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Hybrid Nanofluids: An Overview of their Synthesis and Thermophysical properties

A recent area of interest in thermal applications has been nanofluids, with extensive research conducted in the field, and numerous publications expounding on new results coming to the fore. The properties of such fluids depend on their components, and by the use of combined and complex nanoparticles with diverse characteristics, the desirable qualities of multiple nanoparticle suspensions can be obtained in a single mixture. The paper covers these hybrid nanofluids, the techniques for their synthesis, their properties, characteristics, and the areas of debate and outstanding questions.

physics.app-ph↗

Reconfigurable On-chip Photoconductive Switches

Microwave photonics uses light to carry and process microwave signals over a photonic link. However, light can instead be used as a stimulus to microwave devices that directly control microwave signals. Such optically controlled amplitude and phase-shift switches are investigated for use in reconfigurable microwave systems, but they suffer from large footprint, high optical power level required for switching, lack of scalability and complex integration requirements, restricting their implementation in practical microwave systems. Here, we report Monolithic Optically Reconfigurable Integrated Microwave Switches (MORIMSs) built on a CMOS compatible silicon photonic chip that addresses all of the stringent requirements. Our scalable micrometer-scale switches provide higher switching efficiency and require optical power orders of magnitude lower than the state-of-the-art. Also, it opens a new research direction on silicon photonic platforms integrating microwave circuitry. This work has important implications in reconfigurable microwave and millimeter wave devices for future communication networks.

eess.SP↗

Catalyst-Free And Morphology-Controlled Growth Of 2D Perovskite Nanowires for Polarized Light Detection

Two-dimensional (2D) perovskites or Ruddleson Popper (RP) perovskites have emerged as a class of material inheriting the superior optoelectronic properties of two different materials: perovskites and 2D materials. The large exciton binding energy and natural quantum well structure of 2D perovskite not only make these materials ideal platforms to study light-matter interactions, but also render them suitable for fabrication of various functional optoelectronic devices. Nanoscale structuring and morphology control have led to semiconductors with enhanced functionalities. For example, nanowires of semiconducting materials have been extensively used for important applications like lasing and sensing. Catalyst-assisted Vapor Liquid Solid (VLS) techniques, and template assisted growth, have conventionally been used for nanowire growth. However, catalyst and template-free scalable growth with morphology control of 2D perovskites have remained elusive. In this manuscript, we demonstrate a facile approach for morphology-controlled growth of high-quality nanowires of 2D perovskite, (BA)2PbI4. We demonstrate that the photoluminescence (PL) from the nanowires are highly polarized with a polarization ratio as large as ~ 0.73, which is one of the largest reported for perovskites. We further show that the photocurrent from the device based on the nanowire/graphene heterostructure is also sensitive to the polarization of the incident light with the photocurrent anisotropy ratio of ~3.62 (much larger than the previously reported best value of 2.68 for perovskite nanowires), thus demonstrating the potential of these nanowires as highly efficient photodetectors of polarized light.

physics.app-ph↗

Alternating strain regimes for failure propagation in flexural systems

We consider both analytical and numerical studies of a steady-state fracture process inside a discrete mass-beam structure, composed of periodically placed masses connected by Euler-Bernoulli beams. A fault inside the structure is assumed to propagate with a constant speed and this occurs as a result of the action of a remote sinusoidal, mechanical load. The established regime of fracture corresponds to the case of an alternating generalised strain regime. The model is reduced to a Wiener-Hopf equation and its solution is presented. We determine the minimum feeding wave energy required for the steady-state fracture process to occur. In addition, we identify the dynamic features of the structure during the steady-state fracture regime. A transient analysis of this problem is also presented, where the existence of steady-state fracture regimes, revealed by the analytical model, are verified and the associated transient features of this process are discussed.

physics.app-ph↗

A tunable ferroelectric based unreleased RF resonator

This paper introduces the first tunable ferroelectric capacitor (FeCAP) based unreleased RF MEMS resonator, integrated seamlessly in Texas Instruments' 130nm Ferroelectric RAM (FeRAM) technology. An array of FeCAPs in this complementary metal-oxide-semiconductor (CMOS) technology's back-end-of-line (BEOL) process were used to define the acoustic resonance cavity as well as the electromechanical transducers. To achieve high quality factor (Q) of the resonator, acoustic waveguiding for vertical confinement within the CMOS stack is studied and optimized. Additional design considerations are discussed to obtain lateral confinement and suppression of spurious modes. An FeCAP resonator is demonstrated with fundamental resonance at 703 MHz and Q of 1012. This gives a frequency quality factor product fQ = 7.11$\times$10$^1$$^1$ which is 1.6$\times$ higher than the most state-of-the-art Pb(Zr,Ti)O$_3$ (PZT) resonators. Due to the ferroelectric characteristics of the FeCAPs, transduction of the resonator can be switched on and off by adjusting the electric polarization. In this case, the resonance can be turned off completely at $\pm$0.3V corresponding to the coercive voltage of the constituent FeCAP transducers. These novel switchable resonators may have promising applications in on-chip timing, ad-hoc radio front ends, and chip-scale sensors.

