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arXiv2019

Common Source of Light Emission and Nonlocal Molecular Manipulation on the Si(111)-7x7 Surface

The tip of a scanning tunnelling microscope can inject hot electrons into a surface with atomic precision. Their subsequent dynamics and eventual decay can result in atomic manipulation of an adsorbed molecule, or in light emission from the surface. Here, we combine the results of these two near identical experimental techniques for the system of toluene molecules chemisorbed on the Si(111)-7x7 surface at room temperature. The radial dependence of molecular desorption away from the tip injection site conforms to a two-step ballistic-diffusive transport of the injected hot electrons across the surface, with a threshold bias voltage of +2.0 V. We find the same threshold voltage of +2.0 V for light emission from the bare Si(111)-7x7 surface. Comparing these results with previous published spectra we propose that both the manipulation and the light emission follow the same hot electron dynamics, only differing in the outcome of the final relaxation step which may result in either molecular manipulation, or photon emission.

physics.chem-ph↗

arXiv2019

Ultrasensitive charge detection utilizing coupled nonlinear micromechanical resonators

Since the discovery of electrons, an accurate detection of electrical charges has been the dream of scientific community. Due to some remarkable advantages, micro/nano-electromechanical systems (M/NEMS) based resonators have been used to design electrometers with exquisite sensitivity and resolution. Inevitably, some limits including requisite ultra-low environmental temperature, complicated resonator structure and measurement circuit, required linear dynamic response, will cause a gap with respect to practical application. Here, we demonstrate a novel ultra-sensitive charge detection based on the linear dependence of peak frequency drift on the coupling voltage variation of two coupled nonlinear micromechanical resonators. We achieved ultra-high resolution of 2.051E-3 fC (about 13 electrons) of charge detection at the room temperature. We also show an extra application of this device for weak and ultra-low-frequency (ULF) signal detection. Our findings provide a simple strategy for measuring electron charges in an extreme accuracy and developing electrometers in smaller sizes.

cond-mat.mes-hall↗

arXiv2019

Dynamic multi-focus laser writing with acousto-optofluidics

Laser writing of materials is normally performed by the sequential scanning of a single focused beam across a sample. This process is time-consuming and it can severely limit the throughput of laser systems in key applications such as surgery, microelectronics, or manufacturing. Here we report a parallelization strategy based on ultrasound waves in a liquid to diffract light into multiple beamlets. Adjusting amplitude, frequency, or phase of ultrasound allows tunable multi-focus distributions with sub-microsecond control. When combined with sample translation, the dynamic splitting of light leads to high-throughput laser processing, as demonstrated by locally modifying the morphological and wettability properties of metals, polymers, and ceramics. The results illustrate how acousto-optofluidic systems are universal tools for fast multi-focus generation, with potential impact in fields such as imaging or optical trapping.

physics.app-ph↗

arXiv2019

Application Usability Levels: A Framework for Tracking Project Product Progress

The space physics community continues to grow and become both more interdisciplinary and more intertwined with commercial and government operations. This has created a need for a framework to easily identify what projects can be used for specific applications and how close the tool is to routine autonomous or on-demand implementation and operation. We propose the Application Usability Level (AUL) framework and publicizing AULs to help the community quantify the progress of successful applications, metrics, and validation efforts. This framework will also aid the scientific community by supplying the type of information needed to build off of previously published work and publicizing the applications and requirements needed by the user communities. In this paper, we define the AUL framework, outline the milestones required for progression to higher AULs, and provide example projects utilizing the AUL framework. This work has been completed as part of the activities of the Assessment of Understanding and Quantifying Progress working group which is part of the International Forum for Space Weather Capabilities Assessment.

astro-ph.IM↗

arXiv2019

Hardware Constraints in Compressive Sensing Based Antenna Array

New constraints based on practical hardware are introduced in compressive sensing (CS) based rectangular antenna array thinning technique. In a standard CS array sparsity enforcement, antenna elements are considered as ideal point sources which do not comply with the practical hardware. It also does not consider the impact of mutual coupling of neighbouring antenna elements on the impedance mismatch. In this work, we propose a combination of constraints based on physical antenna array specifications, mutual coupling and practical antenna element radiation performance in the CS-based array thinning enforcement. Analytical modelling along with a design example is presented and discussed. Array performance based on full-wave electromagnetic simulations shows the reliability of the proposed approach.

