Applications In Nanoelectromechanical Systems Research Articles

Four ribbons of double-layer graphene suspending masses for NEMS applications

Graphene ribbons with a suspended proof mass for nanomechanical systems have been rarely studied. Here, we report three types of nanomechanical devices consisting of graphene ribbons (two ribbons, four ribbons-cross and four ribbons-parallel) with suspended Si proof masses and studied their mechanical properties. The resonance frequencies and built-in stresses of three types of devices ranged from tens of kHz to hundreds of kHz, and from 82.61 MPa to 545.73 MPa, respectively, both of which decrease with the increase of the size of proof mass. The devices with four graphene ribbons featured higher resonance frequencies and spring constants, but lower built-in stresses than two ribbon devices under otherwise identical conditions. The Young’s modulus and fracture strain of double-layer graphene were measured to be 0.34 TPa and 1.13% respectively, by using the experimental data and finite element analysis (FEA) simulations. Our studies would lay the foundation for understanding of mechanical properties of graphene ribbons with a suspended proof mass and their potential applications in nanoelectromechanical systems.

Deformation state of a graphene sheet within the framework of the continuum moment-membrane theory of elasticity

The paper proposes an approach to finding the stress-strain state (SSS) of structures containing graphene, a novel nanomaterial that has currently found а wide range of practical applications in nanoelectromechanical systems. Graphene is a 2D basic building block for other carbon structures such as membranes, sheets, nanotubes, etc. To describe the SSS of a graphene sheet, the phenomenological continuum moment-membrane theory of plates is used, from which, due to the fact that graphene is an ultrathin material, the concept of thickness is excluded. The physical elasticity relationships of a graphene sheet are expressed through its rigidity characteristics, determined using the harmonic potential of interatomic interactions in carbon. A differential formulation and the corresponding variational formulation are given for the problem of static deformation and determination of the natural frequencies and modes of vibration of a graphene sheet. The variational formulation is based on the Lagrange principle and is implemented numerically using the finite element method. Finite element relations are constructed taking into account moment effects of the behavior of a graphene sheet. For approximation, a 4-node rectangular finite element is used. Numerical solutions to several problems of static deformation of a graphene sheet under conditions of a plane stress state and transverse bending are presented, and the analysis of its natural vibrations is also performed. Good convergence of numerical simulation results in all considered problems is demonstrated. The obtained numerical solutions are essential in designing and calculating resonators in which ultrathin nanostructures are used. The establishment of the fact that a graphene sheet has a high intrinsic frequency falling in the GHz region (for example, quartz resonators are characterized by megahertz frequencies) opens up new prospects for using graphene itself as an ultrasensitive nanomechanical resonator for detecting small masses and ultrasmall displacements.

Nonlocal strain gradient‐based nonlinear dynamics of sinusoidal impulsive actuated porous/piezoelectric multilayer energy nanoharvesters

AbstractThe applications of nanoelectromechanical systems integrating simultaneously the mechanical and electrical functionalities at nanoscale have been gotten wider in the last decade. The main objective of this exploration is to analyze the small scale‐dependent nonlinear dynamical feedback of multilayer energy nanoharvesters containing a graded porous passive core coated by piezoelectric facesheets under a sinusoidal impulsive external actuation. For this purpose, the technique of meshless collocation is constructed at the same time the nonlocal stress and strain gradient tensors without any necessary background meshes and integration procedure. It is found that by taking the nonlocal stress tensor into account, the average of extremum points of maximum lateral deflection increases from to , and from to for simply supported and clamped multilayer nanoharvesters, respectively. On the contrary, through considering the strain gradient tensor, the average of extremum values of the maximum lateral deflection reduces from to for the simply supported nanoharvester, and from to for the clamped one.Highlights Development a third‐order shear flexible nonlocal strain gradient (NSG)‐based plate‐type nanoharvester model Incorporating the role of nonlocal stress and strain gradient tensors in nonlinear dynamics of nanoharvesters Time‐histories of achieved voltage of sinusoidal impulsive loaded plate‐type nanoharvesters Influence of porosity on the NSG‐based nonlinear dynamic performance.

