Nanoelectromechanical Sensors Research Articles

Vapor Sensing of Colorectal Cancer Biomarkers in Isolation by Bare and Functionalized Nanoelectromechanical Sensors

Vapor Sensing of Colorectal Cancer Biomarkers in Isolation by Bare and Functionalized Nanoelectromechanical Sensors

Mechanical Detection of Magnetic Phase Transition in Suspended CrOCl Heterostructures

With their outstanding mechanical and magnetic characteristics, two-dimensional magnetic materials have attracted wide attentions in the field of nanoelectromechanics and spintronics. By tuning the mechanical resonance with external knobs, such as strain, electric and magnetic control, nanoelectromechanical sensors with novel functionalities have been successfully demonstrated. Here, we investigate the mechanical properties of the suspended membranes with few-layered antiferromagnetic material CrOCl. The results show that the Young’s modulus of CrOCl resonators is ~137.29 GPa by using a static detection method. Below the transition temperature TN, the mechanical resonance is found to strongly depend on the magnetic fields with an enormous blueshift of ~3.1% in the magnetic-field-induced phase transition. In addition, we also found that the variation of strain of system ∆ϵ was about 1.5 × 10−3 during the transition. Our study shows the great potential of two-dimensional magnetic materials in future nanoelectronic applications.

Research Progress of Graphene Nano-Electromechanical Resonant Sensors-A Review.

Graphene nano-electromechanical resonant sensors have wide application in areas such as seawater desalination, new energy, biotechnology, and aerospace due to their small size, light weight, and high sensitivity and resolution. This review first introduces the physical and chemical properties of graphene and the research progress of four preparation processes of graphene. Next, the principle prototype of graphene resonators is analyzed, and three main methods for analyzing the vibration characteristics of a graphene resonant sheet are described: molecular structural mechanics, non-local elastic theory and molecular dynamics. Then, this paper reviews research on graphene resonator preparation, discussing the working mechanism and research status of the development of graphene resonant mass sensors, pressure sensors and inertial sensors. Finally, the difficulties in developing graphene nano-electromechanical resonant sensors are outlined and the future trend of these sensors is described.

Graphene foam resonators: Fabrication and characterization

Three-dimensional graphene foams (GFs) benefit from a large surface area and unique physical properties. We present here the first-ever miniaturized GF-based resonators. We developed a simple yet reliable fabrication process, in which GFs are synthesized and assembled on a cavity to form suspended GF devices. We electrostatically excited these devices and analyzed their resonance and ring-down responses. We observed significant energy dissipation, as the quality factor of the devices was in the order of several tens. Additionally, we investigated the influence of temperature on the operation of the devices and found that high temperatures mechanically soften the resonators but also considerably enhance energy dissipation. Finally, our devices demonstrated a mode-coupling of a resonance mode and a mode having twice its frequency. Thus, this work paves the way toward the development of novel GF resonators that could be integrated into future devices, such as GF-based nano-electromechanical sensors, electrical circuits, and oscillators.

From micro to nano. Problems of modeling of nanoelectromechanical sensors

Microelectromechanical (MEMS) sensors are a class of devices that appeared relatively recently, only 50-60 years ago but are widely used in various fields of science and technology due to such characteristics as small sizes, low power consumption, and sufficient accuracy. The next step in miniaturization led to the creation of nanoelectromechanical sensors (NEMS) – measuring instruments that combine electronic and mechanical components that do not exceed 100 nm in size. On the one hand, the development and manufacture of NEMS require a high level of nanotechnologies. On the other hand, the development and manufacture of NEMS lead to the development of new materials with new effects such as surface and quantum effects. At the same time, the range of tasks that can be solved with using NEMS is quite wide – it’s expecting that the mass implementations of NEMS sensors and devices on their base can significantly improve the quality of people’s life, expand their physical capabilities, or compensate disadvantages. For NEMS, as well as for MEMS, such issues as temperature influence, electronic and mechanical noises, the possibility of chaotic outside signal appearance, and so on are relevant. However, because of the small sizes of NEMS, classical approaches may not be fully applicable to solving these issues. Besides that, during the NEMS design, the bunch of specific problems that not relevant for MEMS has appeared. The article provides a brief review of the state of developments in the area of NEMS sensors and problems that significant for NEMS due to their small size.