physics.app-ph↗

A pseudo-capacitive chalcogenide-based electrode with dense 1-dimensional nanoarrays for enhanced energy density in asymmetric supercapacitors

To achieve the further development of supercapacitors (SCs), which have intensively received attention as a next-generation energy storage system, the rational design of active electrode materials with electrochemically more favorable structure is one of the most important factors to improve the SC performance with high specific energy and power density. We propose and successfully grow copper sulfide (CuS) nanowires (NWs) as a chalcogenide-based electrode material directly on a Cu mesh current collector using the combination of a facile liquid-solid chemical oxidation process and an anion exchange reaction. We found that the as-prepared CuS NWs have well-arrayed structures with nanosized crystal grains, a high aspect ratio and density, as well as a good mechanical and electrical contact to the Cu mesh. The obtained CuS NW based electrodes, with additional binder- and conductive material-free, exhibit a much higher areal capacitance of 378.0 mF/cm2 and excellent cyclability of an approximately 90.2 percentage retention during 2000 charge/discharge cycles due to their unique structural, electrical, and electrochemical properties. Furthermore, for practical SC applications, an asymmetric supercapacitor is fabricated using active carbon as an anode and CuS NWs as a cathode, and exhibits the good capacitance retention of 91% during 2000 charge/discharge processes and the excellent volumetric energy density of 1.11 mW h/cm3 compared to other reported pseudo-capacitive SCs.

physics.app-ph↗

Nb$_x$Ti$_{1-x}$N low timing jitter single-photon detectors with unity internal efficiency at 1550 nm and 2.5 K

The requirements in quantum optics experiments for high single photon detection efficiency, low timing jitter, low dark count rate and short dead time have been fulfilled with the development of superconducting nanowire single photon detectors. Although they offer a detection efficiency above 90%, achieving a high time resolution in devices made of amorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices made from niobium nitride and niobium titanium nitride allow to reach the best timing jitter, but in turn have stronger requirements in terms of film quality to achieve a high efficiency. Here we take advantage of the flexibility of reactive co-sputter deposition to tailor the composition of NbxTi1-xN superconducting films, and show that a Nb fraction of x = 0.62 allows for the fabrication of detectors from films as thick as 9 nm and covering an active area of 20 μm, with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm. This is a signature of an internal detection efficiency saturation, achieved while maintaining the high time resolution associated with NbTiN and operation at 2.5K. With our optimized recipe, we reliably fabricated detectors with high critical current densities reaching a saturation plateau at 1550 nm with 80% system detection efficiency, and with a FWHM timing jitter as low as 19.47 ps.

physics.ins-det↗

On the Wave Turbulence Theory for the Nonlinear Schrödinger Equation with Random Potentials

We derive a new kinetic and a porous medium equations from the nonlinear Schrödinger equation with random potentials. The kinetic equation has a very similar form with the 4-wave turbulence kinetic equation in the wave turbulence theory. Moreover, we construct a class of self-similar solutions for the porous medium equation. These solutions spread infinitely as time goes to infinity and this fact answers the 'weak turbulence' question for the nonlinear Schrödinger equation with random potentials positively. We also derive Ohm's law for the porous medium equation.

math-ph↗

Tuning the work function of graphene toward application as anode and cathode

The rapid technological progress in the 21st century demands new multi-functional materials applicable to a wide variety of industries. Two-dimensional (2D) materials are predicted to have a revolutionary impact on the cost, size, weight, and functions of future electronic and optoelectronic devices. Graphene, which shows potential as an alternative to conventional conductive transparent metal oxides, may play a central role. Since its work function (WF) is tunable, graphene exhibits the interesting ability to serve two different roles in electronic and optoelectronic devices, both as an anode and a cathode. After introducing some basic concepts, this work reviews the most important advances in controlling the tuned WF of graphene, highlighting special features of graphene electronic band structure and recognizing different methods for measuring WF. The impact of thickness, type of contact, chemical doping, UV and plasma treatments, defects, and functional groups of graphene oxide are considered and related with the applications of the modulated material. The results of the review, organized in lookup tables, have been used to identify the advantages and main challenges of the tuning methods.

