Food environments in times of crises: Examining menu changes in response to COVID-19 among Hispanic Caribbean restaurants in New York City.

The COVID-19 pandemic has affected independently-owned restaurants with implications for food access and health equity. Changes in healthy food availability (HFA) were examined in a randomly selected sample of Hispanic Caribbean restaurants in New York City, before and after the COVID-19 onset (n=76), using an adapted Nutrition Environment Measurement Survey for Restaurants. An overall decrease in HFA scores was found and changes HFA components (fried foods and vegetarian options increased, 100% fruit juice decreased, p<0.10). Changes were examined against restaurant characteristics. This work augments our understanding of ethnic restaurants and the nutrition implications of business adaptations when responding to emergencies.

Imaging Nanomechanical Vibrations and Manipulating Parametric Mode Coupling via Scanning Microwave Microscopy.

In this study, we present a novel platform based on scanning microwave microscopy for manipulating and detecting tiny vibrations of nanoelectromechanical resonators using a single metallic tip. The tip is placed on the top of a grounded silicon nitride membrane, acting as a movable top gate of the coupled resonator. We demonstrate its ability to map mechanical modes and investigate mechanical damping effects in a capacitive coupling scheme, based on its spatial resolution. We also manipulate the energy transfer coherently between the mode of the scanning tip and the underlying silicon nitride membrane, via parametric coupling. Typical features of optomechanics, such as anti-damping and electromechanically induced transparency, have been observed. Since the microwave optomechanical technology is fully compatible with quantum electronics and very low temperature conditions, it should provide a powerful tool for studying phonon tunnelling between two spatially separated vibrating elements, which could potentially be applied to quantum sensing.

3D-Printed MEMS in Italy.

MEMS devices are more and more commonly used as sensors, actuators, and microfluidic devices in different fields like electronics, opto-electronics, and biomedical engineering. Traditional fabrication technologies cannot meet the growing demand for device miniaturisation and fabrication time reduction, especially when customised devices are required. That is why additive manufacturing technologies are increasingly applied to MEMS. In this review, attention is focused on the Italian scenario in regard to 3D-printed MEMS, studying the techniques and materials used for their fabrication. To this aim, research has been conducted as follows: first, the commonly applied 3D-printing technologies for MEMS manufacturing have been illustrated, then some examples of 3D-printed MEMS have been reported. After that, the typical materials for these technologies have been presented, and finally, some examples of their application in MEMS fabrication have been described. In conclusion, the application of 3D-printing techniques, instead of traditional processes, is a growing trend in Italy, where some exciting and promising results have already been obtained, due to these new selected technologies and the new materials involved.

Graphene photodetectors integrated with silicon and perovskite quantum dots.

Photodetectors (PDs) play a crucial role in imaging, sensing, communication systems, etc. Graphene (Gr), a leading two-dimensional material, has demonstrated significant potential for photodetection in recent years. However, its relatively weak interaction with light poses challenges for practical applications. The integration of silicon (Si) and perovskite quantum dots (PQDs) has opened new avenues for Gr in the realm of next-generation optoelectronics. This review provides a comprehensive investigation of Gr/Si Schottky junction PDs and Gr/PQD hybrid PDs as well as their heterostructures. The operating principles, design, fabrication, optimization strategies, and typical applications of these devices are studied and summarized. Through these discussions, we aim to illuminate the current challenges and offer insights into future directions in this rapidly evolving field.

Modeling and Simulation of Graphene-Based Transducers in NEMS Accelerometers.

