Absorbing Medium Research Articles

Flexible 1.3 μm photodetector fabricated with InN nanowires and graphene on overhead projector transparency sheet.

We report the first demonstration of flexible photodetectors, operating at the wavelength window of 1.3 μm, fabricated with InN nanowires (NWs) and graphene on an overhead projector transparency (OHP) sheet. The InN NWs, used as an absorption medium for the device, were formed on a Si substrate and exhibited strong emission with a peak wavelength of 1.3 μm at room temperature. They were randomly and horizontally embedded in the graphene sandwich structure functioned as a carrier channel. The photocurrent and photoresponsivity of the flexible photodetector were found to be 1.17 mA and 0.48 A W-1, respectively, at a voltage of 1 V and a light intensity of 60 mW cm-2 of a xenon lamp. The photocurrent measured when the photodetector was bent under a strain of 3% was 1.15 mA, which corresponds to 98.3% compared to that before bending. Moreover, the photocurrent and photoresponsivity of the flexible photodetector measured after the 200 cyclic-bending tests are comparable to those measured before bending.

Effect of pulse duration and confinement on laser-induced stress waves for high strain-rate material testing

Laser-induced stress waves have been a powerful technique for high strain-rate material characterization. The stress amplitude and duration can be strongly influenced by both laser characteristics and sample configuration. In this study, stress histories of silicon substrates loaded by pico- and nanoseconds laser pulses, with and without confinement of the interaction volume, were investigated. Shorter pulse duration and confinement of the absorbing medium have been found to increase the amplitude of laser-induced stress waves, but they may also alter the stress evolution. Without confinement or at low energy densities the stress wave profile is similar to that of the laser pulse. At high energy densities with confinement shock loading with stretched unloading is observed.

Qualitative assessment of air pollution in the working area of energy-intensive materials production by nanoscale aerosols with a solid dispersed phase

The presence of grinding, mixing, and fractionation of solid components of formulations leads to the formation of aerosols in the air of the working area with a wide range of dispersion of the solid phase - all this characterizes the organization of technological processes for the production of energy-intensive materials. The study aims to give a qualitative assessment of possible air pollution of the working area of energy-intensive materials production by nanoscale aerosols with a solid dispersed phase. The researchers carried out the sampling of the working area air and flushes from solid horizontal surfaces to produce energy-intensive materials. We carried out the sampling by forced circulation of the test air through the absorption devices of Polezhaev. Scientists used Triton TX-114 solution with a mass concentration of 2.0 mg/dm3 as an absorption medium. The researchers performed flushing from surfaces using cloth tampons moistened with Triton TX-114 solution with a mass concentration of 2.0 mg/dm3. We determined the particle sizes in the samples using NanotracULTRA (Microtrac). Scientists found aluminum and nitrocellulose particles with sizes from 36 to 102 nm in the air of the working area and flushes from horizontal surfaces. The study of the fractional composition of RDX and aluminum powders of the ASD-1 brand showed the presence of nanoscale particles in them. Nanoscale dust particles pollute the air of the working area and solid horizontal surfaces at certain stages of the production of energy-intensive materials. There are nanoscale particles in the composition of powders of some standard components of formulations. Flushes from solid horizontal surfaces are an adequate qualitative indicator of the presence of nanoaerosols in the air of the working area.

Optical and thermal studies of Nd3+ doped inorganic liquid medium for scalable laser source