Nanoelectromechanical Sensors Based on Suspended 2D Materials.

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.

Characterization of single polyvinylidene fluoride (PVDF) nanofiber for flow sensing applications

The use of Polyvinylidene Fluoride (PVDF) based piezoelectric nanofibers for sensing and actuation has been reported widely in the past. However, in most cases, PVDF piezoelectric nanofiber mats have been used for sensing applications. This work fundamentally characterizes a single electrospun PVDF nanofiber and demonstrates its application as a sensing element for nanoelectromechanical sensors (NEMS). PVDF nanofiber mats were spun by far field electrospinning (FFES) process and complete material characterization was conducted by means of scanning electron microscope (SEM) imaging, Raman Spectroscopy and FTIR spectroscopy. An optimized recipe was developed for spinning a single suspended nanofiber on a specially designed MEMS substrate which allows the nano-mechanical and electrical characterization of a single PVDF nanofiber. Electrical characterization is conducted using a single suspended nanofiber to determine the piezoelectric coefficient (d33) of the nanofiber to be -58.77 pm/V. Also the mechanical characterization conducted using a nanoindenter revealed a Young’s Modulus and hardness of 2.2 GPa and 0.1 GPa respectively. Finally, an application that utilizes the single PVDF nanofiber as a sensing element to form a NEMS flow sensor is demonstrated. The single nanofiber flow sensor is tested in presence of various oscillatory flow conditions.

Thermal Diffusivity of a Single Carbon Nanocoil: Uncovering the Correlation with Temperature and Domain Size

The helical geometries and polycrystalline-amorphous structure of carbon nanocoils (CNCs), an exotic class of low-dimensional carbon nanostructures, distinguish them from carbon nanotubes and graphene. These distinct structures result in very different energy transport from that in carbon nanotubes and graphene, leading to important roles in applications as wave absorbers, near-infrared sensors, and nanoelectromechanical sensors. Here we report a systematic study of the thermal diffusivity (α) and conductivity (κ) of CNCs from 290 to 10 K and uncover their property-structure aspects. Our room-temperature α study reveals a correlation between α and the line diameter (d): α = (5.43 × 104 × e-d/37.7 + 9.5) × 10-7 m2/s. Combined with the Raman-based grain size (La) characterization, α and La are correlated as α = [81.2 × (La - 3.32)1.5 + 9.5] × 10-7 m2/s. With temperature decreasing from 290 K to 10 K, α has a 1-1.6-fold increase, and κ shows a peak around 75 K. To best understand the defect level and polycrystalline-amorphous structure of CNCs, the thermal reffusivity (Θ = α-1) of CNCs is studied and compared with that of graphite and graphene foam from 290 K down to 10 K. Very interestingly, CNC's Θ linearly decreases with decreased temperature, while Θ of graphite and graphene foam have an exponential decrease. The extrapolated 0 K-limit Θ is determined by low-momentum phonon scattering and gives a structure domain size of CNC samples (d = 455, 353, and 334 nm) of 1.28, 2.03 and 3.24 nm. These sizes are coherent with the X-ray diffraction results (3.5 nm) and the Raman spectroscopy study and confirm the correlation among d, La, and α.

Nanoscale mass detection based on vibrating piezoelectric ultrathin films under thermo-electro-mechanical loads

The potential applications of piezoelectric nanofilms (PNFs) and double-piezoelectric-nanofilm (DPNF) systems as nanoelectromechanical mass sensors are examined. The PNFs carrying multiple nanoparticles at arbitrary locations are modeled as rectangular nonlocal plates with attached concentrated masses. Using the nonlocal elasticity theory and Hamilton’s principle, the differential equations of motion are derived for both PNF-based and DPNF-based nanosensors. The influences of small scale, initial stress and temperature change on the frequency shifts of the nanoelectromechanical sensors are taken into consideration. Explicit expressions are derived for the resonance frequencies of the nanosensors by employing the Galerkin method. The present results show that when the value of nonlocal parameter decreases, the frequency shifts of piezoelectric nanosensors increase. Further, the frequency shifts of DPNF-based mass sensors are always greater than those of PNF-based mass sensors. The present work would be helpful in the design of nanoelectromechanical mass sensors using PNFs.