physics.app-ph↗

A multi-physics methodology for four-states of matter

We propose a numerical methodology for the simultaneous numerical simulation of four states of matter; gas, liquid, elastoplastic solids and plasma. The distinct, interacting physical processes are described by a combination of compressible, inert and reactive forms of the Euler equations, multiphase equations, elastoplastic equations and resistive MHD equations. Combinations of systems of equations are usually solved by coupling finite element for solid modelling and CFD models for fluid modelling or including material effects through boundary conditions rather than full material discretisation. Our simultaneous solution methodology lies on the recasting of all the equations in the same, hyperbolic form allowing their solution on the same grid with the same finite-volume numerical schemes. We use a combination of sharp and diffuse interface methods to track or capture material interfaces, depending on the application. The communication between the distinct systems of equations (i.e., materials separated by sharp interfaces) is facilitated by means of mixed-material Riemann solvers at the boundaries of the systems, which represent physical material boundaries. To this end we derive approximate mixed Riemann solvers for each pair of the above models based on characteristic equations. To demonstrate the applicability of the new methodology we consider a case study where we investigate the possibility of ignition of a combustible gas that lies over a liquid in a metal container that is struck by a plasma-arc akin to a lightning strike. We study the effect on the ignition of the metal container material and conductivity, of the presence of a dielectric coating, of insensitive combustible gases and sealed and pre-damaged metal surfaces.

physics.comp-ph↗

An Algebraic Approach to Fast Estimation of the Threshold Voltage of Junctionless Double Gate MOSFETs Using the Gram Schmidt Method

The effect of decreasing Drain-Induced Barrier Lowering (DIBL) is one of the non-desirable short-channel effects in the MOSFETs family, which causes the threshold voltage of the transistor to be reduced by increasing the voltage of the drain. This effect makes it impossible for circuit designers to consider VT as a constant value, and hence, it is necessary to calculate VT as a function of the drain voltage. Therefore, to consider the effect of DIBL in the design of integrated circuits, a large computational burden is imposed on the system, which slows down the simulation process in circuit-level simulators, particularly when a large number of transistors are to be simulated. Accordingly, in this paper, a multiple input single output (MISO) Nonlinear Autoregressive (N-AR) model using the Gram-Schmidt orthogonalization approach is proposed, that calculates the threshold voltage of the new generation of MOSFETs, i.e., Junctionless Double-Gate MOSFETs (JL-DG-MOSFETs), with a high precision and a significant speed-up in the computational procedure of the model. It is shown that, on average, the proposed numerical method is 313 times faster than the state-of-the-art analytical model. The calculated percentage of normalized mean square error between the proposed model and analytical one is 0.435% on average, showing that the proposed approach can be a fast and accurate candidate for replacing the analytical modeling.

cs.DC↗

Kinetic studies on using photocatalytic coatings for removal of indoor volatile organic compounds

Titanium dioxide (TiO2) is a known photocatalyst with a capability of decomposing organic substance. However, the photocatalysis of the pure TiO2 is not effective for the indoor environment due to a lack of the ultraviolet irradiation inside the building. Doping TiO2 with substance such as C, N or metal can extend the threshold of the absorption spectrum to the visible spectrum region. Thus, doped-TiO2 is able to decompose volatile organic compounds (VOCs) under an indoor environment. To date, most experimental work reported on photocatalytic kinetics were conducted inside small-scale devices. The performance of air purification function under the actual indoor application scenery need to be further clarified. For this purpose, it is crucial to predict the performance of autogenous air quality improvements by visible light driven photocatalyst for the actual applications. This work has developed a model to evaluate the performance of functional coating with photocatalyst in removing VOCs. Factors such as the effects of coating designs and indoor ambient conditions on the air purification efficiency were studied. This work demonstrates that doped-TiO2 photocatalytic coating is effective to improve the indoor air quality.

physics.app-ph↗

Chemical vapor deposition of hexagonal boron nitride and its use in electronic devices

Dielectrics are insulating materials used in many different electronic devices and play an important role in all of them. Current advanced electronic devices use dielectric materials with a high dielectric constant and avoid high leakage currents. However, these materials show several intrinsic problems, and also a bad interaction with adjacent materials. Therefore, the race for finding a suitable dielectric material for current and future electronic devices is still open. In this context two dimensional [2D] materials have become a serious option, not only thanks to their advanced properties, but also to the development of scalable synthesis methods. Graphene has been the most explored 2D material for electronic devices. However, graphene has no band gap, and therefore it cannot be used as dielectric. MoS2 and other 2D transition metal dichalcogenides (TMDs) are semiconducting 2D materials that can provide more versatility in electronic devices. In this PhD thesis I have investigated the use of monolayer and multilayer hexagonal boron nitride (h-BN) as dielectric for electronic devices, as it is a 2D material with a band gap of ~5.9 eV. My work has mainly focused on the synthesis of the h-BN using chemical vapor deposition, the study of its intrinsic morphological and electrical properties at the nanoscale, and its performance as dielectric in different electronic devices, such as capacitors and memristors. Overall, our experiments indicate that h-BN is a very reliable dielectric material, and that it can be successfully used in capacitors and memristors. Moreover, h-BN shows additional performances never observed in traditional dielectrics, such as volatile resistive switching, which may also open the door for new applications.

