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One of the biggest challenges for in situ heating transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) is the ability to measure the local temperature of the specimen accurately. Despite technological improvements in the construction of TEM/STEM heating holders, the problem of being able to measure the real sample temperature is still the subject of considerable discussion. In this study, we review the present literature on methodologies for temperature calibration. We analyze calibration methods that require the use of a thermometric material in addition to the specimen under study, as well as methods that can be performed directly on the specimen of interest without the need for a previous calibration. Finally, an overview of the most important characteristics of all the treated techniques, including temperature ranges and uncertainties, is provided in order to provide an accessory database to consult before an in situ TEM/STEM temperature calibration experiment.
Heating coils utilize the concept of resistive heating to convert electrical energy into thermal energy. Uniform heating of the target area is the key performance indicator for heating coil design. Highly uniform distribution of temperature can be achieved by using a dense metal distribution in the area under consideration, however, this increases the cost of production significantly. A low-cost and efficient heating coil should have excellent temperature uniformity while having minimum metal consumption. In this work, space-filling fractal curves, such as Peano curve, Hilbert curve and Moore curve of various orders, have been studied as geometries for heating coils. In order to compare them in an effective way, the area of the geometries has been held constant at 30 mm × 30 mm and a constant power of 2 W has been maintained across all the geometries. Further, the thickness of the metal coils and their widths have been kept constant for all geometries. Finite Element Analysis (FEA) results show Hilbert and Moore curves of order-4, and Peano curve of order-3 outperform the typical double-spiral heater in terms of temperature uniformity and metal coil length.
In this paper, a new reconfigurable microstrip fractal ultra-wideband antenna with a capability of variable rejection frequency bands is presented. The main patch of this antenna has two modified C-shaped gaps. Also, on these c-shaped gaps, 10 ideal MEMS switches are used to produce band-notch frequencies at six different frequencies of: 5.4 GHz (5.2–5.5), 5.8 GHz (5.7–5.9), 6.1 GHz (5.9–6.3), 7 GHz (6.9–7.2), 7.9 GHz (7.7–8.1), and 8.4 GHz (8.2–8.6). This antenna is fed by a 50 Ω microstrip line and works in a wide bandwidth of 2.9–11 GHz. The antenna is designed and fabricated on an inexpensive substrate of FR4. Dimensions of the antenna are 31.2 × 38.4 mm. Measurement and simulation results are in good agreement.
In situ nanomechanical testing provides critical insight into the fundamental processes that lead to deformation phenomena in materials. Often, in situ tests are performed in relevant conditions such as high or low temperatures, tribological contact, gas environments, or under radiation exposure. Modern diffraction and imaging methods of materials under load provide high spatial resolution and enable extraction of quantitative mechanical data from local microstructure components or nano-sized objects. The articles in this issue cover recent advances in different types of in situ nanomechanical testing methods, spanning from dedicated nanomechanical testing platforms and microelectromechanical systems devices to deformation analyses via in situ diffraction and imaging methods. This includes scanning electron microscopy, advanced scanning transmission electron microscopy, electron diffraction, x-ray diffraction, and synchrotron techniques. Emerging areas such as in situ tribology enable novel insights into the origin of deformation mechanisms, while the evolution of microelectromechanical systems for controlled in situ testing provide opportunities for advanced control and loading strategies. Discussion on the current state of the art for in situ nanomechanical testing and future opportunities in imaging, strain sensing, and testing environments are also addressed.
The field of in situ nanomechanics is greatly benefiting from microelectromechanical systems (MEMS) technology and integrated microscale testing machines that can measure a wide range of mechanical properties at nanometer scales, while characterizing the damage or microstructure evolution in electron microscopes. This article focuses on the latest advances in MEMS-based nanomechanical testing techniques that go beyond stress and strain measurements under typical monotonic loadings. Specifically, recent advances in MEMS testing machines now enable probing key mechanical properties of nanomaterials related to fracture, fatigue, and wear. Tensile properties can be measured without instabilities or at high strain rates, and signature parameters such as activation volume can be obtained. Opportunities for environmental in situ nanomechanics enabled by MEMS technology are also discussed.
