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arXiv2017

Electroforming-Free TaOx Memristors using Focused Ion Beam Irradiations

We demonstrate creation of electroforming-free TaOx memristive devices using focused ion beam irradiations to locally define conductive filaments in TaOx films. Electrical characterization shows that these irradiations directly create fully functional memristors without the need for electroforming. Ion beam forming of conductive filaments combined with state-of-the-art nano-patterning presents a CMOS compatible approach to wafer level fabrication of fully formed and operational memristors.

physics.app-ph↗

arXiv2018

Micromachining of PMN-PT Crystals with Ultrashort Laser Pulses

Lead-magnesium niobate lead-titanate (PMN-PT) has been proven as an excellent material for sensing and actuating applications. The fabrication of advanced ultra-small PMN-PT-based devices relies on the availability of sophisticated procedures for the micro-machining of PMN-PT thin films or bulk substrates. Approaches reported up to date include chemical etching, excimer laser ablation and ion milling. To ensure an excellent device performance, a key mandatory feature for a micro-machining process is to preserve as far as possible the crystalline quality of the substrates; in other words, the fabrication method must induce a low density of cracks and other kind of defects. In this work, we demonstrate a relatively fast procedure for the fabrication of high-quality PMN-PT micro-machined actuators employing green femtosecond laser pulses. The fabricated devices feature absence of extended cracks and well defined edges with relatively low roughness, which is advantageous for the further integration of nanomaterials onto the piezoelectric actuators.

physics.app-ph↗

arXiv2018

Diagnostic of electron temperature from bremsstrahlung in overdense targets

Models for characterization of laser-accelerated electron via its produced bremsstrahlung are provided for both thin and thick targets. An effective temperature functional is proposed to overcome the so-called cold and hot "temperatures" in the emission spectra, which are shown not to describe the underlying electron energy distribution. In contrast, this functional allows for identifying the real effect of a hot electron component. A false "heating" effect due to added noise is also exposed. The models are shown to be in good agreement with Monte Carlo simulations, as well as in good agreement with other experimental methods when applied to experimental data.

physics.ins-det↗

arXiv2018

Simulation of force-insensitive optical cavities in cubic spacers

We analyze the properties of optical cavities contained in spacers with approximate octahedral symmetry and made of different materials,following the design of Webster and Gill (S. Webster, P. Gill, Optics Letters 36(18), 3572 (2011)). We show that for isotropic materials with Young's modulus less than 200 GPa, the Poisson's ratio $ν$ must lie in a "magic" range 0.13<$ν$<0.23 in order to null the influence of the forces supporting the spacer. This restriction can be overcome with the use of anisotropic materials such as silicon. A detailed study aiming at identification of all suitable crystal orientations of silicon with respect to the resonator body is performed and the relation to the Poisson's ratio and the Young's modulus along these orientations is discussed. We also perform an analysis of the sensitivity of the cavity performance to errors in spacer manufacturing. We find that the orientation of the [110] or [100] crystallographic directions oriented along one of the three optical axes of the resonator provides low sensitivities to imprecise manufacturing and interesting options for fundamental physics experiments.

physics.ins-det↗

arXiv2018

Optofluidic sensor system with Ge PIN photodetector for CMOS-compatible sensing

Vertical optofluidic biosensors based on refractive index sensing promise highest sensitivities at smallest area foot-print. Nevertheless, when it comes to large scale fabrication and application of such sensors, cheap and robust platforms for sample preparation and supply are needed - not to mention the expected ease of use in application. We present an optofluidic sensor system using a cyclic olefin copolymer microfluidic chip as carrier and feeding supply for a complementary metal-oxide-semiconductor-compatibly fabricated Ge PIN photodetector. Whereas typically only passive components of a sensor are located within the microfluidic channel, here the active device is directly exposed to the fluid, enabling top-illumination. The capability for detecting different refractive indices was verified by different fluids with subsequent recording of the optical responsivity. All components excel in their capability to be transferred to large scale fabrication and further integration of microfluidic and sensing systems. The photodetector itself is intended to serve as a platform for further sophisticated collinear sensing approaches.

physics.app-ph↗

arXiv2018

The Sech(Xi)-type profiles: a Swiss-Army knife for exact analytical modelling of thermal diffusion and wave propagation in graded media