The optical and thermal properties of Nd3+ doped inorganic liquid medium are investigated for the development of a scalable laser source. The homogenous liquid medium is synthesized by mixing rare earth Nd3+ ions in a POCl3 solvent host with Lewis acid SnCl4. The optical studies are carried out to assess the lasing potential of the medium and to discern its absorption and emission spectra. The observed results show that peak absorption of the liquid medium occurs at 800 nm with peak emission at 1054 nm marginally blue-shifted as compared to corresponding ones in Nd:YAG single-crystal. Judd-Ofelt theory is successfully used to determine the stimulated emission cross-section and quantum yield of the synthesized liquid medium. Fourier Transform Infrared (FTIR) Spectroscopic studies reveal that the medium is free from hydrogen-containing species which may impede lasing. The synthesized liquid medium is transparent at lasing wavelength showing a transmission loss coefficient of less than 0.5 % cm−1. Thermal studies of the synthesized liquid medium under high pump irradiance are performed both in sealed-off static as well as circulating liquid medium. This enables to identify the plausible configuration for lasing. It is observed that thermal-induced convection effects appearing in the sealed-off static medium can be mitigated by circulating the liquid medium. The liquid medium flows under a laminar regime at rates of 10–12 L per minute (lpm) below the critical Reynolds number. Hence, the characterization studies of Nd3+ doped inorganic liquid medium are promising towards the development of scalable laser sources.

Recent Advances in Modeling of Perovskite Solar Cells Using SCAPS-1D: Effect of Absorber and ETM Thickness

With the massive breakthrough recorded in the power conversion efficiency (PCE) of perovskite solar cells (PSCs) from 3.8 % to > 25 %, PSCs have attracted considerable attention in both the academia and industries. However, some challenges remain as barrier in realizing its deployment. To develop a highly efficient PSCs as well as environmentally benign device, simulation and optimization of such devices is desirable. Its impractical as well as wastage of time and money to design a solar cell without simulation works. It minimizes not only the risk, time and money rather analyzes layers’ properties and role to optimize the solar cell to best performance. Numerical modeling to describe PV thin layer devices is a convenient tool to better understand the basic factors limiting the electrical parameters of the solar cells and to increase their performance. In this review article, we focused on the recent advances in modelling and optimization of PSCs using SCAPS-1D with emphasis on absorber and electron transport medium (ETM) thickness.

Light-matter coupling in large-area van der Waals superlattices.

Two-dimensional (2D) crystals have renewed opportunities in design and assembly of artificial lattices without the constraints of epitaxy. However, the lack of thickness control in exfoliated van der Waals (vdW) layers prevents realization of repeat units with high fidelity. Recent availability of uniform, wafer-scale samples permits engineering of both electronic and optical dispersions in stacks of disparate 2D layers with multiple repeating units. Here we present optical dispersion engineering in a superlattice structure comprising alternating layers of 2D excitonic chalcogenides and dielectric insulators. By carefully designing the unit cell parameters, we demonstrate greater than 90% narrow band absorption in less than 4 nm of active layer excitonic absorber medium at room temperature, concurrently with enhanced photoluminescence in square-centimetre samples. These superlattices show evidence of strong light-matter coupling and exciton-polariton formation with geometry-tuneable coupling constants. Our results demonstrate proof of concept structures with engineered optical properties and pave the way for a broad class of scalable, designer optical metamaterials from atomically thin layers.

Identifying Circumgalactic Medium Absorption in QSO Spectra: A Bayesian Approach

Abstract We present a study of candidate galaxy–absorber pairs for 43 low-redshift QSO sightlines (0.06 < z < 0.85) observed with the Hubble Space Telescope/Cosmic Origins Spectrograph that lie within the footprint of the Sloan Digital Sky Survey with a statistical approach to match absorbers with galaxies near the QSO lines of sight using only the SDSS Data Release 12 photometric data for the galaxies, including estimates of their redshifts. Our Bayesian methods combine the SDSS photometric information with measured properties of the circumgalactic medium to find the most probable galaxy match, if any, for each absorber in the line-of-sight QSO spectrum. We find ∼630 candidate galaxy–absorber pairs using two different statistics. The methods are able to reproduce pairs reported in the targeted spectroscopic studies upon which we base the statistics at a rate of 72%. The properties of the galaxies comprising the candidate pairs have median redshift, luminosity, and stellar mass, all estimated from the photometric data, z = 0.13, L = 0.1L *, and log ( M * / M ⊙ ) = 9.7 . The median impact parameter of the candidate pairs is ∼430 kpc, or ∼3.5 times the galaxy virial radius. The results are broadly consistent with the high Lyα covering fraction out to this radius found in previous studies. This method of matching absorbers and galaxies can be used to prioritize targets for spectroscopic studies, and we present specific examples of promising systems for such follow-up.