Considering the nonlocal small-scale effect and surface effect, we perform the size-dependent vibration analysis of carbon nanotube (CNT). The modified governing equations for CNT’s vibration behaviors are derived by using the nonlocal Euler–Bernoulli and Timoshenko beam models, together with the consideration of surface tension and surface elasticity. According to the numerical experiments, both small-scale effect and surface effect make a substantial difference. For flexural vibration, size effect for CNT’s vibration behaviors weakens with the increase of its diameter, but strengthens with the increase of the length–diameter ratio; for shear vibration with constant length–diameter ratio, a nonlinear correlation between size effect and CNT’s diameter exists, suggesting that there is a typical diameter for CNTs, which corresponds to the “strongest” size effect. In addition, the effects of elastic substrate modulus, temperature change, and axial preloading on the vibration behaviors and their size-dependence are analyzed, respectively.
The interaction of a thin viscous film with an elastic sheet results in coupling of pressure and deformation, which can be utilized as an actuation mechanism for surface deformations in a wide range of applications, including microfluidics, optics and soft robotics. Implementation of such configurations inherently takes place over finite domains and often requires some pre-stretching of the sheet. Under the assumptions of strong pre-stretching and small deformations of the lubricated elastic sheet, we use the linearized Reynolds and Föppl–von Kármán equations to derive closed-form analytical solutions describing the deformation in a finite domain due to external forces, accounting for both bending and tension effects. We provide a closed-form solution for the case of a square-shaped actuation region and present the effect of pre-stretching on the dynamics of the deformation. We further present the dependence of the deformation magnitude and time scale on the spatial wavenumber, as well as the transition between stretching- and bending-dominant regimes. We also demonstrate the effect of spatial discretization of the forcing (representing practical actuation elements) on the achievable resolution of the deformation. Extending the problem to an axisymmetric domain, we investigate the effects arising from nonlinearity of the Reynolds and Föppl–von Kármán equations and present the deformation behaviour as it becomes comparable to the initial film thickness and dependent on the induced tension. These results set the theoretical foundation for implementation of microfluidic soft actuators based on elastohydrodynanmics.
Stretchable electronics fabrication generally relies on fine-tuning adhesion forces, putting some restrictions on what the carrier layer can be. In contrast to adhesion, mechanical tangling makes more kinds of carrier materials available. Antibacterial, conductive, heat-responsive and other functions can be brought in by fiber networks as long as they are compatible with the highly selective silicon etch process. Mechanical grippers can also bring electronic contacts from one side of a mesh to the other, which is difficult to do on continuous thin films of other soft materials like silicone or polyimide. Our solution uses mechanical strain to produce large arrays of redundant grippers from planar thin-film designs.
The patterning of gold and silver micro and nanostructures on rigid and flexible substrates is investigated by microcontact printed thiol based self-assembled monolayers. The aspect ratio of the noble metal micro and nanostructures is determined by interaction of the -SH head group of the CH3(CH2)19SH molecules and the surface of the noble metal. Silver micro and nanostructures with >10 times higher aspect ratios can be realized in comparison to commonly realized gold micro and nanostructures. The printing process is described, and the etching process is characterized in terms of etching window and etching selectivity. Potential electronic and photonic applications of the micro and nanostructures are discussed taking the boundary conditions of the printing process and the selected material system into consideration.
Microsupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things’ sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.
In this paper, we studied the temperature dependency effect of thermal coefficient of resistance (TCR) in amorphous silicon (a-Si) on the properties of uncooled microbolometer with a-Si as a resistance layer by simulation. The temperature of the microbolometer rises during the operation mainly due to the heat generated by Joule heating as well as IR radiation. Generally, the TCR of a-Si is treated as a constant for the simplicity but the absolute value of TCR has been reported to decrease as the temperature increases. Therefore, to improve the device characteristics, the effect of temperature dependency of TCR in a-Si should be considered carefully in the range of the operating temperature. The responsivities of microbolometer are simulated according to the width of the resistance layer (W) with TCR as a function of temperature, which shows that the optimal W condition is affected by the TCR value changed by the temperature.