An analytical model for nanoscale flexoelectric doubly curved shells

The phenomenon of flexoelectricity, wherein the generation of electrical polarization results from strain gradients, has garnered significant attention in electromechanics. This phenomenon holds immense potential for diverse applications in nanoelectromechanical systems. Doubly curved shells present a particularly compelling structure for implementing flexoelectric devices, representing the most general scenario. To comprehensively understand the mechanical behavior of nanoscale flexoelectric doubly curved shells, we present a novel analytical model in this study. Our model incorporates a reformulated strain gradient elasticity theory, a modified expression of electric enthalpy density considering Maxwell’s self-field gradient, and a moderately thick shell configuration. To further elucidate this model, we establish complete formulations and analytical solutions of static bending and free vibration problems. This study reveals the crucial roles that various parameters such as principal curvature radii, length scale parameters, transverse structural sizes, and the Winkler–Pasternak foundation play in controlling the mechanical behavior of nanoscale flexoelectric doubly curved shells. These theoretical findings offer valuable insights into the design of nanodevices based on the direct flexoelectric effect.

Theoretical investigations of Sc2C based functionalized MXenes for applications in nanoelectromechanical systems

The piezoelectricity of functionalized MXenes is of increasingly interest in theoretical and experimental research due to many advantages, such as narrowing the electromechanical coupling size, enhancing the piezoelectric coefficients and producing the out-of-plane piezoelectricity. In this work, employing the first-principle calculations, the piezoelectricity together with related electronic and elastic properties of six functionalized MXenes Sc2CTT′ monolayers where T and T′ are functional groups were comprehensively investigated. All of them are mechanically stable and more flexible than graphene, indicating their potential use in flexible devices. Furthermore, the semiconducting nature and broken inversion symmetry endow them with piezoelectricity for nanoelectromechanical facilities. In terms of the in-plane piezoelectricity, Sc2CFCl possesses the biggest d22 and Sc2COHH has the biggest d15. Sc2CHCl and Sc2CFCl monolayers have stronger out-of-plane piezoelectricity when the strain is applied along the x axis due to their larger absolute value of d31 than other monolayers. In addition, with relative to MoSTe which has relatively good out-of-plane piezoelectricity, Sc2COHF and Sc2CHCl monolayers possess comparable out-of-plane piezoelectric strain coefficient d33, which is favorable for their applications in out-of-plane piezoelectric sensing. Excitingly, the value of d33 (35.64 pm/V) for Sc2COHH monolayer is surprisingly over three times of that for MoSTe. It is expected that the studied Sc2CTT’ monolayers with commendable piezoelectric properties can be utilized in certain nanoelectromechanical systems, such as the blood-pressure meter, bionic skin of robots and energy harvesting equipments.

Theoretical Evaluation of Impact Characteristics of Wavy Graphene Sheets with Disclinations Formed by Origami and Kirigami.

Evaluation of impact characteristics of carbon nanomaterials is very important and helpful for their application in nanoelectromechanical systems (NEMS). Furthermore, disclination lattice defects can generate out-of-plane deformation to control the mechanical behavior of carbon nanomaterials. In this study, we design novel stable wavy graphene sheets (GSs) using a technique based on origami and kirigami to control the exchange of carbon atoms and generate appropriate disclinations. The impact characteristics of these GSs are evaluated using molecular dynamics (MD) simulation, and the accuracy of the simulation results is verified via a theoretical analysis based on continuum mechanics. In the impact tests, the C60 fullerene is employed as an impactor, and the effects of the different shapes of wavy GSs with different disclinations, different impact sites on the curved surface, and different impact velocities are examined to investigate the impact characteristics of the wavy GSs. We find that the newly designed wavy GSs increasingly resist the kinetic energy (KE) of the impactor as the disclination density is increased, and the estimated KE propagation patterns are significantly different from those of the ideal GS. Based on their enhanced performance in the impact tests, the wavy GSs possess excellent impact behavior, which should facilitate their potential application as high-impact-resistant components in advanced NEMS.

