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We discuss bioinspired pumping mechanism in a microfluidic configuration, consistent with the newly formulated propagative rhythmic contraction–expansion of a membrane attached to the channel wall. We aptly demonstrate the kinematics of the proposed membrane function and describe the wall profile developed due to the propagative expansion–contraction phases of the actuation cycle. The transport equations governing the flow dynamics are solved analytically in the purview of the lubrication theory. An analysis of the proposed model establishes that the fluidic functionality of a channel equipped with a single elastic membrane that operates following the propagation expansion-contraction modes can produce a unidirectional flow, and acts as a micropump in the process. By depicting the flow velocity, velocity contours, and streamlines patterns in the flow pathway, we discuss and demonstrate the eventual consequence of these flow parameters to the net throughput during both the compression and expansion phases of the process. We establish the efficacy of the novel membrane function by demonstrating augmented net throughput obtained from the proposed configuration. The membrane function developed in this endeavor will provide greater flexibility to the researchers to carry out further research in the field and will make the underlying analysis even easier in systems that utilize electromagnetic fields in the flow system. [ABSTRACT FROM AUTHOR]

The proposed work numerically investigates the buoyancy-driven flow of Casson fluid from a vertical wavy surface under the influence of a magnetic field and evaluates the underlying transport of heat in the free convective regime both quantitatively and qualitatively. Pertaining to this analysis, the primitive forms of coupled non-linear partial differential equations are evaluated with the help of an efficient and straightforward Crank–Nicolson implicit finite difference technique. By representing the graphical plots of flow velocity, temperature, and friction-factor coefficients, obtained for different physical parametric values pertinent to this analysis, we discuss the influence of the Hartmann number, surface waviness parameter, and rheological parameter of the fluid on the underlying thermohydrodynamics. In addition to the isotherm and streamline plots, by demonstrating the functional form, we discuss an extensive flow visualization technique that provides unique heat flow visualization for the wavy surface based on Bejan's heat function concept. The results indicate that for increasing the magnitude of the magnetic parameter, the evolution of isotherms, streamlines, and heatlines deviates periodically with a higher amplitude, which signifies the transfer of high heat energy as well as the efficient transport of heat in the convective regime. [ABSTRACT FROM AUTHOR]

We here discuss a novel bioinspired pumping mechanism of non-Newtonian fluids in a microfluidic configuration, consistent with the propagative rhythmic contraction–expansion of a membrane attached to the wall of the fluidic channel. We consider the Rabinowitsch model to represent the rheology of non-Newtonian fluids. By employing lubrication theory and approximating the underlying flow to be in the creeping regime, the transport equations governing the pumping process are framed pertaining to the chosen setup. The transport equations are then evaluated by employing a well-established perturbation technique. By depicting the flow velocity components, streamline patterns, and velocity contours graphically, we aptly discuss the flow structure developed in the flow pathway and demonstrate the eventual consequence of these flow parameters to the net throughput during both compression and expansion phases of the pumping process. Finally, by demonstrating a phase-space diagram, we also discuss the impact of fluid rheology and membrane kinematics on the pumping capacity. The results obtained from the proposed model establish that the net flow owing to propagative rhythmic membrane contraction strongly relies on exponent parameter M and rheological parameter β. These consequences are expected to be of substantial practical relevance in designing micropumps intended to yield unidirectional flow of the complex fluids with improved efficiency, commonly used in biochemical/biomicrofluidic applications. [ABSTRACT FROM AUTHOR]

To understand the different mechanism occurring at the MoS2-silicon interface, we have fabricated a MoS2/Si heterojunction by exfoliating MoS2 on top of the silicon substrate. Raman spectroscopy and atomic force microscopy (AFM) measurement expose the signature of few-layers in the deposited MoS2 flake. Herein, the temperature dependence of the energy barrier and carrier density at the MoS2/Si heterojunction has been extensively investigated. Furthermore, to study band alignment at the MoS2/Si interface, we have calculated a valence band offset of 0.66 ± 0.17 eV and a conduction band offset of 0.42 ± 0.17 eV using X-ray and Ultraviolet photoelectron spectroscopy. We determined a type-II band alignment at the interface which is very conducive for the transport of photoexcited carriers. As a proof-of-concept application, we extend our analysis of the photovoltaic behavior of the MoS2/Si heterojunction. This work provides not only a comparative study between MoS2/p-Si and MoS2/n-Si heterojunctions but also paves the way to engineer the properties of the interface for the future integration of MoS2 with silicon. [ABSTRACT FROM AUTHOR]