Sprays are a class of multiphase flows which exhibit a wide range of drop size and velocity scales spanning several orders of magnitude. The objective of the current work is to experimentally investigate the prospect of dynamical similarity in these flows. We are also motivated to identify a choice of length and time scales which could lead towards a universal description of the drop size and velocity spectra. Towards this end, we have fabricated a cohort of geometrically similar pressure swirl atomizers using micro-electromechanical systems (MEMS) as well as additive manufacturing technology. We have characterized the dynamical characteristics of the sprays as well as the drop size and velocity spectra (in terms of probability density functions, p.d.f.s) over a wide range of Reynolds (
) and Weber numbers (
) using high-speed imaging and phase Doppler interferometry, respectively. We show that the dimensionless Sauter mean diameter (
) scaled to the boundary layer thickness in the liquid sheet at the nozzle exit (
) exhibits self-similarity in the core region of the spray, but not in the outer zone. In addition, we show that global drop size spectra in the sprays show two distinct characteristics. The spectra from varying
collapse onto a universal p.d.f. for drops of size
, a residual effect of
persists in the size spectra. We explain this characteristic by the fact that the physical mechanisms that cause large drops is different from that which is responsible for the small drops. Similarly, with the liquid sheet velocity at the nozzle exit (
) as the choice of velocity scale, we show that drops moving with a velocity
collapse onto a universal p.d.f., while drops with
exhibit a residual effect of
. From these observations, we suggest that physically accurate models for drop size and velocity spectra should rely on piecewise descriptions of the p.d.f. rather than invoking a single mathematical form for the entire distribution. Finally, we show from a dynamical modal analysis that the conical liquid sheet flapping characteristics exhibit a sharp transition in Strouhal number (
) at a critical
Third-generation semiconductors, such as ZnO and GaN, exhibit strong piezoelectric polarization due to the lack of inversion symmetry. The piezotronic effect observed in these semiconductors was proposed for tuning carrier transport in electronic devices by utilizing the induced piezoelectric potential as a virtual gate. This novel concept allows effective interactions between micro-/nanoelectronic devices and external mechanical stimuli. Piezotronics provide a promising approach for designing future electronic devices beyond Moore’s Law with potential for developing smart sensors, environment monitoring systems, human–machine interaction elements, and other transducers. In this article, we review recent progress in piezotronics using one-dimensional materials, heterojunctions, and large-scale arrays. We provide guidance for future piezotronic devices based on these materials.
When uniform strain is applied to noncentrosymmetric semiconductor crystals, which are piezoelectric, static polarization charges are induced at the surface. If the applied strain is not uniform, these charges can even be created inside the crystal. The applied strain affects electronic transport and also photonic processes, and thus can be used to tune the material properties statically or dynamically. As a result, two new fields have emerged, namely piezotronics and piezo-phototronics. This article reviews the history of the two fields and gives a perspective on their applications. The articles in this issue of MRS Bulletin highlight progress in these two fields, and this article places this progress into perspective.
This paper reports an extended state observer (ESO)-based robust dynamic surface control (DSC) method for triaxial MEMS gyroscope applications. An ESO with non-linear gain function is designed to estimate both velocity and disturbance vectors of the gyroscope dynamics via measured position signals. Using the sector-bounded property of the non-linear gain function, the design of an
-robust ESO is phrased as a convex optimization problem in terms of linear matrix inequalities (LMIs). Next, by using the estimated velocity and disturbance, a certainty equivalence tracking controller is designed based on DSC. To achieve an improved robustness and to remove static steady-state tracking errors, new non-linear integral error surfaces are incorporated into the DSC. Based on the energy-to-peak (
) performance criterion, a finite number of LMIs are derived to obtain the DSC gains. In order to prevent amplification of the measurement noise in the DSC error dynamics, a multi-objective convex optimization problem, which guarantees a prescribed
performance bound, is considered. Finally, the efficacy of the proposed control method is illustrated by detailed software simulations.
Strong strain-mediated magnetoelectric (ME) coupling in magnetic/ferroelectric heterostructures has great potential for different high-frequency multiferroic devices. In this article, we present the most recent progress in integrated multiferroic devices. Integrated magnetic tunable inductors with a wide operation frequency range, integrated nonreciprocal bandpass filters with dual magnetic and electric-field tunability based on magnetostatics surface waves, and novel radio-frequency nanomechanical ME resonators with pico-Tesla sensitivity for direct current magnetic fields are presented. Finally, a new antenna miniaturization mechanism, acoustically actuated nanomechanical ME antennas, which can successfully miniaturize the size by 1–2 orders, is introduced. With the advantages of high magnetic field sensitivity, highest antenna gain among all nanoscale antennas at similar frequency, integrated capability with complementary metal oxide semiconductor technology, and ground-plane immunity from metallic surfaces and the human body, ME antennas have a bright future for biomedical applications, wearable antennas, and the Internet of Things due to their unique and particular properties.