The mechanical characteristics of graphene ribbons with an attached proof mass that can be used as NEMS transducers have been minimally studied, which hinders the development of graphene-based NEMS devices. Here, we simulated the mechanical characteristics of graphene ribbons with an attached proof mass using the finite element method. We studied the impact of force, residual stress, and geometrical size on displacement, strain, resonant frequency, and fracture strength of graphene ribbons with an attached proof mass. The results show that the increase of width and thickness of graphene ribbons would result in a decrease of the displacement and strain but also an increase of resonant frequency. The increase of the length of graphene ribbons has an insignificant impact on the strain, but it could increase the displacement and decrease the resonant frequency. The increase of residual stress in the graphene ribbons decreases its strain and displacement. The estimated fracture strength of graphene shows limited dependence on its thickness, with an estimated value of around 148 GPa. These findings contribute to the understanding of the mechanical characteristics of graphene ribbons with an attached proof mass and lay the solid foundation for the design and manufacture of high-performance graphene-based NEMS devices such as accelerometers.

Materials for electronically controllable microactuators.

Abstract: Electronically controllable actuators have shrunk to remarkably small dimensions, thanks to recent advances in materials science. Currently, multiple classes of actuators can operate at the micron scale, be patterned using lithographic techniques, and be driven by complementary metal oxide semiconductor (CMOS)-compatible voltages, enabling new technologies, including digitally controlled micro-cilia, cell-sized origami structures, and autonomous microrobots controlled by onboard semiconductor electronics. This field is poised to grow, as many of these actuator technologies are the firsts of their kind and much of the underlying design space remains unexplored. To help map the current state of the art and set goals for the future, here, we overview existing work and examine how key figures of merit for actuation at the microscale, including force output, response time, power consumption, efficiency, and durability are fundamentally intertwined. In doing so, we find performance limits and tradeoffs for different classes of microactuators based on the coupling mechanism between electrical energy, chemical energy, and mechanical work. These limits both point to future goals for actuator development and signal promising applications for these actuators in sophisticated electronically integrated microrobotic systems.

A toroidal SAW gyroscope with focused IDTs for sensitivity enhancement.

A surface acoustic wave (SAW) gyroscope measures the rate of rotational angular velocity by exploiting a phenomenon known as the SAW gyroscope effect. Such a gyroscope is a great candidate for application in harsh environments because of the simplification of the suspension vibration mechanism necessary for traditional microelectromechanical system (MEMS) gyroscopes. Here, for the first time, we propose a novel toroidal standing-wave-mode SAW gyroscope using focused interdigitated transducers (FIDTs). Unlike traditional SAW gyroscopes that use linear IDTs to generate surface acoustic waves, which cause beam deflection and result in energy dissipation, this study uses FIDTs to concentrate the SAW energy based on structural features, resulting in better focusing performance and increased SAW amplitude. The experimental results reveal that the sensitivity of the structure is 1.51 µV/(°/s), and the bias instability is 0.77°/s, which are improved by an order of magnitude compared to those of a traditional SAW gyroscope. Thus, the FIDT component can enhance the performance of the SAW gyroscope, demonstrating its superiority for angular velocity measurements. This work provides new insights into improving the sensitivity and performance of SAW gyroscopes.

Photostrictive Actuators Based on Freestanding Ferroelectric Membranes.

Complex oxides offer a wide range of functional properties, and recent advances in the fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, photoactuation is demonstrated in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent holographic interferometry provide combined evidence for the photostrictive strain in BaTiO3 originating from a partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated by light.

Electrostatic generator enhancements for powering IoT nodes via efficient energy management.

Electrostatic generators show great potential for powering widely distributed electronic devices in Internet of Things (IoT) applications. However, a critical issue limiting such generators is their high impedance mismatch when coupled to electronics, which results in very low energy utilization efficiency. Here, we present a high-performance energy management unit (EMU) based on a spark-switch tube and a buck converter with an RF inductor. By optimizing the elements and parameters of the EMU, a maximum direct current output power of 79.2 mW m-2 rps-1 was reached for a rotary electret generator with the EMU, achieving 1.2 times greater power output than without the EMU. Furthermore, the maximum power of the contact-separated triboelectric nanogenerator with an EMU is 1.5 times that without the EMU. This excellent performance is attributed to the various optimizations, including utilizing an ultralow-loss spark-switch tube with a proper breakdown voltage, adding a matched input capacitor to enhance available charge, and incorporating an RF inductor to facilitate the high-speed energy transfer process. Based on this extremely efficient EMU, a compact self-powered wireless temperature sensor node was demonstrated to acquire and transmit data every 3.5 s under a slight wind speed of 0.5 m/s. This work greatly promotes the utilization of electrostatic nanogenerators in practical applications, particularly in IoT nodes.

