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At least 163 records · Page 9Linked to original sources

arXiv2018

Plasmonic sensor based on the Ebbesen effect

We present a new method for measuring low concentrations and simultaneously small volumes of fluorescent molecules based on the use of the Ebbesen effect of the extraordinary transmission (EOT) of light through an array of nano-holes. In the method the EOT effect is realized at the fluorescence wavelength of the detected molecules with a low transmission of light at the absorption wavelength. The approach allows realizing high level of the sensor sensitivity due to suppression of the inevitable parasitic luminescence of the sensor substrate. The method was demonstrated by detecting an ultra low concentration (at a level of 20 pg/ml (3 p.p.t.)) and an ultra-small volume (about 5 μl) of Cy-5 fluorescent markers in a dimethyl sulfoxide solution.

physics.app-ph↗

arXiv2018

Indium Tin Oxide/Barium Strontium Titanate THz Sensor Antenna

A Bow-Tie ITO/BST and Au/BST antennas were designed and analyzed using the finite element, Multiphysics COMSOL program. The study shows that the outputs peak at several modes and ITO antennas allow for the integration of the antenna with optoelectronic devices.

physics.app-ph↗

arXiv2018

A technology agnostic RRAM characterisation methodology protocol

The emergence of memristor technologies brings new prospects for modern electronics via enabling novel in-memory computing solutions and affordable and scalable reconfigurable hardware implementations. Several competing memristor technologies have been presented with each bearing distinct performance metrics across multi-bit memory capacity, low-power operation, endurance, retention and stability. Application needs however are constantly driving the push towards higher performance, which necessitates the introduction of standard characterisation protocols for fair benchmarking. At the same time, opportunities for innovation are missed by focusing on excessively narrow performance aspects. To that end our work presents a complete, technology agnostic, characterisation methodology based on established techniques that are adapted to memristors/RRAM characterisation needs. Our approach is designed to extract information on all aspects of device behaviour, ranging from deciphering underlying physical mechanisms to benchmarking across a variety of electrical performance metrics that can in turn support the generation of device models.

physics.app-ph↗

arXiv2018

Time-domain Brillouin Scattering as a Local Temperature Probe in Liquids

We present results of time-domain Brillouin scattering (TDBS) to determine the local temperature of liquids in contact to an optical transducer. TDBS is based on an ultrafast pump-probe technique to determine the light scattering frequency shift caused by the propagation of coherent acoustic waves in a sample. Since the temperature influences the Brillouin scattering frequency shift, the TDBS signal probes the local temperature of the liquid. Results for the extracted Brillouin scattering frequencies recorded at different liquid temperatures and at different laser powers - i.e. different steady state background temperatures- are shown to demonstrate the usefulness of TDBS as a temperature probe. This TDBS experimental scheme is a first step towards the investigation of ultrathin liquids measured by GHz ultrasonic probing.

cond-mat.soft↗

arXiv2018

Exploring rotational resonance in elastic metamaterial plates to realize doubly negative property

We report the realization of simultaneously negative effective mass density and shear modulus in a single-phase asymmetric double-sided pillared metamaterial. The negative effective mass density is achieved by the combination of bending and compressional resonances of one pillar whereas the rotational resonance of the other pillar leads to the negative effective shear modulus. The coupling between these two pillars is investigated to describe the formation of the doubly negative property. Then, a pillared system featuring chirality is designed in order to make efficient the excitation of the rotational vibration, the occurrence of which is demonstrated by the transmission spectrum. Finally, numerical simulations of the zero-index refraction are carried out to prove the occurrence of the doubly negative property.

physics.app-ph↗

arXiv2018

Mid-infrared GeSn Electro-Absorption Optical Modulators on Silicon

Mid-infrared silicon photonics has recently emerged as a new technology for a wide range of applications such as optical communication, lidar, and bio-sensing. One key component enabling this technology is the mid-infrared optical modulator used for encoding optical signals. Here, we present a GeSn electro-absorption modulator that can operate in the mid-infrared range. Importantly, this device is monolithically integrated on a silicon substrate, which provides compatibility with standard complementary metal-oxide-semiconductor technology for scalable manufacturing. By alloying Ge with Sn to engineer the bandgap, we observed a clear Franz-Keldysh effect and achieved optimal modulation in the mid-infrared range of 2067-2208 nm with a maximum absorption ratio of 1.8. The results on the Si-based mid-infrared optical modulator open a new avenue for next-generation mid-infrared silicon photonics.