eess.SP↗

arXiv2019

A Time Domain Coupled Electronic-Optical Simulation Model for GaN-based LEDs

In this paper, we present a coupled carrier-photon model that accounts for the time-domain interactions between carrier transport and light emission in Gallium Nitride (GaN)-based LEDs that hasn't been reported so far. Carrier transport is modeled using the drift-Diffusion formulation, whereas light emission and propagation is modeled using Maxwell's equations. The drift Diffusion equation is solved self-consistently with Poisson equation. The carrier transport and photon emission are coupled by formulating an appropriate relation between radiative recombinations and dipole sources such that the strength of the dipole sources is given by the radiative recombination rates gauged to an appropriate value. This gauging factor is obtained by calibrating the External Quantum Efficiency (EQE) of homojunction GaN LED with the experimental value.

physics.app-ph↗

arXiv2019

Evaluation of the mechanical behaviour of tufted preforms

The weak properties in the thickness of the laminates in terms of rigidity, fatigue and impact resistance involve delamination sensitivity for thick structures. This issue has led to the development of three-dimensional (3D) preforms with reinforcement through-the-thickness, making it possible to combine good mechanical performance in-plane and out-of-plane. In this study, the tufting technology is used to strength through-the-thickness of stacked layers. This reinforcement technique has extensively gained attention in the composite industry due to its ability to reinforce thick pieces. The present study focuses on the mechanical behaviour of tufted preforms before resin impregnation due to their application in the forming steps during the manufacturing process. Therefore, an experimental investigation of the mechanical behaviour (tensile, bending and in-plane shear) was carried out in order to outline the influence of tufting on the mechanical properties of the final structure.

physics.app-ph↗

arXiv2019

Modeling and Simulation of Curved Fibers in Dry Spinning Scenarios

Dry spinning is characterized by the simultaneous production of multiple thin polymeric fibers in airflows and the evaporation of the solvent contained in these fibers. This involves fiber-air interactions as well as radial diffusion effects over the fiber cross-sections. Recent models for fibers in such production processes assume the fiber curves to be strictly uni-axial. But there are industrial setups showing airflow induced lateral movements of the fibers which creates the need for curved fiber models. In this paper we present a special Cosserat rod model that describes curved fibers in such dry spinning processes. Adapting the efficient simulation framework from the uni-axial fiber setting makes the simulation of industrial setups for multiple curved fibers with two-way coupled airflows possible, for which we present results for the first time in literature.

physics.app-ph↗

arXiv2019

Graded metasurface for enhanced sensing and energy harvesting

In elastic wave systems, combining the powerful concepts of resonance and spatial grading within structured surface arrays enable resonant metasurfaces to exhibit broadband wave focusing, mode conversion from surface (Rayleigh) waves to bulk (shear) waves, and spatial frequency selection. Devices built around these concepts allow for precise control of surface waves, often with structures that are subwavelength, and utilise rainbow trapping that separates the signal spatially by frequency. Rainbow trapping yields large amplifications of displacement at the resonator positions where each frequency component accumulates. We investigate whether this amplification, and the associated control, can be used to create energy harvesting devices; the potential advantages and disadvantages of using graded resonant devices as energy harvesters is considered. We concentrate upon elastic plate models for which the A0 mode dominates, and take advantage of the large displacement amplitudes in graded resonant arrays of rods, to design innovative metasurfaces that focus waves for enhanced piezoelectric sensing and energy harvesting. Numerical simulation allows us to identify the advantages of such graded metasurface devices and quantify its efficiency, we also develop accurate models of the phenomena and extend our analysis to that of an elastic half-space and Rayleigh surface waves.

