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arXiv2018

Topological Regard to Graphene: Elucidating the Morphology-Strain Correlation

Graphene, dubbed as a two-dimensional material represents the topological concept of "surface" embedded in a three-dimensional space. This regard enables to employ existing theories/tools in topology to understand different properties/observations in graphene. Under the light of the long-established "Gauss's Theorema Egregium" we study wrinkled graphene, observing a peculiar correlation between morphology and strain distribution. Compressing graphene on water serves as an effectual platform to realize wrinkles; we explain the evolution of the wrinkles and the global distribution of the strain field while progressing the compression. The introduced platform in this paper offers an efficient approach to precisely control the generation and evolution of the wrinkles, transforming into a naturally occurring 3D landscape as a result of graphene buckling.

cond-mat.mes-hall↗
arXiv2018

On conditions for long-wave equivalent medium to be isotropic and on analysis of parameters indicating anisotropy of equivalent TI medium

In this paper, we consider a long-wave equivalent medium to a finely parallel-layered inhomogeneous medium, obtained using the Backus average. Following the work of Postma and Backus, we show explicitly the derivations of the conditions to obtain the equivalent isotropic medium. We demonstrate that there cannot exist a transversely isotropic (TI) equivalent medium with the coefficients $c^{\overline{\rm TI}}_{1212} \neq c^{\overline{\rm TI}}_{2323}$, $c^{\overline{\rm TI}}_{1111} = c^{\overline{\rm TI}}_{3333}$ and $c^{\overline{\rm TI}}_{1122} = c^{\overline{\rm TI}}_{1133}$. Moreover, we consider a new parameter, $φ$, indicating the anisotropy of the equivalent medium, and we show its range and properties. Subsequently, we compare $φ$ to the Thomsen parameters, emphasizing its usefulness as a supportive parameter showing the anisotropy of the equivalent medium or as an alternative parameter to $δ$. We argue with certain Berryman et al. considerations regarding the properties of the anisotropy parameters $ε$ and $δ$. Additionally, we show an alternative way---to the one mentioned by Berryman et al.---of indicating changing fluid content in layered Earth.

physics.geo-ph↗
arXiv2018

Influence of KCl and HCl on a Laser Clad FeCrAl Alloy: In-Situ SEM and Controlled Environment High Temperature Corrosion

Increasing pressure on the power industry to reduce carbon emissions has led to increased research into the use of biomass feedstocks. This work investigates the effects of HCl and KCl, key species influencing biomass boiler corrosion, on a laser clad coating of the FeCrAl alloy Kanthal APMT. In-Situ SEM exposure of the coating at 450 oC for 1 h was performed to investigate the initial effects of KCl on the corrosion process. The same coatings were exposed to 250 h exposures in both an air environment and a HCl rich environment. The influence of KCl was investigated in both. Evidence of a slow growing aluminium oxide was observed. It was found that HCl allowed chlorine based corrosion to occur suggesting it can interact from the gas phase. It was also observed that the presence of both HCl and KCl reduced the mass gain compared to KCl in an air environment.

physics.app-ph↗
arXiv2018

Analysis and design of a SiGe-HBT based terahertz detector for imaging arrays applications

In this paper, we will introduce a new designed direct conversion terahertz detector and we will compare its characteristics with a prefabricated design in order to obtain better performance of our new proposed design. Differences between our new work and prefabricated device are in both physical structure by introducing an exponentially graded base SiGe-HBT instead of linearly graded ones, and configuration of components by means of merging two transistor of the initial common base structure into a single transistor with two base contacts, which equivalent to two transistors in common emitter configuration. New proposed detector, at first will be analyzed with a compact circuit model and then for more accurate analysis, two dimensional carrier transport analysis will be performed with numerical methods. Comparison of new and prefabricated detector will be done by simulation of both new and prefabricated devices with the same simulator. Because of only a slight change in transistor physical structure, if our simulation results and previous empirical data have a good matching for prefabricated device then with a high degree of precision we can claim our comparison is verified, but of course, for better confirmation of our ideas, fabrication and experimental measurements should be done in the next steps. Responsivity and minimum noise equivalent power of new detector are about 4.9A/W and 6.5pW/Hz1/2 respectively, while these characteristics for prefabricated detector, are about 1A/W and 50pW/Hz1/2 respectively. Also about 231uW/pixel decrement in power consumption for the same responsivity, and a same bandwidth have been achieved.