physics.app-ph↗

arXiv2018

Overall constitutive description of symmetric layered media based on scattering of oblique SH waves

This papers investigates the scattering of oblique shear horizontal (SH) waves off finite periodic media made of elastic and viscoelastic layers. It further considers whether a Willis-type constitutive matrix (in temporal and spatial Fourier domain) may reproduce the scattering matrix (SM) of such a system. In answering this question the procedure to determine the relevant overall constitutive parameters for such a medium is presented. To do this, first the general form of the dispersion relation and impedances for oblique SH propagation in such coupled Willis-type media are developed. The band structure and scattering of layered media are calculated using the transfer matrix (TM) method. The dispersion relation may be derived based on the eigensolutions of an infinite periodic domain. The wave impedances associated with the exterior surfaces of a finite thickness slab are extracted from the scattering of such a system. Based on reciprocity and available symmetries of the structure and each constituent layer, the general form of the dispersion and impedances may be simplified. The overall quantities may be extracted by equating the scattering data from TM with those expected from a Willis-type medium. It becomes evident that a Willis-type coupled constitutive tensor with components that are assumed independent of wave vector is unable to reproduce all oblique scattering data. Therefore, non-unique wave vector dependent formulations are introduced, whose SM matches that of the layered media exactly. It is further shown that the dependence of the overall constitutive tensors of such systems on the wave vector is not removable even at very small frequencies and incidence angles and that analytical considerations significantly limit the potential forms of the spatially dispersive constitutive tensors.

physics.app-ph↗

arXiv2018

Electrical Parameters for Planar Transport in Graphene and 2-D Materials

Classical electrodynamics has been revisited with a view to recast the electrical parameters for planar transport in 2-dimensional (2-D) materials like graphene. In this attempt a new line integral, named transverse line integral, with extensive applications in 2-D, is defined. Since the existing divergence theorem in not applicable in 2-D, we introduced a new divergence theorem. A new definition for the in-plane flux of any 2-D vector is introduced. A new vector named electric vector potential is defined and Gauss law is modified in terms of the 2-D flux of the new vector. The new Gauss law in presence of dielectric is obtained and a new electric displacement vector is defined for the 2-D materials. The conduction and displacement current densities in 2-D are defined. Resistance and resistivity in 2-D materials are discussed. The continuity equation for planar transport is derived.

cond-mat.mes-hall↗

arXiv2018

High-temperature Ultraviolet Photodetectors: A Review

Wide bandgap semiconductors have become the most attractive materials in optoelectronics in the last decade. Their wide bandgap and intrinsic properties have advanced the development of reliable photodetectors to selectively detect short wavelengths (i.e., ultraviolet, UV) in high temperature regions (up to 300°C). The main driver for the development of high-temperature UV detection instrumentation is in-situ monitoring of hostile environments and processes found within industrial, automotive, aerospace, and energy production systems that emit UV signatures. In this review, a summary of the optical performance (in terms of photocurrent-to-dark current ratio, responsivity, quantum efficiency, and response time) and uncooled, high-temperature characterization of III-nitride, SiC, and other wide bandgap semiconductor UV photodetectors is presented.

physics.app-ph↗

arXiv2018

Fabrication of photonic nanostructures from hexagonal boron nitride

Growing interest in devices based on layered van der Waals (vdW) materials is motivating the development of new nanofabrication methods. Hexagonal boron nitride (hBN) is one of the most promising materials for studies of quantum photonics and polaritonics. Here, we report in detail on a promising nanofabrication processes used to fabricate several hBN photonic devices using a hybrid electron beam induced etching (EBIE) and reactive ion etching (RIE) technique. We highlight the shortcomings and benefits of RIE and EBIE and demonstrate the utility of the hybrid approach for the fabrication of suspended and supported device structures with nanoscale features and highly vertical sidewalls. Functionality of the fabricated devices is proven by measurements of high quality cavity optical modes (Q~1500). Our nanofabrication approach constitutes an advance towards an integrated, monolithic quantum photonics platform based on hBN and other layered vdW materials.