The chemical states of epitaxial PbZrxTi1-xO3 films were investigated by an X-ray photoelectron spectroscopy as a function of the gamma-ray doses. An anomalous behaviour was observed in Pb4f states, and a core level of Pb4f shifts towards a higher binding energy at 50 kGy and towards a lower binding energy at 200 kGy. The behaviour can be explained by a radiation induced reduction of PbO to metallic Pb. The metal-insulator-metal electrodes were fabricated by lithography, and the current-voltage characteristics were measured. A negative differential resistance (NDR) was observed in the leakage currents at room temperature. A higher current and disappearance of NDR characteristics were found in the 200 kGy irradiated samples, which further confirms the presence of metallic Pb. [ABSTRACT FROM AUTHOR]

The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET) mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices. [ABSTRACT FROM AUTHOR]

Write once read many times (WORM) memory devices based on the resistive switching mechanism of a sputtered amorphous BaTiO3 (am-BTO) thin film in a metal–insulator–metal structure is fabricated on a FTO coated glass substrate with a silver top contact. Fabricated devices show the switching from a low-conductance state to a high-conductance state with the formation of conductive filament(s) in the am-BTO layer. The memory characteristics are investigated as a function of thickness of am-BTO layer, which is determined by varying the deposition time. Devices with all deposited thicknesses show data retention for more than 4000 s and 300 reading cycle. Devices with 180 nm thickness show a high on-off ratio on the order of 106. The fabricated WORM devices exhibit good reading-endurance and data-retention characteristics. [ABSTRACT FROM AUTHOR]

Vertically well aligned ZnO nanorods (NRs) were grown on Si(100) substrate using RF magnetron sputtering technique. Scanning electron microscopy images confirms uniform distribution of NRs on 2 in. wafer with average diameter, height and density being ~75 nm, ~850 nm, and ~1.5 × 1010 cm-2, respectively. X-ray diffraction reveals that the ZnO NRs are grown along c-axis direction with wurtzite crystal structure. Cathodoluminescence spectroscopy, which shows a single strong peak around 3.24 eV with full width half maxima 130 meV, indicates the high crystalline and optical quality of ZnO and very low defect density. Vertically aligned nanosensors were fabricated by depositing gold circular Schottky contacts on ZnO NRs. Resistance responses of nanosensors were observed in the range from 50 to 150 °C in 1% and 5% hydrogen in argon environment, which is below and above the explosive limit (4%) of hydrogen in air. The nanosensor's sensitivity increases from 11% to 67% with temperature from 50 to 150 °C and also shows fast response time (9-16 s) and moderate recovery time (100-200 s). A sensing mechanism is proposed based on Schottky barrier changes at heterojunctions and change in depletion region of NRs. [ABSTRACT FROM AUTHOR]

We report the ultrafast carrier dynamics of an SnSe2–SnSe composite thin film (∼150 nm thick) deposited using thermal evaporation of in-house synthesized SnSe2 powder. Raman and UV–visible spectroscopy supports the optical properties (direct and indirect bandgaps of 1.86 eV and 0.96 eV, respectively). Ultrafast transient spectroscopy is used to study the charge excited state dynamics in the SnSe2–SnSe composite thin film in the femtosecond to nanosecond interval. An energy model has been proposed based on the ultrafast transient absorption and the thin film's steady-state absorption studies. This article provides comprehensive knowledge about the excited carriers and their relaxations in 0.9 ps–31.1 ns via different trap states. [ABSTRACT FROM AUTHOR]

We report on a high-performance NO2 sensor based on a one dimensional MoS2 nanowire (NW) network. The MoS2 NW network was synthesized using chemical transport reaction through controlled turbulent vapor flow. The crystal structure and surface morphology of MoS2 NWs were confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Further, the sensing behavior of the nanowires was investigated at different temperatures for various concentrations of NO2 and the sensor exhibited about 2-fold enhanced sensitivity with a low detection limit of 4.6 ppb for NO2 at 60 °C compared to sensitivity at room temperature. Moreover, it showed a fast response (16 s) with complete recovery (172 s) at 60 °C, while sensitivity of the device was decreased at 120 °C. The efficient sensing with reliable selectivity toward NO2 of the nanowires is attributed to a combination of abundant active edge sites along with a large surface area and tuning of the potential barrier at the intersections of nanowires during adsorption/desorption of gas molecules. [ABSTRACT FROM AUTHOR]