physics.app-ph↗
arXiv2018

Thermal noise in complex systems

We present a method to calculate the power spectral density of Brownian noise in complex optomechanical systems using Levin's approach of virtual pressure and present first mechanical loss measurements for high-purity GaAs over a wide temperature range from 7 K to 250 K. The loss reveals three Debye loss peaks. Each peak corresponds to an Arrhenius-like relaxation process with activation energies of 17.9 meV, 65.4 meV and 123 meV respectively. Additional light induced damping was observed for photon energies below and above the fundamental gap of GaAs in contrast to observations by Okamoto et al.

physics.app-ph↗
arXiv2018

Silver plasmonic density tuned polarity switching and anomalous behaviour of high performance self-powered \b{eta}-gallium oxide solar-blind photodetector

Deep understanding of plasmonic nanoparticles (PNPs)-light interaction over semiconductors surface shows great promises in enhancing their optoelectronic devices efficiency beyond the conventional limit. However, PNP-light interaction critically decided by the distribution density of PNPs over the semiconductor surface which is not entirely understood. Here, a systematic study depicting how the interparticle gap between Silver (Ag) NPs influences the performance of the \b{eta}-Ga2O3 based solar-blind photodetector. Interestingly, a remarkable transition is observed, where the varied interparticle gap not only changes the polarity but also reverses the traditional photodetector behaviour. The positive transient response of bare \b{eta}-Ga2O3 photodetector with feeble DUV light switches its behaviour remarkably to 20 times enhance negative-photoresponse when decorated by sparsely-spaced Ag-PNPs with ultra-high responsivity of 107.47 A/W at moderate power and an incredible report-highest responsivity of 4.29 mA/W on single semiconducting \b{eta}-Ga2O3 layer at self-powered mode. Moreover, as the density of the Ag-PNPs was further increased, the photocurrent decreases with illumination which dynamically reverses the traditional photodetector to unnatural anomalous effect. In particular, our study represents the first demonstration of plasmonic tuning effect to two active dynamic switching modes; i.e. reverse switchable and anomalous behaviour, the fundamentals of which have not studied experimentally yet. Finally, we propose a unified well-explained model to rationalize all observed experimental trends while set-up fundamental basis for establishing potential applications.

physics.app-ph↗
arXiv2018

Diffraction limited centimeter scale radiator: metasurface grating antenna for phased array LiDAR

In this paper, we demonstrate a radiation-strength-chirped metasurface centimeter-long grating antenna, whose beam quality is approaching the diffraction limit in its footprint with 90 percent efficiency.Instead of chirping the duty cycle to tune radiation strength, which calls for non-scalable fabrication resolution, we design a 2D fish-bone surface grating with apodized width of the bone.The meta surface is made by silicon nitride on top of silicon waveguide to weakly perturb the mode. Moreover, a Monte Carlo Markov Chain(MCMC) algorithm is implemented to design the radiation strength profile, making the optimized trade off between efficiency, beam quality and fabrication challenge. A metal mirror is designed to deposit on the top of the cladding for unidirectional upside-down radiation and uniform lateral gain. For the 1cm grating, our design is for a 0.01 degree beam with 37000 1D directional gain and 90% efficiency, with 200nm feature size. Finally, we fabricated the antenna and measured the beam quality with Fourier imaging system, which gives result of 0.02 degree -10dB beam divergence. To the best of our knowledge, this is the state-of-the-art on-chip antenna with CMOS- foundry-compatible technology.

physics.app-ph↗
arXiv2018

Fractal-Based Electrolytic Capacitor Electrodes: Scaling Behavior with Respect to Fractal Order and Complexity

In past decades, the application of fractals to electrode design for enhanced signaling and electrochemical performance was a popular subject and enabled the growth of consumer micro-electronics. Supercapacitors, which are energy storage devices with many promising characteristics, have largely grown alongside of such developments in electronics, but little work has been done to use fractal electrodes in supercapacitors. In this work, plane-filling and fractal patterns were used in designing laser scribed graphene supercapacitor electrodes, allowing the scaling laws of capacitance with respect to fractal order and complexity to be examined for the first time. An interesting exponential relationship between capacitance and fractal order for the more open structured fractals was observed, the exponent of which was proportional to the Hausdorff dimension. Additional non-linear relationships between capacitance and order were observed for other structures which was correlated with inter-plate repulsion and differences in path length. These findings provide the first step in maximizing the efficiency of fractal-based electrolytic devices by exploring the non-intuitive trends in capacitance with respect to fractal order and complexity.