physics.app-ph↗

arXiv2018

Interfacial friction-induced electronic excitation mechanism for tribo-tunneling current generation

Direct-current (d.c.) electricity generation using moving Schottky contact is emerging as a new strategy for mechanical energy conversion. Here, we demonstrate the generation of d.c.tunneling current with a density of ~35 A/m2 at a metal-insulator-semiconductor (MIS) sliding system using micro-tips. The measured current densities were found to be three to four orders of magnitude higher than that observed with the conventional polymer-based triboelectric nanogenerators (TENGs). The electromotive force for the tribo-tunneling transport comes from the dynamic electronic excitation at the frictional interface rather than from the electrostatically trapped surface charges as in the case of conventional TENGs. The strong electronic excitation can give rise to a non-equilibrium interfacial charge variation. Depending on the energy distribution of the excited electrons/holes, the charge variation subsequently dissipates non-adiabatically into tunneling current and trapped surface charges, or adiabatically into heat. These fundamental results not only enhance our understanding of the triboelectric phenomenon, but also open up new paths for the development of next-generation mechanical energy harvesting and sensing techniques.

physics.app-ph↗

arXiv2018

Getting to the Bottom of Negative Capacitance FETs

In this paper, we take a fresh look at the physics and operation of Negative Capacitance FETs, and provide unambiguous feedback to the device designers by examining NC-FETs' design space for sub-60 mV/dec Subthreshold Swing (SS). Straightforward design rule is derived, for the first time, based on the capacitor network in NC-FETs. Contrary to many ongoing efforts, it is found that: 1) state-of-the-art MOSFET platforms, such as SOI, FinFET, 2D-FET etc., are not suitable for constructing small-SS NC-FETs, unless internal metal gate is introduced; 2) quantum capacitance prevents NC-FETs from achieving hysteresis-free small-SS, and low densityof-states (DOS) material can alleviate this issue, to some extent; 3) NC non-linearity can be engineered to reach a tradeoff between sub-60 SS and hysteresis; 4) it is more encouraging and practical to use NC to recycle subthreshold voltage loss in short-channel MOSFETs, and overdrive voltage (essentially a type of loss).

physics.app-ph↗

arXiv2018

Analytical and numerical modeling of capacitance voltage characteristics of organic solar cells

We report a charge based model to establish the analytical equation, describing the nature of capacitance-voltage ($C$-$V$) characteristics of organic solar cells under dark condition (or organic diodes) over a wide range of voltage, extending from deep reverse bias to well above the built-in potential. The present model enables to explain the unusual peak in $C$-$V$ characteristics of these devices, as observed experimentally by various groups. The results are further validated using self-consistent numerical simulation. Finally, we discuss the discrepancy and limitation of using Mott-Schottky relation to extract the built-in potential, doping density etc. in organic solar cells/diodes.

physics.app-ph↗

arXiv2018

Re-estimation of thermal contact resistance considering near-field thermal radiation effect

Thermal contact has always been a hot issue in many engineering fields and thermal contact resistance (TCR) is one of the important indicators weighing the heat transfer efficiency among the interfaces. In this paper, the contact heat transfer of conforming rough surfaces is theoretically re-estimated considering both the heat transfer from contact and non-contact regions. The fluctuational electrodynamics (an ab initio calculation) is adopted to calculate the thermal radiation. The contribution of contact regions is estimated by the CMY TCR model and further studied by modelling specific surfaces with corresponding surface roughness power spectrum (PSD). Several tests are presented where aluminum and amorphous alumina are mainly used in the simulations. Studies showed that there exists a significant synergy between the thermal conduction and near-field thermal radiation at the interface in a certain range of effective roughness. When the effective roughness is near to the scales of submicron, the near-field radiation effect should not be neglected even at room temperature.

