Nanoelectromechanical Systems Research Articles

Molecular dynamics study of graphene-coated reinforced tribomechanical properties: Hard versus soft substrates

As a two-dimensional material, graphene film is a good solid lubricant candidate for improving the tribomechanical performance of micro-and nano-electromechanical systems. Graphene has a significant impact on protecting the top layer of a substrate from wear and reducing friction. However, the frictional behavior has been found to vary when coating graphene onto different substrates. In the present study, using molecular dynamics (MD) simulations, graphene was deposited as a monolayer coating on the substrate sliding against the diamond tip, which revealed not only significant improvement in tribological behavior by reducing both friction and contact deformation volume, but also notably demonstrated the difference between hard and soft substrate coating with graphene. Under 58.5nN loading, the optimal antifriction effect of graphene coating on Au substrate was 94.2%, with a higher friction indicating a greater indentation depth and greater contact deformation. The contact deformation volume can be used as a standard to measure the surface friction of graphene. Unlike hard Si substrates, monolayer graphene coatings are prone to rupture at 200 nN loads. At low loads, the single graphene coating has the best anti-friction effect on the soft gold substrate, and at higher loads, the graphene on the hard silicon substrate is not prone to rupture, providing continuous and stable lubrication. The study also revealed a tunable toughening mechanism of graphene layers. The mechanism entails a reduction in the volume of substrate contact deformation with the progressive addition of graphene layers. This finding has the potential to enhance the tribological performance of the graphene-coated substrate.

Casimir interaction with black phosphorus sheets.

We calculate the Casimir interaction between isotropic plates (gold or graphene) and black phosphorus (BP) sheets with Lifshitz theory. It is found that the Casimir force with BP sheets is of the order of α times the perfect metal limit, and α is the fine structure constant. Strong anisotropy of the BP conductivity gives rise to a difference in the Casimir force contribution between the two principal axis. Furthermore, increasing the doping concentration both in BP sheets and graphene sheets can enhance the Casimir force. Moreover, introducing substrate and increased temperature can also enhance the Casimir force, by this way we reveal that the Casimir interaction can be doubled. The controllable Casimir force opens a new avenue for designing next generation devices in micro- and nano-electromechanical systems.

Graphene-Based ESD Protection for Future ICs.

On-chip electrostatic discharge (ESD) protection is required for all integrated circuits (ICs). Conventional on-chip ESD protection relies on in-Si PN junction-based device structures for ESD. However, such in-Si PN-based ESD protection solutions pose significant challenges related to ESD protection design overhead, including parasitic capacitance, leakage current, and noises, as well as large chip area consumption and difficulty in IC layout floor planning. The design overhead effects of ESD protection devices are becoming unacceptable to modern ICs as IC technologies continuously advance, which is an emerging design-for-reliability challenge for advanced ICs. In this paper, we review the concept development of disruptive graphene-based on-chip ESD protection comprising a novel graphene nanoelectromechanical system (gNEMS) ESD switch and graphene ESD interconnects. This review discusses the simulation, design, and measurements of the gNEMS ESD protection structures and graphene ESD protection interconnects. The review aims to inspire non-traditional thinking for future on-chip ESD protection.

Impedance spectroscopy of electrostatically driven MEMS resonators

The electrical response of vibrating, electrostatically driven microelectromechanical and nanoelectromechanical system (MEMS and NEMS) devices was measured electrically using impedance spectroscopy. A physical model of this structure was elaborated, allowing us to predict the electrical response based on the dimensions and mechanical properties of the structure as well as the measurement conditions. This result was correlated with the results of the electrical equivalent circuit model. The physical model predicted that the magnitude of the electrical response is inversely proportional to the distance between the electrodes to the power of 4. Such a strong dependence was verified experimentally using a vibrating electrostatically driven MEMS operating in vacuum. The verified physical model is suitable for optimization of MEMS structures designed for electrical detection of vibrations.

