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In the present study, Rayleigh waves are propagated through a thick Aluminum (Al) plate to evaluate its material nonlinearity based on the second harmonic produced in the response. The experiments and numerical simulations are carried out on the pristine and fatigued thick Al specimens, and an amplitude-based Rayleigh wave nonlinear parameter is used to characterize the material nonlinearity. In addition, a physics-based nonlinear parameter that depends on the sub-structural evolution parameters, and higher-order plastic and elastic constants are also used to characterize the nonlinearity of the pristine and fatigued Al material. They found to be in good agreement for the predefined conditions of tone burst cycles in the actuation signal and propagation distance. The knowledge of material nonlinearity parameters evaluated for the pristine and fatigued thick plate specimens using Rayleigh waves is shown in the present study to be crucial to evaluate the remnant useful life (RUL) of the fatigued specimen with fair accuracy.

Field Effect Transistor (FET)-based electrochemical biosensor is gaining a lot of interest due to its malleability with modern fabrication technology and the ease at which it can be integrated with modern digital electronics. To increase the sensitivity and response time of the FET-based biosensor, many semiconducting materials have been categorized, including 2 dimensional (2D) nanomaterials. These 2D materials are easy to fabricate, increase sensitivity due to the atomic layer, and are flexible for a range of biomolecule detection. Due to the atomic layer of 2D materials each device requires a supporting substrate to fabricate a biosensor. However, uneven morphology of supporting substrate leads to unreliable output from every device due to scattering effect. This review summarizes advances in 2D material-based electrochemical biosensors both in supporting and suspended configurations by using different atomic monolayer, and presents the challenges involved in supporting substrate-based 2D biosensors. In addition, we also point out the advantages of nanomaterials over bulk materials in the biosensor domain.

Conducting polymer actuators have shown wide application prospects in the field of biomedical sensors and micro-/nanorobotics. In order to explore more applications in biomedical sensing and robotics, it is essential to understand the actuator static behavior from an engineering perspective, before incorporating them into a design. In this article, we have established the mathematical model of a trilayer polypyrrole (PPy) cantilever actuator and validated it experimentally. The model helps in enhancing the efficiency and in improving the performance, predictability, and control of the actuator. The thermal expansion analogy, which is similar to volume change of the multilayer PPy actuator due to ion migration, has been considered to develop a mathematical model in COMSOL Multiphysics. To further validate the actuator deformation predicted by the mathematical modeling, a multilayer PPy actuator was fabricated by electrochemical synthesis and the experimentally determined deflection of the actuator was compared to simulation data. Both the theoretical and experimental results depict that the model is effective for predicting the bending behavior of multilayer PPy actuators at different input voltages.

The Lamb wave-based localization of damage is presented here separately for the plain and riveted aluminium (Al) specimens. The first part of this paper deals with the experimental damage localization of the plain Al specimen using Lamb waves and four piezoelectric wafer (PW) transducers. The PW transducers mounted onto the specimen in a collocated way are used to actuate and sense Lamb waves. The responses are obtained for both the pristine and damaged states of the Al specimen. The signal processing is carried out on the residual response using the continuous wavelet transform (CWT), and time of arrival (TOA) data is obtained for each collocated actuator-sensor pair. The TOA data of the wave reflected from the damage is used in the two arrival time difference and astroid algorithms to locate the damage in an enclosed area. The genetic optimization (GO) method is used to further refine the location of damage within the enclosed area obtained using astroid algorithm. The second part of the paper deals with the localization of a faulty rivet in a riveted specimen. The responses are obtained in the cases of both healthy and faulty riveted specimens. The presence of a faulty rivet is indicated by the inflation in amplitude of the second harmonic. A new algorithm is therefore proposed by the authors to localize the faulty rivet, using the spectral content information. The results obtained through both the studies manifest the ability of the proposed methods for locating different types of defects and faulty rivets using an array of PW transducers.

