Nanoelectromechanical Systems Research Articles

Thickness-dependent nanoscale friction across the first-order charge density wave phase transition in 1T-TaS2

The layered charge density wave (CDW) phase transition material 1T-TaS2 has garnered significant attention due to its modulable bandgap and electrical transport properties. These unique properties make 1T-TaS2 highly promising for applications in fields such as optoelectronic devices and microstructure physics devices. In various micro-/nanodevices made from quasi-two-dimensional 1T-TaS2, it is often utilized in thin layers, making the understanding of its frictional properties crucial for practical applications. However, the layer-dependent frictional properties of 1T-TaS2 have not been thoroughly investigated. In this article, we examine the CDW phase transition between the nearly commensurate (NCCDW) and commensurate (CCDW) phases in 1T-TaS2 around 183 K using atomic force microscopy, focusing on the number of layers in the samples. Our results indicate that for thicker samples with more than approximately 17 layers, a friction peak is observed during the NCCDW–CCDW phase transition. In contrast, thinner samples do not exhibit this friction peak, and their friction continuously increases as the temperature decreases. This behavior is attributed to the suppressed NCCDW–CCDW phase transition in thinner samples. These results enhance our understanding of the frictional behavior of 1T-TaS2 in the context of micro-/nano-electromechanical systems. Furthermore, our observations offer a straightforward method to identify the NCCDW–CCDW phase transition, providing an alternative to traditional, more complex techniques such as electrical resistance measurements and Raman spectroscopy.

Density Modulated Vertical Carbon Nanotube Architectures with Bolometric Effect

Novel density‐modulated carbon nanotube (CNT) blocks with controlled and tunable CNT densities in adjacent layers have been developed. Regions with varying densities are laterally patterned into different shapes with submicron resolution, enhancing the fabrication flexibility of new 3D nanoelectromechanical systems for diverse sensing applications. This technology platform adjusts lateral electrical resistance, mechanical properties such as effective Young's modulus, and both lateral and vertical thermal conductivity, which can vary by several orders of magnitude. Highlighting its potential, the CNTs exhibit broadband blackbody absorption from ultraviolet (UV) to terahertz (THz). The initial bolometric detector demonstrates features such as a voltage responsivity = 20.5 V W−1, a response time of less than 0.1 ms, measured robust operation up to 200 °C, with fabricated device dimensions of 20 × 30 μm2, and a low‐cost design suitable for mass production. Further optimizations of the lateral design can reduce the device dimensions to as small as 5 × 5 μm2 and improve the absorption in the main resistance region. Thus, this architecture provides a platform technology to increase the responsivity of the fabricated new 3D‐based bolometer devices by several orders of magnitude. Tiny objects such as biological cells can be characterized in real time.

Theoretical insights into the ultrahigh piezoelectric performance of (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices

Perovskite structures have attracted extensive attention in microelectromechanical systems and nanoelectromechanical systems devices due to the high piezoelectric response and the low dielectric constant. The piezoelectric and dielectric properties of the tetragonal BiFeO3/BaTiO3 superlattices grown along the c-axis direction are investigated using density functional theory (DFT) and density functional perturbation theory. The calculated results demonstrate that the (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices exhibit a profoundly increased piezoelectric response compared to their bulk structures. The (BiFeO3)2/(BaTiO3)2 possesses the highest piezoelectric d33 of 697 pC/N among known lead-free perovskite systems. Furthermore, the (BiFeO3)2/(BaTiO3)2 superlattice possesses a low dielectric ɛ33, and its d33 at 2% tensile strain is 16 times larger than that of an unstrained equilibrium structure. This demonstrates that biaxial tensile strain significantly enhances the piezoelectric response. Combining the special quasirandom structure method with DFT, the structures of a 0.5BiFeO3–0.5BaTiO3 solid solution are predicted, and its calculated d33 is 58 pC/N, which is much smaller than that of a (BiFeO3)2/(BaTiO3)2 superlattice. The results suggest that the (BiFeO3)2/(BaTiO3)2 superlattice might be a potential candidate for nonvolatile random access memory, transducers and actuators, and nanoscale electronic devices.