Hydrodynamic function and spring constant calibration of FluidFM micropipette cantilevers.

Fluidic force microscopy (FluidFM) fuses the force sensitivity of atomic force microscopy with the manipulation capabilities of microfluidics by using microfabricated cantilevers with embedded fluidic channels. This innovation initiated new research and development directions in biology, biophysics, and material science. To acquire reliable and reproducible data, the calibration of the force sensor is crucial. Importantly, the hollow FluidFM cantilevers contain a row of parallel pillars inside a rectangular beam. The precise spring constant calibration of the internally structured cantilever is far from trivial, and existing methods generally assume simplifications that are not applicable to these special types of cantilevers. In addition, the Sader method, which is currently implemented by the FluidFM community, relies on the precise measurement of the quality factor, which renders the calibration of the spring constant sensitive to noise. In this study, the hydrodynamic function of these special types of hollow cantilevers was experimentally determined with different instruments. Based on the hydrodynamic function, a novel spring constant calibration method was adapted, which relied only on the two resonance frequencies of the cantilever, measured in air and in a liquid. Based on these results, our proposed method can be successfully used for the reliable, noise-free calibration of hollow FluidFM cantilevers.

A C-shaped hinge for displacement magnification in MEMS rotational structures.

The design, analysis, fabrication, and characterization of two distinct MEMS rotational structures are provided; these structures include a classical symmetrical lancet structure and a novel symmetrical C-shaped structure provided with a tilted arm, and both are actuated by thermal actuators. Our proposed C-shaped structure implemented a curved beam mechanism to enhance the movement delivered by the thermal actuators. The geometrical parameters of our proposed device were optimized using the design of experiment (DOE) method. Furthermore, the analytical modeling based on Castigliano's second theorem and the simulations based on the finite element method (FEM) were used to predict the behavior of the symmetrical C-shaped structure; the results were in good agreement with each other. The MEMS-based rotational structures were fabricated on silicon-on-insulator (SOI) wafers using bulk micromachining technology and deep reactive ion etching (DRIE) processes. The fabricated devices underwent experimental characterization; our results showed that our proposed MEMS rotational structure exhibited a 28% improvement in the delivered displacement compared to the symmetrical lancet structure. Furthermore, the experimental results showed good agreement with those obtained from numerical analysis. Our proposed structures have potential applications in a variety of MEMS devices, including accelerometers, gyroscopes, and resonators, due to their ability to maximize displacement and thus enhance sensitivity.

Correction: Integrated silicon photonic MEMS.

[This corrects the article DOI: 10.1038/s41378-023-00498-z.].

Ultrafast (∼0.6 s), Robust, and Highly Linear Hydrogen Detection up to 10% Using Fully Suspended Pure Pd Nanowire.

The high explosiveness of hydrogen gas in the air necessitates prompt detection in settings where hydrogen is used. For this reason, hydrogen sensors are required to offer rapid detection and possess superior sensing characteristics in terms of measurement range, linearity, selectivity, lifetime, and environment insensitivity according to the publicized protocol. However, previous approaches have only partially achieved the standardized requirements and have been limited in their capability to develop reliable materials for spatially accessible systems. Here, an electrical hydrogen sensor with an ultrafast response (∼0.6 s) satisfying all demands for hydrogen detection is demonstrated. Tailoring structural engineering based on the reaction kinetics of hydrogen and palladium, an optimized heating architecture that thermally activates fully suspended palladium (Pd) nanowires at a uniform temperature is designed. The developed Pd nanostructure, at a designated temperature distribution, rapidly reacts with hydrogen, enabling a hysteresis-free response from 0.1% to 10% and durable characteristics in mechanical shock and repetitive operation (>10,000 cycles). Moreover, the device selectively detects hydrogen without performance degradation in humid or carbon-based interfering gas circumstances. Finally, to verify spatial accessibility, the wireless hydrogen detection system has been demonstrated, detecting and reporting hydrogen leakage in real-time within just 1 s.