physics.app-ph↗
arXiv2018

Pulsed Schlieren Imaging of Ultrasonic Haptics and Levitation using Phased Arrays

Ultrasonic acoustic fields have recently been used to generate haptic effects on the human skin as well as to levitate small sub-wavelength size particles. Schlieren imaging and background-oriented schlieren techniques can be used for acoustic wave pattern and beam shape visualization. These techniques exploit variations in the refractive index of a propagation medium by applying refractive optics or cross-correlation algorithms of photographs of illuminated background patterns. Here both background-oriented and traditional schlieren systems are used to visualize the regions of the acoustic power involved in creating dynamic haptic sensations and dynamic levitation traps. We demonstrate for the first time the application of back-ground-oriented schlieren for imaging ultrasonic fields in air. We detail our imaging apparatus and present improved algorithms used to visualize these phenomena that we have produced using multiple phased arrays. Moreover, to improve imaging, we leverage an electronically controlled, high-output LED which is pulsed in synchrony with the ultrasonic carrier frequency.

physics.med-ph↗
arXiv2018

Design and simulation of 1.28 Tbps dense wavelength division multiplex system suitable for long haul backbone

Wavelength division multiplex (WDM) system with on / off keying (OOK) modulation and direct detection (DD) is generally simple to implement, less expensive and energy efficient. The determination of the possible design capacity limit, in terms of the bit rate-distance product in WDM-OOK-DD systems is therefore crucial, considering transmitter / receiver simplicity, as well as energy and cost efficiency. A 32-channel wavelength division multiplex system is designed and simulated over 1000 km fiber length using Optsim commercial simulation software. The standard channel spacing of 0.4 nm was used in the C-band range from 1.5436-1.556 nm. Each channel used the simple non return to zero - on / off keying (NRZ-OOK) modulation format to modulate a continuous wave (CW) laser source at 40 Gbps using an external modulator, while the receiver uses a DD scheme. It is proposed that the design will be suitable for long haul mobile backbone in a national network, since up to 1.28 Tbps data rates can be transmitted over 1000 km. A bit rate-length product of 1.28 Pbps.km was obtained as the optimum capacity limit in 32 channel dispersion managed WDM-OOK-DD system.

eess.SP↗
arXiv2018

Synchrotron radiation based photoemission studies of indium oxide passivation of ZnO(0001) surface at high temperature

Passivation of surface reactive ZnO(0001)-Zn terminated surface is carried out by in-situ deposition of indium metal and post deposition annealing at high temperature (600 C - 1000 C). After the every cycle of indium deposition and annealing the ZnO(0001) surface is characterised by synchrotron radiation based photoemission. The photoemission studies confirmed the formation of deposited indium turned into indium oxide (In2O3 and In2Ox) as surface passivation layer. The core level spectra for Zn, C, O, were acquired at different photon energy for high surface sensitivity. Overall core level peaks (Zn 3p, In 4d, O 1s) having average binding shift ranging from 0.5 eV to 0.8 eV. The valance band spectra shows fermi level shift of 0.9 eV after passivation at 1000 C and work function raises form 4.06 eV to 4.77 eV. Downward band bending of ZnO(0001) surface is turned into upward bending of 0.98 eV by indium oxide passivation at high temperature, which is suitable for making ZnO schotty contact and devices.

cond-mat.mtrl-sci↗
arXiv2018

Carboxyl Carbon Quantum Dots: a Novel Type of Environmental-Friendly Scale Inhibitor

In this work, we demonstrate high inhibition efficiency of carboxyl carbon quantum dots (CCQDs) for the first time. The as-prepared CCQDs have excellent scale inhibition performance for calcium sulfate and barium sulfate. With static test of scale inhibition within temperature below 80 degrees, the anti-scaling efficiency can reach 100 % with low additions of CCQDs.

physics.app-ph↗
arXiv2018

Sodium-Ion-Conducting Polymer Nanocomposite Electrolyte of TiO2/PEO/PAN Complexed with NaPF6

A free standing transparent film of solid state polymer electrolyte based on PEO/PAN + NaPF6 with different compositions of nano sized TiO2 in weight percent (x = 0, 1, 2, 5, 10, 15, 20 ) is synthesized by using standard solution cast technique. The homogeneous surface of above polymer composition is examined by FESEM. The microscopic interaction among polymer, salt and nanoceramic filler has been analyzed by Fourier Transformed Infra-Red (FTIR) spectroscopy. The reduction of ion pair formation in polymeric separator is clearly observed on addition of nanofiller in the polymer salt complex film. Electrical conductivity has been recorded of the prepared polymeric separator which is of the order of ~10-3 Scm-1 after addition of nanofiller (15% wt/wt) which support the FTIR results. Electrochemical potential window has been observed of the order of ~6V by the cyclic voltammetry results. The observed data of the prepared separator are at par with the desirable value for device applications.