Data-driven fingerprint nanoelectromechanical mass spectrometry

Fingerprint analysis is a ubiquitous tool for pattern recognition with applications spanning from geolocation and DNA analysis to facial recognition and forensic identification. Central to its utility is the ability to provide accurate identification without an a priori mathematical model for the pattern. We report a data-driven fingerprint approach for nanoelectromechanical systems mass spectrometry that enables mass measurements of particles and molecules using complex, uncharacterized nanoelectromechanical devices of arbitrary specification. Nanoelectromechanical systems mass spectrometry is based on the frequency shifts of the nanoelectromechanical device vibrational modes that are induced by analyte adsorption. The sequence of frequency shifts constitutes a fingerprint of this adsorption, which is directly amenable to pattern matching. Two current requirements of nanoelectromechanical-based mass spectrometry are: (1) a priori knowledge or measurement of the device mode-shapes, and (2) a mode-shape-based model that connects the induced modal frequency shifts to mass adsorption. This may not be possible for advanced nanoelectromechanical devices with three-dimensional mode-shapes and nanometer-sized features. The advance reported here eliminates this impediment, thereby allowing device designs of arbitrary specification and size to be employed. This enables the use of advanced nanoelectromechanical devices with complex vibrational modes, which offer unprecedented prospects for attaining the ultimate detection limits of nanoelectromechanical mass spectrometry.

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.

Current trends in micro‐supercapacitor devices

AbstractRecently, efforts have been made to design miniaturized energy storage devices according to custom requirements. The application of micro‐electronic equipment has increased significantly in information technology and biotechnology. Microelectromechanical systems, nanoelectromechanical systems, maintenance‐free wireless sensor networks, implantable medical devices, micro‐robots, and integrating energy conversion devices require micropower sources in small dimensions. Conventional supercapacitor devices cannot fulfill such high‐power demand, but miniaturization within the microscale helps enhance the working efficiency due to the shortening of diffusion path length. Micro‐supercapacitors (MSCs) in the micron to centimeter dimension range integrated with circuits and microelectronic components have gained great interest due to their high‐power density, high‐frequency response, and long cycling stability. Research on the design and fabrication of MSCs has progressed enormously. Integrating MSCs with other electronic units helps to achieve a highly efficient self‐powered system. This review presents a critical summary of the recent progress of novel materials for MSCs, fabrication methods, advanced design, and challenges in the MSCs industry.

Efficient prediction of mechanical properties of Boron Nitride Nanosheets using artificial neural networks

This paper aims to evaluate the mechanical properties of Boron Nitride Nanosheets (BNNS) and their vital use in nano-electromechanical systems (NEMS). By employing molecular Dynamics (MD) simulation, modelling of the atomic structure was done. The mechanical response of BNNS under various parameters (strain rate, temperature, chirality and dimension) enabled the generation of a comprehensive data set that accurately represents their elastic properties. The dataset obtained from MD simulation was subsequently utilized to construct an artificial neural network (ANN) model, tailored to predict the Young’s modulus of BNNS accurately. This work aimed to improve the model’s efficiency by refining the design of ANN, which significantly reduces the computational time while maintaining higher accuracy predictions. The findings demonstrate precise and rapid prediction for developing components based on BNNS in NEMS. This paper establishes an analogy between in-depth atomistic simulations and real-world engineering applications presenting a new approach for precisely predicting the attributes of nanomaterials.

Influence of flexoelectricity on coupled electromechanical response of 2D MXene/graphene-based hybrid piezocomposites.

