Unraveling Spatiotemporal Transient Dynamics at the Nanoscale via Wavelet Transform-Based Kelvin Probe Force Microscopy.

Mechanistic probing of surface potential changes arising from dynamic charge transport is the key to understanding and engineering increasingly complex nanoscale materials and devices. Spatiotemporal averaging in conventional heterodyne detection-based Kelvin probe force microscopy (KPFM) inherently limits its time resolution, causing an irretrievable loss of transient response and higher-order harmonics. Addressing this, we report a wavelet transform (WT)-based methodology capable of quantifying the sub-ms charge dynamics and probing the elusive transient response. The feedback-free, open-loop wavelet transform KPFM (OL-WT-KPFM) technique harnesses the WT's ability to simultaneously extract spatial and temporal information from the photodetector signal to provide a dynamic mapping of surface potential, capacitance gradient, and dielectric constant at a temporal resolution 3 orders of magnitude higher than the lock-in time constant. We further demonstrate the method's applicability to explore the surface-photovoltage-induced sub-ms hole-diffusion transient in bismuth oxyiodide semiconductor. The OL-WT-KPFM concept is readily applicable to commercial systems and can provide the underlying basis for the real-time analysis of transient electronic and electrochemical properties.

Internet of Things-Based ECG and Vitals Healthcare Monitoring System.

Health monitoring and its associated technologies have gained enormous importance over the past few years. The electrocardiogram (ECG) has long been a popular tool for assessing and diagnosing cardiovascular diseases (CVDs). Since the literature on ECG monitoring devices is growing at an exponential rate, it is becoming difficult for researchers and healthcare professionals to select, compare, and assess the systems that meet their demands while also meeting the monitoring standards. This emphasizes the necessity for a reliable reference to guide the design, categorization, and analysis of ECG monitoring systems, which will benefit both academics and practitioners. We present a complete ECG monitoring system in this work, describing the design stages and implementation of an end-to-end solution for capturing and displaying the patient's heart signals, heart rate, blood oxygen levels, and body temperature. The data will be presented on an OLED display, a developed Android application as well as in MATLAB via serial communication. The Internet of Things (IoT) approaches have a clear advantage in tackling the problem of heart disease patient care as they can transform the service mode into a widespread one and alert the healthcare services based on the patient's physical condition. Keeping this in mind, there is also the addition of a web server for monitoring the patient's status via WiFi. The prototype, which is compliant with the electrical safety regulations and medical equipment design, was further benchmarked against a commercially available off-the-shelf device, and showed an excellent accuracy of 99.56%.

Total electrification of large-scale nanophotonic arrays by frictional charges.

Localized surface plasmon resonance (LSPR) of metallic nanostructures is a unique phenomenon that controls the light in sub-wavelength volumes and enhances the light-matter interactions. Traditionally, the excitation and measurement of LSPR require bulky external light sources, and efforts to scale down to nano-plasmonic devices have predominantly relied on the system's miniaturization and associated accessories. Addressing this, here we show the generation and detection of LSPR wavelength (λLSPR) shifts in large-area nanostructured Au surfaces using frictional charges generated by triboelectric surfaces. We observe a complex interplay of the localized surface plasmons with frictional charges via concurrent spectroscopic and triboelectric measurements undertaken for the detection of bioconjugation in the streptavidin-biotin complex. When subjected to multivariate principal component analysis, a strong correlation between the triboelectric peak-to-peak voltage output response and the λLSPR shift is observed. Furthermore, we reveal a landscape of the interfacial events involved in the electrical generation/detection of the LSPR by using theoretical models and surface characterization. The demonstrated concept of electrification of plasmon resonance thus provides the underlying basis for the subsequent development of self-powered nano-plasmonic sensors and opens new horizons for advanced nanophotonic applications.

Disposable Paper-Based Biosensors: Optimizing the Electrochemical Properties of Laser-Induced Graphene.