The uneven morphology and the trapped charges at the surface of the traditionally used supporting substrate-based 2D biosensors produces a scattering phenomenon, which leads to irregular signal from individually fabricated device. Though suspended 2D channel material has the potential to overcome scattering effects from the substrates but achieving reliability and selectivity, have been limiting the biosensor technology. Here, we have demonstrated nanogap electrodes fabrication by using the self-assembly technique, which provides suspension to the 2D-MoS2. These nano-spacing electrodes not only give suspension but also provide robust strength to the atomic layer, which remains freestanding after coating of the Hafnium oxide (HfO2) as well as linkers and antibodies. For evaluating the electrical characteristics of suspended MoS2 FET, gating potential was applied through electrolyte on suspended MoS2 transistor, which achieved lower subthreshold swing 70 mV/dec and ON/OFF ratio 107. Afterward, pH detection has demonstrated at room temperature, which shows an impressive sensitivity of ∼880 by changing 1 unit of pH. Besides, we have successfully shown Escherichia coli (E. coli) bacteria sensing from suspended MoS2 transistor by functionalizing dielectric layer with E. coli antibodies. The reported biosensor has shown the ∼9% of conductance changes with a lower concentration of E. coli (10 CFU/mL; colony-forming unit per mL) as well as maintain the constant sensitivity in three fabricated devices. This type of the architecture has a potential to detect range of biomolecules such as COVID-19 viruses also by altering the oxide surface., Highlights • A suspended MoS2 atomic layer field-effect transistors is reported. • Self-assembled nanogap electrodes provide remarkable robust strength to the MoS2 atomic layer. • Suspended MoS2 field-effect transistor device exhibits impressive pH sensitivity and Escherichia coli bacteria detection. • The sensing mechanism highly selective to Escherichia coli bacteria.

Continuously growing and miniaturizing autonomous electronic devices and sensors for large temperature window is mostly depends on stability and performance of power-up systems. The net achievable power and energy densities of such miniatured rechargeable energy storage systems are largely dominated by internal hardware and external packaging materials. Similarly, temperature stability of electrochemically active materials and packaging components is also crucial to realize desired activity at few millimeter scale devices. Herein, we explore energy storage devices at tunable miniatured scale by selecting optimal electroactive materials, thermally stable packaging components, and their fabrication process. Further, an assembled device is subjected to evaluate its energy and power density per foot-print-area along with other key electrochemical parameters such as internal resistance, self-discharge, and thermal stability. Detailed studies reveal that the presently packaged millimeter size rechargeable batteries (2 mm–5 mm) have the ability to work up to 120 °C with minimal load loss and compatible with energy harvesting renewable source of the solar cell.

Due to its unique electronic band characteristics (presence of d-orbital in both Mo and Se atoms), MoSe2 has potential to exhibit high electrical conductivity and superior hydrogen evolution reaction (HER) kinetics when compared to other transition-metal dichalcogenides. Though various strategies were employed earlier to obtain MoSe2 structure with different shapes and morphologies, precise control on achieving both Mo- and Se-edge sites and understanding their interaction with reactants in HER remains to be challenging. Here, we successfully demonstrate the vapor diffusion method to grow highly crystalline MoSe2 nanoflowers on carbon cloth in a vertical orientation. Uniformly dispersed nanoflowers with Mo- and Se-edge sites exhibited remarkable electrocatalytic activity on hydrogen reduction in terms of low Tafel slope and high exchange current density. The existence of a strong interaction between MoSe2 and carbon cloth assists in long-term hydrogen production and confirms the exceptional durability of the catalyst. A comprehensive evidence for hydrogen adsorption on dual active sites, viz., Mo- and Se-edges of MoSe2, is provided using X-ray photoelectron spectroscopy and in situ Raman spectroscopy containing a specially designed liquid immersion objective lens.

This paper addresses the studies carried out on an I-beam to reveal the wave propagation characteristics and tackle the multi-mode propagation of Lamb waves. The experimental setup consisted of a new 3D Scanning Laser Doppler Vibrometer manufactured by Polytec (3D-SLDV) and was used to acquire high resolution time-space Lamb waves that were propagating in the I-beam. A high power and pulsed Nd:YAG laser was used to emit the required Lamb waves. The emission and sensing of the waves were carried out simultaneously. The wave propagation data was recorded by scanning the surface of the I-beam in a sequential manner. The measured data was used to construct the wave patterns that were propagating in the I-beams at different time instants. Furthermore, as the waves in an I-Beam propagate with multiple modes even at low frequency range, filtering was carried out in the frequency-wavenum- ber domain in order to decompose the modes. The results presented thereby confirm that the new 3D-SLDV possesses tremendous capability in revealing the wave propagation characteristics and its interaction with defect. The results could be the first time that the waves propagating in a real I-beam can be visually observed, whilst in the past, it can only be visualized through simulation. The capability of using such totally laser-based 3D inspection system to reveal the characteristics of Lamb wave and its interaction with defects are substantial.

