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Super-resolution fluorescence imaging that surpasses the classical optical resolution limit is widely utilized for resolving the spatial organization of biological structures at molecular length scales. In one example, single-molecule localization microscopy, the lateral positions of single molecules can be determined more precisely than the diffraction limit if the camera collects individual photons separately. Using several schemes that introduce engineered optical aberrations in the imaging optics, super-resolution along the optical axis (perpendicular to the sample plane) has been achieved, and single-molecule localization microscopy has been successfully applied for the study of 3D biological structures. Nonetheless, the achievable axial localization accuracy is typically three to five times worse than the lateral localization accuracy. Only a few exceptional methods based on interferometry exist that reach nanometer 3D super-resolution, but they involve enormous technical complexity and restricted sample preparations that inhibit their widespread application. We developed metal-induced energy transfer imaging for localizing fluorophores along the axial direction with nanometer accuracy, using only a conventional fluorescence lifetime imaging microscope. In metal-induced energy transfer, experimentally measured fluorescence lifetime values increase linearly with axial distance in the range of 0-100 nm, making it possible to calculate their axial position using a theoretical model. If graphene is used instead of the metal (graphene-induced energy transfer), the same range of lifetime values occurs over a shorter axial distance (~25 nm), meaning that it is possible to get very accurate axial information at the scale of a membrane bilayer or a molecular complex in a membrane. Here, we provide a step-by-step protocol for metal- and graphene-induced energy transfer imaging in single molecules, supported lipid bilayer and live-cell membranes. Depending on the sample preparation time, the complete duration of the protocol is 1-3 d.

Hybrid devices consisting of graphene or transition metal dichalcogenides (TMDs) and semiconductor quantum dots (QDs) were widely studied for potential photodetector and photovoltaic applications, while for photodetector applications, high internal quantum efficiency (IQE) is required for photovoltaic applications and enhanced carrier diffusion length is also desirable. Here, we reported the electrical measurements on hybrid field-effect optoelectronic devices consisting of compact QD monolayer at controlled separations from single-layer graphene, and the structure is characterized by high IQE and large enhancement of minority carrier diffusion length. While the IQE ranges from 10.2% to 18.2% depending on QD-graphene separation, ds, the carrier diffusion length, LD, estimated from scanning photocurrent microscopy (SPCM) measurements, could be enhanced by a factor of 5-8 as compared to that of pristine graphene. IQE and LD could be tuned by varying back gate voltage and controlling the extent of charge separation from the proximal QD layer due to photoexcitation. The obtained IQE values were remarkably high, considering that only a single QD layer was used, and the parameters could be further enhanced in such devices significantly by stacking multiple layers of QDs. Our results could have significant implications for utilizing these hybrid devices as photodetectors and active photovoltaic materials with high efficiency.

The next decade is likely to witness considerable growth in the application of plug-in electric vehicles (PEVs). However, uncoordinated PEV charging in low-voltage distribution networks may cause grid issues, such as transformer overload and voltage unbalance (VU). Therefore, it is essential to consider a more suitable methodology of voltage regulation for the consumers placed at the end of the feeder when the network is predominantly resistive. With this background, this article investigates the capability of dynamic PEV load transfer within the three phases of a distribution network to propose a new hybrid PEV coordination approach. In addition to the online centralized battery charging and var discharging, this approach performs local voltage profiles improvement by switching PEV at selected single-phase residential houses such that a PEV can be switched from a heavily loaded phase to a (relatively) lightly loaded phase. This results in better voltage regulations and VU reductions. The impacts of uncoordinated and proposed genetic algorithm (GA) coordinated PEV charging on VU and node voltage profiles and losses are simulated for a real unbalanced Western Australian distribution network in the Perth solar city over 24 h.

Gas chromatography-mass spectrometry is an essential tool for metabolomics. In this research we have selected photosynthetic organs- leaf and sepal of a wild Indian tea tree from north-east India to study wild tea metabolites. The result of this study reveals that photosynthetic parts of wild Indian tea tree are rich in 'patchouli' components unlike established cultivated varieties which are known to be rich in polyphenols or flavonoids. Twenty six compounds were detected in sesquiterpene rich leaf while nineteen were detected in the waxy sepal. The remarkable outcome of this study is presence of fourteen 'patchouli' compounds including patchouli alcohol as the major compound (44.81% in leaf and 19.59% in sepal) which can promote this plant to a top-notch position in fields of botany, pharmaceuticals and essential oil industry by occupying the throne of patchouli.

Moire superlattices of two-dimensional (2D) materials oriented at low twist angles generate a large-scale interference pattern leading to strong interlayer coupling, which influences the band structure and introduces flatbands. Conventional electronic transport measurements have shown the effects of flatband physics, manifesting as correlated insulating states and emergent superconductivity. In this study, we probe the electronic states in a trinary hybrid of graphene and twisted bilayer (tbl) MoS2. Graphene acts as a sensing layer, which captures the electronic effects of the underlying substrate, and we observe certain anomalies in the electronic characteristics of graphene only in the presence of an underlying 58.5 $$^\circ$$ tbl MoS2, at low temperatures. Interestingly, graphene on tbl MoS2, with twist angle near 0 $$^\circ$$ or on natural bilayer MoS2, does not show any anomalies. Density functional theory calculations show several distinguishable peaks in the density of states at the conduction band edge of twisted MoS2 near 60 $$^\circ$$ . We speculate that the anomaly appears due to fermi level pinning of graphene owing to a large density of states in the flatbands of twisted bilayer MoS2. An analysis of the energetics in the graphene-MoS2 hybrid quantitatively agree with theoretical predictions.

