Piezoelectric Combination Research Articles

CuS@MoS2 p[sbnd]n heterojunction photocatalyst integrating photothermal and piezoelectric enhancement effects for tetracycline degradation

Photocatalysis is an environmentally friendly and low-cost technology for the degradation of pollutants. In addition to the construction of heterojunction which may decrease the recombination of charge carriers and extend the photo-response range, the utilization of piezoelectricity and photothermal conversion also provides the promising routes to improve the photocatalytic performance. Herein, a CuS@MoS2 heterostructure was developed to simultaneously meet the needs of these enhancement mechanisms. The formation of pn heterojunction was confirmed and the associated energy band diagram was constructed with band gaps of CuS and MoS2 as 1.56 and 1.80 eV, respectively. For the degradation of tetracycline, it was demonstrated that the inherent piezoelectric property of MoS2 surface enhanced the piezocatalytic activity by inducing an electric field to aid charge separation. The heat generated by illumination raised the photocatalytic reaction rate by supplying extra energy to carriers. The CuS@MoS2 heterostructure exhibited significantly better catalytic performance than the individual CuS or MoS2 due to the formation of pn heterojunction. Furthermore, the combination of piezoelectricity and photothermal conversion also led to a significant synergistic effect, achieving a degradation efficiency of over 95% within 30 min. As compared to the conditions under ultrasonic vibration, visible light irradiation and visiblenearinfrared light irradiation alone, the combination of visiblenearinfrared irradiation and ultrasonic vibration could lead to 96, 205 and 81% enhancement. This work provides valuable insights into the design of novel heterojunction photocatalysts integrating the piezoelectric and photothermal enhancement effects.

Propagation characteristics of elastic longitudinal wave in a piezoelectric semiconductor metamaterial rod and its tuning

Elastic metamaterial structures have many distinct wave properties such as band gap structure and topological phase inversion. The coexistence and interaction of piezoelectricity and semiconductor behavior in piezoelectric semiconductor (PS) materials endow metamaterials with some new physical effects. We investigate the propagation characteristics of elastic longitudinal waves in a metamaterial rod made of n-type PS material and piezoelectric (PE) dielectric material. Based on one-dimensional rod model, we present the transfer matrixes for the PS and PE phases as well as the interfacial transfer matrix of unit cell. The analytical dispersion relations of the considered PS-PE metamaterial rod are obtained by utilizing Bloch's theorem. Numerical results show that band gap structures of the metamaterial rod are dependent on the initial electron concentration, length ratio of PE phase, interfacial condition, and capacitor connected with the PE phase. The selection of certain initial electron concentration, length ratio of PE phase, and capacitor can lead to the appearance of topological phase inversion, highlighting the potential for controlling and manipulating the wave propagation properties of PS metamaterial structures. This paper provides a theoretical guidance on the development of smart devices based on PS metamaterial structures. The novel combination of piezoelectricity and semiconductor behavior in these materials opens up new avenues for designing and engineering advanced devices with tailored wave properties and functionalities.