Ultrafast charge carrier dynamics as well as the generation of polaron pair in squaraine (SQ) and squaraine:[6,6]-phenyl-C 71-butyric acid methyl ester (SQ:PCBM71) have been studied using ultrafast transient absorption spectroscopy (UTAS). The current study reveals that the pure SQ exhibits the creation of singlet and triplet states; however, incorporation of PCBM71 in SQ results in the formation of polaron pairs with ∼550ps lifetime, which in turn leads to the creation of free electrons in the device. We show that the considerable increment in monomolecular and bimolecular recombination in SQ:PCBM71 compared to pure SQ which describes the interfacial compatibility of SQ and PCBMC71 molecules. The present work not only provides the information about the carrier generation in SQ and SQ:PCBM71 but also gives the facts relating to the effect of PCBM71 mixing into the SQ which is very significant because the SQ has donor-acceptor-donor (D-A-D) structure and mixing one more acceptor can introduce more complex recombinations in the blend. These findings have been complimented by the charge transport study in the device using impedance spectroscopy. The various important transport parameters are transit time (τt), diffusion constant (Dn), global mobility (μ) and carrier lifetime (τr). The values of these parameters are 26.38 μs, 4.64x10-6 cm2s-1, 6.12x10-6 cm2V-1s-1 and 399 μs, respectively. To the best of our knowledge such study related to SQ is not present in the literature comprehensively. [ABSTRACT FROM AUTHOR]

The increased usage of hydrogen as a next generation clean fuel strongly demands the parallel development of room temperature and low power hydrogen sensors for their safety operation. In this work, we report strong evidence for preferential hydrogen adsorption at edge-sites in an edge oriented vertically aligned 3-D network of MoS2 flakes at room temperature. The vertically aligned edge-oriented MoS2 flakes were synthesised by a modified CVD process on a SiO2/Si substrate and confirmed by Scanning Electron Microscopy. Raman spectroscopy and PL spectroscopy reveal the signature of few-layer MoS2 flakes in the sample. The sensor's performance was tested from room temperature to 150 °C for 1% hydrogen concentration. The device shows a fast response of 14.3 s even at room temperature. The sensitivity of the device strongly depends on temperature and increases from ~1% to ~11% as temperature increases. A detail hydrogen sensing mechanism was proposed based on the preferential hydrogen adsorption at MoS2 edge sites. The proposed gas sensing mechanism was verified by depositing ~2-3 nm of ZnO on top of the MoS2 flakes that partially passivated the edge sites. We found a decrease in the relative response of MoS2-ZnO hybrid structures. This study provides a strong experimental evidence for the role of MoS2 edge-sites in the fast hydrogen sensing and a step closer towards room temperature, low power (0.3 mW), hydrogen sensor development. [ABSTRACT FROM AUTHOR]

In this work, we report enhanced power conversion efficiency (PCE) of bulk heterojunction polymer solar cells by Förster resonance energy transfer (FRET) from samarium-doped luminescent gadolinium orthovanadate (GdVO4:Sm3+) quantum dots (QDs) to polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) polymer. The photoluminescence emission spectrum of GdVO4:Sm3+ QDs overlaps with the absorption spectrum of PTB7, leading to FRET from GdVO4:Sm3+ to PTB7, and significant enhancements in the charge-carrier density of excited and polaronic states of PTB7 are observed. This was confirmed by means of femtosecond transient absorption spectroscopy. The FRET from GdVO4:Sm3+ QDs to PTB7 led to a remarkable increase in the power conversion efficiency (PCE) of PTB7:GdVO4:Sm3+:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) polymer solar cells. The PCE in optimized ternary blend PTB7:GdVO4:Sm3+:PC71BM (1:0.1:1.5) is increased to 8.8% from 7.2% in PTB7:PC71BM. This work demonstrates the potential of rare-earth based luminescent QDs in enhancing the PCE of polymer solar cells. [ABSTRACT FROM AUTHOR]

Using the envelope-function approximation, the single-particle states of electrons and holes in spherical GaN nanocrystals embedded in different amorphous dielectric matrices (SiO2, Al2O3, HfO2 and Si3N4) have been calculated. Ground state energies of electrons and holes in GaN nanocrystals are determined using the isotropic approximation of the k · p -Hamiltonian. All the ground state energies are found to increase with lowering the nanocrystal size and are proportional to the R-n, where R is the nanocrystal radius, n =1.5-1.9 for electrons and 1.7-2.0 for holes. The optical gap of GaN nanocrystals changes from 3.8 to 5 eV for the nanocrystal radius ranging from 3 to 1 nm. [ABSTRACT FROM AUTHOR]

ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2"-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 × 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ~3.275 eV to ~3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications. [ABSTRACT FROM AUTHOR]

Uniformly distributed and defect-free vertically aligned ZnO nanorods (NRs) with high aspect ratio are deposited on Si by sputtering technique. X-ray diffraction along with transmission electron microscopy studies confirmed the single crystalline wurtzite structure of ZnO. Absence of wide band emission in photoluminescence spectra showed defect-free growth of ZnO NRs which was further conformed by diamagnetic behavior of the NRs. H2 sensing mechanism based on the change in physical dimension of channel is proposed to explain the fast response (~21.6 s) and recovery times (~27 s) of ZnO NRs/Si/ZnO NRs sensors. Proposed H2 sensor operates at low temperature (~70°C) unlike the existing high temperature (>150°C) sensors. [ABSTRACT FROM AUTHOR]