The worldwide acceptance of plug-in electric vehicles (PEVs) is expected to tremendously grow in the next few years. Uncoordinated PEV charging can cause serious grid issues such as overloading of transformers and unacceptable voltage drops. Single-phase residential charging can also initiate or contribute to voltage unbalance in distribution networks. A potential solution for the PEV integration is shifting the charging activities from peak to valley periods. Therefore, this paper firstly investigates the impacts of uncoordinated single-phase PEV charging at residential houses on three-phase distribution networks. Then, it proposes a novel PEV charging coordination strategy based on heuristic genetic algorithm (GA) to perform online centralized charging considering transformer loading and bus voltage profiles. Based on this, a decentralized PEV reactive power discharging approach is presented where the reactive power is discharged at selected nodes for further reduction of voltage unbalance. The impacts of uncoordinated PEV charging as well as the performance of the proposed centralized PEV charging and decentralized var discharging strategies are tested on a real unbalanced Western Australian distribution network under the Perth Solar City project over 24 hours.

The myriad technological applications of infrared radiation sensors make the search for ultra-sensitive detectors extremely crucial. Materials such as bismuth telluride (Bi2Te3), having a small bulk band gap of 0.17 eV, are ideal infrared detectors. However, due to the high recombination rate of photo-generated charge carriers in the bulk, the electrical response under optical illumination is typically very weak in these materials. We have circumnavigated this by sensitizing graphene with Bi2Te3 nano-wires. These hybrid devices show an ultra-high sensitivity of ∼106 A W−1, under incident electromagnetic radiation from 940 nm to 1720 nm. The theoretical limit of the noise equivalent power and specific detectivity in these devices are ∼10−18 W Hz−1/2 and ∼1011 Jones respectively, which are comparable to those of some of the best known detectors.

Engineering the properties of layered metal dichalcogenides (LMDs) requires stringent control of their morphology. Herein, using a scalable one-step solvothermal technique, we report the synthesis of SnSe2 under two different conditions, leading to the formation of nanoflakes and nanoflowers. The use of oleic acid in the reaction leads to the formation of nanoflowers, and the presence of ethanol in the reaction medium leads to the formation of nanoflakes. Ab initio density functional theory calculations rationalise this observation, revealing a stronger adsorption of ethanol on the {0001} facet compared to the acid. Furthermore, these SnSe2 nanoflakes, when integrated with graphene, also respond to incident electromagnetic radiation, from the visible to near infrared regime, with a specific detectivity of ∼5 × 1010 Jones, which is comparable to that of the best available photodetectors, making them suitable for use in various technological applications.

The intriguing electronic properties of graphene and the strong light-matter interaction in layered transition-metal dichalcogenide (TMDC) make them a natural partner for hybrid devices, not only for optoelectronic device applications, but also to understand the conversion of light to electricity in this atomic scale prototype of a donor-acceptor complex. Here, we describe graphene-on-${\mathrm{WS}}_{2}$ binary heterostructure FET device, displaying gate-tunable persistent photoconductivity. Our time-dependent photovoltage relaxation experiments suggest that the charge-transfer time scale in this heterostructure is dependent on the input optical power, contrary to what is observed for the bare TMDC and is orders of magnitude slower than that observed for various other vdW hybrids. The optoelectronic responsivity of this device at low optical power is found to be as high as ${10}^{10}\phantom{\rule{0.1em}{0ex}}\mathrm{V/W}$, and thus shows the potential to be one of the most sensitive visible range photodetectors, while the gate tunability of the persistent photoconductivity can be utilized in the memory device applications. We identify that the photoresponse is the outcome of a photogating mechanism, due to the exciton dissociation under optical excitation, followed by the trapping of holes in ${\mathrm{WS}}_{2}$ and subsequent electron transfer to graphene.

The study of walking pattern also known as gait is affected by several underlying musculoskeletal and neurological factors. All humans have contrasting gait pattern however the pattern lies within a predictable range for all human with no underlying health disorders affecting gait. However, deviation from a regular distribution range can indicate underlying health conditions. The gait could be regularly and inexpensively monitored in real-time with help of smartphones embedded sensors such as tri-axial accelerometers and tri-axial gyroscopes as smartphones are widely available. The advancements in computational power and artificial intelligence led to the development of several supervised machine learning algorithms which could be used to detect certain patterns associated with different gait conditions. However, the machine learning has widely been used to study different gait diseases, with this paper we have proposed a more efficient motion tracking approach and a new algorithm utilizing Dynamic Time Warping for an optimized locomotor disorder detection with affordable, practically applicable and globally deployable setup to monitor gait. In this experiment, we have tracked motion of 30 healthy and gait deformed human subjects with the proposed motion tracking approach and utilizing the proposed algorithm, we have achieved 35.95 times faster classification with up to 95.20% detection accuracy.

Graphene grain boundaries (GBs) have attracted interest for their ability to host nearly dispersionless electronic bands and magnetic instabilities. Here, we employ quantum transport and universal conductance fluctuation measurements to experimentally demonstrate a spontaneous breaking of time-reversal symmetry across individual GBs of chemical vapor deposited graphene. While quantum transport across the GBs indicate spin-scattering-induced dephasing and hence formation of local magnetic moments, below T4 K we observe complete lifting of time-reversal symmetry at high carrier densities (n5A�1012 cm-2) and low temperature (T2 K). An unprecedented thirtyfold reduction in the universal conductance fluctuation magnitude with increasing doping density further supports the possibility of an emergent frozen magnetic state at the GBs. Our experimental results suggest that realistic GBs of graphene can be a promising resource for new electronic phases and spin-based applications. © 2021 American Physical Society.