Transient dynamic, energy absorption and out-phase/in-phase vibration response of coupled annular/circular SMA nanoplates assuming surface effects on frictional substrates

Shape and size are two important factors that affect the mechanical properties of nanostructures. Therefore, various forms of nano-scaled structures such as annular and circular ones have been applied in the engineering fields. Shape Memory Alloy (SMA), which can be used as the actuator because of its ability to change shapes, has potential applications in nano-electro mechanical system (NEMS). Dynamic behavior and the ability to absorb energy are two critical characteristics of advanced structures that are under static or various forms of dynamic loadings to be specific, this research numerically examined the in-phase/out-phase vibration, transient dynamic behavior under impulse load, and energy absorption in SMA annular/circular nanoplates with ferroelastic and pseudoelastic effects coupled together via damper and spring, placed between two frictional layers. In addition, an assumption of the Kuhn–Tucker phase transformation conditions was made. Moreover, the governing equations were derived based on Hyperbolic Higher Order Shear Deformation Theory (HHSDT) and solved using Differential Cubature Method (DCM). The constitutive equation of SMA proposed by Brinson was employed to model the pseudo-elastic behavior of SMA. Besides, Gurtin-Murdoch and modified couple stress theories were employed to calculate surface and micro-scale effects. As revealed by numerical achievements, under out-phase vibration mode, by increasing the surface effect coefficient to 0.4 when the annular nanoplate inner to outer radius ratio was 0.35, the natural frequency enhanced about 174%. As the material length scale parameter to thickness ratio was increased to 0.3 and the surface effects were considered, the energy absorption capacity was enhanced by nearly 28% and 23%, respectively.

Electromechanical resonances and field-emission-induced self-oscillations of single crystal diamond needles

Due to its outstanding mechanical characteristics, diamond is an ideal material for use in micro- and nano-electromechanical systems. In this paper, we report on the investigation of vibrational properties of singly clamped needlelike diamond microcrystallites with nanoscale tips. The single-crystal diamond needles were produced by selective oxidation of polycrystalline films grown using chemical vapor deposition. The study of resonant oscillations driven by the AC voltage indicated that the elastic modulus of such diamond needles is close to that of bulk single crystal diamond. A self-oscillation regime induced by the DC voltage during field emission from the apex of a diamond needle is also demonstrated. It is shown that this regime can be used for efficient DC–AC conversion in microdevices. The high structural quality of diamond needles, their remarkable mechanical properties, and the relative ease of their mass fabrication make them promising candidates for application in various electromechanical systems, field-emission devices, and scanning probe techniques.

Effect of Diametric ratio on Eigen Frequency of Functionally Graded Piezoelectric Round Disc

Abstract: Functionally graded piezoelectric material has very enormous application in the field of engineering and science. It is very useful for smart device like micro electric mechanical system, nano electro mechanical system. In the present work the effect of diametric ratio has been observed for functionally graded piezoelectric circular plate. d15 effect has been utilized for exited shear induced flexural vibration. Plate has been readily polarized and electric effect is applied along the thickness direction.

Selectively Tuning the Substrate Adhesion Strength of Aligned Carbon Nanotube Arrays via Thermal Postgrowth Processing.

The excellent intrinsic properties of aligned nanofibers, such as carbon nanotubes (CNTs), and their ability to be easily formed into multifunctional 3D architectures motivate their use for a variety of commercial applications, such as batteries, chemical sensors for environmental monitoring, and energy harvesting devices. While controlling nanofiber adhesion to the growth substrate is essential for bulk-scale manufacturing and device performance, experimental approaches and models to date have not addressed tuning the CNT array-substrate adhesion strength with thermal processing conditions. In this work, facile "one-pot" thermal postgrowth processing (at temperatures Tp = 700-950 °C) is used to study CNT-substrate pull-off strength for millimeter-tall aligned CNT arrays. CNT array pull-off from the flat growth substrate (Fe/Al2O3/SiO2/Si wafers) via tensile testing shows that the array fails progressively, similar to the response of brittle microfiber bundles in tension. The pull-off strength evolves nonmonotonically with Tp in three regimes, first increasing by 10 times through Tp = 800 °C due to graphitization of disordered carbon at the CNT-catalyst interface, and then decreasing back to a weak interface through Tp = 950 °C due to diffusion of the Fe catalyst into the substrate, Al2O3 crystallization, and substrate cracking. Failure is observed to occur at the CNT-catalyst interface below 750 °C, and the CNTs themselves break during pull-off after higher Tp processing, leaving residual CNTs on the substrate. Morphological and chemical analyses indicate that the Fe catalyst remains on the substrate after pull-off in all regimes. This work provides new insights into the interfacial interactions responsible for nanofiber-substrate adhesion and allows tuning to increase or decrease array strength for applications such as advanced sensors, energy devices, and nanoelectromechanical systems (NEMS).