This work deals with exact analytical modelling of transfer phenomena in heterogeneous materials exhibiting one-dimensional continuous variations of their properties. Regarding heat transfer, it has recently been shown that by applying a Liouville transformation and multiple Darboux transformations, infinite sequences of solvable profiles of thermal effusivity can be constructed together with the associated temperature (exact) solutions, all in closed-form expressions (vs. the diffusion-time variable and with a growing number of parameters). In addition, a particular class of profiles, so-called sech(xi)-type profiles, exhibit high agility and in the same time parsimony. In this paper we go further into the description of these solvable profiles and their properties. Most importantly, their quadrupole formulation is provided which allows building smooth synthetic profiles of effusivity of arbitrary complexity and thereafter getting very easily the corresponding temperature dynamic response. Examples are given with increasing variability of effusivity and increasing number of elementary profiles. These highly flexible profiles are equally relevant for providing an exact analytical solution to wave propagation problems in 1D graded media (i.e. Maxwell's equations, acoustic equation, telegraph equation...). From now on, let it be for diffusion-like or wave-like problems, when the leading properties present (possibly piecewise-) continuously heterogeneous profiles, the classical staircase model can be advantageously replaced by a "high-level" quadrupole model consisting of one or more sech(xi)-type profiles, which makes the latter a true Swiss-Army knife for analytical modelling.

physics.comp-ph↗

arXiv2018

Study of the non-linear dynamics of micro-resonators based on a Sn-whisker in vacuum and at mK temperatures

The dynamics of micro-resonators (or any mechanical resonators) can be studied by two complementary methods allowing the measurements in two different domains: (i) in the frequency domain - by the frequency sweeps using cw-excitation, and (ii) in the time domain - by the pulse techniques, when the free-decay oscillations are investigated. To broaden the knowledge about the intrinsic mechanical properties of micro-resonators based on a Sn-whisker we used both methods. We show that the dynamics of the Sn-whisker can be described by a phenomenological theory of the Duffing oscillator. Furthermore, we present the results of theoretical analysis based on the Duffing's model provided in the time and frequency domains, and we show that these results are qualitatively the same with those measured experimentally.

cond-mat.mes-hall↗

arXiv2019

Review of borophene and its potential applications

Since two-dimensional boron sheet (borophene) synthesized on Ag substrates in 2015, research on borophene has grown fast in the fields of condensed matter physics, chemistry, material science, and nanotechnology. Due to the unique physical and chemical properties, borophene has various potential applications. In this review, we summarize the progress on borophene with a particular emphasis on the recent advances. First, we introduce the phases of borophene by experimental synthesis and theoretical predictions. Then, the physical and chemical properties, such as mechanical, thermal, electronic, optical and superconducting properties are summarized. We also discuss in detail the utilization of the borophene for wide ranges of potential application among the alkali metal ion batteries, Li-S batteries, hydrogen storage, supercapacitor, sensor and catalytic in hydrogen evolution, oxygen reduction, oxygen evolution, and CO2 electroreduction reaction. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

cond-mat.mtrl-sci↗

arXiv2018

Effect of Variation of Different Nano filler on Structural, Electrical, Dielectric and Transport Properties of Blend Polymer Nanocomposites

In the present work, the effect of different nanofiller (BaTiO3, CeO2, Er2O3 or TiO2) on blend solid polymer electrolyte comprising of PEO and PVC complexed with bulky LiPF6 have been explored. The XRD analysis confirms the polymer nanocomposite formation. FTIR provides evidence of interaction among the functional groups of the polymer with the ions and the nanofiller in terms of shifting and changing peak profile. The highest ionic conductivity is ~2.3x10-5 S cm-1 with a wide electrochemical stability window of ~3.5 V for 10 wt. % Er2O3. The real and imaginary part of dielectric permittivity follows the identical trend of the decreasing value with increase in the frequency. The particle size and the dielectric constant shows an abnormal trend with different nanofiller. The ac conductivity follows the universal power law. An effective mechanism has been proposed to understand the nanofiller interaction with cation coordinated polymer in the investigated system.

physics.app-ph↗

arXiv2019

Carbon nanotube synthesis from propane decomposition on a pre-treated Ni overlayer