Switching Rashba spin-splitting by reversing electric-field direction

The manipulation of the Rashba spin-splitting is crucial for the development of nanospintronic technology. Here, it is proposed that the Rashba spin-splitting can be turned on and off by reversing electric-field direction. By the first-principles calculations, our proposal is illustrated by a concrete example of Janus monolayer RbKNaBi. The designed RbKNaBi possesses dynamical, thermal, and mechanical stabilities, and is a large-gap quantum spin Hall insulator (QSHI) with Rashba spin-splitting near the Fermi level. A small built-in electric field is predicted due to very small electronegativity difference between the bottom and top atoms, which is very key to switch Rashba spin-splitting through the experimentally available electric field intensity. Due to out-of-plane structural asymmetry, the Janus monolayer has distinctive behaviors by applying external electric field $E$ with the same magnitude but different directions ($z$ or $\ensuremath{-}z$). Our results reveal that the Rashba energy (${E}_{R}$) and Rashba constant (${\ensuremath{\alpha}}_{R}$) are increased by the positive $E$, while a negative $E$ suppresses the Rashba splitting to disappear, and then appears again. In a certain $E$ region (0.15 $\mathrm{V}/\AA{}$ to 0.25 $\mathrm{V}/\AA{}$), switching Rashba spin-splitting can be achieved by only reversing electric-field direction. Besides, the piezoelectric strain coefficients ${d}_{11}$ and ${d}_{31}$ (5.52 pm/V and --0.41 pm/V) are predicted, which are higher than or compared with those of many 2D materials. By piezoelectric effect, the strain can also be used to tune Rashba spin-splitting of RbKNaBi. In Janus RbKNaBi monolayer, the combination of piezoelectricity and Rashba spin-splitting with topological insulating phase can promote the integration of various physical phenomena. Moreover, a possible spintronic device is proposed to realize the function of spintronic switch. Our proposed manipulation of the Rashba spin-splitting may make a special contribution to semiconductor spintronics.

Piezoelectric manipulation of spin-orbit coupling in a Wurtzite heterostructure.

The combination of piezoelectricity and spin-orbit coupling (SOC) effect makes wurtzite semiconductors attractive for the development of exotic spin-related physics as well as spintronic applications. Triggering piezoelectricity, particularly by an external stimulus, provides a new perspective for manipulating SOC, but until now, a comprehensive understanding of this mechanism is lacking. Herein, by means of self-consistent calculations and Löwdin perturbation approach, we have explored the manipulation of SOC in the wurtzite (Al, Ga)N/GaN heterostructure by external stress-induced piezoelectric polarization. The results suggest that the Rashba SOC depends weakly on stress due to the wide-gap feature of the wurtzite crystal that makes Rashba SOC predominant by a bulk term instead of the structural inversion term. The piezoelectric polarization diminishes and even turns off Dresselhaus coupling by reducing the interfacial electric field. Moreover, piezoelectricity is shown to improve the poorly gate-tunable SOC. In the heterostructure with two occupied subbands, the Dresselhaus coupling of the second subband is more sensitive than the first one in response to stress. As an extension, we further demonstrate that the correlation effect in the wurtzite heterostructure can be significantly enhanced by piezoelectric polarization. This study offers an in-depth insight into piezoelectric modulation of spin-orbit physics, which has the potential for stimulating new quantum correlation states or designing functional spintronic devices.

Large out-of-plane piezoelectric response in ferromagnetic monolayer NiClI

The combination of piezoelectricity and ferromagnetic (FM) order in a two-dimensional (2D) material, namely, 2D piezoelectric ferromagnetism (PFM), may open up unprecedented opportunities for device applications. Here, we predict an in-plane FM semiconductor Janus monolayer NiClI with a considerably large magnetic anisotropy energy of 1.439 meV, exhibiting dynamical, mechanical, and thermal stabilities. The NiClI monolayer possesses larger in-plane piezoelectricity (d11 = 5.21 pm/V) comparable to that of MoS2. Furthermore, NiClI has large out-of-plane piezoelectricity (d31 = 1.89 pm/V), which is highly desirable for ultrathin piezoelectric device application. It is proved that large out-of-plane piezoelectricity is robust against electronic correlation, which confirms reliability of large d31. Finally, being analogous to NiClI, PFM with large out-of-plane piezoelectricity can also be achieved in the Janus monolayers of NiClBr and NiBrI, with the predicted d31 of 0.73 and 1.15 pm/V, respectively.

A piezoelectric quantum spin Hall insulator VCClBr monolayer with a pure out-of-plane piezoelectric response.