Nano-Interfacial Layer Effects on Dielectric and Piezoelectric Characteristics in Chemical Solution-Derived (K,Na)NbO3 Thin Films

Since non-piezoelectric interfacial layers even at the nanoscale significantly affect the performance of lead-free piezoelectric thin films, the quantitative characterization of property changes of thin films due to interfacial layers is of great importance and should be precisely undertaken for piezoelectric microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) devices. In contrast to widely accepted concepts for interfacial layer thickness estimation based on the existing series capacitor model, we find that the interfacial layer thickness at the top and the bottom interfaces is clearly different in chemical solution deposition (CSD)-derived (K0.5,Na0.5)(Mn0.005,Nb0.995)O3 (KNMN) thin films. Interestingly, the thickness of the bottom interface increases linearly with increasing the thin film thickness, while the thickness of the top interface is constant regardless of the thin film thickness. In this work, nano-interfacial layer effects of CSD-derived KNMN thin films are theoretically and experimentally addressed in a combinatorial way using a modified series capacitor model. The gained information is used to envisage the origins and the mechanisms of non-piezoelectric interfacial layers and associated dielectric and ferroelectric properties of KNMN thin films. Our research connects macroscopic properties with the microscopic origins and is greatly facilitated by separating intrinsic and extrinsic contributions to phenomenological behaviors, as well as engineering interface-related properties of the films. We believe these studies to be crucial for the further development and applications of KNN-based lead-free piezoelectric devices, and will also open the door to future studies on other lead-free piezoelectric material systems for practical MEMS and NEMS applications.

A self-powered vibration sensing element based on three-dimensional graphene field effect transistor

Piezoelectricity of two-dimensional layered materials is of great significance for electromechanical coupling applications in nanoelectromechanical systems. The nanoscale devices based on graphene have attracted intense interest due to its excellent electronic and mechanical properties. However, the centrosymmetric crystal structure in intrinsic graphene severely restricts its applications in mechanical sensors, transducers, and energy harvesters. In this paper, a self-powered vibration sensing element based on rolled-up single-layer graphene is proposed and demonstrated, which realizes the conversion from mechanical vibrations into electrical signals. In contrast to previous pioneering works requiring silica cavities or Si/SiO2 calibration grating substrate to support the graphene, a three-dimensional (3D) non-closed tubular structure is adopted to develop the piezoelectricity in single-layer graphene, where the inversion symmetry of single-layer graphene is broken via self-rolled-up process induced strain. Hence, apparent piezoresponse from the 3D non-closed tubular graphene field effect transistor is observed. Moreover, a peak-to-peak amplitude for the piezoelectric current up to 4.2 is achieved, corresponding to the periodicity of mechanical vibration, and the value can increase to 10.8 nA by applying a small source–drain voltage of 6 mV. The device is also sensitive to mechanical vibration with different frequencies and shows similar currents. The electromechanical coupling in rolled-up graphene provides a basis for the applications in sensing, actuating, and energy harvesting.

Nanointerfacial Layer Effect on Dielectric and Piezoelectric Responses in Chemical Solution-Derived Lead-Free Alkaline Niobate-Based Thin Films.