Growth of carbon nanotubes (CNTs) was performed by atmospheric pressure chemical vapour deposition (APCVD) of propane on Si(111) with a pre-treated Ni overlayer acting as a catalyst. Prior to the growth of CNTs, a thin film of Ni was deposited on Si(111) substrate by evaporation and heat treated at 900°C. The growth of nanotubes was carried out at 850°C using propane as a source of carbon. Distribution of the catalyst particles over the Si substrate was analysed before and after heat treatment by atomic force microscopy (AFM). The X-ray diffraction (XRD) pattern of the grown material revealed that they are graphitic in nature. Field emission scanning electron microscopy (FESEM) was used to investigate the growth process and it was found that a catalytic particle was always situated at the tip of the tube thus implying a tip growth mechanism. Evidence for the presence of radial breathing mode from multi-wall nanotubes (MWNTs) in the grown sample was obtained from micro-Raman analysis. Finally, high-resolution transmission electron microscopic (HRTEM) analysis confirmed that the graphene layers of the CNTs are well ordered with typical 0.34 nm spacing.

cond-mat.mtrl-sci↗

arXiv2018

Energy Absorption and Low Velocity Impact Response of Open-Cell Polyurea Foams

The energy absorption and impact attenuation of low density polyurea (PU) foams (140 - 220 kg/m3) is presented. The stress-strain behavior, energy absorption, cushioning efficiency, and energy return (resilience) are measured at a quasi-static strain rate using an Instron load frame. In addition, the low velocity impact attenuation of the polyurea foams at 5 J and 7 J impact energies were investigated according to the American Society for Testing and Materials (ASTM) test methods F1976. The polyurea foams were then compared with widely used ethylene vinyl acetate (EVA) and thermoplastic polyurethane (TPU) foam technologies at similar densities. The PU foams displayed a 5 % increase in cushioning efficiency and 30 % greater energy absorption over TPU and EVA foams under quasi-static compression. Under impact testing, PU foams resulted in a reduction of up to 28.6 % and 36.9 % in peak transmitted impact forces when compared to EVA and TPU foams of the same thickness (20 mm) at 5 J and 7 J, respectively. These properties should allow these materials to have a wide range of cushioning/impact applications, especially in protective body and headgear systems.

cond-mat.soft↗

arXiv2018

Meissner States of Type II Superconductors

This paper concerns mathematical theory of Meissner states of a bulk superconductor of type $I\!I$, which occupies a bounded domain $Ω$ in $\Bbb R^3$ and is subjected to an applied magnetic field below the critical field $H_{S}$. A Meissner state is described by a solution $(f,\mathbf A)$ of a nonlinear partial differential system called Meissner system, where $f$ is a positive function on $Ω$ which is equal to the modulus of the order parameter, and $\mathbf A$ is the magnetic potential defined on the entire space such that the inner trace of the normal component on the domain boundary $\partialΩ$ vanishes. Such a solution is called a Meissner solution. Various properties of the Meissner solutions are examined, including regularity, classification and asymptotic behavior for large value of the Ginzburg-Landau parameter $κ$. It is shown that the Meissner solution is smooth in $Ω$, however the regularity of the magnetic potential outside $Ω$ can be rather poor. This observation leads to the ides of decomposition of the Meissner system into two problems, a boundary value problem in $Ω$ and an exterior problem outside of $Ω$. We show that the solutions of the boundary value problem with fixed boundary data converges uniformly on $Ω$ as $κ$ tends to $\infty$, where the limit field of the magnetic potential is a solution of a nonlinear curl system. This indicates that, the magnetic potential part $\mathbf A$ of the solution $(f,\mathbf A)$ of the Meissner system, which has same tangential component of $curl \mathbf A$ on $\partialΩ$, converges to a solution of the curl system as $κ$ increases to infinity, which verifies that the curl system is indeed the correct limit of the Meissner system in the case of three dimensions.

math.AP↗

arXiv2019

Water vapor assisted sintering of silver nanoparticle inks for printed electronics

In printed electronics, conductive traces are often produced by printing inks of silver nanoparticles dispersed in solvents. A sintering process is usually needed to make the printed inks conductive by removing the organic dispersants and allowing metal-to-metal contacts among nanoparticles for atomic diffusion and neck formation. It has been challenging to sinter silver nanoparticle inks in a thermal oven at a temperature < 150 C to avoid thermal damage to the plastic substrate while achieving desired conductivity. This work presents a simple yet effective way to sinter a silver nanoparticle ink below 120 C (even at 80 C) by exposing the printed ink to water vapor in the oven. The results consistently show a significant reduction of line resistivity for the samples sintered in a moist oven compared to those sintered in a dry oven. Hence, solvent vapor-assisted sintering of metal nanoparticle inks can become an enabling approach to broaden product range of printed electronics.