Efficient transfer of carbon nanotubes for device fabrication using an LOR resist sacrificial layer

A novel approach for transferring carbon nanotubes (CNTs) from quartz growth substrates to target substrates is presented. The fabrication of sensors based on CNTs requires the integration of nanotubes into device structures which are often not compatible with the synthesis process associated with the nanostructures. CNT transfer is an option for assembling carbon nanotubes if chemical vapor deposition (CVD) growth processes cannot be used on the device substrate, for example, due to the high synthesis temperatures. The novelty of the transfer process introduced here is the use of a thick lift-off resist (LOR, MicroChem) sacrificial layer as a transfer medium. This layer provides mechanical robustness for more convenient handling, and can be dissolved with mild chemistry resulting in only low amounts of residues on the CNTs. The process involves few and simple steps, making it a robust and efficient alternative to transfer processes with other transfer media. The successful demonstration of transistors based on transferred individual CNTs, which can e.g. serve as building blocks for nano electromechanical sensors, confirmed the suitability of the reported process for device fabrication.

Edge-, width- and strain-dependent semiconductor–metal transition in SnSe nanoribbons

First-principles calculations were employed to explore the electronic properties of SnSe nanoribbons. Our results showed that a semiconductor–metal or metal–semiconductor transition can be realized in SnSe nanoribbons by controlling the edge shape, width parameter and different levels of strain. It was found that the transition always occurs in SnSe nanoribbons with a zigzag edge (ZNR). With the width parameter of ZNRs less than 8, their optimized structures are perfect (P-structures) without any Sn–Se bond breaking and the electronic calculations demonstrate they display a metallic character. However, the structures became deformed (D-structures) with some Sn–Se bond rupture when tensile strain was applied, accompanied by the transition occurring from metal to indirect band gap semiconductors. On the other hand, compressive strain cannot induce the metal–semiconductor transition as ZNRs still keep their P-structures. With the width parameter greater than or equal to 8, ZNRs change to D-structure exhibiting a semiconductive feature at equilibrium state. The semiconductor–metal transition cannot be induced through applying tensile strain while a certain extent of compressive strain can trigger it. The localized–delocalized partial charge distribution of the conduction band minimum near the strained domains can be used to explain the metal–semiconductor or semiconductor–metal transition in SnSe ZNRs. Our results suggest that the SnSe ZNRs have potential applications in nanoelectromechanical sensors and switches, which will promote further experimental investigations on SnSe and other fascinating graphene-like metal chalcogenides.

Piezoresistive Sensing Performance of Junctionless Nanowire FET

This letter investigates junctionless nanowire field-effect transistor (NWFET) (JL-NWFET) parameters such as piezoresistance and low-frequency noise (LFN) with respect to channel doping and gate bias. The JL-NWFET is piezoresistive, and its gauge factor (GF ) is increased from 24 to 47 by reducing the channel doping ten times from 6.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> to 6.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Significant variations of GF and LFN are observed when the JL-NWFET is operated from subthreshold to on-state regime, and resolution (minimum detectable strain) is improved four times compared to inversion-mode NWFET. The simple fabrication and superior resolution formulate JL-NWFET as a promising sensing element for miniaturized nanoelectromechanical sensors.

DFT investigations of the piezoresistive effect of carbon nanotubes for sensor application

AbstractWe investigate the piezoresistive effect of carbon nanotubes (CNTs) within density functional theory (DFT) aiming at application‐relevant CNTs. CNTs are excellent candidates for the usage in nano‐electromechanical sensors (NEMSs) due to their small band gap at zero strain leading to a finite resistivity at room temperature. The application of strain induces a band gap‐opening leading to a tremendous change in the resistivity. DFT with the LDA approximation yields reasonable results for pure carbon systems like CNTs and is applied to calculate the electronic structure of experimentally relevant CNTs. For the transport part, a simple ballistic transport model based on the band gap is used. We compare our DFT results for the band gaps of strained CNTs to results of tight binding (TB) models. By introducing a scaling factor of $\sqrt {2} $, an excellent agreement of the DFT data with TB model, published by Yang and Han [Phys. Rev. Lett. 85, 154 (2000)], is obtained.