This study proposes a sensitive and baseline-free method to evaluate the health status of a 1018 steel I-beam by measuring its material nonlinearity using a new nonlinearity parameter defined for Rayleigh waves. This parameter yields a true value of material nonlinearity using the Rayleigh wave harmonics obtained from the experiments carried out at the intact and impacted states of the I-beam. Accordingly, the evaluated nonlinearities are inherent and damaged induced respectively. The results show that, for an intact state, the nonlinearity obtained using the new parameter and the experimental results for different propagation distances, consist of several peaks and the first peak reaches the true material nonlinearity. Whereas, in case of damaged state, the nonlinearity parameter at the impacted location shows a sudden increase and reaches a value higher than that of the nonlinearity evaluated at the same location for intact state. Thus, the health status can be easily tracked by comparing the nonlinearity obtained from the current state of the I-beam at its first peak with that of a physics based nonlinearity parameter evaluated at the intact state using the higher order elastic coefficients of the material. Therefore, this method is termed as baseline-free. Lastly, a novel concept of evaluating the population of dislocations formed in the material as a result of impact loading, using the new nonlinearity parameter is introduced and an equation for its estimation is given. The trend of the results given by this new equation are in accordance with those reported in the literature. In contrast, deviation between the linear parameter such as the wave velocity at the intact and impacted state remains marginal. Thus, by using the new nonlinearity parameter, it has been proven that the inspected steel specimen can be easily differentiated whether it is at the intact or damaged state.

This paper acquaints the investigations using Rayleigh waves to surveil the structural integrity of an T-Beam. Unlike the conventional contact-type of sensors, such as the piezoelectric transducers and magnetostrictive sensors, a fully non-contact 3D type of laser-based transduction system was used in the present study to generate and receive the propagating Rayleigh waves. This laser-based transduction system is a new and attractive inspection technique because it can be used where contactable sensors cannot be applied directly to the target structure; such as those with high temperature surface, having limited access for mounting the sensors, and operating in a hazardous environment. Tn this study, a high power and pulsed Nd: YAG laser was used to generate the Rayleigh waves. The emission and sensing were effectuated simultaneously and the wave propagation data was recorded by scanning the surface of the T-beam sequentially. The 3D laser scanner measured the in-plane and out-of-plane velocities across a user-defined grid. Note that less research effort had been focused on specimens like T-Beam due its structural complexity and complex wave propagation phenomena. Explication of wave propagation in such specimens is still a challenge. The research presented here is an attempt to fill these gaps and solve these problems. Additionally, numerous experiments are conducted in order to corroborate the effectiveness of the proposed experimental setup in detecting the defect. An artificial defect was created on the web part of the I-Beam which mimics a real damage case. The responses were recorded using the 3D laser-based transduction system before and after creating the defect. The presented results thereby confirm the robustness of the non-contact generation and measurement setup for the structural health monitoring of I-Beams. The aptness of using such totally laser-based transduction system to unveil the characteristics of the propagating Rayleigh waves and its interaction with defects are notable.

Currently, nanomaterials are one of the materials being used commercially almost in all domains to improve the quality of products due to its physical, chemical, optical, antimicrobial and catalytic properties. In present paper, one of its roles in polymer chemistry has been explored, in this regards, the fabrication method developed for uniform coating of PET films with ZnO nanoparticles. In this direction, ZnO nanomaterials are very important as they are biocompatible, non- cytotoxic, cheap and easy to produce. The ZnO nanoparticles were obtained by facile hydrothermal route using zinc acetate and urea as precursors in water. The surface coating of nanomaterials on PET/PU films were achieved by bar spreader and chemical bath deposition method. Further, the structural and morphological analysis reveals uniform coating of ZnO nanostructures on to the PET/PU films.