Radiative contribution to thermal grating decay

The decay of a spatially sinusoidal temperature perturbation (thermal grating) via thermal transport by both conduction and radiation is analyzed theoretically. The intrinsic non-radiative conduction is described by the heat diffusion equation while radiative transport is described by the radiation transport equation for a non-scattering absorbing medium. We solve the coupled equations analytically and obtain the thermal grating decay rate, which leads to an explicit expression for the radiative contribution to the effective thermal conductivity measured with the laser-induced transient thermal grating technique. We find that at a given thermal grating period, the radiative contribution to thermal transport is maximized when the absorption length of thermal radiation is about 1/4 of the period. We present the expression for an upper bound for the radiative contribution and discuss the results for representative materials. We conclude that in a typical transient grating measurement with the grating period in the micrometer range, the radiative contribution is negligible, but it may be significant if the grating period is in the millimeter or centimeter range. Our analysis also provides a Fourier-domain Green's function that can be used to find the temperature field produced by an arbitrary spatiotemporal distribution of heat sources.

Kramers-Kronig Relation for Attenuated Total Reflection from a Metal-Dielectric Interface Where Surface Plasmon Polaritons Are Excited.

The applicability of the Kramers–Kronig relation for attenuated total reflection (ATR) from a metal–dielectric interface that can excite surface plasmon polaritons (SPP) is theoretically investigated. The plasmon-induced attenuation of reflected light can be taken as the resonant absorption of light through a virtual absorptive medium. The optical phase shift of light reflected from the SPP-generating interface is calculated using the KK relation, for which the spectral dependence of ATR is used at around the plasmonic resonance. The KK relation-calculated phase shift shows good agreement with that directly obtained from the reflection coefficient, calculated by a field transfer matrix formula at around the resonance. This indicates that physical causality also produces the spectral dependence of the phase of the leakage field radiated by surface plasmons that would interfere with the reflected part of light incident to the interface. This is analogous with optical dispersion in an absorptive medium where the phase of the secondary field induced by a medium polarization, which interferes with a polarization-stimulating incident field, has a spectral dependence that stems from physical causality.

REMOVAL OF METHYLENE BLUE BY ABSORPTION OF WATER HYACINTH-DERIVED ACTIVATED CARBON EMBEDDED WITH NICKEL NANOPARTICLES

Nanoparticles have proven their dominance in many fields of research in this era. Such dominance resulted from outstanding physical and chemical properties amongst other materials, led to a wide focus from different researchers in various fields to further investigate the role of nanoparticles in various applications from drug delivery systems in medicine to catalysis in chemistry. In this research, active carbon-based catalyst synthesis and characterization were investigated for different applications in catalysis as the catalyst was combined with nickel oxides to be used in dye removal of methylene blue (MB). Water hyacinth is a floating perennial aquatic plant native to tropical and sub-tropical South America. The water hyacinth is one of the fastest-growing plants; it reproduces by way of runners or stolon. Each one can produce thousands of seeds each year, which can survive for more than 28 years. It has been considered as a water purifier and a solution to green water issues. Water hyacinth is used in perfume and cologne products, as well as organic fertilizer. It also absorbs lead, mercury, and carcinogens when used for remediation purposes. As it has amazing biomass, it can be used to produce fuels. Activated carbon, also known as activated charcoal, is a carbonaceous, highly porous absorptive medium of a complex structure composed of carbon atoms. It is used in gas purification, gold purification, metal extraction, medicine, sewage treatment, air filters, in gas masks used to purify liquids in many applications, including drinking water and odor removal. This research aims to prepare active carbon derived from water hyacinth and embedded with nickel nanoparticles. The water hyacinth will be converted into active carbon and used as a support for nickel nanoparticles. A comparison between active carbon derived from water hyacinth and activated nickel nanoparticles will be conducted to test the rate of absorbance based on the effect of time, concentration, and kinetic energy.