physics.class-ph↗

arXiv2019

Distributed Quantum Fiber Magnetometry

Nitrogen-vacancy (NV) quantum magnetometers offer exceptional sensitivity and long-term stability. However, their use to date in distributed sensing applications, including remote detection of ferrous metals, geophysics, and biosensing, has been limited due to the need to combine optical, RF, and magnetic excitations into a single system. Existing approaches have yielded localized devices but not distributed capabilities. In this study, we report on a continuous system-in-a-fiber architecture that enables distributed magnetic sensing over extended lengths. Key to this realization is a thermally drawn fiber that has hundreds of embedded photodiodes connected in parallel and a hollow optical waveguide that contains a fluid with NV diamonds. This fiber is placed in a larger coaxial cable to deliver the required RF excitation. We realize this distributed quantum sensor in a water-immersible 90-meter-long cable with 102 detection sites. A sensitivity of 63 nT Hz-1/2 per site, limited by laser shot noise, was established along a 90 m test section. This fiber architecture opens new possibilities as a robust and scalable platform for distributed quantum sensing technologies.

physics.app-ph↗

arXiv2019

Complete inclusion of bioactive molecules and particles in polydime-thylsiloxane: a straightforward process under mild conditions

By applying a slow curing process, we show that biomolecules can be incorporated via a simple process as liquid stable phases inside a polydimethylsiloxane (PDMS) matrix. The process is carried out under mild conditions with regards to temperature, pH and relative humidity, and is thus suitable for application to biological entities. Fluorescence and enzymatic activity measurements, show that the biochemical properties of the proteins and enzyme tested are preserved, without loss due to adsorption at the liquid-polymer interface. Protected from external stimuli by the PDMS matrix, these soft liquid composite materials are new tools of interest for robotics, microfluidics, diagnostics and chemical microreactors.

physics.app-ph↗

arXiv2019

Wireless and Batteryless Surface Acoustic Wave Sensors for High Temperature Environments

Surface acoustic wave (SAW) devices are widely used as filter, resonator or delay line in electronic systems in a wide range of applications: mobile communication, TVs, radar, stable resonator for clock generation, etc. The resonance frequency and the delay line of SAW devices are depending on the properties of materials forming the device and could be very sensitive to the physical parameters of the environment. Since SAW devices are more and more used as sensor for a large variety of area: gas, pressure, force, temperature, strain, radiation, etc. The sensors based SAW present the advantage to be passive (batteryless) and/or wireless. These interesting properties combined with a small size, a low cost radio request system and a small antennas when operating at high frequency, offer new and exiting perspectives for wireless measurement processes and IDTAG applications. When the materials constituting the devices are properly selected, it becomes possible to use those sensors without embedded electronic in hostile environments (as high temperature, nuclear site, ...) where no solutions are currently used. General principle of the SAW sensor in wired and wireless configurations will be developed and a review of recent works concerning the field of high temperature applications will be presented with specific attention given to the choice of materials constituting the SAW device.

physics.app-ph↗

arXiv2019

A Study on the Multi-axial Fatigue Failure Behavior of Notched Composite Laminates

Composite structures must endure a great variety of multi-axial stress states during their lifespan while guaranteeing their structural integrity and functional performance. Understanding the fatigue behavior of these materials, especially in the presence of notches that are ubiquitous in structural design, lies at the hearth of this study which presents a comprehensive investigation of the fracturing behavior of notched quasi-isotropic [+45/90/$-$45/0]$_{s}$ and cross-ply [0/90]$_{2s}$ laminates under multi-axial quasi-static and fatigue loading. The investigation of the S-N curves and stiffness degradation, and the analysis of the damage mechanisms via micro-computed tomography clarified the effects of the multi-axiality ratio and the notch configuration. Furthermore, it allowed to conclude that damage progression under fatigue loading can be substantially different compared to the quasi-static case. Future efforts in the formulation of efficient fatigue models will need to account for the transition in damaging behavior in the context of the type of applied load, the evolution of the local multi-axiality ratio, the structure size and geometry, and stacking sequence. By providing important data for model calibration and validation, this study represents a first step towards this important goal.

physics.app-ph↗

arXiv2019

Flexible perovskite/Cu(In,Ga)Se2 monolithic tandem solar cells

We report a proof-of-concept two-terminal perovskite/Cu(In, Ga)Se2 (CIGS) monolithic thin-film tandem solar cell grown on ultra-thin (30-microns thick), light-weight, and flexible polyimide foil with a steady-state power conversion efficiency of 13.2% and a high open-circuit voltage over 1.75 V under standard test condition.