This study investigates the influence of flexoelectricity on the coupled electromechanical behavior of MXene/graphene-based hybrid piezocomposite (MGHPC) plates. We developed an analytical model based on Navier's solution and Kirchhoff's plate theory, as well as an approximate model based on the Ritz method for validation purposes. A three-phase micromechanical modeling is developed for determining the effective properties of MGHPC composed of 2D MXene and graphene nano-reinforcements embedded in an epoxy matrix. These micromechanical models were implemented to predict the static and dynamic electromechanical response of MGHPC plates subject to various edge support and loading conditions. Both the analytical and approximate solutions provided unequivocal evidence of the profound impact of the flexoelectric effect on the bending and modal analysis of MGHPC nanoplates. The flexoelectric effect enhanced the stiffness of the nanoplate, irrespective of the support condition. This implies that MGHPC plates can be tailored for precise resonance frequencies and static deflection within nanoelectromechanical systems. This can be achieved by manipulating parameters such as boundary conditions and geometric attributes, including plate thickness/aspect ratio and graphene/MXene nano-reinforcements volume fractions.

RECENT ADVANCES IN GAS, LIQUID AND SUPERCRITICAL FLUID CHROMATOGRAPHY IN THE CONTEXT OF SUSTAINABLE/ GREEN CHEMISTRY

Background: Chromatographic techniques such as gas chromatography (GC), liquid chromatography (LC) and supercritical fluid chromatography (SFC) have long been employed in analytical chemistry. However, using or producing certain organic solvents and non-renewable gases is hazardous to the environment. Green chemistry is essential for addressing the environmental hazards associated with traditional procedures. Objectives: This review focuses on recent updates and profound insights into new, greener techniques introduced in GC, LC and SFC. Methodology: To compile this review, several electronic databases were searched, preferably from January 2019-December 2023. Results: This review highlights advancements in miniaturization, rapid methods, and eco-friendly solvents in chromatographic techniques. Integrating micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS) in GC enhances sensitivity and resolution while reducing solvent consumption. Innovations like monolithic micro-GC chips and the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method further streamline analysis times. In LC, supercritical fluids are utilized as green mobile phases, optimizing techniques like electrochemical flow liquid chromatography (EFLC), high-performance liquid chromatography (HPLC), and ultra-high-performance liquid chromatography UHPLC. In contrast, SFC employs rapid methods, such as ultra-high-performance supercritical fluid chromatography-mass spectrometry (UHPSFC-MS). These developments collectively promote sustainability and efficiency in chromatographic practices. Conclusion: Green chromatography has become an essential tool in pharmaceutical analysis because it safeguards the operator’s health and the environment. It opens new horizons and generates new ideas for further experimentation while focusing on recent cutting-edge green technologies incorporated in GC, LC and SFC. These advancements significantly enhance safety and sustainability in analytical practices.

Novel carboxylic-MWCNTs photoresist for fabricating sub-diffraction polymer nanowires via STED lithography

A novel composite photoresist, derived from acrylates and carboxylic-functionalized multi-walled carbon nanotubes (MWNTs-COOH), has been developed for the fabrication of sub-diffraction-sized polymer nanowires using STED-inspired lithography. The MWNTs-COOH dispersed in highly cross-linking acrylate monomers benefits to a reduced inhibition laser power for improving lithography. With the MWNTs-COOH, the inhibition laser power is decreased from 5 mW to 3 mW, while the achievable minimum feature size is increased from 121 nm to 48 nm. This innovative approach holds significant promise for the development of sub-diffraction MWCNTs/polymer composite-based devices in the fields of Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS).

Unveiling the tradeoff between device scale and surface nonidealities for an optimized quality factor at room temperature in 2D MoS2 nanomechanical resonators