On the Dependency of the Electromechanical Response of Rotary MEMS/NEMS on Their Embedded Flexure Hinges' Geometry.

This paper investigates how the electromechanical response of MEMS/NEMS devices changes when the geometrical characteristics of their embedded flexural hinges are modified. The research is dedicated particularly to MEMS/NEMS devices which are actuated by means of rotary comb-drives. The electromechanical behavior of a chosen rotary device is assessed by studying the rotation of the end effector, the motion of the comb-drive mobile fingers, the actuator's maximum operating voltage, and the stress sustained by the flexure when the flexure's shape, length, and width change. The results are compared with the behavior of a standard revolute joint. Outcomes demonstrate that a linear flexible beam cannot perfectly replace the revolute joint as it induces a translation that strongly facilitates the pull-in phenomenon and significantly increases the risk of ruptures of the comb-drives. On the other hand, results show how curved beams provide a motion that better resembles the revolute motion, preserving the structural integrity of the device and avoiding the pull-in phenomenon. Finally, results also show that the end effector motion approaches most precisely the revolute motion when a fine tuning of the beam's length and width is performed.

Coupled Nanomechanical Graphene Resonators: A Promising Platform for Scalable NEMS Networks.

Arrays of coupled nanoelectromechanical resonators are a promising foundation for implementing large-scale network applications, such as mechanical-based information processing and computing, but their practical realization remains an outstanding challenge. In this work, we demonstrate a scalable platform of suspended graphene resonators, such that neighboring resonators are persistently coupled mechanically. We provide evidence of strong coupling between neighboring resonators using two different tuning methods. Additionally, we provide evidence of inter-resonator coupling of higher-order modes, demonstrating the rich dynamics that can be accessed with this platform. Our results establish this platform as a viable option for realizing large-scale programmable networks, enabling applications such as phononic circuits, tunable waveguides, and reconfigurable metamaterials.

Probing Linear to Nonlinear Damping in 2D Semiconductor Nanoelectromechanical Resonators toward a Unified Quality Factor Model.

In resonant nanoelectromechanical systems (NEMS), the quality (Q) factor is essential for sensing, communication, and computing applications. While a large vibrational amplitude is useful for increasing the signal-to-noise ratio, the damping in this regime is more complex because both linear and nonlinear damping are important, and an accurate model for Q has not been fully explored. Here, we demonstrate that by combining the time-domain ringdown and frequency-domain resonance measurements, we extract the accurate Q for two-dimensional (2D) MoS2 and MoTe2 NEMS resonators at different vibration amplitudes. In particular, in the transition region between linear and nonlinear damping, Q can be precisely extracted by fitting to the ringdown characteristics. By varying AC driving, we tune the Q by ΔQ/Q = 269% and extract the nonlinear damping coefficient. We develop the dissipation model that well captures the linear to nonlinear damping, providing important insights for accurately modeling and optimizing Q in 2D NEMS resonators.

Nanomechanical Sensing for Mass Flow Control in Nanowire-Based Open Nanofluidic Systems.