Graphene, a two-dimensional nanomaterial, has gained immense interest in biosensing applications due to its large surface-to-volume ratio, and excellent electrical properties. Herein, a compact and user-friendly graphene field effect transistor (GraFET) based ultrasensitive biosensor has been developed for detecting Japanese Encephalitis Virus (JEV) and Avian Influenza Virus (AIV). The novel sensing platform comprised of carboxy functionalized graphene on Si/SiO2 substrate for covalent immobilization of monoclonal antibodies of JEV and AIV. The bioconjugation and fabrication process of GraFET was characterized by various biophysical techniques such as Ultraviolet–Visible (UV–Vis), Raman, Fourier-Transform Infrared (FT-IR) spectroscopy, optical microscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The change in the resistance due to antigen–antibody interaction was monitored in real time to evaluate the electrical response of the sensors. The sensors were tested in the range of 1 fM to 1 μM for both JEV and AIV antigens, and showed a limit of detection (LOD) upto 1 fM and 10 fM for JEV and AIV respectively under optimised conditions. Along with ease of fabrication, the GraFET devices were highly sensitive, specific, reproducible, and capable of detecting ultralow levels of JEV and AIV antigen. Moreover, these devices can be easily integrated into miniaturized FET-based real-time sensors for the rapid, cost-effective, and early Point of Care (PoC) diagnosis of JEV and AIV.

The fundamental origin of low-frequency noise in graphene field effect transistors (GFETs) has been widely explored but a generic engineering strategy towards low noise GFETs is lacking. Here, we systematically study and eliminate dominant sources of electrical noise to achieve ultralow noise GFETs. We find that in edge contacted, high-quality hexagonal boron nitride (hBN) encapsulated GFETs, the inclusion of a graphite bottom gate and long (≳1.2 μm) channel-contact distance significantly reduces noise as compared to global Si/SiO2 gated devices. From the scaling of the remaining noise with channel area and its temperature dependence, we attribute this to the traps in hBN. To further screen the charge traps in hBN, we place few layers of MoS2 between graphene and hBN, and demonstrate that the noise is as low as ∼5.2 × 10−9 μm2 Hz−1 (corresponding to minimum Hooge parameter ∼5.2 × 10−6) in GFETs at room temperature, which is an order of magnitude lower than the earlier reported values.

Polyethylene terephthalate-based nanocomposites with hexagonal boron nitride nanosheets (BNNs) were prepared by a solution casting method with varying concentrations of BNNs from 0.5 wt% to 4 wt%. Melting and crystallization behaviour of the composites were investigated by differential scanning calorimetry, which suggests that with increasing presence of nanosheets, the crystallinity increases and hence the polyethylene terephthalate chain mobility gets restricted, which leads to suppression of crystal growth. The nanoindentation measurements on the composite films exhibit improved mechanical properties. Enhancement of 33.3% of elastic modulus and 32.4% of hardness was observed with 2 wt% infusion of boron nitride nanosheets in polyethylene terephthalate.

There have been several reports of plasmonically enhanced graphene photodetectors in the visible and the near infrared regime but rarely in the ultraviolet. In a previous work, we have reported that a graphene-silver hybrid structure shows a high photoresponsivity of 13 A/W at 270 nm. Here, we consider the likely mechanisms that underlie this strong photoresponse. We investigate the role of the plasmonic layer and examine the response using silver and gold nanoparticles of similar dimensions and spatial arrangement. The effect on local doping, strain, and absorption properties of the hybrid is also probed by photocurrent measurements and Raman and UV-visible spectroscopy. We find that the local doping from the silver nanoparticles is stronger than that from gold and correlates with a measured photosensitivity that is larger in devices with a higher contact area between the plasmonic nanomaterials and the graphene layer.

Resolving low-energy features in the density of states (DOS) holds the key to understanding wide variety of rich novel phenomena in graphene based 2D heterostructures. Lifshitz transition in bilayer graphene (BLG) arising from trigonal warping has been established theoretically and experimentally. Nevertheless, the experimental realization of its effects on the transport properties has been challenging because of its relatively low energy scale ($\sim 1$ meV). In this work, we demonstrate that the thermoelectric power (TEP) can be used as an effective probe to investigate fine changes in the DOS of BLG. We observe additional entropy features in the vicinity of the charge neutrality point (CNP) in gapped BLG. This apparent violation of Mott formula can be explained quantitatively by considering the effects of trigonal warping, thereby serving as a possible evidence of a Lifshitz transition.

The worldwide application and off-grid charging of plug-in electric vehicles (PEVs) are expected to grow in the next few years tremendously. However, uncoordinated PEV charging in low-voltage (LV) distribution networks can lead to grid problems such as transformer overloading and voltage unbalance. A potential solution and also a key challenge for PEV integration is the smart shifting of charging activities from peak hours to off-peak. In this background, this paper investigates the impacts of stochastic single-phase PEV charging based on time, rating and location of charging at residential houses on voltage and voltage unbalance factor (VUF). Additionally, Monte Carlo simulation is applied to describe the stochastic behaviour of PEVs. Different aspects like penetration level, PEV charging rate and location are investigated to better understand the impacts of PEVs on the LV distribution network. The impacts of uncoordinated and coordinated PEV charging on VUF and voltage profiles are simulated on a real Western Australian distribution network in the Perth solar city over 24 hours.

Van der Waals (vdW) heterostructure is a type of metamaterial where multiple layers of 2D materials are vertically aligned at controlled misorientation. The relative rotation in between the adjacent layers, or the twist angle between them plays a crucial role in changing the electronic band structure of the superlattice. The assembly of multi-layers of precisely twisted two dimensional layered materials requires knowledge of the atomic structure at the edge of the flake. It may be artificially created by the ‘tear and stack’ process. Otherwise, the crystallographic orientation needs to be determined through invasive processes such as transmission electron microscopy or scanning tunneling microscopy, and via second-harmonic generation (SHG). Here, we demonstrate a simple and elegant transfer protocol using only an optical microscope as a edge identifier tool through which, controlled transfer of twisted homobilayer and heterobilayer transition metal dichalcogenides is performed with close to 100% yield. The fabricated twisted vdW heterostructures have been characterized by SHG, Raman spectroscopy and photoluminiscence spectroscopy, confirming the desired twist angle within ∼0.5° accuracy. The presented method is reliable, quick and prevents the use of invasive tools which is desirable for reproducible device functionalities.