The performance of devices from organic semiconductors is often governed by charge transfer phenomena at structurally and electronically complex interfaces, which remain challenging to access and study with excellent chemical and temporal resolution. Herein, we report the preparation and X-ray spectroscopic characterization of well-defined model organic-inorganic interfaces. We discover an unexpected trend for our systems' associated charge transfer times, and we rationalize this trend with density functional theory calculations. Our findings hold relevance for understanding interfacial charge transfer phenomena in a variety of organic, biological, and bioinspired systems.

Resistive chemical sensors were developed having as sensitive film graphene oxide (GO) spin-coated on glass. Sensor electrical behaviour to room temperature relative humidity was evaluated. High sensitivity characterizes GO sensor. However, it lacks repeatability and long term stability. To this end, we developed spin-coated GO sensors with different active layer thickness, which were subjected to subsequent thermal annealing steps. It was found that the resulting reduced GO (rGO) sensors demonstrate excellent stability compromising, though, the sensitivity which mainly depends on the number of annealing steps and film thickness. Finally, we propose a rapid, transparent, low-power consumption rGO sensor, enabling its use in relevant applications.

We present a novel methodology to synthesize two-dimensional (2D) lateral heterostructures of graphene and MoS2 sheets with molecular carbon nanomembranes (CNMs), which is based on electron beam induced stitching. Monolayers of graphene and MoS2 were grown by chemical vapor deposition (CVD) on copper and SiO2 substrates, respectively, transferred onto gold/mica substrates and patterned by electron beam lithography or photolithography. Self-assembled monolayers (SAMs) of aromatic thiols were grown on the gold film in the areas where the 2D materials were not present. An irradiation with a low energy electron beam was employed to convert the SAMs into CNMs and simultaneously stitching the CNM edges to the edges of graphene and MoS2, therewith forming a heterogeneous but continuous film composed of two different materials. The formed lateral heterostructures possess a high mechanical stability, enabling their transfer from the gold substrate onto target substrates and even the preparation as freestanding sheets. We characterized the individual steps of this synthesis and the structure of the final heterostructures by complementary analytical techniques including optical microscopy, Raman spectroscopy, atomic force microscopy (AFM), helium ion microscopy (HIM), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) and find that they possess nearly atomically sharp boundaries.

The Letter presents a new design of Sagnac interferometer-based optical system (SIOS) that emits a line-arrayed pattern generating narrowband high-energy waves in a specimen. The SIOS is further used to excite Rayleigh waves in a pristine rail specimen to evaluate its intrinsic nonlinearity resulting from the lattice anharmonicity and dissolved impurities. Such a nonlinearity appears in the response in the form of a second harmonic that is sensed in this Letter using a scanning laser Doppler vibrometer. In addition to this noncontact measurement, a contact measurement of the nonlinearity of rail steel using wedge transducers is also carried out to compare the performance of the SIOS. Both experimentally evaluated nonlinearities are compared with those obtained using the nonlinear elasticity equations. The close agreement with the theoretically estimated nonlinearity and higher repeatability shows that the SIOS is effective in measuring the intrinsic nonlinearity of the rail steel and, thereby, predicting the health status of the rail specimens before fixing them on the track.

Conducting polymer actuators such as polypyrrole (PPy) microactuators are interesting candidates to drive autonomous microrobotic devices that require low weight and low power. Simple PPy tri-layer bending type microactuators that operate in air have been demonstrated previously but they lack individual control and had problems with short circuiting due to electrical connections. The lack of micropatterning methods and proper interfacing are currently major obstacles in the development of PPy tri-layer microactuators. Here, we report for the first time methods for successfully patterning and interfacing of such tri-layer PPy microactuators. The PPy tri-layer actuators were patterned using adapted microfabrication technology including photolithography. The interface was based on a flexible printed circuit board comprising the electronic circuit into which the actuator unit was embedded. It showed that the microfabricated tri-layer actuators functioned as good as the normally fabricated actuators. The new interface seemed to actually improve the actuator performance. This interfacing method could also be applied to other electroactive polymer devices, such as ion polymer metal composites (IPMC) and dielectric elastomers (DE).