New Protic Ionic Liquids as Potential Additives to Lubricate Si-Based MEMS/NEMS

The motivation for this work was to develop new protic ionic liquids (PILs) as additives for the lubrication of micro and nanoelectromechanical systems (MEMS and NEMS). Ten PILs based on the combination of methylimidazolium ([MIMH]), 4-picolinium ([4-picH]), pyridinium ([PyrH]), 1,8-diazabicyclo[5.4.0]-undec-7-ene-8-ium ([DBUH]) and tetramethylguanidinium ([TMGH]) cations with hydrogen sulfate([HSO4]) and mesylate ([MeSO3]) anions were tested as additives in polyethylene glycol (PEG200) to lubricate steel/silicon and silicon/silicon contacts. The best additive was [4-picH][HSO4], which adsorbed strongly on the Si surface, leading to a protective film that reduced wear by up to 15 times compared to PEG200.

Topological vortex induced large recoverable electrostrain with high temperature-stability in ferroelectric nano-dots

Here we report by phase field simulations that in ferroelectric nanodots the single domain generated from the vortex under external electric field will transform back to the vortex structure after removal of the field, which could offer large recoverable electrostrain during the process. Moreover, it is found that the recoverable electrostrain maintains a large value and could exist over a wide temperature range. The good recoverability of the vortex structure and electrostrain in the ferroelectric nanodots is found to be mainly ascribed to the dipole-dipole interaction energy and the elastic interaction energy in the system. This work may shed light on the development of miniaturized actuators in Micro-Electro-Mechanical System (MEMS) or Nano-Electromechanical System (NEMS).

Ultrafast Optomechanical Strain in Layered GeS

Strong coupling between light and mechanical strain forms the foundation for next-generation optical micro- and nano-electromechanical systems. Such optomechanical responses in two-dimensional materials present novel types of functionalities arising from the weak van der Waals bond between atomic layers. Here, by using structure-sensitive megaelectronvolt ultrafast electron diffraction, we report the experimental observation of optically driven ultrafast in-plane strain in the layered group IV monochalcogenide germanium sulfide (GeS). Surprisingly, the photoinduced structural deformation exhibits strain amplitudes of order 0.1% with a 10 ps fast response time and a significant in-plane anisotropy between zigzag and armchair crystallographic directions. Rather than arising due to heating, experimental and theoretical investigations suggest deformation potentials caused by electronic density redistribution and converse piezoelectric effects generated by photoinduced electric fields are the dominant contributors to the observed dynamic anisotropic strains. Our observations define new avenues for ultrafast optomechanical control and strain engineering within functional devices.

Editorial: Design and analysis of CMOS-MEMS transducers

EDITORIAL article Front. Mech. Eng., 02 March 2023Sec. Micro- and Nanoelectromechanical Systems Volume 9 - 2023 | https://doi.org/10.3389/fmech.2023.1142981

Strain‐Sensitive Flexible Magnetoelectric Ceramic Nanocomposites

AbstractMagnetoelectric (ME) oxide materials can convert magnetic input into electric output and vice versa, making them excellent candidates for advanced sensing, data storage, and communication. However, their application has been limited to rigid devices due to their brittle nature. Here, flexible ME oxide composite (BaTiO3/CoFe2O4) thin film nanostructures with distinct ME coupling coefficients are reported. In contrast to rigid bulk counterparts, these ceramic nanostructures display a flexible behavior after being released from the substrate, and can be transferred onto a stretchable substrate such as polydimethylsiloxane. These ceramic films possess high ME coefficients due to minimized clamping effect and preferred crystalline orientation, and exhibit reversibly tunable ME coupling via mechanical stretching thanks to their large elasticity (>4%). It is believed that the study can open up new avenues for integrating ceramic ME composites into micro‐/nanoelectromechanical system and soft robotic devices.