The combination of piezoelectricity with a nontrivial topological insulating phase in two-dimensional (2D) systems, namely piezoelectric quantum spin Hall insulators (PQSHI), is intriguing for exploring novel topological states toward the development of high-speed and dissipationless electronic devices. In this work, we predict a PQSHI Janus monolayer VCClBr constructed from VCCl2, which is dynamically, mechanically and thermally stable. In the absence of spin orbital coupling (SOC), VCClBr is a narrow gap semiconductor with a gap value of 57 meV, which is different from Dirac semimetal VCCl2. The gap of VCClBr is due to a built-in electric field caused by asymmetrical upper and lower atomic layers, which is further confirmed by the external-electric-field induced gap in VCCl2. When including SOC, the gap of VCClBr is increased to 76 meV, which is larger than the thermal energy of room temperature (25 meV). The VCClBr is a 2D topological insulator (TI), which is confirmed by Z2 topological invariant and nontrivial one-dimensional edge states. It is proved that the nontrivial topological properties of VCClBr are robust against strain (biaxial and uniaxial cases) and external electric fields. Due to broken horizontal mirror symmetry, only an out-of-plane piezoelectric response can be observed, when a biaxial or uniaxial in-plane strain is applied. The predicted piezoelectric strain coefficients d31 and d32 are -0.425 pm V-1 and -0.219 pm V-1, respectively, and they are higher than or compared with those of many 2D materials. Finally, Janus monolayer VCFBr and VCFCl (dynamically unstable) are also constructed, and they are still PQSHIs. Moreover, the d31 and d32 of VCFBr and VCFCl are higher than those of VCClBr, and the d31 (absolute value) of VCFBr is larger than one. According to out-of-plane piezoelectric coefficients of VCXY (X ≠ Y = F, Cl and Br), CrX1.5Y1.5 (X = F, Cl and Br; Y = I) and NiXY (X ≠ Y = Cl, Br and I), it is concluded that the size of the out-of-plane piezoelectric coefficient has a positive relation with the electronegativity difference of X and Y atoms. Our studies enrich the diversity of Janus 2D materials, and open a new avenue in the search for PQSHI with a large out-of-plane piezoelectric response, which provides a potential platform in nanoelectronics.

Combination of Piezoelectric and Triboelectric Devices for Robotic Self-Powered Sensors.

Sensors are an important part of the organization required for robots to perceive the external environment. Self-powered sensors can be used to implement energy-saving strategies in robots and reduce their power consumption, owing to their low-power consumption characteristics. The triboelectric nanogenerator (TENG) and piezoelectric transducer (PE) are important implementations of self-powered sensors. Hybrid sensors combine the advantages of the PE and TENG to achieve higher sensitivity, wider measurement range, and better output characteristics. This paper summarizes the principles and research status of pressure sensors, displacement sensors, and three-dimensional (3D) acceleration sensors based on the self-powered TENG, PE, and hybrid sensors. Additionally, the basic working principles of the PE and TENG are introduced, and the challenges and problems in the development of PE, TENG, and hybrid sensors in the robotics field are discussed with regard to the principles of the self-powered pressure sensors, displacement sensors, and 3D acceleration sensors applied to robots.

A piezoelectric quantum spin Hall insulator with Rashba spin splitting in Janus monolayer SrAlGaSe4

The realization of multifunctional two-dimensional (2D) materials is fundamentally intriguing, such as the combination of piezoelectricity with a topological insulating phase in Janus monolayer SrAlGaSe4.

Piezoelectric Nanotopography Induced Neuron‐Like Differentiation of Stem Cells

AbstractThe biophysical characteristics of the extracellular matrix, such as nanotopography and bioelectricity, have a profound influence on cell proliferation, adhesion, differentiation, etc. Recognition of the function of a certain biophysical cue and fabrication of biomaterial scaffolds with specific properties would have important implications and significant applications in tissue engineering. Herein, nanotopographic and piezoelectric biomaterials are fabricated and the combination effect of and individual contribution to proliferation, adhesion, and neuron‐like differentiation of rat bone marrow‐derived mesenchymal stem cells (rbMSCs) are clarified via nanotopography and piezoelectricity. Piezoelectric polyvinylidene fluoride with nanostripe array structures is fabricated, which can generate a surface piezoelectric potential up to millivolt by cell movement and traction. The results reveal a more favorable effect on neuron‐like differentiation of rbMSCs from the combination of piezoelectricity and nanotopography rather than nanotopography alone, whereas nanotopography can increase cellular adhesion. This research provides a new insight into designing biomaterials for the potential application in neural tissue engineering.