physics.app-ph↗
arXiv2018

The Changed Crystal Filed of Gd3+ in Natural Zircon with Heat Treatment in Oxidizing and Reducing Atmosphere Monitor by ESR Spectroscopy

The main purpose of this research is dedicated to the ESR study of the impurity ions such as Gd3+ in the natural zircon crystal because the presence of the impurity ions in the crystal usually causes color in crystal. The Zeeman interaction, the weak hyperfine interaction and the crystal field interaction due to the environments of the impurity ions will be calculated. Furthermore, the relation between the resonance magnetic field positions in the ESR spectra and the applied magnetic field directions will reflect the impurity ion site symmetry. The change in the crystal field parameters of heat-treated zircon at different atmospheres were related to the change in the color of zircon.

cond-mat.mtrl-sci↗
arXiv2018

All-optical Nonlinear Activation Function for Photonic Neural Networks

With the recent successes of neural networks (NN) to perform machine-learning tasks, photonic-based NN designs may enable high throughput and low power neuromorphic compute paradigms since they bypass the parasitic charging of capacitive wires. Thus, engineering data-information processors capable of executing NN algorithms with high efficiency is of major importance for applications ranging from pattern recognition to classification. Our hypothesis is therefore, that if the time-limiting electro-optic conversion of current photonic NN designs could be postponed until the very end of the network, then the execution time of the photonic algorithm is simple the delay of the time-of-flight of photons through the NN, which is on the order of picoseconds for integrated photonics. Exploring such all-optical NN, in this work we discuss two independent approaches of implementing the optical perceptrons nonlinear activation function based on nanophotonic structures exhibiting i) induced transparency and ii) reverse saturated absorption. Our results show that the all-optical nonlinearity provides about 3 and 7 dB extinction ratio for the two systems considered, respectively, and classification accuracies of an exemplary MNIST task of 97% and near 100% are found, which rivals that of software based trained NNs, yet with ignored noise in the network. Together with a developed concept for an all-optical perceptron, these findings point to the possibility of realizing pure photonic NNs with potentially unmatched throughput and even energy consumption for next generation information processing hardware.

physics.app-ph↗
arXiv2018

Incorporation of macroscopic heterogeneity within a porous layer to enhance its acoustic absorptance

We seek the response, in particular the spectral absorptance, of a rigidly-backed periodically-(in one horizontal~~ direction) ~inhomogeneous ~layer ~composed ~of ~alternating rigid and macroscopically-homogeneous porous portions, submitted to an airborne acoustic plane body wave. The rigorous theory of this problem is given and the means by which the latter can be numerically solved are outlined. At low frequencies, a suitable approximation derives from one linear equation in one unknown. This approximate solution is shown to be equivalent to that of the problem of the same wave incident on a homogeneous, isotropic layer. The thickness $h$ of this layer is identical to that of the inhomogeneous layer, the effective complex body wave velocity therein is identical to that of the porous portion of the inhomogeneous layer, but the complex effective mass density, whose expression is given in explicit algebraic form, is that of the reference homogeneous macroscopically-porous layer divided by the filling factor (fraction of porous material to the total material in one grating period). This difference of density is the reason why it is possible for the lowest-frequency absorptance peak to be higher than that of a reference layer. Also, it is shown how to augment the height of this peak so that it attains unity (i.e., total absorption) and how to shift it to lower frequencies, as is required in certain applications.

physics.app-ph↗
arXiv2018

The Core Diffusion-Drift Field-Effect Transistor Theory Including Quantum and Interface Trap Capacitances

We have decomposed the modeling of the field-effect transistors into the two independent parts: the current continuity based kinetics and the charge neutrality based electrostatics. The former part, that is universal for all FETs, leads to an explicit and closed form of I-V characteristics as a function of the total channel charge. The latter part, which is specific for a particular material and geometric configurations can be considered as an independent engineering task. The quantum capacitance and the interface trap density are consistently incorporated into the solution of the current continuity equation in the diffusion-drift approximation, providing a complete consistency in the current and the capacitance small-signal characteristics.

cond-mat.mes-hall↗