Since nonpiezoelectric interfacial layers even at the nanoscale significantly affect the performance of lead-free piezoelectric thin films, the quantitative characterization of property changes of thin films due to interfacial layers is of great importance and should be precisely undertaken for piezoelectric microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) devices. In contrast to widely accepted concepts for interfacial layer thickness estimation based on the existing series capacitor model, we find that the interfacial layer thickness at the top and the bottom interfaces is clearly different in chemical solution deposition (CSD)-derived (K0.5,Na0.5)(Mn0.005,Nb0.995)O3 (KNMN) thin films. Interestingly, the thickness of the bottom interface increases linearly with increasing thin-film thickness, while the thickness of the top interface is constant regardless of the thin-film thickness. In this work, nanointerfacial layer effects of CSD-derived KNMN thin films are theoretically and experimentally addressed in a combinatorial way using a modified series capacitor model. The obtained information is used to envisage the origins and the mechanisms of nonpiezoelectric interfacial layers and associated dielectric and ferroelectric properties of KNMN thin films. Our research connects macroscopic properties with microscopic origins and is greatly facilitated by separating intrinsic and extrinsic contributions to phenomenological behaviors, as well as engineering interface-related properties of the films. We believe these studies to be crucial for the further development and applications of KNN-based lead-free piezoelectric devices, which also open the door to future studies on other lead-free piezoelectric material systems for practical MEMS and NEMS applications.

Tunable Exciton-Optomechanical Coupling in Suspended Monolayer MoSe2.

The strong excitonic effect in monolayer transition metal dichalcogenide (TMD) semiconductors has enabled many fascinating light-matter interaction phenomena. Examples include strongly coupled exciton-polaritons and nearly perfect atomic monolayer mirrors. The strong light-matter interaction also opens the door for dynamical control of mechanical motion through the exciton resonance of monolayer TMDs. Here, we report the observation of exciton-optomechanical coupling in a suspended monolayer MoSe2 mechanical resonator. By moderate optical pumping near the MoSe2 exciton resonance, we have observed optical damping and antidamping of mechanical vibrations as well as the optical spring effect. The exciton-optomechanical coupling strength is also gate-tunable. Our observations can be understood in a model based on photothermal backaction and gate-induced mirror symmetry breaking in the device structure. The observation of gate-tunable exciton-optomechanical coupling in a monolayer semiconductor may find applications in nanoelectromechanical systems (NEMS) and in exciton-optomechanics.

Electromagnetic instability analysis of nano-sensor

The enormous increase in the application of nano-electromechanical systems for biological purposes, as well as modern sensors in the particle accelerators, leads to new operation situations for these devices, such as an external magnetic field. While different physical phenomena on the behavior of nano-electromechanical systems have been addressed, few researchers have focused on the magnetic flux’s inspiration on the performance of electromechanical nano-sensors. In this paper, the dynamic electromagnetic instability of nano-sensors immersed in an external magnetic flux is simulated. As nano-structures have a considerable surface-to-volume ratio, the constitutive equation is developed by incorporating surface energies. The impact of finite dimensions is taken into account in the developed model by using corrected relations for electrical and van der Waals force. The nonlinear dynamic behavior of the system is investigated by employing the Galerkin method. We find that the magnetic flux can significantly reduce the dynamic instability threshold of the nano-sensors.

Size-dependent mechanical properties of twin graphene

Twin Graphene, a novel 2D planar semiconducting carbon allotrope predicted recently, has attracted tremendous attention due to its potential applications in nano electromechanical systems (NEMS). In this paper, we use Molecular Dynamics simulations to investigate the mechanical properties of twin graphene. By performing uniaxial tensile loading, we find that the Young’s modulus, failure stress and fracture strain of a twin graphene sheet are strongly dependent on its size. Rectangular sheets show more apparent anisotropy of mechanical properties than square sheets. Our results also demonstrate that the fracture pattern of twin graphene is dependent on its geometry, as a result of its diverse bond types and orientations. These findings present an in-depth understanding of size dependent mechanical properties of twin graphene, and may benefit its future applications as building blocks of NEMS devices.