physics.app-ph↗

arXiv2018

Self-assembly of magnetic iron oxide nanoparticles into cuboidal superstructures

This chapter describes the synthesis and some characteristics of magnetic iron oxide nanoparticles, mainly nanocubes, and focus on their self-assembly into crystalline cuboids in dispersion. The influence of external magnetic fields, the concentration of particles, and the temperature on the assembly process is experimentally investigated.

cond-mat.soft↗

arXiv2018

A fast and robust numerical scheme for solving models of charge carrier transport and ion vacancy motion in perovskite solar cells

Drift-diffusion models that account for the motion of both electronic and ionic charges are important tools for explaining the hysteretic behaviour and guiding the development of metal halide perovskite solar cells. Furnishing numerical solutions to such models for realistic operating conditions is challenging owing to the extreme values of some of the parameters. In particular, those characterising (i) the short Debye lengths (giving rise to rapid changes in the solutions across narrow layers), (ii) the relatively large potential differences across devices and (iii) the disparity in timescales between the motion of the electronic and ionic species give rise to significant stiffness. We present a finite difference scheme with an adaptive time step that is posed on a non-uniform staggered grid that provides second order accuracy in the mesh spacing. The method is able to cope with the stiffness of the system for realistic parameters values whilst providing high accuracy and maintaining modest computational costs. For example, a transient sweep of a current-voltage curve can be computed in only a few minutes on a standard desktop computer.

physics.app-ph↗

arXiv2018

Electromagnetically driven convection suitable for mass transfer enhancement in liquid metal batteries

Liquid metal batteries (LMBs) were recently proposed as cheap large scale energy storage. Such devices are urgently required for balancing highly fluctuating renewable energy sources. During discharge, intermetallic phases tend to form in the cathode of LMBs. These do not only limit the up-scalability, but also the efficiency of the cells. Generating a mild fluid flow in the fully liquid cell will smoothen concentration gradients and minimise the formation of intermetallics. In this context we study electro-vortex flow numerically. We simulate a recent LMB related experiment and discuss how the feeding lines to the cell can be optimised to enhance mass transfer. The Lorentz forces have to overcome the stable thermal stratification in the cathode of the cell; we show that thermal effects may reduce electro-vortex flow velocities considerable. Finally, we study the influence of the Earth magnetic field on the flow.

physics.app-ph↗

arXiv2018

Surface modified mesoporous g-C3N4@FeNi3 as prompt and proficient magnetic adsorbent for crude oil recovery

Efficient oil adsorption and recovery is a generous universal importance for future energy demand and environmental protection. Adsorbents based on 2D flatland with engineered surfaces can overcome the limitations of conventional methods for selective oil adsorption. Here, we report magnetic hydrophobic/oleophilic graphitic C3N4 nanosheets that exhibit excellent oil sorption performance and rapid removal of adsorbed oil using an external magnet. Combining porous and nanosheets structure along with magnetic FeNi3 and fatty acid surface functionalization make the system an efficient adsorbent for adsorbing and separating crude oil from water. The graphitic sheets selectively adsorb crude oil with enhancement of thickness up to 9 folds and mass by 4.5 times than the pristine nanocomposite system. The smart adsorption property of g-C3N4@FeNi3 has been realized through comprehensive adsorption kinetics and inclusive isotherm studies. The nanocomposite can be further recycled and reused in an eco-friendly manner for oil adsorption and recovery.

physics.app-ph↗

arXiv2019

Femtosecond laser patterning of graphene electrodes for thin-film transistors

The aim of this study is to assess femtosecond laser patterning of graphene in air and in vacuum for the application as source and drain electrodes in thin-film transistors (TFTs). The analysis of the laser-patterned graphene with scanning electron microscopy, atomic force microscopy and Raman spectroscopy showed that processing in vacuum leads to less debris formation and thus re-deposited carbonaceous material on the sample compared to laser processing in air. It was found that the debris reduction due to patterning in vacuum improves the TFT characteristics significantly. Hysteresis disappears, the mobility is enhanced by an order of magnitude and the subthreshold swing is reduced from $S_{sub}~=~2.5~\mbox{V/dec}$ to $S_{sub}~=~1.5~\mbox{V/dec}$.

physics.app-ph↗