physics.app-ph↗

Energy-Efficient Micromixing in Paper Based Devices Mediated by the Interplay of Electrical and Thermal Fields

Biomedical and biochemical processes in paper-based microfluidic devices often deal with mixing of two analytes to perform important functions. Uniform mixing of analytes in paper matrix is a challenging proposition, often necessitating complicated channel design or high energy external fields for realizing the desired functionality. In sharp contrast, here we demonstrate an energy-efficient technique compatible with handing biofluids, to achieve a high level of mixing of two fluids in paper-based microfluidic devices without deploying complex channel shapes. Our method employs a simple, cost-effective printing-based method to fabricate paper channel with interdigitated electrodes laid out using pencil sketch. An alternating current electric field of sufficiently low voltage is used to generate perturbations on the interface of the two fluids streams undertaking spontaneous capillary imbibition. The consequent variations in electric field generate local thermal gradients, leading to localized volumetric forces triggering efficient fluid mixing. Our results find a wide variety of applications ranging from biochemical analysis to medical diagnostics.

physics.app-ph↗

Reply to arXiv:1810.11506: Size Effect According to the Critical Shear Crack Theory (CSCT) for Reinforced Concrete Beams and Slabs

This document is a reply to arXiv:1810.11506. In that document, Dönmez and Bažant raise a number of criticism on the hypotheses Critical Shear Crack Theory (CSCT). The aspects criticized have however been largely discussed in previous works of the CSCT, proving the validity of the theory. This document compiles such previous knowledge as a reply to the authors of the report.

physics.app-ph↗

On-chip microwave-spin-plasmon interface (MSPI)

On-chip scalable integration represents a major challenge for practical quantum devices. One particular challenge is to implement on-chip optical readout of spins in diamond. This readout requires simultaneous application of optical and microwave fields along with an efficient collection of fluorescence. The readout is typically accomplished via bulk optics and macroscopic microwave transmission structures. We experimentally demonstrate an on-chip integrated structure for nitrogen vacancy (NV) spin-based applications, implemented in a single material layer with one patterning step. A nanodiamond with multiple NV centres is positioned at the end of the groove waveguide milled in a thick gold film. The gold film carries the microwave control signal while the groove waveguide acts as a fluorescence collector, partially filtering out the pump excitation. As a result, the device dimensions and fabrication complexity are substantially reduced. Our approach will foster further development of ultra-compact nanoscale quantum sensors and quantum information processing devices on a monolithic platform. NV centre-based nanoscale sensors are the most promising application of the developed interface.

physics.app-ph↗

A self-sensing microwire/epoxy composite optimized by dual interfaces and periodical structural integrity

Self-sensing composites performance largely relies on the sensing fillers property and interface. Our previous work demonstrates that the microwires can enable self-sensing composites but with limited damage detection capabilities. Here, we propose an optimization strategy capitalizing on dual interfaces formed between glass-coat and metallic core (inner interface) and epoxy matrix (outer interface), which can be decoupled to serve different purposes when experiencing stress; outer interfacial modification is successfully applied with inner interface condition preserved to maintain the crucial circular domain structure for better sensitivity. We found out that the damage detection capability is prescribed by periodical structural integrity parameterized by cracks number and location in the case of damaged wires; it can also be optimized by stress transfer efficiency with silane treated interface in the case of damaged matrix. The proposed self-sensing composites enabled by a properly conditioned dual-interfaces are promising for real-time monitoring in restricted and safety-critical environments.

physics.app-ph↗

Two-micron wavelength high speed photodiode with InGaAs/GaAsSb type-II multiple quantum wells absorber

Current optical communication system operating at 1.55 μm wavelength band may not be able to continually satisfy the growing demand on the data capacity within the next few years. Opening a new spectral window at around 2 μm wavelength with recently developed hollow-core photonic band gap fiber and thulium-doped fiber amplifier is a promising solution to increase the transmission capacity due to the low loss and wide bandwidth properties of these components at this wavelength. However, as a key component, the already demonstrated high speed photodetectors at 2 μm wavelength are still not comparable with those at 1.55 μm wavelength band, which chokes the feasibility of the new spectral window. In this work, we, for the first time, demonstrated a high speed uni-traveling carrier photodiode for 2 μm applications with InGaAs/GaAsSb type-II multiple quantum wells as the absorption region, which is lattice matched to InP. The device shows a 3dB bandwidth of 25 GHz at -3 V bias voltage and is, to the best of our knowledge, the fastest photodiodes among all group III-V and group IV photodetectors working in 2 μm wavelength range.

physics.app-ph↗