Despite the many fascinating discoveries of fundamental significance and device applications involving graphene, one area that has been lacking is graphene-based displays and emissive devices. Since graphene by itself has weak and wavelength-independent absorption and no emission in the visible range, such devices must rely on synergistic combination with other highly sensitive optical materials such as quantum dots. However, the well-known strong nonradiative energy transfer between emitters and quantum dots and graphene makes it impossible to create such devices due to strong emission quenching. Here we report the first demonstration of enhanced photoluminescence of quantum dots in close proximity to graphene field effect transistor devices, which are electrically and spectrally tunable. The enhanced emission originates from super-radiance between closely packed quantum dots placed close to single-layer graphene, which overcomes the strong nonradiative quenching observed earlier. Finite difference time ...

The weak interlayer coupling in van der Waals solids allows isolation of individual atomic or molecular layers with remarkable electrical, optical, and structural properties. The applicability of these two dimensional materials in future electronic architectures requires a thorough understanding of the electrical transport mechanisms as well as of the factors limiting the device performance. The study of slow time-varying fluctuations in resistance, often called the 1 / f noise, offers deep insight into the electronic transport and scattering mechanisms, and also acts as a performance benchmark. Here we review the current status on the magnitude and microscopic understanding of low-frequency 1 / f noise in two-dimensional electronic materials, with specific focus on graphene, bismuth chalcogenides, and transition metal dichalcogenides. The noise characteristics differ significantly among these systems, and are directly influenced by the band structure, energy dispersion, and screening properties. The noise in field effect devices from van der Waals materials closely compares with or is even lower than that of conduction channels in conventional electronics. The excellent noise performance, when combined with high carrier mobility, energy efficiency and structural flexibility, renders an excellent platform for future electronic, optoelectronic, and sensor applications.

Several factors can affect performance of an ultrasound system such as quality of excitation signal and ultrasound transducer behaviour. Nonlinearity of piezoelectric ultrasound transducers is a key determinant in designing a proper driving power supply. Although, the nonlinearity of piezoelectric transducer impedance has been discussed in different literatures, the trend of the nonlinearity at different frequencies with respect to excitation voltage variations has not been clearly investigated in practice. In this paper, to demonstrate how the nonlinearity behaves, a sandwich piezoceramic transducer was excited at different frequencies. Different excitation signals were generated using a linear power amplifier and a multilevel converter within a range of 30–200 V. Empirical relation was developed to express the resistance of the piezoelectric transducer as a nonlinear function of both excitation voltage and resonance frequency. The impedance measurements revealed that at higher voltage ranges, the piezoelectric transducer can be easily saturated. Also, it was shown that for the developed ultrasound system composed of two transducers (one transmitter and one receiver), the output voltage measured across receiver is a function of a voltage across the resistor in the RLC branches and is related to the resonance frequencies of the ultrasound transducer.

An LCL filter utilized in an active front end (AFE) converter can generate significant resonance, which can affect quality and stability of the system. Thus, a proper active or passive damping technique and/or a suitable controller is required to be designed for the converter. The duty cycle constraint—though inevitable in practical inverter systems—is often ignored in most of the existing literature. The effects of measurement noise on filter control system performance must be considered and evaluated under different conditions. Finally, almost all inverter control systems are implemented digitally using microcontrollers. Consequently, the effects of sampling on control system stability and performance should be evaluated as well. Thus, this paper presents stability analysis of an AFE converter-based filter design with a complete practical system configuration, including saturation and sampling blocks and measurement noises. Mathematical analysis and simulations have been carried out to validate the proposed method.

The optoelectronic performance of hybrid devices from graphene and optically sensitive semiconductors exceeds conventional photodetectors due to a large in-built optical gain. Tellurium nanowire (TeNW), being a narrow direct band gap semiconductor (∼0.65 eV), is as an excellent potential candidate for near infra-red (NIR) detection. Here we demonstrate a new graphene-TeNW binary hybrid that exhibits a maximum photoresponsivity of ∼106 A W-1 at 175 K in the NIR regime (920 nm-1720 nm), which exceeds the photoresponsivity of the most common NIR photodetectors. The resulting noise-equivalent power (NEP) is as low as 2 × 10-18 W Hz-1/2, and the specific detectivity (D*) exceeds 5 × 1013 cm Hz1/2 W-1 (Jones). The temperature range of optimal operation, which extends up to ≈220 K and ≈260 K for 1720 nm and 920 nm excitation, respectively, is primarily limited by the electrical conductivity of the TeNW layer, and can further be improved by lowering of the defect density as well as inter-wire electronic coupling.

One of the unique features of Dirac Fermions is pseudo-diffusive transport by evanescent modes at low Fermi energies when the disorder is low. At higher Fermi energies i.e. carrier densities, the electrical transport is diffusive in nature and the propagation occurs via plane-waves. In this study, we report the detection of such evanescent modes in the surface states of topological insulator through 1/f noise. While signatures of pseudo-diffusive transport have been seen experimentally in graphene, such behavior is yet to be observed explicitly in any other system with a Dirac dispersion. To probe this, we have studied 1/f noise in topological insulators as a function of gate-voltage, and temperature. Our results show a non-monotonic behavior in 1=f noise as the Fermi energy is varied, suggesting a crossover from pseudo-diffusive to diffusive transport regime in mesoscopic topological insulators. The temperature dependence of noise points towards conductance fluctuations from quantum interference as the dominant source of the noise in these samples., 5 pages, 4 figures

Graphene constitutes one of the key elements in many functional van der Waals heterostructures. However, it has negligible optical visibility due to its monolayer nature. Here we study the visibility of graphene in various van der Waals heterostructures and include the effects of the source spectrum, oblique incidence and the spectral sensitivity of the detector to obtain a realistic model. A visibility experiment is performed at different wavelengths, resulting in a very good agreement with our calculations. This allows us to reliably predict the conditions for better visibility of graphene in van der Waals heterostructures. The framework and the codes provided in this work can be extended to study the visibility of any 2D material within an arbitrary van der Waals heterostructure.

