Broadband THz modulators based on multilayer graphene on PVC

In this study we present the direct terahertz time-domain spectroscopic measurement of CVD-grown multilayer graphene (MLG) on PVC substrate with an electrically tunable Fermi level. In a configuration consisting MLG and injected organic dopant, the transmitted intensity loss of terahertz radiation was observed with an applied voltage between 0 and 3.5 V. We showed that MLG on PVC devices provided approximately 100 % modulation between 0.2 and 1.5 THz at preferentially low operation voltage of ca. 3V. The observed modulation bandwidth in terahertz frequencies appears to be instrument limited. © 2016 IEEE

Hybrid additive manufacturing of 3D electronic systems

A novel hybrid additive manufacturing (AM) technology combining digital light projection (DLP) stereolithography (SL) with 3D micro-dispensing alongside conventional surface mount packaging is presented in this work. This technology overcomes the inherent limitations of individual AM processes and integrates seamlessly with conventional packaging processes to enable the deposition of multiple materials. This facilitates the creation of bespoke end-use products with complex 3D geometry and multi-layer embedded electronic systems. Through a combination of four-point probe measurement and non-contact focus variation microscopy, it was identified that there was no obvious adverse effect of DLP SL embedding process on the electrical conductivity of printed conductors. The resistivity maintained to be less than 4  ×  10−4 Ω centerdot cm before and after DLP SL embedding when cured at 100 °C for 1 h. The mechanical strength of SL specimens with thick polymerized layers was also identified through tensile testing. It was found that the polymerization thickness should be minimised (less than 2 mm) to maximise the bonding strength. As a demonstrator a polymer pyramid with embedded triple-layer 555 LED blinking circuitry was successfully fabricated to prove the technical viability

Dynamically controlled deposition of colloidal nanoparticles suspension in evaporating drops using laser radiation

Dynamic control of the distribution of polystyrene suspended nanoparticles in evaporating droplets is investigated using a 2.9 μm high power laser. Under laser radiation a droplet is locally heated and fluid flows are induced that overcome the capillary flow, and thus a reversal of the coffee-stain effect is observed. Suspension particles are accumulated in a localised area, one order of magnitude smaller than the original droplet size. By scanning the laser beam over the droplet, particles can be deposited in an arbitrary pattern. This finding raises the possibility for direct laser writing of suspended particles through a liquid layer. Furthermore, a highly uniform coating is possible by manipulating the laser beam diameter and exposure time. The effect is expected to be universally applicable to aqueous solutions independent of solutes (either particles or molecules) and deposited substrates

Linear stability of the Vlasov-Poisson system with boundary conditions

We study the linear stability of the Vlasov–Poisson system in one dimension on a finite interval and half line with the in-flow and specular reflection boundary conditions. Conditions for the existence and non-existence of stationary solutions are obtained. The behavior of the perturbed solutions is investigated in different contexts. We show that, if the equilibrium distribution μ is a strictly decreasing function of local energy density, then the Vlasov–Poisson system on a finite interval is stable in the (weighted) L2 sense for the in-flow and specular reflection boundary conditions. For the case μ is strictly increasing, we prove a similar result on a finite interval under some extra assumptions. Finally, in the last part of the article, the spectral stability of the Vlasov–Poisson system on an unbounded interval is studied with similar monotonicity assumptions on μ.111sciescopu

Hierarchical nanowire and nanoplate-assembled NiCo2O4-NiO biphasic microspheres as effective electrocatalysts for oxygen evolution reaction

In this study, NiCo2O4-NiO nanomaterials with two different morphologies were synthesized using urea and cetyltrimethylammonium chloride (CTAC) as structure directing agents. A combination of analytical techniques including XRD, XPS, SEM-EDX, TEM, and BET were utilized for the characterization of the materials. Microscopy images show that urea-stabilized NiCo2O4-NiO (UeNiCo) has urchin-like morphology assembled by nanowires, and CTAC stabilization (C-NiCo) led to the formation of microspheres with nanoplate assembly. In addition, both wires and plates are formed by the assembly of individual NiCo2O4-NiO nanoparticles. Then, glassy carbon electrodes were modified with these hierarchical nanomaterials, and their electrochemical behavior in oxygen evolution reaction was investigated in 0.1 M KOH solution. Although both of the materials had similar onset potentials (1.56 V vs RHE for U-NiCo and 1.57 V vs RHE for C-NiCo), U-NiCo could drive 10 mA cm(-2) of current density at a lower overpotential value (387 mV) than C-NiCo (430 mV). Both of the materials demonstrated impressive kinetic performance with low Tafel slopes (49 mV dec(-1) for U-NiCo and 44 mV dec(-1) for C-NiCo) and good stability during long-term constant potential electrolysis. In addition, NiCo2O4-NiO nanomaterials outperformed RuO2 at high catalytic current densities (i.e., eta(50) = 518 mV for U-NiO and eta(50) = 622 mV for RuO2)

Stationary Solutions of the Vlasov-Poisson System with Diffusive Boundary Conditions

The stationary solutions of the Vlasov-Poisson system for a plasma are studied with general diffusive boundary conditions. The distribution function , which depends on the local energy and angular momentum, is determined uniquely under certain integrability and decay assumptions on the diffusive kernels and the particle injection intensities. The resulting nonlinear Poisson equation is then solved for the electric potential . We study the existence and uniqueness of its solutions in one and higher dimensions under a variety of settings.X1122sciescopu

A new method for alcohol content determination of fuel oils by terahertz spectroscopy

In this study, we developed a simple method for alcohol content analysis in fuel oils by Time-Domain Terahertz (THz) Spectroscopy. Frequency dependent absorption coefficients, refractive indices, and dielectric constants were calculated from the measurements of pure fuel oils and their mixtures with ethanol. Ethanol mixtures of gasoline were modeled successfully with a simple model in which the mixture behavior was described with a basic contribution approach of pure liquids. The results suggest that there is no strong interaction between the ethanol and the molecules in the gasoline. We concluded that this new approach offers a simple and useful method to determine the concentration of ethanol in gasoline currently with a 3% (by volume) maximum absolute error. With improvements, this error would be reduced to below 1%. © 2013 IEEE