Leveraging Deep Statistics for Underwater Image Enhancement

Underwater imaging often suffers from color cast and contrast degradation due to range-dependent medium absorption and light scattering. Introducing image statistics as prior has been proved to be an effective solution for underwater image enhancement. However, relative to the modal divergence of light propagation and underwater scenery, the existing methods are limited in representing the inherent statistics of underwater images resulting in color artifacts and haze residuals. To address this problem, this article proposes a convolutional neural network (CNN)-based framework to learn hierarchical statistical features related to color cast and contrast degradation and to leverage them for underwater image enhancement. Specifically, a pixel disruption strategy is first proposed to suppress intrinsic colors’ influence and facilitate modeling a unified statistical representation of underwater image. Then, considering the local variation of depth of field, two parallel sub-networks: Color Correction Network (CC-Net) and Contrast Enhancement Network (CE-Net) are presented. The CC-Net and CE-Net can generate pixel-wise color cast and transmission map and achieve spatial-varied color correction and contrast enhancement. Moreover, to address the issue of insufficient training data, an imaging model-based synthesis method that incorporates pixel disruption strategy is presented to generate underwater patches with global degradation consistency. Quantitative and subjective evaluations demonstrate that our proposed method achieves state-of-the-art performance.

Photon Recycling in CsPbBr3 All-Inorganic Perovskite Nanocrystals.

Photon recycling, the iterative process of re-absorption and re-emission of photons in an absorbing medium, can play an important role in the power-conversion efficiency of photovoltaic cells. To date, several studies have proposed that this process may occur in bulk or thin films of inorganic lead-halide perovskites, but conclusive proof of the occurrence and magnitude of this effect is missing. Here, we provide clear evidence and quantitative estimation of photon recycling in CsPbBr3 nanocrystal suspensions by combining measurements of steady-state and time-resolved photoluminescence (PL) and PL quantum yield with simulations of photon diffusion through the suspension. The steady-state PL shows clear spectral modifications including red shifts and quantum yield decrease, while the time-resolved measurements show prolonged PL decay and rise times. These effects grow as the nanocrystal concentration and distance traveled through the suspension increase. Monte Carlo simulations of photons diffusing through the medium and exhibiting absorption and re-emission account quantitatively for the observed trends and show that up to five re-emission cycles are involved. We thus identify 4 quantifiable measures, PL red shift, PL QY, PL decay time, and PL rise time that together all point toward repeated, energy-directed radiative transfer between nanocrystals. These results highlight the importance of photon recycling for both optical properties and photovoltaic applications of inorganic perovskite nanocrystals.

Drug-like Properties and Fraction Lipophilicity Index as a combined metric.

Fraction Lipophicity Index (FLI) has been developed as a composite drug-like metric combining log P and log D in a weighted manner. In the present study, an extended data set confirmed the previously established drug-like FLI range 0-8 using two calculation systems for log P/log D assessment, the freeware MedChem Designer and ClogP. The dataset was split into two classes according to the percentage of fraction absorbed (%FA) - class 1 including drugs with high to medium absorption levels and class 2 including poorly absorbed drugs. The FLI and FLI-C (ClogP based FLI) drug-like range covers 92 % and 91 % of class 1 drugs, respectively. Using MlogP, a narrower drug-like FLI-M range 0-7 was established, covering 91 % of class 1 drugs. The dependence of the degree of ionization to intrinsic lipophilicity within the FLI (FLI-C, FLI-M) drug-like range as well as the inter-relation between the other Ro5 properties (Mw, HD, HA) was explored to define drug-like / non-drug-like combinations as a safer alternative to single properties for drug candidates’ prioritization. In this sense, we propose a combined metric of Mw and the number of polar atoms (Mw/NO) to account for both size and polarity. Setting the value 50 as cutoff, a distinct differentiation between class 1 and class 2 drugs was obtained with Mw/NO>50 for more than 70 % of class 1 drugs, while the opposite was observed for class 2 drugs.

