Ordered monolayer gold nano-urchin structures and their size induced control for high gas sensing performance

The synthesis of ordered monolayers of gold nano-urchin (Au-NU) nanostructures with controlled size, directly on thin films using a simple electrochemical method is reported in this study. In order to demonstrate one of the vast potential applications, the developed Au-NUs were formed on the electrodes of transducers (QCM) to selectively detect low concentrations of elemental mercury (Hg0) vapor. It was found that the sensitivity and selectivity of the sensor device is enhanced by increasing the size of the nanospikes on the Au-NUs. The Au-NU-12 min QCM (Au-NUs with nanospikes grown on it for a period of 12 min) had the best performance in terms of transducer based Hg0 vapor detection. The sensor had 98% accuracy, 92% recovery, 96% precision (repeatability) and significantly, showed the highest sensitivity reported to date, resulting in a limit of detection (LoD) of only 32 μg/m3 at 75 °C. When compared to the control counterpart, the accuracy and sensitivity of the Au-NU-12 min was enhanced by ~2 and ~5 times, respectively. The results demonstrate the excellent activity of the developed materials which can be applied to a range of applications due to their long range order, tunable size and ability to form directly on thin-films

Alkali ratio control for lead-free piezoelectric thin films utilizing elemental diffusivities in RF plasma

High performance piezoelectric thin films are generally lead-based, and find applications in sensing, actuation and transduction in the realms of biology, nanometrology, acoustics and energy harvesting. Potassium sodium niobate (KNN) is considered to be the most promising lead-free alternative, but it is hindered by the inability to control and attain perfect stoichiometry materials in the thin film form while using practical large area deposition techniques. In this work, we identify the contribution of the elemental diffusivities in the radio frequency (RF) plasma in determining the alkali loss in the KNN thin films. We have also examined the effect of the substrate temperature during the RF magnetron sputtering deposition on the crystal structure of the substrate and KNN thin films, as well as the effect of the postannealing treatments. These results indicate the need for well-designed source materials and the potential to use the deposition partial pressure to alter the dopant concentrations

Third order nonlinear optical properties of organometal halide perovskite by means of the Z-scan technique

The nonlinear optical response of CH3NH3PbBr3 perovskites is investigated using Z-scan technique, employing 10 ns laser pulses, at 532 nm. The systems were found to exhibit strong nonlinear optical response, dominated by nonlinear refraction. The effect of organic and inorganic composition ratio on the nonlinear susceptibility is studied experimentally. In all cases, the nonlinear absorption and refraction have been determined. The corresponding third-order susceptibilities and second-order hyperpolarizability are determined to be as large as 10−6 (esu) and 10−28 (esu) under ns laser excitation respectively. Showing large third-order optical nonlinearity in CH3NH3PbBr3 thin films, suggesting their potential for photonics applications

Application of the Fokker-Planck molecular mixing model to turbulent scalar mixing using moment methods

An extended quadrature method of moments using the beta kernel density function (beta-EQMOM) is used to approximate solutions to the evolution equation for univariate and bivariate composition probability distribution functions (PDFs) of a passive scalar for binary and ternary mixing. The key element of interest is the molecular mixing term, which is described using the Fokker-Planck (FP) molecular mixing model. The direct numerical simulations (DNSs) of Eswaran and Pope [ Direct numerical simulations of the turbulent mixing of a passive scalar, Phys. Fluids 31, 506 (1988)] and the amplitude mapping closure (AMC) of Pope [ Mapping closures for turbulent mixing and reaction, Theor. Comput. Fluid Dyn. 2, 255 (1991)] are taken as reference solutions to establish the accuracy of the FP model in the case of binary mixing. The DNSs of Juneja and Pope [ A DNS study of turbulent mixing of two passive scalars, Phys. Fluids 8, 2161 (1996)] are used to validate the results obtained for ternary mixing. Simulations are performed with both the conditional scalar dissipation rate (CSDR) proposed by Fox [Computational Methods for Turbulent Reacting Flows (Cambridge University Press, 2003)] and the CSDR from AMC, with the scalar dissipation rate provided as input and obtained from the DNS. Using scalar moments up to fourth order, the ability of the FP model to capture the evolution of the shape of the PDF, important in turbulent mixing problems, is demonstrated. Compared to the widely used assumed beta-PDF model [S. S. Girimaji, Assumed beta-pdf model for turbulent mixing: Validation and extension to multiple scalar mixing, Combust. Sci. Technol. 78, 177 (1991)], the beta-EQMOM solution to the FP model more accurately describes the initial mixing process with a relatively small increase in computational cost