Open nanofluidic systems, where liquids flow along the outer surface of nanoscale structures, provide otherwise unfeasible capabilities for extremely miniaturized liquid handling applications. A critical step toward fully functional applications is to obtain quantitative mass flow control. We demonstrate the application of nanomechanical sensing for this purpose by integrating voltage-driven liquid flow along nanowire open channels with mass detection based on flexural resonators. This approach is validated by assembling the nanowires with microcantilever resonators, enabling high-precision control of larger flows, and by using the nanowires as resonators themselves, allowing extremely small liquid volume handling. Both implementations are demonstrated by characterizing voltage-driven flow of ionic liquids along the surface of the nanowires. We find a voltage range where mass flow rate follows a nonlinear monotonic increase, establishing a steady flow regime for which we show mass flow control at rates from below 1 ag/s to above 100 fg/s and precise liquid handling down to the zeptoliter scale. The observed behavior of mass flow rate is consistent with a voltage-induced transition from static wetting to dynamic spreading as the mechanism underlying liquid transport along the nanowires.

Gold Nanodrum Resonators.

Nanodrum resonators have been fabricated using nanometer-thick gold films as the drumheads. The fabrication method is favorable for large-area array manufacture of arbitrary shapes. The drum resonators exhibit fundamental mode vibration frequencies in the MHz regime. We use the stretched-plate model to describe the natural vibrations of the drum. The Q factor of the fundamental mode increases as the thickness of the drum increases and decreases as the drum diameter goes up. The highest Q factor of the fundamental mode reaches 290 at room temperature and atmospheric pressure. Based on the deduced material properties we estimate that the resonator has a mass sensitivity of 1.11 × 10-22 g/Hz.

Compact and modular system architecture for a nano-resonator-mass spectrometer.

Mass measurements in the mega-to giga-Dalton range are essential for the characterization of natural and synthetic nanoparticles, but very challenging to perform using conventional mass spectrometers. Nano-electro-mechanical system (NEMS) based MS has demonstrated unique capabilities for the analysis of ultra-high mass analytes. Yet, system designs to date included constraints transferred from conventional MS instruments, such as ion guides and high vacuum requirements. Encouraged by other reports, we investigated the influence of pressure on the performances of the NEMS sensor and the aerodynamic focusing lens that equipped our first-generation instrument. We thus realized that the NEMS spectrometer could operate at significantly higher pressures than anticipated without compromising particle focusing nor mass measurement quality. Based on these observations, we designed and constructed a new NEMS-MS prototype considerably more compact than our original system, and which features an improved aerodynamic lens alignment concept, yielding superior particle focusing. We evaluated this new prototype by performing nanoparticle deposition to characterize aerodynamic focusing, and mass measurements of calibrated gold nanoparticles samples. The particle capture efficiency showed nearly two orders of magnitude improvement compared to our previous prototype, while operating at two orders of magnitude greater pressure, and without compromising mass resolution.

A robust lateral shift free (LSF) electrothermal micromirror with flexible multimorph beams.

Electrothermal bimorph-based scanning micromirrors typically employ standard silicon dioxide (SiO2) as the electrothermal isolation material. However, due to the brittle nature of SiO2, such micromirrors may be incapable to survive even slight collisions, which greatly limits their application range. To improve the robustness of electrothermal micromirrors, a polymer material is incorporated and partially replaces SiO2 as the electrothermal isolation and anchor material. In particular, photosensitive polyimide (PSPI) is used, which also simplifies the fabrication process. Here, PSPI-based electrothermal micromirrors have been designed, fabricated, and tested. The PSPI-type micromirrors achieved an optical scan angle of ±19.6° and a vertical displacement of 370 µm at only 4 Vdc. With a mirror aperture size of 1 mm × 1 mm, the PSPI-type micromirrors survived over 200 g accelerations from either vertical or lateral directions in impact experiments. In the drop test, the PSPI-type micromirrors survived falls to a hard floor from heights up to 21 cm. In the standard frequency sweeping vibration test, the PSPI-type micromirrors survived 21 g and 29 g acceleration in the vertical and lateral vibrations, respectively. In all these tests, the PSPI-type micromirrors demonstrated at least 4 times better robustness than SiO2-type micromirrors fabricated in the same batch.