Ferroelectric Nanotubes: Free‐Standing Ferroelectric Nanotubes Processed via Soft‐Template Infiltration (Adv. Mater. 9/2012)

The image depicts an array of free-standing ferroelectric perovskite PbZrTiO nanotube islands, processed with soft-template infiltration using a solution precursor. Such high aspect ratio nanotube/pillar arrays, described on page 1160 by N. Bassiri-Gharb and co-workers, find diverse application in actively tunable photonic and phononic crystals, terahertz emitters, energy harvesters, and nanoelectromechanical sensors, actuators, and transducers.

Modelling and testing of a MEMS accelerometer controlled and read-out beyond the pull-in instability limit

Electrostatic forces caused by the readout circuit and parasitic capacitances have much relevance in the scaling considerations of Micro and Nano electro mechanical (M/NEMS) parallel-plate motion sensors. The reduction of minimum geometrical dimensions (spring width, air gap), aimed at an improvement of the sensitivity/area ratio, is indeed limited by the pull-in instability determined by the electrostatic attraction between parallel plates. In this paper it is presented a compact MEMS accelerometer built in the ST Microelectronics ThELMA technology, together with a 0.35μm CMOS switched-capacitor circuit, suitably designed to avoid the pull-in. In particular we focus on the model of the MEMS, written in a Hardware Description Language file to be used directly in the VLSI circuit simulator. Although the MEMS is unstable at the chosen biasing conditions when read-out at fixed voltage, the experimental results show that the closed-loop circuit allows the biasing beyond the pull-in voltage, in good agreement with the simulation prediction. The sensing range is larger than ±9 g with a resolution of 2mg/Hz.

In situ probing electrical response on bending of ZnO nanowires inside transmission electron microscope

In situ electrical transport measurements on individual bent ZnO nanowires have been performed inside a high-resolution transmission electron microscope, where the crystal structures of ZnO nanowires were simultaneously imaged. A series of consecutively recorded current-voltage (I-V) curves along with an increase in nanowire bending show the striking effect of bending on their electrical behavior. The bending-induced changes of resistivity, electron concentration, and carrier mobility of ZnO nanowires have been retrieved based on the experimental I-V data, which suggests the applications of ZnO nanowires as nanoelectromechanical sensors.

Development of Carbon Nanotube-Based Sensors—A Review

Carbon nanotubes (CNTs) have shown great promise as sensing elements in nanoelectromechanical sensors. In this review paper, we discuss the electrical, mechanical, and electromechanical properties of CNTs that are used in such applications. This investigation indicates which nanotube properties should be carefully considered when designing nanotube-based sensors. We then present the primary techniques that have been used for the integration of nanotubes into devices and proceed to give a description of sensors that have been developed using CNTs as active sensing elements

Micro- and nanomechanical sensors for environmental, chemical, and biological detection

Micro- and nanoelectromechanical systems, including cantilevers and other small scale structures, have been studied for sensor applications. Accurate sensing of gaseous or aqueous environments, chemical vapors, and biomolecules have been demonstrated using a variety of these devices that undergo static deflections or shifts in resonant frequency upon analyte binding. In particular, biological detection of viruses, antigens, DNA, and other proteins is of great interest. While the majority of currently used detection schemes are reliant on biomarkers, such as fluorescent labels, time, effort, and chemical activity could be saved by developing an ultrasensitive method of label-free mass detection. Micro- and nanoscale sensors have been effectively applied as label-free detectors. In the following, we review the technologies and recent developments in the field of micro- and nanoelectromechanical sensors with particular emphasis on their application as biological sensors and recent work towards integrating these sensors in microfluidic systems.

The entangled dance of physics

Physics so permeates today’s world that we often can’t even see it.

Resolving Radial Composition Gradients in Polarized Confocal Raman Spectra of Individual 3C-SiC Nanowires

Silicon carbide nanowires are being actively pursued as components for nanoelectromechanical sensors, nanocatalytic elements, and nano-optical circuits able to operate in harsh environment, high temperature, and high power applications. The effect of geometric confinement and polarization anisotropy in confocal Raman spectroscopy has been employed to detect axial and radial composition information in individual nanowires. Polarization anisotropy causes a significant increase in signal from the surface layer (relative to bulk), and combined with the increased surface-to-volume ratio at the nanoscale, it allows for the direct characterization of bulk and surface defects.