PARTICLES SIZE DISTRIBUTION EFFECT ON 3D PACKING OF NANOPARTICLES INTO A BOUNDED REGION

Abstract In this paper, the effects of two different Particle Size Distributions (PSD) on packing behavior of ideal rigid spherical nanoparticles using a novel packing model based on parallel algorithms have been reported. A mersenne twister algorithm was used to generate pseudorandom numbers for the particles initial coordinates. Also, for this purpose a nanosized tetragonal confined container with a square floor (300 * 300 nm) were used in this work. The Andreasen and the Lognormal PSDs were chosen to investigate the packing behavior in a 3D bounded region. The effects of particle numbers on packing behavior of these two PSDs have been investigated. Also the reproducibility and the distribution of packing factor of these PSDs were compared. Keyword

Experimental Investigation of Flow and Coherent Properties of Excited Non-Circular Liquid Jets

Non-circular jet is identified as an efficient passive flow-control technique that attracts many research topics. The existence of twine-vortexes is the main reason for dissimilarity between circular and non-circular jets. Which also influences the production of droplets and satellites as well as the jet instability. This investigation presents instability analysis of liquid-gas interface as an applicable conception in free-jet flows. We experiment different jet geometries within a gas ambient in order to study their hydrodynamic behavior. These studies give an appropriate perception about contributing forces that play essential roles in fluid instability. We focus on varying viscosity and surface tension as our excitation techniques. These methods are vital to examine the key properties of non-circular jets such as breakup and decay length, axis-switching wavelength as well as produced droplets and satellites characteristics. First, instabilities of charged liquid jets are investigated by considering the interaction between electric and inertial forces. Also, the viscosity effect was studied for its interaction with the inertial and surface tension forces. In each case, liquid jet in-stability for various nozzle geometries over a specific range of jet velocity is examined. The obtained results illustrate that the geometry of nozzle has an important effect on jet instability. In addition, by increment of We number, the breakup and decay length as well as the axis-switching wavelength are raising. However, by the rise of twin-vortex number, the breakup length increases but the decay length and axis-switching wavelength decrease

Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices

Au nanospikes as a non-enzymatic glucose sensor: Exploring morphological changes with the elaborated chronoamperometric method

There is a continuous increasing demand for more sensitive and selective non-enzymatic glucose sensor applications ranging from medical diagnostics to food quality assurance. Here, we deposited gold nanostructures (referred to as Au nanospikes) on Au thin-film substrates under different electrodeposition conditions in order to determine the optimal growth parameters to obtain an enhanced glucose sensor. A modified chronoamperometric technique was employed to determine the glucose electrooxidation and sensing capabilities of the developed Au nanospikes toward 20muM-10mM glucose concentrations. The sensing method used here allowed for accurate determination of glucose concentrations whilst providing reproducible and stable response profiles. The sensor produced a low detection limit of 20muM, a very high sensitivity of 201muAmM-1cm-2 compared to 16.19muAmM-1cm-2 for the unmodified Au substrate. The sensor also showed good selectivity when analysed against common physiological contaminants that usually interfere with conventional sensors

Zinc oxide/ Silver nanoarrays as reusable SERS substrates with controllable 'hot-spots' for highly reproducible molecular sensing

Hypothesis: The reproducible surface enhanced Raman scattering (SERS)-based sensing of an analyte relies on high quality SERS substrates that offer uniformity over large areas. Uniform ZnO nanoarrays are expected to offer an appropriate platform for SERS sensing. Moreover, since ZnO has good photocatalytic properties, controllable decoration of silver nanoparticles on ZnO nanoarrays may offer an additional opportunity to clean up SERS substrates after each sensing event. Experiments: This study employs a facile soft chemical synthesis strategy to fabricate Raman-active and recyclable ZnO/Ag nanorod arrays as reproducible SERS substrates. Arrays of ZnO nanorods were synthesized using hydrothermal method, which was followed by controllable decoration of ZnO with silver nanoparticles (AgNPs) using an electroless plating technique. Findings: The uniform density of SERS-active 'hot-spots' on ZnO nanoarrays could be controlled on a large 1 1 cm2 substrate. These ZnO/Ag nanoarrays showed high reproducibility (0.132 RSD) towards acquiring SERS spectra of rhodamine B (RB) at 30 random locations on a single substrate. The photocatalytic nature of ZnO/Ag semiconductor/metal hybrid endowed these substrates with reusability characteristics. By controlling metal loading on a semiconductor surface, photocatalytic activity and high SERS performance can be integrated within a single package to obtain high quality, reproducible, stable and recyclable SERS substrates

Nano-engineered surfaces for mercury vapor sensing: Current state and future possibilities

Mercury is a well-known toxic element and it has been claimed that 75,000 new-born babies in USA alone are at risk of neurological diseases due to high mercury concentration in their mothers' bloodstream during pregnancy. The preventative measures of mercury need to start from the detection and removal of the elemental form as (i) it represents 66-94% of anthropogenic air emissions, (ii) is hard to detect/remove and (iii) it can travel over long distances globally before converting to more toxic forms (oxidized/organic mercury). Therefore elemental mercury needs to be detected and removed at its point source before it can be converted into the more toxic compounds. Here, we undergo a comprehensive review on the development and progress of solid-state-based elemental mercury vapor sensors which stand out from the well-established area of mercury ion sensing