A high quality (Q) factor is essential for enhancing the performance of resonant nanoelectromechanical systems (NEMS). NEMS resonators based on two-dimensional (2D) materials such as molybdenum disulfide (MoS2) have high frequency tunability, large dynamic range, and high sensitivity, yet room-temperature Q factors are typically less than 1000. Here, we systematically investigate the effects of device size and surface nonidealities on Q factor by measuring 52 dry-transferred fully clamped circular MoS2 NEMS resonators with diameters ranging from 1 μm to 8 μm, and optimize the Q factor by combining these effects with the strain-modulated dissipation model. We find that Q factor first increases and then decreases with diameter, with an optimized room-temperature Q factor up to 3315 ± 115 for a 2-μm-diameter device. Through extensive characterization and analysis using Raman spectroscopy, atomic force microscopy, and scanning electron microscopy, we demonstrate that surface nonidealities such as wrinkles, residues, and bubbles are especially significant for decreasing Q factor, especially for larger suspended membranes, while resonators with flat and smooth surfaces typically have larger Q factors. To further optimize Q factors, we measure and model Q factor dependence on the gate voltage, showing that smaller DC and radio-frequency (RF) driving voltages always lead to a higher Q factor, consistent with the strain-modulated dissipation model. This optimization of the Q factor delineates a straightforward and promising pathway for designing high-Q 2D NEMS resonators for ultrasensitive transducers, efficient RF communications, and low-power memory and computing.

ANN based optimization of nano-beam oscillations with intermolecular forces and geometric nonlinearity

In this study, we investigate the effect of Van der Waals and Casimir forces on the mathematical model of nano-electromechanical systems (NEMS) such as nano-beam actuators that contain cantilever and double cantilever beams. The singular nonlinear boundary value problem governing the beam-type actuators, including geometric nonlinearity is solved by using an intelligent strength of feedforward artificial neural networks (ANNs) and hybridization of optimization algorithms such as arithmetic optimization algorithm (AOA) and active set algorithm (ASA). The proposed ANN-AOA-AS algorithm is employed to quantify the effect of changes in applied voltage, dispersion forces, geometric nonlinearity parameters, and initial axial strain on the deflection of the beam. Furthermore, to validate the results obtained by the proposed algorithm, statistical analyses are conducted to compare the approximate solutions with state-of-the-art methodologies available in the latest literature. In addition, performance indicators are defined such as mean square error (MSE), Nash–Sutcliffe efficiency (NSE), mean absolute deviations (MAD), root mean square error (RMSE), and Error in Nash–Sutcliffe efficiency (ENSE) to study the accuracy and efficiency of the solutions. The results show that these indicators’ mean percentage values lie around 10−4 to 10−6 which reflects the perfect modeling of the approximate solutions.

Analysis of the magnetic-thermal response of viscoelastic rotating nanobeams based on nonlocal theory and memory effect

Size-dependent effects in elastic deformation and thermal hysteresis effects in the heat transfer process are significant for small-size structures or devices. As an important component of micro- and nanoelectromechanical systems, the analysis of the thermodynamic properties of rotating nanobeams is crucial for the safe operation of the system. This work aims to construct a new nonlocal thermo-viscoelastic model and use this model to analyze the thermodynamic behavior of rotating nanobeams at the microscale. In this work, fractional order Kelvin-Voigt theory describes the viscoelasticity of materials. Moreover, the theory of continuous medium mechanics is improved by introducing nonlocal parameters to capture the size effect during deformation. Based on the generalized thermoelasticity theory, memory-dependent derivatives predict hysteresis effects during heat transfer. Nanobeams are placed in a longitudinal magnetic field. Graphene strips connected to a power supply are used as the nanobeam heat source. The effects of nonlocal parameters, damping coefficients, and fractional order parameters on the dynamic response of the system are analyzed. In addition, a new comparative study of the effects of voltage and resistance on the system is made in the context of the nonlocal generalized thermoelasticity theory.

Tunable Stochastic State Switching in 2D MoS2 Nanomechanical Resonators with Nonlinear Mode Coupling and Internal Resonance.

Coupled nanomechanical resonators have unveiled fascinating physical phenomena, including phonon-cavity coupling, coupled energy decay pathway, avoided crossing, and internal resonance. Despite these discoveries, the mechanisms and control techniques of nonlinear mode coupling phenomena with internal resonances require further exploration. Here, we report on the observation of stochastic switching between the two resonance states with coupled 1:1 internal resonance, for resonant two-dimensional (2D) molybdenum disulfide (MoS2) nanoelectromechanical systems (NEMS), which is directly driven to the critical coupling regime without parametric pumping. We further demonstrate that the probability of state switching is linearly tunable from ∼0% to ∼100% by varying the driving voltage. Furthermore, we gradually increase the white noise amplitude and show that the probability of obtaining the higher-energy state decreases, and the stochastic switching phenomenon eventually disappears. The results provide insights into the dynamics of coupled NEMS resonators and open up new possibilities for sensing and stochastic computing.