Overview Bottom-contact (BC) organic field-effect transistors (OFETs), though more industry-relevant than top-contact (TC) OFETs, are prone to low source-drain currents. The underlying mechanisms behind this remain debated. Thus, our work uses photocurrent microscopy (PCM) to examine charge injection in BC and TC geometries. PCM maps were generated first for OFETs with no electrode or gate dielectric treatments. Potential plots were quantitatively derived from the results using a method from previous work. [1] PCM maps were then collected for devices treated with 1. pentafluorobenzenethiol (PFBT), known to improve semiconductor morphology [2], and 2. UV-ozone, which is thought to enhance trap-assisted carrier transport. [3] These treatments were chosen, because they significantly increase source-drain current in BC devices, but in vastly different ways. In addition, unlike other photocurrent studies, we used a range of illumination wavelengths so as to probe various exciton states.

Ionizing radiation challenges the operation and reliability of electronic devices. While bulk devices have been well studied in the presence of ionizing radiation, there is limited information on the performance of 2D materials such as graphene in radiation harsh environments.1 Despite the expectation of a low radiation cross-section due to its single-atom thickness and low atomic number, prior work has shown that radiation has an effect on graphene-based devices, creating electrically active defects and degrading device performance.2 We demonstrate that a primary effect of gamma radiation on graphene field-effect transistors (GFETs) is degradation associated with activated atmospheric oxygen, and further improvement of device radiation hardness can be achieved by developing a charge shielded back-gated GFET architecture that protects against substrate charging effects. This represents a clear demonstration of radiation-hardened graphene devices.

An ultra thin implantable system using flexible organic light emitting diodes (OLEDs) and organic photodetectors (OPDs) on parylene substrate shows biocompatibility and high conformability on any surface. This system was used to monitor variations in cerebral blood volume (CBV) corresponding to an epileptic seizure, along with baseline signals such as heartbeat, respiration and slow sinusoidal hemodynamic oscillations (SSHOs). As such, this system shows strong potential for implantable and/or wearable biosensors for continuous health monitoring.

Despite the massive success for high energy density, the charge–discharge current rate performance of the lithium-ion batteries are still a major concern owing to inherent sluggish Li-ion kinetics. Herein, we demonstrate three-dimensional porous electrodes engineered on highly conductive graphene current collectors to enhance the Li-ion conductivity, thereby c-rate performance. Such high-quality graphene provides surface area for loading a large amount of electrochemically active material and strong adhesion with the electrode. The synergism of porous structure and conductive current collector enables us to realize high-performance new-generation silicon anodes with a high energy density of 1.8 mAh cm−2. Further, silicon electrodes revealed with excellent current rates up to 5C with a capacity of 0.37 mAh cm−2 for 500 nm planar thickness.

We demonstrate permanent water trapping in reduced graphene oxide after high relative humidity exposure. For this purpose, we grew graphene oxide films via spin-coating on glass substrates followed by thermal reduction. The electrical resistance of the planar device was then measured. We observed that resistance is significantly increased after water vapor exposure and remains stable even after 250 days in ambient conditions. Various techniques were applied to desorb the water and decrease (recover) the material's resistance, but it was achieved only with low temperature thermal annealing (180 °C) under forming gas (H2/N2 mixture). The permanent effect of water absorption was also detected by x-ray photoelectron spectroscopy.

Electroactive polymer actuators such as polypyrrole (PPy) are exciting candidates to drive autonomous devices that require low weight and low power. A simple PPy tri-layer bending type cantilever which operates in the air has been demonstrated previously, but the environmental effect on this actuator is still unknown. The major obstacle in the development of the PPy tri-layer actuator is to create proper packaging that reduces oxidation of the electrolyte and maintains constant displacement. Here, we report the variation in the displacement as well as the charge transfer at the different environmental condition. PPy trilayer actuators were fabricated by depositing polypyrrole on gold-coated porous poly(vinylidene fluoride) (PVDF) using the electro-synthesis method. It has been demonstrated that the charge transfer of tri-layer actuators is more in an inert environment than in open air. In addition, tri-layer actuators show constant deflection and enhancement of life due to the negligible oxidation rate of the electrolyte in an inert environment.