In recent years single-molecule localization super-resolution microscopy (SMLM) has become an indispensable tool for many fields of research. Here, for any image of a single molecule one determines its center position with much higher accuracy than the size of that image itself. A challenge of SMLM is to achieve super-resolution also along the third dimension. Recently, Metal-Induced Energy Transfer or MIET [1,2] was introduced. It exploits the energy transfer from an excited fluorophore to plasmons in a thin metal film. Similar to Forster Resonance Energy Transfer (FRET), this coupling shows a strong distance dependence, but over a range up to 150 nm and enables axial localization of fluorophores with 5-6 nm resolution at a photon budget of 1000 photons. [3,4] Here, we show that using a graphene layer the localization accuracy of MIET reaches Angstrom accuracy. At such accuracy, minute details such as nanometer-scale roughness of the sample surfaces becomes important. For proof of principle, we determined absolute distances of single molecules from a surface for samples with an a priori well-known sample geometry. We spin-coated fluorescent dye molecules (Atto655) on top of three different substrates with spacer thickness values of 10, 15, and 20 nm, defining the distance of the molecules from the graphene layer. Next, we determined the thickness of supported lipid bilayers (SLBs) by localizing fluorescent dyes attached to lipid head groups in the bottom and top leaflet of the SLB. We have demonstrated that by using graphene as the energy acceptor in MIET, the axial localization accuracy and resolution reaches sub-nanometer levels at photon budgets which are typical in conventional SMLM experiments. An interesting feature of graphene-MIET is that it provides an axial localization accuracy which now surpasses significantly that of lateral localization provided by most SMLM approaches. [1] A. I. Chizhik et al. Nat. Photonics 8, 124 (2014). [2] S. Isbaner et al. Nano Lett. 18, 2616 (2018). [3] N. Karedla et al. ChemPhysChem 15, 705 7 (2014). [4] N. Karedla et al. J. Chem. Phys. 148, 204201 (2018).

Chlorpyrifos is one of the most widely used pesticides that acts on the nervous system by inhibiting acetylcholinesterase. Prolonged use of chlorpyrifos causes severe neurological, autoimmune, and persistent developmental disorders in humans. Therefore, in this study, a highly sensitive and robust biosensor platform was devised by fabricating graphene field effect transistors (graFET) on Si/SiO2 substrate for the detection of chlorpyrifos in real samples. Anti-chlorpyrifos antibodies were immobilized successfully on the graphene surface. Under optimal conditions, graFET sensor showed an excellent response for chlorpyrifos detection in the linear range of 1 fM to 1 µM with a limit of detection up to 1.8 fM in spiked samples. The developed graFET biosensor is highly stable, sensitive, and specific for chlorpyrifos as confirmed by its significant ability to detect changes in electrostatic potential. These findings signify useful efficacy of immunobiosensors for the detection of chlorpyrifos and other organophosphates in fruits and vegetables.

Soft−hard (CoFe2O4)x(SrFe12O19)1-x (0.0≤x ≤1.0) nano-composite(s) were prepared by novel one pot reaction sol-gel auto-combustion route and annealed at 800 °C for 4 hours. X-ray diffraction (XRD), and vibration sample magnetometer (VSM) were utilized to monitor the effect of substitution on structural, and magnetic properties. XRD confirms the existence of soft (CoFe2O4), and hard (SrFe12O19) phase with average grain size (D) ranging between 57.7 nm to 59.4 nm for hexagonal and 34.6 to 64.5 nm for cubic phase. The magnetization of nano-composites demonstrates hysteresis loop that is characteristic of the exchange coupled system showing structurally two phases, but magnetically single phase. As a result of exchange coupling, between Co, and Sr ferrite enhanced saturation magnetization (70.65 Am2/kg), and remanence (26.29 Am2/kg) were observed as compared to pure SrFe12O19. Observed enhancement in energy product (BH)max (0.83 − 28.96 kJ/m3) of nano composite also favors good exchange coupling between hard and soft phase.

A four-level inverted Y-type atomic system is subjected to three coherent laser fields simultaneously. The system has two closely spaced ground energy levels, one intermediate energy level and an uppermost energy level. Transition from the two ground levels to the intermediate level as well as from the intermediate level to the uppermost level are dipole allowed. Transition from the two ground energy levels to the uppermost level is dipole forbidden. A weak laser beam, known as the probe beam, acts between one of the ground levels and the intermediate level. A strong laser field, known as the control or pump field, couples the intermediate level with the uppermost level. A repump filed of intensity usually higher than the probe field acts between the other ground level and the intermediate level. The probe transmission through such a medium is investigated at different values of the control and repump Rabi frequencies under Doppler free condition as well as with thermal averaging. The nonradiative population transfer rates between the ground energy levels have been incorporated.

The transfer of charge carriers across the optically excited hetero-interface of graphene and semiconducting transition metal dichalcogenides (TMDCs) is the key to convert light to electricity, although the intermediate steps from the creation of excitons in TMDC to the collection of free carriers in the graphene layer are not fully understood. Here, we investigate photo-induced charge transport across graphene–MoS2 and graphene–WSe2 hetero-interfaces using time-dependent photoresistance relaxation with varying temperature, wavelength, and gate voltage. In both types of heterostructures, we observe an unprecedented resonance in the inter-layer charge transfer rate as the Fermi energy ( E F) of the graphene layer is tuned externally with a global back gate. We attribute this to a resonant quantum tunneling from the excitonic state of the TMDC to E F of the graphene layer and outline a new method to estimate the excitonic binding energies ( E b) in the TMDCs, which are found to be 400 meV and 460 meV in MoS2 and WSe2 layers, respectively. The gate tunability of the inter-layer charge transfer timescales may allow precise engineering and readout of the optically excited electronic states at graphene–TMDC interfaces.