Strong magnetoelectric (ME) coupling realized in magnetic/ferroelectric multiferroic heterostructures provides great potential for different integrated multiferroic devices for sensing, power, RF, and µ-wave electronics. Here, we present the most recent progress on new integrated multiferroic devices including novel integrated magnetic tunable inductors with a wide operation frequency range; integrated nonreciprocal bandpass filter with dual H- and E-field tunability based on magnetostatics surface waves; dual H- and E-field tunable RF bandpass filters with nanomechanical ME resonators; RF nanomechanical ME resonators with pico-Tesla DC magnetic fields sensitivity; a new antenna miniaturization mechanism, acoustically actuated nanomechanical ME antennas, which successfully miniaturize the magnitude in 1-2 orders with the advantages of the high magnetic field sensitivity, highest antenna gain within all nanoscale antennas at the similar frequency, and ground plane immunity on the metallic surface and the human body.
Dynamic-mode cantilever sensors are used in many different applications but especially in materials research to study properties of novel (nano)materials. Decreasing sample sizes require an increase in sensitivity of the analysis tools. For cantilever-based methods that is achieved through a reduction in cantilever dimensions. However, the increase in sensitivity has to be balanced with the detectability as also for a small cantilever a reliable detection of its oscillatory state has to be ensured. A recently introduced co-resonant measurement principle for cantilever sensors addresses this challenge by coupling and eigenfrequency matching of a micro- and a nanocantilever. Here, the sensor concept is reviewed with focus on the application in materials research by the instructive example of an iron-filled carbon nanotube, giving insight into the features and benefits of the sensor concept and demonstrating the reliable derivation of magnetic sample properties.
This article focuses on the finite element modeling of toroidal microinductors, employing first-of-its-kind nanocomposite magnetic core material and superparamagnetic iron nanoparticles covalently cross-linked in an epoxy network. Energy loss mechanisms in existing inductor core materials are covered as well as discussions on how this novel core material eliminates them providing a path toward realizing these low form factor devices. Designs for both a 2 μH output and a 500 nH input microinductor are created via the model for a high-performance buck converter. Both modeled inductors have 50 wire turns, less than 1 cm3 form factors, less than 1 Ω AC resistance, and quality factors, Q’s, of 27 at 1 MHz. In addition, the output microinductor is calculated to have an average output power of 7 W and a power density of 3.9 kW/in3 by modeling with the 1st generation iron nanocomposite core material.
Recent experiments have demonstrated that small-scale rotary devices installed in a microfluidic channel can be driven passively by the underlying flow alone without resorting to conventionally applied magnetic or electric fields. In this work, we conduct a theoretical and numerical study on such a flow-driven ‘watermill’ at low Reynolds number, focusing on its hydrodynamic features. We model the watermill by a collection of equally spaced rigid rods. Based on the classical resistive force (RF) theory and direct numerical simulations, we compute the watermill’s instantaneous rotational velocity as a function of its rod number
, position and orientation. When
, the RF theory predicts that the watermill’s rotational velocity is independent of
and its orientation, implying the full rotational symmetry (of infinite order), even though the geometrical configuration exhibits a lower-fold rotational symmetry; the numerical solutions including hydrodynamic interactions show a weak dependence on
and the orientation. In addition, we adopt a dynamical system approach to identify the equilibrium positions of the watermill and analyse their stability. We further compare the theoretically and numerically derived rotational velocities, which agree with each other in general, while considerable discrepancy arises in certain configurations owing to the hydrodynamic interactions neglected by the RF theory. We confirm this conclusion by employing the RF-based asymptotic framework incorporating hydrodynamic interactions for a simpler watermill consisting of two or three rods and we show that accounting for hydrodynamic interactions can significantly enhance the accuracy of the theoretical predictions.