We are currently developing a range of microdevices based on polypyrrole (PPy) tri-layer microactuators that function in air. Here, we present recently developed microfabrication and patterning methods using photolithography for both thick, membrane and thin film poly(vinylidene difluoride) (PVDF) based PPy tri-layer actuators. We fabricated monolithically integrated, articulated actuator devices, i.e. comprising individually controllable actuators. We also introduce an interface for such PPy actuators based on a flexible printed circuit board, comprising the electrical contacts, into which the actuator device was inserted. Compartive evaluations showed that the microfabricated tri-layer actuators functioned as good as the normally fabricated actuators. The new interface seemed to actually improve the actuator performance.

Ionizing radiation poses a significant challenge to the operation and reliability of conventional silicon-based devices. Here, we report the effects of gamma radiation on graphene field-effect transistors (GFETs), along with a method to mitigate those effects by developing a radiation-hardened version of our back-gated GFETs. We demonstrate that activated atmospheric oxygen from the gamma ray interaction with air damages the semiconductor device, and damage to the substrate contributes additional threshold voltage instability. Our radiation-hardened devices, which have protection against these two effects, exhibit minimal performance degradation, improved stability, and significantly reduced hysteresis after prolonged gamma radiation exposure. We believe this work provides an insight into graphene's interactions with ionizing radiation that could enable future graphene-based electronic devices to be used for space, military, and other radiation-sensitive applications.

Photocurrent spectroscopy (PCS) and photocurrent microscopy (PCM) are powerful tools that can probe the underlying mechanisms of charge generation and transport in organic semiconductor devices. There has been significant progress in the use of these techniques, which has yielded a number of insights into the underlying materials and operation of the devices. Despite the potential for PCS and PCM to become standard tools, however, a consensus has not been reached on (1) its uses and (2) the underlying mechanisms which produce the photoresponse. This is particularly true for measurements of pentacene devices, as the energy dynamics of pentacene are complex. Accordingly, here we report the current body of PCS and PCM of pentacene devices, offer interpretations of the data, and discuss which questions remain unanswered. We have divided the reviewed work into four categories based on the goals of the study and the technique used: photocurrent spectroscopy, scanning photocurrent microscopy, mobility, and trap density-of-states.

This paper presents a novel microelectrode arrays using high-temperature grown vertically aligned carbon nanotubes (CNTs) integrated on a flexible and biocompatible parylene substrate. A simple microfabrication process is proposed to unite the high quality vertical CNTs grown at high temperature with the heat sensitive parylene substrate in a highly controllable manner. Briefly, the CNTs electrode is encapsulated by two layers of parylene and the device is released using xenon difluoride (XeF2). The process is compatible with wafer-scale post complementary metal oxide semiconductor integration. Lower impedance and larger interfacial capacitance have been demonstrated using CNTs compared to a Pt electrode. The flexible CNT electrodes have been utilized for extracellular neuronal recording and stimulation in rats. The signal-to-noise ratio of the device is about 12.5. The threshold voltage for initiating action potential is about 0.5 V.

The development of green experimental processes for the synthesis of nanoparticles is a need in the field of nanotechnology. In the present study, the authors reported rapid synthesis of silver nanoparticles using fresh leaves extract of Cymbopogan citratus (lemongrass) with increased stability. The synthesised silver nanoparticles were found to be stable for several months. UV-visible spectrophotometric analysis was carried out to assess the synthesis of silver nanoparticles. The synthesised silver nanoparticles were further characterised by using nanoparticle tracking analyser (NTA), transmission electron microscope (TEM) and energy-dispersive x-ray spectra (EDX). The NTA results showed that the mean size was found to be 32 nm. Silver nanoparticles with controlled size and shape were observed under TEM micrograph. The EDX of the nanoparticles confirmed the presence of elemental silver. These silver nanoparticles showed enhanced quorum quenching activity against Staphylococcus aureus biofilm and prevention of biofilm formation which can be seen under inverted microscope (40X). In the near future, silver nanoparticles synthesised using green methods may be used in the treatment of infections caused by a highly antibiotic resistant biofilm.