Nonlinear buckling analysis of double-layered graphene nanoribbons based on molecular mechanics

Double-layer graphene nanoribbons promise potential application in nanoelectromechanical systems and optoelectronic devices, and knowledge about mechanical stability is a crucial parameter to flourish the application of these materials at the next generation of nanodevices. In this paper, molecular mechanics is utilized to investigate nonlinear buckling behavior, critical buckling stress, and lateral deflection of double-layered graphene nanoribbons under various configurations of stacking mode and chirality. The implicit arc-length iterative method (modified Riks method) with Ramm’s algorithm is utilized to analyze the nonlinear structural stability problem. The covalent bonds are modeled using three-dimensional beam elements in which elastic moduli are calculated based on molecular structural mechanics technique, and the interlayer van der Waals (vdW) interactions are modeled with nonlinear truss elements. An analytical expression for Young’s modulus of nonlinear truss elements is derived based on the Lennard–Jones potential function and implemented in numerical simulation with a UMAT subroutine based on FORTRAN code to capture the nonlinearity of the vdW interactions during the buckling analysis. The results indicate that the highest critical buckling stress and the minimum lateral deflection occur for armchair and zigzag chirality, both with AB stacking mode, respectively. Moreover, the critical buckling stress is found to be directly dependent on the mode shape number regardless of in-phase or anti-phase deflection direction of layers. Lateral deflection exhibits a similar trend with mode shape in anti-phase mode; however, it is decreasing by increasing mode shape number in in-phase mode.

Metamaterial Vibration of Tensioned Circular Few-Layer Graphene Sheets

Abstract The present work aims to examine the metamaterial vibrational behavior of circular few-layer graphene sheets under layerwise tension forces. For this objective, a simplified three-membrane model is developed to simulate flexural vibration of tensioned circular few-layer graphene sheets, in which tensioned top and bottom layers are modeled as two elastic membranes while all less-tensioned or tension-free inner layers together are treated as a single membrane, and the three membranes are coupled through the van der Waals interaction between adjacent layers. Our results show that when the two outermost layers are highly tensioned but the inner layers are free of tension, circular few-layer graphene sheets exhibit negative effective mass within a certain terahertz frequency range. Moreover, such few-layer graphene sheets with negative effective mass demonstrate remarkable vibration isolation and vibration suppression. This research broadens our perspectives for designing and analyzing graphene-based metamaterials and resonators and could find potential application in nanoelectromechanical systems.

Regulating the electrical conductivity of hexagonal boron nitride nanosheets with excellent tribological performance for micro and nano electromechanical system applications

Abstract The outstanding electrical insulativity greatly restricts the applications of hexagonal boron nitride nanosheets (h-BNNSs) in semiconductive or conductive micro and nano electromechanical systems (M/NEMSs). Therefore, regulating the electrical conductivity of h-BNNSs becomes critical for their applications in semiconductive or conductive M/NEMSs. In this report, a facile and effective method via introduction of F and H atoms to regulate the electrical conductivity of h-BNNS bilayers is proposed based on first-principle calculations within the framework of density functional theory. The geometry and electronic density of states of F and H codoped h-BNNS bilayers are systematically investigated. The results demonstrate that F and H atoms can strongly bind to h-BNNSs realizing the conversion of h-BNNSs from insulator to semiconductor or conductor. More importantly, due to the electron redistribution induced by the introduction of F and H atoms, the doped h-BNNS bilayers exhibit very low interlayer friction under a certain compressive interlayer spacing. These F and H codoped h-BNNS bilayers with improved electrical conductivity, high structural stability, lower interlayer friction and higher load-bearing capacity will bring prosperous applications of h-BNNSs in semiconductive or conductive M/NEMSs.

Spatially resolved optical excitation of mechanical modes in graphene NEMS

Emerging applications in nanoelectromechanical systems (NEMS) made from two-dimensional (2D) materials demand simultaneous imaging and selective actuation of the mechanical modes. Focused optical probes to measure and actuate motion offer a possible solution, but their lateral spatial resolution must be better than the size of the resonator. While optical interferometry is known to have excellent spatial resolution, the spatial resolution of the focused, laser-based optical driving is not currently known. Here, we combine separately scanned interferometry and optical drive probes to map the motion and forces on a suspended graphene nanomechanical resonator. By analyzing these maps with a force density model, we determine that the optical drive force has a spatial resolution on the order of the size of the focused laser spot. Using the optical force probe, we demonstrate the selective actuation and suppression of a pair of orthogonal antisymmetric mechanical modes of the graphene resonator. Our results offer a powerful approach to image and actuate any arbitrary high-order mode of a 2D NEMS.