Transport and Lymphatic Uptake of Biotherapeutics Through Subcutaneous Injection

Drug transport and uptake in the subcutaneous tissue receives increasing attention in biomechanical and pharmaceutical researches, as subcutaneous administration becomes a common approach for the delivery of biotherapeutics, such as monoclonal antibodies. In this paper, high-fidelity numerical simulations are used to investigate the mechanisms governing drug transport and absorption in the subcutaneous tissue, which is expressed as a porous medium modeled by Darcy’s law. The effects of tissue properties (permeability and porosity), the injection flow rate, and the vascular permeability of lymphatic vessels on the lymphatic uptake are studied. Additionally, an empirical formula for the lymphatic uptake during the injection is developed based on the numerical results. The roles of lymphatic drainage, blood perfusion, osmotic pressure, and the drug binding to the cells and the extracellular matrix in the lymphatic uptake are systematically studied. Furthermore, the drug distribution and absorption in a multi-layered porous medium are investigated to illustrate the effect of heterogeneity of permeability, as the permeability varies over a wide range in different layers of the tissue (such as dermis, subcutaneous tissue, muscle). While the interstitial pressure plays an essential role in the mechanisms regulating the absorption of free monoclonal antibodies, the binding and metabolism of drug proteins also affect the drug absorption by reducing the total free monoclonal antibodies.

Plasmonic nano-particles mediated energy harvesting in thin-film organic solar cells

A Cd-doped ZnO nano-composite (Cd:ZnO) was synthesized using wet chemistry, and then incorporated into the photo-active layer of a thin film organic solar cell (TFOSC) to assist photon harvesting. The nano-composite (NC) formed different sized nano-structures that are beneficial to optical absorption and charge transport processes in the TFOSC. The effects on the NC were studied using a solar absorber medium composed of a poly(3-hexylthiophene) (P3HT) and 6-6-phenyl-C61-butyric acid methyl ester (PCBM) blend with standard device architecture: ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al. The electrical and optical properties of the photoactive films were investigated at various doping levels of Cd:ZnO NC in the medium. The composite showed interesting local surface plasmon resonance, which significantly impacted on the performance of the cells. Consequently, the power conversion efficiency of the TFOSC grew by 84% compared to the reference cell. It is also noted that Cd:ZnO is environmentally stable and compatible for solution device processing.

Coupled-mode field computations for media with locally reacting irregular boundaries.

Coupled-mode methods have been used in underwater acoustics to compute three-dimensional sound propagation and scattering. Significant computational simplifications are possible for media with a lateral variation restricted to cylindrically symmetric anomalies, such as seamounts, and also for media which are invariant in one of the horizontal directions. Typically, the upper and lower depth boundaries of the medium have then been horizontal and flat. This paper generalizes the discrete coupled-mode method with a reflection- (or scattering-) matrix formulation to media with irregular and locally reacting boundaries. Horizontal and vertical segments thereby approximate a sloping boundary. Incorporation of the boundary conditions in a correct way necessitates modifications of the basic equation systems. Additional coupling matrices appear, involving integration of normal-mode products over the depth increments for adjacent regions of the medium. The paper includes three computational examples. One is from underwater acoustics with an island that rises above the sea level. The other two are from atmospheric acoustics with sound propagation over a locally reacting irregular ground surface. Using nonlinear optimization, it is possible to select a suitable artificial absorbing medium termination for a mode representation of the field.

Study of geological processes of absorption of pressure waves from injected fluids in the rock structure

The paper presents a detailed study of the propagation of oscillations in an infinite absorbing medium in order to discuss the behavior of a material under various conditions during pulsed injection of fluids into an injection well. The dependence of deformation and stress was solved mathematically on the basis of the modified Hooke’s law, which includes the rate of change in deformation. As a result, graphical dependences of the phase velocity of propagation of oscillations and the absorption coefficient on the oscillation frequency were obtained for the most common types of rocks. Analysis of the obtained results showed that the absorption coefficient attains its maximum values in the region of resonance frequencies, and further increase in the oscillation frequency leads to a slight decrease in the absorption coefficient. In our opinion, the most optimal frequency range for the propagation of oscillations in the rock structure varies from 100 to 800 Hz with regard to the natural frequencies of the rocks studied.