Strong optoelectronic response in the binary van der Waals heterostructures of graphene and transition metal dichalcogenides (TMDCs) is an emerging route towards high-sensitivity light sensing. While the high sensitivity is an effect of photogating of graphene due to inter-layer transfer of photo-excited carriers, the impact of intrinisic defects, such as traps and mid-gap states in the chalcogen layer remain largely unexplored. Here we employ graphene/hBN (hexagonal boron nitride)/MoS2 (molybdenum disulphide) trilayer heterostructures to explore the photogating mechanism, where the hBN layer acts as interfacial barrier to tune the charge transfer timescale. We find two new features in the photoresponse: First, an unexpected positive component in photoconductance upon illumination at short times that preceeds the conventional negative photoconductance due to charge transfer, and second, a strong negative photoresponse at infrared wavelengths (up to 1720 nm) well-below the band gap of single layer MoS2. Detailed time and gate voltage-dependence of the photoconductance indicates optically-driven charging of trap states as possible origin of these observations. The responsivity of the trilayer structure in the infrared regime was found to be extremely large (> 108 A/W at 1550 nm using 20 mV source drain bias at 180 K temperature and ≈ −30 V back gate voltage). Our experiment demonstrates that interface engineering in the optically sensitive van der Waals heterostructures may cast crucial insight onto both inter- and intra-layer charge reorganization processes in graphene/TMDC heterostructures.

The weak light–matter interaction in graphene can be enhanced with a number of strategies, among which sensitization with plasmonic nanostructures is particularly attractive. This has resulted in the development of graphene–plasmonic hybrid systems with strongly enhanced photodetection efficiencies in the visible and the IR, but none in the UV. Here, we describe a silver nanoparticle–graphene stacked optoelectronic device that shows strong enhancement of its photoresponse across the entire UV spectrum. The device fabrication strategy is scalable and modular. Self-assembly techniques are combined with physical shadow growth techniques to fabricate a regular large-area array of 50 nm silver nanoparticles onto which CVD graphene is transferred. The presence of the silver nanoparticles resulted in a plasmonically enhanced photoresponse as high as 3.2 A W−1 in the wavelength range from 330 nm to 450 nm. At lower wavelengths, close to the Van Hove singularity of the density of states in graphene, we measured an even higher responsivity of 14.5 A W−1 at 280 nm, which corresponds to a more than 10 000-fold enhancement over the photoresponse of native graphene.

The out-of-plane electric polarization at the surface of SrTiO3 (STO), an archetypal perovskite oxide, may stabilize new electronic states and/or host novel device functionality. This is particularly significant in proximity to atomically thin membranes, such as graphene, although a quantitative understanding of the polarization across graphene–STO interface remains experimentally elusive. Here, we report direct observation and measurement of a large intrinsic out-of-plane polarization at the interface of single-layer graphene and TiO2-terminated STO (100) crystal. Using a unique temperature dependence of anti-hysteretic gate-transfer characteristics in dual-gated graphene-on-STO field-effect transistors, we estimate the polarization to be as large as ≈12 μC cm−2, which is also supported by the density functional theory calculations and low-frequency noise measurements. The anti-hysteretic transfer characteristics is quantitatively shown to arise from an interplay of band bending at the STO surface and electrostatic potential due to interface polarization, which may be a generic feature in hybrid electronic devices from two-dimensional materials and perovskite oxides. The dipole field at the surface of SrTiO3 strongly impacts the transfer characteristics of graphene/SrTiO3 field-effect transistors. A team led by Arindam Ghosh at the Indian Institute of Science (Bangalore) fabricated dual-gated field-effect transistors with graphene on a TiO2-terminated SrTiO3 (100) crystal, and observed a large, intrinsic out-of-plane electric polarization at the hetero-interface. The measured polarization, detected by means of gate-transfer characteristics and further supported by density functional theory calculations, was found to be as large as 12 μC cm−2. The nature of the anti-hysteretic transfer characteristics in both resistance and noise is indicative of formation of trap states at the SrTiO3 interface, due to band renormalization and electrostatic confinement. These results improve the physical understanding of the interfaces between atomically thin materials and polarizable substrates.

This paper introduces a control technique for proportional load sharing in a DC microgrid during both islanded and utility connected modes. The DC microgrid is connected to a utility system through an interlinking voltage source converter and a unidirectional DC-DC converter. The DC-DC converter draws the desired amount of power from the utility, while the interlinking converter holds the DC bus voltage. The DERs in the DC microgrid are operated under droop sharing using DC-DC converters. Each DC-DC converter is equipped with a state feedback with integral controller that can regulate its output voltage for a wide range of input voltage fluctuation and load variation. Simulation studies are conducted on PSCAD/EMTDC to validate the proposal.

Combining oblique angle deposition with standard graphene transfer protocols, two planar arrays of metal nanoparticles are fabricated that are vertically separated by atomic dimensions, corresponding precisely to the thickness of a single layer of graphene, i.e., 0.34 nm. Upon illumination of light at an appropriate wavelength, the local electromagnetic field at the junction of the dimers can be increased dramatically, thereby resulting in the most sensitive graphene-plasmonic hybrid photodetector reported to date.

