structures is of great value especially in nanotechnology field, it is hoped that the results presented here may be helpful for exact behavior determination of piezoelectric nano-structures.

Piezoelectric Response of ZnO Thin Films Grown By Plasma-Enhanced Atomic Layer Deposition

ZnO is a direct band gap semiconductor with attractive piezoelectrical, optical, and electrical properties, particularly appealing for a variety of functional devices. Especially the utilization of piezoelectric properties of ZnO nanostructures for transforming mechanical to electrical energy has attracted much research interest. For most of these so called nanogenerators, solution based deposition methods have been applied to create the desired nanostructures, often lacking a precise control of the deposition parameters. Atomic layer deposition, on the other hand, allows conformal and uniform deposition on high aspect ratio structures with Å-level thickness control. In this study, we investigate the piezoelectric response of ZnO thin films on flexible substrates as a starting point for piezoelectric nanostructures. The films are grown by plasma-enhanced atomic layer deposition (PE-ALD) to thicknesses below 100 nm by adapting diethylzinc and O2-plasma as reactants. In comparison to thermal ALD (where diethylzinc and water are used as reactants), PE-ALD allows the deposition of films with higher resistivity, an important property to minimize the leakage of piezoelectric charges. Commercially available Polyethylenterephthalat (PET) coated with Indium Tin Oxide (ITO) serves as the flexible substrate and bottom electrode, respectively. The deposition of ZnO thin films is carried out at substrate temperatures between room temperature and 100 °C, as a change in preferential crystal orientation from (100) to (002) can be observed in this temperature range. [1] The macroscopic piezoelectric characterization is performed in a home-built stamp station, in which a defined periodic force is exerted onto the samples and the generated piezoelectric charges are measured. Out of this, the longitudinal piezoelectric coefficient d33 can be obtained. Preliminary results show d33 coefficients > 7 pC/N, which is comparable to literature results. [2] The piezoelectric characterization is made for the different samples to understand how the d33 coefficient changes for films deposited at different substrate temperatures and thus having different crystal orientation. Since the [002] is the polar axis in the ZnO wurtzite crystal structure, films with preferred orientation in this direction are therefore expected to show higher d33 coefficients. The work lays the basis for developing functional piezoelectric generators and sensors in thin film form. However, the concepts can be easily transferred to depositions on lithographically defined templates in order to create nanostructured ZnO, which exhibits increased piezo response. [1] J.Pilz, A. Perrotta, G. Leising, A. M. Coclite, ZnO thin films grown by plasma-enhanced atomic layer deposition: material properties within and outside the “ALD window”, submitted. [2] M. Laurenti, S. Stassi, M. Lorenzoni, M. Fontana, G. Canavese, V. Cauda, C.F. Pirri, Evaluation of the piezoelectric properties and voltage generation of flexible zinc oxide thin films, Nanotechnology. 26 (2015) 215704. doi:10.1088/0957-4484/26/21/215704.