Monolayer group IV monochalcogenides T-MX (M = Sn, Ge; X = S, Se) with fine piezoelectric performance and stability

Monolayer group monochalcogenides (MX; M = Sn, Ge; X = S, Se) in the orthogonal α-phase are excellent piezoelectric materials. In this study, a configuration with bonding features similar to the α-phase is proposed (T-phase) for monolayer MX using the first-principles method. Based on the modern theory of polarization, as implemented in Vienna Ab initio Simulation Package, the T-phase is determined to be an excellent piezoelectric phase for monolayer MX. The in-plane piezoelectric coefficient d11 of T-SnS is 452.3 pm/V, which is larger than that reported for most two-dimensional binary compounds in the α-phase, including α-SnSe (∼250 pm/V). The large piezoelectric coefficients of T-MX mainly stem from its distinctive puckered configuration, which make it extraordinarily flexible along the polarization direction. The study results suggest a possibility for designing high piezoelectric coefficient materials with MX, and the potential application of T-MX in the fields of energy collection and nanoelectromechanical systems needs to be analyzed in future studies.

Probing the atomic-scale deformation mechanism of single-crystal nanowires coated with a multi-component alloyed shell

Metallic nanowires have attained considerable attention as applied for the building blocks in nano-electromechanical systems. Surface coating is needed for nanowires to prevent their degradation from the external environment. Multi-component alloys (MCAs) exhibit a combination of exceptional fracture tolerance and desirable corrosion resistance, which are promising coating materials for nanowires. However, few attempts have been made to investigate the deformation mechanisms of nanowires coated with an MCA shell. To address this gap, we employ atomic simulations on investigating the tensile deformation of single-crystal nickel nanowires coated with MCA shells, and study the microstructural features governing the necking behavior of these specimens. The results indicate that the dislocation nucleation method controlling the incipient plasticity of the nanowire turns from a typical homogeneous surface nucleation mode to another interface nucleation one after coating, lowering the maximum stress during the tensile loading. Ductile necking with dispersed plastic events prevails in the uncoated nanowire, while severely localized shear dominates the necking mode of the single- and poly-crystalline MCA nanowire due to their lower dislocation contents as well as the sluggish dislocation mobility caused by lattice distortion and high-entropy effect. The necking mode of nanowires is not altered by the MCA coating due to the predominant volume fraction of the nickel core in the present configurations. Noteworthily, the deformation stability is highly enhanced by polycrystalline MCA coating, thus the stress no longer drops to zero before the final fracture. This work gives new insights into developing reliable nanowires with enhanced deformability via using MCA coating.

Subgigahertz Multilayer-Graphene Nanoelectromechanical System Integrated with a Nanometer-Scale Silicon Transistor Driven by Reflectometry

A high-frequency nanoelectromechanical system (NEMS) based on a graphene membrane is a candidate for sensing applications, as well as a platform for fundamental research, but detecting such high-frequency oscillations of small membrane displacement is technically challenging. The authors integrate a high-sensitivity transistor with a multilayer graphene NEMS and drive the transistor via double resonant circuits at an electrical resonance. By optimizing the resonant circuits and driving the transistor with an rf signal, the high-frequency NEMS signal can be detected. This technique is useful for realizing NEMS applications at subgigahertz or higher frequencies.