The authors report a detailed investigation of the flicker noise (1/f noise) in graphene films obtained from chemical vapour deposition (CVD) and chemical reduction of graphene oxide. The authors find that in the case of polycrystalline graphene films grown by CVD, the grain boundaries and other structural defects are the dominant source of noise by acting as charged trap centres resulting in huge increase in noise as compared with that of exfoliated graphene. A study of the kinetics of defects in hydrazine-reduced graphene oxide (RGO) films as a function of the extent of reduction showed that for longer hydrazine treatment time strong localised crystal defects are introduced in RGO, whereas the RGO with shorter hydrazine treatment showed the presence of large number of mobile defects leading to higher noise amplitude.

Electron-irradiation induced changes in structural and, magnetic properties of Co 57.6 Fe 14.4 Si 4.8 B 19.2 Nb 4 , Fe 72 Si 4.8 B 19.2 Nb 4 and, Co 72 Si 4.8 B 19.2 Nb 4 metallic glasses were studied using magnetic hysteresis and, synchrotron X-ray diffraction measurements. Results reveal composition dependent changes of magnetic properties in electron irradiated metallic glasses. A low electron irradiation dose (15 kGy) enhances saturation magnetization (up to 62%) in Fe-based alloy (Fe 72 Si 4.8 B 19.2 Nb 4 ). Synchrotron XRD measurements reveal that electron irradiation transforms the amorphous matrix to a more ordered phase, accountable for changes in magnetic properties.

Van der Waals hybrids of graphene and transition metal dichalcogenides exhibit an extremely large response to optical excitation, yet counting of photons with single-photon resolution is not achieved. Here, a dual-gated bilayer graphene (BLG) and molybdenum disulphide (MoS2 ) hybrid are demonstrated, where opening a band gap in the BLG allows extremely low channel (receiver) noise and large optical gain (≈1010 ) simultaneously. The resulting device is capable of unambiguous determination of the Poissonian emission statistics of an optical source with single-photon resolution at an operating temperature of 80 K, dark count rate 0.07 Hz, and linear dynamic range of ≈40 dB. Single-shot number-resolved single-photon detection with van der Waals heterostructures may impact multiple technologies, including the linear optical quantum computation.

We exhibit a technique to detect and estimate precipitation over the global oceans using the radar back scattering coefficient and brightness temperature measurements from Oceansat-II scatterometer along with numerical weather prediction model derived rain sensitive parameters via a neural network (NN) based setup. Rain/no-rain labels are generated by analyzing rainfall observations from Tropical Rainfall Measuring Mission (TRMM) and Advanced Microwave Scanning Radiometer for Earth Observation Satellite (EOS) (AMSR-E) which are concurrent (within a spatiotemporal bin 0.25° × 0.25° latitude–longitude and 900 s) to Oceansat-II overpasses. The rain sensitivity of all the parameters is examined. NN is applied in two stages: (1) rain identification and (2) rain quantification with training samples from five different overlapping geographical regions [I(25°N–25°S), II(15°N–45°N), III(35°N–70°N), IV(15°S–45°S) and V(35°S–70°S)]. Rain identification accuracy is about 93%, 87%, 90%, 79%, and 85%, and no-rain detection accuracy of about 97%, 87%, 86%, 84% and 86% for these regions. The missing rain cases are few compared to the size of no-rain samples and are largely from the low rain regime. The RMS error of instantaneous rain estimation for regions I to V (rain rates varying from > 0 to approximately 45, 25, 25, 45, and 20 mm h− 1) is found to be 1.86, 0.69, 0.47, 0.56, and 0.46 mm h− 1, respectively. The qualitative comparisons of instantaneous, 3-days, monthly and seasonal rain rates from scatterometer and AMSR-E demonstrate a good agreement between them. Probability distribution of monthly rain rates from scatterometer and AMSR-E is also compared, indicating the consistency of scatterometer derived rain with AMSR-E rain in a climatic scale.

The impact of the intrinsic time-dependent fluctuations in the electrical resistance at the graphene-metal interface or the contact noise, on the performance of graphene field effect transistors, can be as adverse as the contact resistance itself, but remains largely unexplored. Here we have investigated the contact noise in graphene field effect transistors of varying device geometry and contact configuration, with carrier mobility ranging from 5,000 to 80,000$~$cm$^{2}$V$^{-1}$s$^{-1}$. Our phenomenological model for contact noise due to current crowding in purely two dimensional conductors, confirms that the contacts dominate the measured resistance noise in all graphene field effect transistors in the two-probe or invasive four probe configurations, and surprisingly, also in nearly noninvasive four probe (Hall bar) configuration in the high mobility devices. The microscopic origin of contact noise is directly linked to the fluctuating electrostatic environment of the metal-channel interface, which could be generic to two dimensional material-based electronic devices., Revised version after peer review. Main: 9 pages, 4 figures

Electric fields have been widely used to manipulate cells in microfluidic devices. The versatility and the ease of implementation and fabrication of electric field-based microfluidic systems have made them very popular for a whole host of different biomedical applications. In this chapter, various techniques that are commonly used for manipulating, characterizing, and separating cells in lab-on-a-chip devices and their applications are discussed. Starting from a description of the polarization of a cell and the forces that can act on it in an electric field, the theory that drives different electrokinetic phenomena and the application of these phenomena for on-chip cellular manipulation are herein reviewed. The models that are used to predict the responses of cells in electric fields, as well as techniques commonly used for the numerical modeling of various electrokinetic and electric field-based cellular manipulation techniques, are also detailed. Finally, the electrical modifications of cells in microfluidic devices, specifically electroporation and electrofusion, have been reviewed.

As one of the most important members of the two dimensional chalcogenide family, molybdenum disulphide (MoS2) has played a fundamental role in the advancement of low dimensional electronic, optoelectronic and piezoelectric designs. Here, we demonstrate a new approach to solid state synaptic transistors using two dimensional MoS2 floating gate memories. By using an extended floating gate architecture which allows the device to be operated at near-ideal subthreshold swing of 77 mV/decade over four decades of drain current, we have realised a charge tunneling based synaptic memory with performance comparable to the state of the art in neuromorphic designs. The device successfully demonstrates various features of a biological synapse, including pulsed potentiation and relaxation of channel conductance, as well as spike time dependent plasticity (STDP). Our device returns excellent energy efficiency figures and provides a robust platform based on ultrathin two dimensional nanosheets for future neuromorphic applications.