Laser-induced graphene (LIG) on paper substrates is a desirable material for single-use point-of-care sensing with its high-quality electrical properties, low fabrication cost, and ease of disposal. While a prior study has shown how the repeated lasing of substrates enables the synthesis of high-quality porous graphitic films, however, the process-property correlation of lasing process on the surface microstructure and electrochemical behavior, including charge-transfer kinetics, is missing. The current study presents a systematic in-depth study on LIG synthesis to elucidate the complex relationship between the surface microstructure and the resulting electroanalytical properties. The observed improvements were then applied to develop high-quality LIG-based electrochemical biosensors for uric acid detection. We show that the optimal paper LIG produced via a dual pass (defocused followed by focused lasing) produces high-quality graphene in terms of crystallinity, sp2 content, and electrochemical surface area. The highest quality LIG electrodes achieved a high rate constant k0 of 1.5 × 10-2 cm s-1 and a significant reduction in charge-transfer resistance (818 Ω compared with 1320 Ω for a commercial glassy carbon electrode). By employing square wave anodic stripping voltammetry and chronoamperometry on a disposable two-electrode paper LIG-based device, the improved charge-transfer kinetics led to enhanced performance for sensing of uric acid with a sensitivity of 24.35 ± 1.55 µA µM-1 and a limit of detection of 41 nM. This study shows how high-quality, sensitive LIG electrodes can be integrated into electrochemical paper analytical devices.

High-isolation antenna array using SIW and realized with a graphene layer for sub-terahertz wireless applications.

This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2 × 3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 µm for operation across 0.19-0.20 THz. The dimensions of the array were 20 × 13.5 × 0.125 mm3. Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits.

Triboelectric Effect Enabled Self-Powered, Point-of-Care Diagnostics: Opportunities for Developing ASSURED and REASSURED Devices.

The use of rapid point-of-care (PoC) diagnostics in conjunction with physiological signal monitoring has seen tremendous progress in their availability and uptake, particularly in low- and middle-income countries (LMICs). However, to truly overcome infrastructural and resource constraints, there is an urgent need for self-powered devices which can enable on-demand and/or continuous monitoring of patients. The past decade has seen the rapid rise of triboelectric nanogenerators (TENGs) as the choice for high-efficiency energy harvesting for developing self-powered systems as well as for use as sensors. This review provides an overview of the current state of the art of such wearable sensors and end-to-end solutions for physiological and biomarker monitoring. We further discuss the current constraints and bottlenecks of these devices and systems and provide an outlook on the development of TENG-enabled PoC/monitoring devices that could eventually meet criteria formulated specifically for use in LMICs.

Emulsion Electrospinning of Polytetrafluoroethylene (PTFE) Nanofibrous Membranes for High-Performance Triboelectric Nanogenerators.

Electrospinning is a simple, versatile technique for fabricating fibrous nanomaterials with the desirable features of extremely high porosities and large surface areas. Using emulsion electrospinning, polytetrafluoroethylene/polyethene oxide (PTFE/PEO) membranes were fabricated, followed by a sintering process to obtain pure PTFE fibrous membranes, which were further utilized against a polyamide 6 (PA6) membrane for vertical contact-mode triboelectric nanogenerators (TENGs). Electrostatic force microscopy (EFM) measurements of the sintered electrospun PTFE membranes revealed the presence of both positive and negative surface charges owing to the transfer of positive charge from PEO which was further corroborated by FTIR measurements. To enhance the ensuing triboelectric surface charge, a facile negative charge-injection process was carried out onto the electrospun (ES) PTFE subsequently. The fabricated TENG gave a stabilized peak-to-peak open-circuit voltage (Voc) of up to ∼900 V, a short-circuit current density (Jsc) of ∼20 mA m-2, and a corresponding charge density of ∼149 µC m-2, which are ∼12, 14, and 11 times higher than the corresponding values prior to the ion-injection treatment. This increase in the surface charge density is caused by the inversion of positive surface charges with the simultaneous increase in the negative surface charge on the PTFE surface, which was confirmed by using EFM measurements. The negative charge injection led to an enhanced power output density of ∼9 W m-2 with high stability as confirmed from the continuous operation of the ion-injected PTFE/PA6 TENG for 30 000 operation cycles, without any significant reduction in the output. The work thus introduces a relatively simple, cost-effective, and environmentally friendly technique for fabricating fibrous fluoropolymer polymer membranes with high thermal/chemical resistance in TENG field and a direct ion-injection method which is able to dramatically improve the surface negative charge density of the PTFE fibrous membranes.