Acoustic Performance Evaluation of Sugarcane Bagasse Using Ambient Sound Meter and Scanning Electron Microscopy

Abstract: Non-stop research is afoot to replace synthetic materials with green-materials for sound absorption purposes. Employing of agricultural waste as building materials has been a successful trend throughout the years. This research targets to utilize sugarcane bagasse (SB) fibers as sound barriers with sodium silicate as an adhesive. The SB fibers were treated in an alkaline solution for delignification and to improve the surface morphology. The SB fibers were casted into sheet and further tested for sound transmission loss. Experimentation revealed that the fabricated sheets can be viable option as a sound absorbing medium. A tubular porous structure was observed through Field Emission Scanning Microscope (FESEM). It has the capability to be used as a low-cost, biodegradable, and eco-friendly acoustic material as compared to glass wool and other synthetic acoustic materials. Keywords: Acoustic material, Alkali-treatment, Ambience, FESEM microscopy, Low-cost, Natural fiber, Performance, Sugarcane Bagasse, Sustainability

Blow up and global solvability for an absorptive porous medium equation with memory at the boundary

Abstract We study the characterization of global solvability versus blow up in finite time for a porous medium model including a balance of internal absorption with memory driven flux through the boundary. Such a boundary condition was previously investigated as part of a model for the transmission of tumour-released growth factor from the site of a pre-vascularized tumour up to and across the wall of a nearby capillary, initiating the process of new capillary growth known as angiogenesis. In previous studies of the model without absorption, we have established the characterization of global solvability in a manner that exactly parallels known results for the corresponding model with localized boundary flux conditions. To include models accounting for internal uptake of growth factor, this analysis has recently been extended to a heat equation with absorption, and herein, we consider the case of a porous medium equation with absorption. Conditions for global solvability emerge naturally out of integral estimates and again provide close parallels with results for localized boundary flux models. It is noted that the results provide a complete characterization in a wide range of models considered.

Retrieval of Optical Constants of Undoped Flash-Evaporated Lead Iodide Films from an Analysis of Their Normal Incidence Transmission Spectra Using Swanepoel’s Transmission Envelope Theory of Non-Uniform Films

Abstract: Normal-incidence transmission-wavelength (T_exp (λ)-λ) spectra of 1 and 1.2 m thick flash-evaporated lead iodide (PbI2) films on 1.1 mm thick glass slides held at 200 ℃ display well-spaced several interference-fringe maxima and minima in the λ-range 520-900 nm, without exhibiting a transparent region and with the maxima lying well below the substrate transmission. Below 520 nm, these T_exp (λ)-λ curves drop steeply to zero (at λ ≼ 505 nm), signifying crystalline-like PbI2 film absorption. As corrections of measured (PbI2 film/substrate) transmittance data for substrate absorption and spectrometer slit-width effect were marginal over the studied λ-range, the observed low transmittance of (PbI2 film/substrate) system was related to PbI2 film thickness non-uniformity (∆d), which causes shrinkage of both maxima and minima and leads to significant film optical absorption that reduces both maxima and minima. The McClain ENVELOPE algorithm was utilized, with a minor modification, to construct maxima T_M (λ_max/λ_min) and minima T_m (λ_min/λ_max) envelope curves, which were analyzed by Swanepoel’s envelope method of non-uniform films using an approach that takes account of dispersive substrate refractive index n_s (λ) and circumvents the non-availability of a high-λ transparency region. In such analytical approach, ∆d was varied till a re-generated T_gen (λ)-λ curve matches the T_exp (λ)-λ curve. An average thickness d ̅ of the film, besides its refractive index n(λ) and absorption coefficient α(λ) in the weak, medium and strong absorption regions, were then obtained. The energy-dependence of α(λ) is discussed in view of interband electronic transition models. The obtained results are consistent with other literature studies on similar flash-evaporated PbI2 films. Keywords: PbI2, Optical constants and bandgap, Swanepoel's transmission envelope method, Non-uniform films.