First-Principles Prediction of a Room-Temperature Ferromagnetic Janus VSSe Monolayer with Piezoelectricity, Ferroelasticity, and Large Valley Polarization.

Inspired by recent experiments on the successful fabrication of monolayer Janus transition-metal dichalcogenides [ Lu , A.-Y. ; Nat. Nanotechnol. 2017 , 12 , ( 8 ), 744 and ferromagnetic VSe2 [ Bonilla , M. ; Nat. Nanotechnol. 2018 , 13 , ( 4 ), 289 ], we predict a highly stable room-temperature ferromagnetic Janus monolayer (VSSe) by density functional theory methods and further confirmed the stability by a global minimum search with the particle-swarm optimization method. The VSSe monolayer exhibits a large valley polarization due to the broken space- and time-reversal symmetry. Moreover, its low symmetry C3 v point group results in giant in-plane piezoelectric polarization. Most interestingly, a strain-driven 90° lattice rotation is found in the magnetic VSSe monolayer with an extremely high reversal strain (73%), indicating an intrinsic ferroelasticity. The combination of piezoelectricity and valley polarization make magnetic 2D Janus VSSe a tantalizing material for potential applications in nanoelectronics, optoelectronics, and valleytronics.

The Applications of Smart Materials in Hydraulic Machineries: Combination of Piezoelectricity and Bubbles

The Applications of Smart Materials in Hydraulic Machineries: Combination of Piezoelectricity and Bubbles

Periodical Microstructures Based on Novel Piezoelectric Material for Biomedical Applications.

A novel cantilever type piezoelectric sensing element was developed. Cost-effective and simple fabrication design allows the use of this element for various applications in the areas of biomedicine, pharmacy, environmental analysis and biosensing. This paper proposes a novel piezoelectric composite material whose basic element is PZT and a sensing platform where this material was integrated. Results showed that a designed novel cantilever-type element is able to generate a voltage of up to 80 µV at 50 Hz frequency. To use this element for sensing purposes, a four micron periodical microstructure was imprinted. Silver nanoparticles were precipitated on the grating to increase the sensitivity of the designed element, i.e., Surface Plasmon Resonance (SPR) effect appears in the element. To tackle some issues (a lack of sensitivity, signal delays) the element must have certain electronic and optical properties. One possible solution, proposed in this paper, is a combination of piezoelectricity and SPR in a single element.

SAW propagation loss mechanism in piezoelectric ceramics

The surface acoustic wave (SAW) propagation loss mechanism of piezoelectric ceramics is examined using lead titanate (PbTiO3) ceramics modified with additives of Nd2O3, MnO2, and In2O3, which have zero temperature coefficients of SAW delay time. The propagation loss L in the frequency range 30 to 300 MHz consists of two parts. One is the Rayleigh scattering loss LS caused by grain, and the other is the true dissipative loss LF caused by internal friction. Thus, total loss results in L(dB/cm) = LS+LF = 3.2×103D3f4+6.8×10−4f2 (where D and f denote average grain size in cm and frequency in MHz, respectively). It is also revealed experimentally that the internal friction causing the latter loss has a close correlation with the dielectric loss through piezoelectric combination. Therefore, materials with fine grain (<0.5 μm) and low dielectric loss (<10−3) must be developed to reduce SAW propagation losses which prevent the piezoelectric ceramics from being used in higher frequency (≳100 MHz) SAW applications. Based on these requirements, fine grained (∼0.5 μm) specimens are fabricated. The propagation losses obtained from these specimens, 9 dB/cm at 100 MHz, are the lowest values ever reported for piezoelectric ceramics. This result suggests that the present ceramics have high potential as materials for high-frequency SAW devices.