Tunable electronic properties of InSe by biaxial strain: from bulk to single-layer

In the present work, we consider the electronic properties of bulk and single-layer InSe using the density functional theory. Our calculations show that at the equilibrium state, the single-layer InSe is a semiconductor with an indirect energy bandgap of 1.382 1 eV, nearly twice the bandgap of bulk InSe. Focusing on the effect of biaxial strain εb on electronic properties of single-layer InSe, our calculated results indicate that tensile biaxial strain changes slightly the valence subbands near Fermi level, while the band structure of the single-layer InSe depends tightly on the compressive biaxial strain. Also, the energy gap of the single-layer InSe depends almost linearly on the εb. However, the energy gap tends to increase slowly when the large compressive biaxial strain is applied. We believe that the control of the energy gap of the single-layer InSe by strain engineering can be useful in its application in nanoelectromechanical systems and nanoelectronic devices.

Port-Hamiltonian modelling of nonlocal longitudinal vibrations in a viscoelastic nanorod

ABSTRACTAnalysis of nonlocal axial vibration in a nanorod is a crucial subject in science and engineering because of its wide applications in nanoelectromechanical systems. The aim of this paper is to show how these vibrations can be modelled within the framework of port-Hamiltonian systems. It turns out that two port-Hamiltonian descriptions in physical variables are possible. The first one is in descriptor form, whereas the second one has a non-local Hamiltonian density. In addition, it is shown that under appropriate boundary conditions these models possess a unique solution which is non-increasing in the corresponding ‘energy’, i.e., the associated infinitesimal generator generates a contraction semigroup on a Hilbert space, whose norm is directly linked to the Hamiltonian.

Reduction of interlayer friction between bilayer hexagonal boron nitride nanosheets induced by electron redistribution

The reduction of interfacial friction among hexagonal boron nitride nanosheets (h-BNNSs) is important for their application in nanoelectromechanical systems. In this work, a novel method via adjusting the electron redistribution to reduce the interlayer friction of the h-BNNS bilayers is proposed based on the theoretical calculation of the relationship between electron distribution state and corresponding friction performance. The theoretical calculation is performed based on density functional theory with a fluoride h-BNNS bilayer as a model. Calculations suggested that fluorine atoms can strongly bond to the h-BNNS and promote electron redistribution, inducing interesting surface behaviors of the h-BNNS bilayer. Fluorine doping can reduce the interlayer friction and even make the upper layer bend when the fluorine doping ratios increase further. This bending can promote the upper layer slide relative to the lower one, achieving superlubricity. The reduction is related to the electron transfer between layers and within layers, which is caused by the change in electrostatics and van der Waals interaction between the layers that resulted from the electron redistribution. This work opens up a new strategy to control the frictional properties of two-dimensional nanomaterials and provides a favorable proof for experimental analysis.

Stressed carbon nanotube devices for high tunability, high quality factor, single mode GHz resonators

The emerging applications of nanoelectromechanical systems (NEMS) in ground-state cooling, quantum manipulation, communication devices, etc., call for a nanoresonator with high frequency, quality factor, and tunability, as well as easy integration. Here we show that such a nanoresonator can be achieved by using a unique assembly technique that transfers the stressed inner shell of carbon nanotubes (CNTs) to a self-aligned device geometry. The as-fabricated nanoresonator shows excellent comprehensive performance, i.e., high frequency (2–3 GHz), high tunability (80–110 MHz/V), high quality factor (3 × 104), and single mode operation. The defect-free nature of the inner shell of the CNT gives rise to a high quality factor, and the preloaded tension improves the resonant frequency and tunability. This resonator with excellent performance also enables the integration of homogeneous devices and will play a key role in the emerging applications of NEMS.