physics.app-ph↗

arXiv2019

Thermal characterization of convective heat transfer in microwires based on modified steady state "hot wire" method

The convection plays a very important role in heat transfer when MEMS work under air environment. However, traditional measurements of convection heat transfer coefficient require the knowledge of thermal conductivity, which makes measurements complex. In this work, a modified steady state "hot wire" (MSSHW) method is proposed, which can measure the heat transfer coefficient of microwires' convection without the knowledge of thermal conductivity. To verify MSSHW method, the convection heat transfer coefficient of platinum microwires was measured in the atmosphere, whose value is in good agreement with values by both traditional measurement methods and empirical equations. Then, the convection heat transfer coefficient of microwires with different materials and diameters were measured by MSSHW. It is found that the convection heat transfer coefficient of microwire is not sensitive on materials, while it increases from 86 W/(m$^2$K) to 427 W/(m$^2$K) with the diameter of microwires decreasing from 120 $μ$m to 20 $μ$m. Without knowing thermal conductivity of microwires, the MSSHW method provides a more convenient way to measure the convective effect.

physics.app-ph↗

arXiv2019

Functionalization of Single-walled Carbon Nanotubes with Bis-astraphloxin

This dissertation aims to demonstrate that photoluminescence spectroscopy could be an efficient technique of functionalized carbon nanotube detection and imaging. The advances in nanotechnology and the potential growth in carbon nanotubes production, in which if control mechanisms not in place for safely disposing off nanotubes, these nanotubes could pose as an environmental pollutant, due to the severe, persistent and bio-accumulative nature of these compounds. Therefore, the need for this scientific research is timely in case of some technological disaster. Besides, the study on interaction of carbon nanotubes with various organic materials provide a new knowledge and opportunities for potential application of the nanotubes.

physics.app-ph↗

arXiv2019

Robust quantitative single-exposure laser speckle imaging with true flow speckle contrast in the temporal and spatial domains

A systematic and robust laser speckle contrast imaging (LSCI) method and procedure is presented, covering the LSCI system calibration, static scattering removal, and measurement noise estimation and correction to obtain a true flow speckle contrast and the flow speed from single-exposure LSCI measurements. We advocate to use as the speckle contrast instead of the conventional contrast K as the former relates simply to the flow velocity and is with additive noise alone. We demonstrate the efficacy of the proposed true flow speckle contrast by imaging phantom flow at varying speeds, showing that (1) the proposed recipe greatly enhances the linear sensitivity of the flow index (inverse decorrelation time) and the linearity covers the full span of flow speeds from 0 mm/s to 40 mm/s; and (2) the true flow speed can be recovered regardless of the overlying static scattering layers and the type of speckle statistics (temporal or spatial). The fundamental difference between the apparent temporal and spatial speckle contrasts is further revealed. The flow index recovered in the spatial domain is much more susceptible to static scattering and exhibit a shorter linearity range than that obtained in the temporal domain. The proposed LSCI analysis framework paves the way to estimate the true flow speed in the wide array of laser speckle contrast imaging applications.

physics.app-ph↗

arXiv2019

Coupling-enhanced Dual ITO Layer Electro-absorption Modulator in Silicon Photonics

Electro-optic signal modulation provides a key functionality in modern technology and information networks. Photonic integration has enabled not only miniaturizing photonic components, but also provided performance improvements due to co-design addressing both electrical and optical device rules. However, the millimeter-to-centimeter large footprint of many foundry-ready photonic electro-optic modulators significantly limits on-chip scaling density. To address these limitations, here we experimentally demonstrate a coupling-enhanced electro-absorption modulator by heterogeneously integrating a novel dual-gated indium-tin-oxide (ITO) phase-shifting tunable absorber placed at a silicon directional coupler region. Our experimental modulator shows a 2 dB extinction ratio for a just 4 um short device at 4 volt bias. Since no material nor optical resonances are deployed, this device shows spectrally broadband operation as demonstrated here across the entire C-band. In conclusion we demonstrate a modulator utilizing strong index-change from both real and imaginary part of active material enabling compact and high-performing modulators using semiconductor foundry-near materials.

physics.app-ph↗