physics.app-ph↗

arXiv2018

Multi-Information Source Fusion and Optimization to Realize ICME: Application to Dual Phase Materials

Integrated Computational Materials Engineering (ICME) calls for the integration of computational tools into the materials and parts development cycle, while the Materials Genome Initiative (MGI) calls for the acceleration of the materials development cycle through the combination of experiments, simulation, and data. As they stand, both ICME and MGI do not prescribe how to achieve the necessary tool integration or how to efficiently exploit the computational tools, in combination with experiments, to accelerate the development of new materials and materials systems. This paper addresses the first issue by putting forward a framework for the fusion of information that exploits correlations among sources/models and between the sources and `ground truth'. The second issue is addressed through a multi-information source optimization framework that identifies, given current knowledge, the next best information source to query and where in the input space to query it via a novel value-gradient policy. The querying decision takes into account the ability to learn correlations between information sources, the resource cost of querying an information source, and what a query is expected to provide in terms of improvement over the current state. The framework is demonstrated on the optimization of a dual-phase steel to maximize its strength-normalized strain hardening rate. The ground truth is represented by a microstructure-based finite element model while three low fidelity information sources---i.e. reduced order models---based on different homogenization assumptions---isostrain, isostress and isowork---are used to efficiently and optimally query the materials design space.

physics.app-ph↗

arXiv2018

Understanding of droplet dynamics and deposition area in electrospraying process: Modeling and experimental Approaches

Electrospraying is a widely-used technique for generating microspherical droplets in biomedical and chemical applications and considered as an effective approach for the deposition on substrate. However, studies on effects of controllable parameters on deposition area of electrosprayed droplets have not been reported yet. In this study, a simplified two-dimensional model is developed to study the dynamic process of droplets and electrosprayed area. The effects of distance between the needle tip and collector, and syringe feed rate on the size of sprayed area are quantified. Experiments have been conducted to validate the simulation results. Both modeling and experimental data demonstrate that the diameter of sprayed area increases with increased distance between the tip and collector as well as feed rate. This fundamental understanding should contribute to a wise choice of controllable parameters to achieve an efficient utilization of electrosparyed droplets or substrate for real applications.

physics.app-ph↗

arXiv2018

Crystal Hybridized Pyro-Piezoelectric Ferrofluidic Harvester

This paper investigates the usage of a hybridized Pyro-Piezo Ferrofluidic harvester to capture useful energy from ambient vibration and temperature fluctuation. Consisting of a ferrofluidic core, the proposed device utilizes pyro and piezoelectric materials to charge an integrated ultracapacitor for 'trickle' energy harvesting and usage. In particular, a wearable or implantable hybridized crystal quartz piezoelectric and PZT pyroelectric based ferrofluidic harvester is characterized under human ambient energy boundaries. The frequency associated with typical bodily movement such as walking and strenuous bodily movement such as running was determined via accelerometer and analyzed via fast fourier transform, with determined mean frequencies of 1.7 Hz for typical bodily movement and 4.3 Hz for strenuous movement. Under an optimal continuous harvestation period of ~24 hours, the CQF harvester was characterized with a energy harvestation of 7.89 MJ

physics.app-ph↗

arXiv2018

Quasi-ballistic heat conduction due to Lévy phonon flights in silicon nanowires

Future of silicon-based microelectronics relies on solving the heat dissipation problem. A solution may lie in a nanoscale phenomenon known as ballistic heat conduction, which implies heat conduction without heating the conductor. But, attempts to demonstrate this phenomenon experimentally are controversial and scarce whereas its mechanism in confined nanostructures is yet to be fully understood. Here, we experimentally demonstrate quasi-ballistic heat conduction in silicon nanowires (NWs). We show that the ballisticity is strongest in short NWs at low temperatures but weakens as the NW length or temperature is increased. Yet, even at room temperature, quasi-ballistic heat conduction remains visible in short NWs. To better understand this phenomenon, we probe directionality and lengths of phonon flights. Our experiments and simulations show that the quasi-ballistic phonon transport in NWs is the Lévy walk with short flights between the NW boundaries and long ballistic leaps along the NW.

cond-mat.mes-hall↗