Graphene supported graphone/graphane bilayer nanostructure material for spintronics.

We report an investigation into the magnetic and electronic properties of partially hydrogenated vertically aligned few layers graphene (FLG) synthesized by microwave plasma enhanced chemical vapor deposition. The FLG samples are hydrogenated at different substrate temperatures to alter the degree of hydrogenation and their depth profile. The unique morphology of the structure gives rise to a unique geometry in which graphane/graphone is supported by graphene layers in the bulk, which is very different from other widely studied structures such as one-dimensional nanoribbons. Synchrotron based x-ray absorption fine structure spectroscopy measurements have been used to investigate the electronic structure and the underlying hydrogenation mechanism responsible for the magnetic properties. While ferromagnetic interactions seem to be predominant, the presence of antiferromagnetic interaction was also observed. Free spins available via the conversion of sp(2) to sp(3) hybridized structures, and the possibility of unpaired electrons from defects induced upon hydrogenation are thought to be likely mechanisms for the observed ferromagnetic orders.

Sedimentation behaviour in electrorheological fluids based on suspensions of zeolite particles in silicone oil.

Sedimentation is a known and expected shortcoming of electrorheological fluids (ERFs) due to the inherent difference in the constituent densities. The long-term sedimentation causes loss of the electrorheological phenomenon and the exploitable electromechanical and viscoelastic properties despite the presence of the stimulating electric field. In this work, we report the effect of temperature and surfactant concentration on the stability of ERFs prepared from zeolite particles and silicone oil with primary focus on the sedimentation of the particles in the ERF. As the temperature stability of the ERFs is fundamentally important, we have studied three different ERF suspensions composed of different zeolite particles, in silicone oil. These ERFs have been comparatively evaluated for their sedimentation over time, across a wide range of temperatures (-40°C to +60°C). The influence of surfactant concentration on the colloidal stability of the ERFs has also been investigated. A novel method of acoustic stirring (kHz range) on the homogenisation of the ERFs has been proposed and its effect on the sedimentation process evaluated. These results are useful for assessment of alternative suspension methods for specific applications.

Enhanced field emission and improved supercapacitor obtained from plasma-modified bucky paper.

The surface morphology of bucky papers (BPs) made from single-walled carbon nanotubes (CNTs) is modified by plasma treatment resulting in the formation of vertical microstructures on the surface. The shapes of these structures are either pillarlike or conelike depending on whether the gas used during plasma treatment is Ar or CH(4) . A complex interplay between different factors, such as the electric field within the plasma sheath, polarization of the CNT, intertubular cohesive forces, and ion bombardment, result in the formation of these structures. The roles played by these factors are quantitatively and qualitatively analyzed. The final material is flexible, substrate-free, composite-free, made only of CNTs, and has discrete vertically aligned structures on its surface. It shows enhanced field emission and electrochemical charge-storage capabilities. The field enhancement factor is increased by 6.8 times, and the turn-on field drops by 3.5 times from an initial value of 0.35 to 0.1 V µm(-1) as a result of the treatment. The increase in Brunauer-Emmett-Teller surface area results in about a fourfold improvement in the specific capacitance of the BP electrodes. Capacitance values before and after the treatments are 75 and 290 F g(-1) , respectively. It is predicted that this controlled surface modification technique could be put to good use in several applications based on macroscopic CNT films.