Frequency response of cantilevered plates of small aspect ratio immersed in viscous fluids

Comprehensive theoretical models for the dynamic response of slender cantilevered beams immersed in fluid have been widely reported, while the distinct behavior of wide cantilevered plates has received comparatively little attention. In this article, we develop an exact analytical theory for the resonant response of rectangular cantilevered plates of zero length-to-width aspect ratio that are immersed in unbounded viscous fluids. Unlike the opposite slender limit of large aspect ratio, the hydrodynamic load experienced by zero-aspect-ratio cantilevered plates is inherently non-local, which can strongly affect the individual mode shapes of the plate. In addition, finite-element-method simulations are reported for two- and three-dimensional cases of zero and finite aspect ratio, respectively. Accuracy of the present theory and that of Atkinson and Manrique de Lara [J. Sound Vib. 300, 352 (2007)] for small viscosity and zero aspect ratio is assessed using the former simulations. The latter simulations are used to clarify the regime of validity of the present theory as a function of aspect ratio, along with that of existing theory for slender (large aspect ratio) beams. The results of this study are expected to be of practical importance to micro- and nano-electromechanical system design and their applications.

Large torsional rotation and rotational inversion coupling with linear deformation of electromechanical actuators based on conductive micro-/nano-helices

A great variety of electrically conductive micro-/nano-helices provide the unique interconversion of torsional rotation and linear deformation, which makes them the excellent elements as electromechanical actuators in artificial muscle. In this paper, a comprehensive theory has been constructed for quantitatively analyzing the electromechanical properties involving coupled torsional rotation and linear deformation of the close packed and non-close packed electrically conductive helices with the aid of the concept of Cosserat curve. The distributed force in our model can be used to describe the resultant electromagnetic force and the internal pressure on the current carrying helices, which agree well with the experimental results. It is revealed that if the designers intend to realize the mechanical actuation of coupled rotational inversion and large axial contraction, they can choose the close packed conductive micro-/nano-helices; while if they want the much larger torsional stroke of unwinding during the contraction process, the non-close packed ones will be a good choice. The currents make both kinds of helices stronger, and decreasing helix angle is an additional option for the non-close packed ones. The present study supplies a reliable theoretical reference for further experimental research on the applications of conductive helices in micro-/nanoelectromechanical systems.

Cyclic Buckling Characterization of an Individual MWCNT Using Quantitative In Situ TEM Axial Compression.

Carbon nanotubes (CNTs) are extremely conductive and flexible, making them ideal for applications such as flexible electronics and nanoelectromechanical systems. However, in order to properly apply them in such devices, their long-term durability must be assessed. In the present study, we demonstrate cyclic loading of a thick MWCNT (175 nm) under axial compression, observed in situ under a transmission electron microscope (TEM). The force was applied via controlled displacement, while real-time TEM videos of the deformation process were gathered to produce the morphological data. The in situ observations combined with force-displacement curves revealed the onset of buckling instabilities, and the elastic limits of the tube were assessed. The MWCNT retained its original structure even after 68 loading-unloading cycles, despite observed clues for structural distortions. The stiffness of the tube, calculated after each loading cycle, was in a 0.15 to 0.28 TPa range-comparable to the literature, which further validates the measurement set-up. These in situ tests demonstrate the resilience of CNTs to fatigue which can be correlated with the CNTs' structure. Such correlations can help tailoring CNTs' properties to specific applications.

The Second Quantum Revolution: Development of Subatomic Quantum Nanotechnologies of Intelligent Materials

The article analyzes the future development of quantum nanotechnology based on attosecond physics of the subatomic level of the condensed state. The ways of realizing the main achievements of the second quantum revolution in subatomic nanotechnologies of materials, namely quantum entanglement, quantum contextuality and quantum dissipativity are considered. The theoretical analysis of the prospects for this direction in the development of quantum subatomic nanotechnologies has been carried out within the framework of the well-known theory of thermal field dynamics of the condensed state. The analysis shows that subatomic entanglement of electron pairs is realized by attosecond single-cycle photons. The entangled electron pairs form the interfaces of supra-atomic capsules — quantum nanoelectromechanical systems (NEMS) of the condensed state of the material. The Coulomb blockade of quantum NEMS interfaces is complemented by the fact that they are controlled by the infrastructure of subatomic two-electron sensors and actuators located at the interface boundaries. When the primary subatomic interfaces of NEMS function, secondary supra-atomic scale entangled pairs of electrons are generated, which dissipate the NEMS energy and form a dissipative multilevel hierarchy of condensed state interfaces at higher spatio-temporal scales of intelligent materials