Here we present the fabrication and characterization of a new class of hybrid devices where the constituents are graphene and ultrathin molybdenum di-sulphide (MoS2). This device is one of the simplest member of a family of hybrids where the desirable electrical characteristics of graphene such as high mobility are combined with optical activity of semiconductors. We find that in the presence of an optically active substrate, considerable photoconductivity is induced in graphene which is persistent up to a time scale of at least several hours. This photo induced memory can be erased by the application of a suitable gate voltage pulse. This memory operation is stable for many cycles. We present a theoretical model based on localized states in MoS2 which explains the data. (C) 2013 Elsevier Ltd. All rights reserved.

Combining the electronic properties of graphene(1,2) and molybdenum disulphide (MoS2)(3-6) in hybrid heterostructures offers the possibility to create devices with various functionalities. Electronic logic and memory devices have already been constructed from graphene-MoS2 hybrids(7,8), but they do not make use of the photosensitivity of MoS2, which arises from its optical-range bandgap(9). Here, we demonstrate that graphene-on-MoS2 binary heterostructures display remarkable dual optoelectronic functionality, including highly sensitive photodetection and gate-tunable persistent photoconductivity. The responsivity of the hybrids was found to be nearly 1 x 10(10) A W-1 at 130 K and 5 x 10(8) A W-1 at room temperature, making them the most sensitive graphene-based photodetectors. When subjected to time-dependent photoillumination, the hybrids could also function as a rewritable optoelectronic switch or memory, where the persistent state shows almost no relaxation or decay within experimental timescales, indicating near-perfect charge retention. These effects can be quantitatively explained by gate-tunable charge exchange between the graphene and MoS2 layers, and may lead to new graphene-based optoelectronic devices that are naturally scalable for large-area applications at room temperature.

Summary form only given. In this paper, a new comprehensive planning methodology is proposed for implementing distribution network reinforcement. The load growth, voltage profile, distribution line loss, and reliability are considered in this procedure. A time-segmentation technique is employed to reduce the computational load. Options considered range from supporting the load growth using the traditional approach of upgrading the conventional equipment in the distribution network, through to the use of Distributed Generators (DG). The objective function is composed of the construction cost, loss cost and reliability cost. As constraints, the bus voltages and the feeder currents should be maintained within the standard level. The DG output power should not be less than a ratio of its rated power because of efficiency. A hybrid optimization method, called Modified Discrete Particle Swarm Optimization, is employed to solve this nonlinear and discrete optimization problem. A comparison is performed between the optimized solution based on planning of capacitors along with tap-changing transformer and line upgrading and when DGs are included in the optimization.

An iterative based strategy is proposed for finding the optimal rating and location of fixed and switched capacitors in distribution networks. The substation Load Tap Changer tap is also set during this procedure. A Modified Discrete Particle Swarm Optimization is employed in the proposed strategy. The objective function is composed of the distribution line loss cost and the capacitors investment cost. The line loss is calculated using estimation of the load duration curve to multiple levels. The constraints are the bus voltage and the feeder current which should be maintained within their standard range. For validation of the proposed method, two case studies are tested. The first case study is the semi-urban 37-bus distribution system which is connected at bus 2 of the Roy Billinton Test System which is located in the secondary side of a 33/11 kV distribution substation. The second case is a 33 kV distribution network based on the modification of the 18-bus IEEE distribution system. The results are compared with prior publications to illustrate the accuracy of the proposed strategy.

The present paper reports the unusual enhancement of endurance life of ball bearings subjected to carbonitriding treatment. The microstructure was characterized by scanning electron microscopy and correlated with hardness and X-ray diffraction analysis. Endurance tests at 90% reliability revealed that the carbonitrided bearings exhibit nearly ten times more life than the non-carbonitrided bearings. This is attributed to synergic combination of retained austenitic, fine martensitic microstructure and ultrafine carbide precipitates obtained by carbonitriding treatment.

To cover wide range of pulsed power applications, this paper proposes a modularity concept to improve the performance and flexibility of the pulsed power supply. The proposed scheme utilizes the advantage of parallel and series configurations of flyback modules in obtaining high-voltage levels with fast rise time (dv/dt). Prototypes were implemented using 600-V insulated-gate bipolar transistor (IGBT) switches to generate up to 4-kV output pulses with 1-kHz repetition rate for experimentation. To assess the proposed modular approach for higher number of the modules, prototypes were implemented using 1700-V IGBTs switches, based on ten-series modules, and tested up to 20 kV. Conducted experimental results verified the effectiveness of the proposed method.

The atomically precise: doping of silicon with phosphorus (Si:P) using scanning tunneling microscopy (STM) promises ultimate miniaturization of field effect transistors. The one-dimensionaI (1D) Si:P nanowires :;are of particular interest, retaining exceptional conductivity down to the atomic scale, and are predicted as interconnects-for a scalable silicon-based quantum computer. Here, we show that ultrathin Si:P nanowires form one of the most-stable electrical conductors, with the phenomenological Hooge parameter of low-frequency noise-being as low as approximate to 10(-8) at 4.2 K, nearly 3-orders of magnitude lower than even carbon-nanotube-based 1D conductors. A in-built isolation from the-surface charge fluctuations due to encapsulation of the wires within the epitaxial-Si matrix is the dominant cause for the observed suppression of noise.-Apart from quantum information technology, Our results confirm the promising prospects for precision-doped Si:P structures in atomic-scale Circuitry for the 11 nm technology node and beyond.