Mode-dependent scaling of nonlinearity and linear dynamic range in a NEMS resonator

Even a relatively weak drive force is enough to push a typical nanomechanical resonator into the nonlinear regime. Consequently, nonlinearities are widespread in nanomechanics and determine the critical characteristics of nanoelectromechanical systems' (NEMSs) resonators. A thorough understanding of the nonlinear dynamics of higher eigenmodes of NEMS resonators would be beneficial for progress, given their use in applications and fundamental studies. Here, we characterize the nonlinearity and the linear dynamic range (LDR) of each eigenmode of two nanomechanical beam resonators with different intrinsic tension values up to eigenmode n = 11. We find that the modal Duffing constant increases as n4, while the critical amplitude for the onset of nonlinearity decreases as 1/n. The LDR, determined from the ratio of the critical amplitude to the thermal noise amplitude, increases weakly with n. Our findings are consistent with our theory treating the beam as a string, with the nonlinearity emerging from stretching at high amplitudes. These scaling laws, observed in experiments and validated theoretically, can be leveraged for pushing the limits of NEMS-based sensing even further.

A Multi‐Directional GaN/TiO2 Cuboidal Nanowire Junctionless FET‐Based Ultra‐High Pressure Sensor: A Design Perspective

AbstractIn this work, a nanoelectromechanical system (NEMS) field‐effect transistor (FET)‐based ultra‐high pressure (PR) multi‐directional sensor utilizing a junctionless profile and gate‐all‐around geometry is proposed with the advanced materials GaN/TiO2, named MD‐JLFET PR sensor. A design guide approach is considered, and accurate analysis is conducted starting from the bending of cantilevers based on materials' Young's moduli due to applied pressure and finally extracting the dynamic range of the proposed PR sensor. For the first time, the direction and magnitude of pressure can be measured using gate‐source capacitances (CGS). By employing oxide engineering and fringing field, the sensor achieves distinguishable states compared to previous works. Simulation results demonstrate that the PR sensor can measure pressures ranging from 10 to 30 MPa with high sensitivity in terms of CGS, IOFF, ION, and ION/IOFF. Therefore, the proposed FET‐based PR sensor holds promise for widespread industrial applications requiring ultra‐high pressure range measurement, directional pressure sensing, and high sensitivity.

Coexistence of Large In-Plane and Out-of-Plane Piezoelectric Response in Group III–VI XMAY2 (X = I; M = Ti, Zr; A = Al, Ga; Y = S, Se) Monolayers

Flexible materials with both in-plane and out-of-plane piezoelectric coefficients are needed in the development of advanced nanoelectromechanical systems. However, the challenge is to find flexible materials with the coexistence of in-plane and -out-of-plane piezoelectric responses, which hinders the progress of high-performance piezoelectric sensor development. In this paper, we propose the flexible XMAY2 (X = I; M = Ti, Zr; A = Al, Ga; Y = S, Se) monolayers, which belong to the group III-VI XMAY2 family, which showcase notable in-plane and out-of-plane piezoelectric coefficients. The in-plane (d11) and out-of-plane (d31) piezoelectric coefficients of the XMAY2 monolayers vary from 5.20 to 7.04 pm/V and from −0.23 to 0.48 pm/V, respectively. The large in-plane and out-plane piezoelectric responses coexist (d11 = 7.04 pm/V; d31 = 0.48 pm/V) in the IZrGaS2 monolayer, which is larger than other materials in the XMAY2 family, such as SMoSiN2 (d11 = 2.51; d31 = 0.28 pm/V). In addition, the mechanical and transport properties of XMAY2 demonstrate its impressive flexibility characteristics as well as its efficient electrical conductivity. Due to inversion symmetry breaking in both atomic structure and charge distribution of XMAY2 monolayers, the group III-VI XMAY2 family exhibits a potentially rich scope of applications in the field of piezoelectricity.

Enhancing mechanical and corrosion properties of GO and Al2O3 reinforced Cu composite coatings

Despite their significant functions and properties, the performance characteristics of Al2O3 ceramic particles and graphene oxide (GO) within hybrid copper composite coatings have been seldom investigated. This study successfully fabricated a Cu-GO- Al2O3 composite coating featuring fine particulate spherical network-like structures on St37 low carbon steel using an ultrasonic-electroless coating method. The effects of Al2O3-decorated graphene oxide hybrid reinforcement on the texture and nanomechanical properties of the copper matrix were examined. The tribological performance of the Cu-GO- Al2O3 composite coating under dry sliding conditions was evaluated, and the wear mechanism was investigated in detail. Results demonstrate that the Cu-GO- Al2O3 composite coating effectively reduces the wear rate and friction of the GO/ Al2O3 hybrid reinforced composite coating. Potentiodynamic polarization tests indicated that the Cu-GO- Al2O3 composite coating exhibits higher corrosion resistance compared to the copper matrix. The enhanced mechanical, tribological, and corrosion properties of the Cu-GO- Al2O3 composite coating are primarily attributed to: (i) the fine particulate spherical network-like structure; (ii) the synergistic effect of the GO and ceramic particle hybrid with a decorated structure; (iii) the formation of graphene oxide/ Al2O3 nanorolls in tribofilms and the excellent self-lubrication properties of graphene oxide. The Cu-GO- Al2O3 composite coating significantly improves the frictional and electrochemical properties of the copper matrix, offering new perspectives for next-generation electrical contacts and nanoelectromechanical systems.

The influence of piezoelectric on the nonlinear stochastic vibration of BN nanoresonator

The outstanding physical properties of hexagonal boron nitride (h-BN) make it highly valuable for use in nanoelectromechanical systems. We investigate the nonlinear stochastic vibration of h-BN nanowire affected by piezoelectric. The nonlinear beam model considering the impact of piezoelectric effect excited by random force is established. Molecular dynamic simulations were utilized to determine the potential energy of h-BN nanowires under varying amplitudes affected by an external electric field. The findings suggest that an increase in the intensity of the electric field can result in buckling behavior, leading to the appearance of two stable points. The cases of pre-buckling and post-buckling of nonlinear dynamic behavior of h-BN nanowire induced by piezoelectric effect is discussed in this paper. Furthermore, the impact of the intensity of random force on the nonlinear stochastic vibration characteristics of h-BN nanowire is also examined.

Effect of applied electrical potential and humidity on friction of Graphene-Based thin films

Understanding the nanofrictional characteristics of thin films in various conditions is important for fabricating nanoelectronic devices and micro-/nanoelectromechanical systems with high functionality and reliability. This study investigated the nanofrictional characteristics of composite thin films of graphene oxide (GO) and cellulose nanocrystals (CNCs) and of reduced graphene oxide (rGO) and CNCs, namely GO/CNC and rGO/CNC thin films, under an applied electrical potential and humidity by using a conductive atomic force microscope (AFM). For all films, the coefficient of friction (CoF) was affected by the applied electrical potential and enhanced mechanical properties resulting from strong interactions of GO and rGO with CNCs. Furthermore, the friction force increased with the electrical potential at low humidities (relative humidity (RH) < 40 %) because of the electrostatic force effect, while for RH>40 %, the friction force sensitively increased with the electrical potential because of the puckering effect. At high humidities (RH>40 %) and high electrical potentials (>4 V), the friction force decreased as the electrical potential increased, owing to the electron leakage phenomenon. This study also characterized the altered nanofrictional behavior influenced by interfacial phenomena in the films under an electrical potential and humidity, and it provides design guidelines for fabricating nanoelectronic devices and micro/nanoelectromechanical systems.