Surface Absorptions Research Articles

Surface absorption channels in light absorption by a 2D-material-coated particle

Light absorption enhancement in micro- and nanoparticles has garnered considerable attention through coated 2D materials, which are physically homogenized by surface conductivities and surface currents within the electromagnetic boundary conditions. However, the electromagnetic absorption through the surface channel remains unexamined, hindering a deeper understanding of the underlying mechanisms of light absorption. In this work, we analytically derive the effective cross sections of surface absorption for a 2D-material-coated sphere, based on the framework of Mie theory amended by the surface conductivity. Our theoretical analysis confirms the absorption unitarity in wrapped particles, whereby the total absorption is equivalent to the sum of surface and volume absorptions. Considering optical dispersion of a polar interior, we identify a blue shift in the resonance wavelength induced by the 2D coating, which leads to a decrease in material dissipation and thus volume absorption within the particle itself in spite of a large field enhancement inside the particle. Finally, through a realistic case of small graphene-wrapped MgO spheres, we illustrate the dominant role of the surface absorption channel on the mechanism of absorption enhancements.

A Cytidine-Modified surfactant anchored liquid crystal Droplet-Based sensor for rapid and accurate detection of silver ions

Liquid crystal (LC) droplets exhibit unique and sensitive response behaviors to surface absorptions, making them promising candidates for sensing aplications. Here, we have developed a label-free, portable, and cost-effective sensor for the specific and rapid detection of silver ions (Ag+) in drinking-water samples. To achieve this, we have modified cytidine into a surfactant (denoted as C10–M–C) and anchored it onto the surface of LC droplets. The specific binding ability between cytidine and Ag+ enables LC droplets anchored with C10–M–C to respond rapidly and specifically to Ag+ ions. Furthermore, the sensitivity of the response meets requirements for the harmless concentration of Ag+ in drinking-water. The sensor we developed is label-free, portable, and cost-effectively. We believe that the sensor reported here can be applied to the detection of Ag+ in drinking-water and environmental samples.

Evaluation and Improvement of Reverberation Time in the Current Enclosed Spaces with Speech Action

There are subjective and objective acoustic parameters in the creation of acoustic performance for speech action in room acoustics. Control of reverberation time affecting subjective and objective acoustic parameters is a main parameter in room acoustics. In this study, the acoustic performance assessment of the TOBB Twins Headquarters Reception Hall, which is current enclosed space with square plan and flat floor, has been performed as a case study. The evaluation focused on the relationship between reverberation time and interior surface absorption. Primarily, the reverberation time was determined according to the international standard with in-situ measurements in the current enclosed space. The reverberation time of the space was found over the reference value range. Models have been developed with the use of materials to reduce the reverberation time. In the assessment of room acoustics parameters, reverberation times of the models developed using Ecotect v.5.20 and Odeon 14.00 simulation programs have been determined. The model in which the optimum reverberation time for the speech action was obtained was constructed. After the construction, reverberation time measurements have been made again. As a result of the study, the effect of surface absorptions on the improvement of reverberation time in the enclosed spaces with square plan and flat floor for speech action has been evaluated. Suggestions have been developed to control the reflective and absorption properties of all surfaces in accordance with the evaluation and improvement of reverberation time.

Martian Atmospheric CO2 and Pressure Profiling With Differential Absorption Lidar: System Consideration and Simulation Results

AbstractThis study explores a new concept of Martian differential absorption Lidar operating at the 2‐μm CO2 absorption band for atmospheric CO2 and pressure observations. For the considered system, two or more closely spaced wavelengths are selected, so that environmental factors such as surface reflection, atmospheric scattering, and absorptions from other trace gases on the lidar return signals are very similar for all selected wavelengths, but the difference in CO2 absorption is substantial. Thus, Martian CO2 amount and air pressure could be retrieved from the measured CO2 differential absorption optical depth at the selected wavelengths. Simulations based on Mars's environmental conditions and technically feasible lidar systems show that lidar returns from the surface could have sufficient signal strengths that allow surface air pressure measurements with 1 Pa precision after a horizontally 5‐km averaging when dust optical depth is smaller than 1.5. Even when the dust optical depth increases to 3, the uncertainty in the air pressure and column CO2 amount measurements with a random error is still smaller than 1%. In the presence of moderate dust aerosol loads and with the optimal selection of offline and online wavelengths, atmospheric CO2 and pressure profiles could also be retrieved from the surface up to an ∼13‐km altitude with the random error smaller than 1% for a horizontal resolution of 100 km and a vertical resolution of 100 m during night or 400 m during day. These CO2 and pressure measurements would significantly improve weather and climate modeling and prediction.

Assessing surface air pressure sensing using 118 GHz O2-absorption radar system

This study assesses surface air pressure remote sensing using a differential absorption radar at the 118 GHz O2 line. The considered system would have, at least two, closely-spaced frequency channels. Environmental impacts like surface reflections and absorptions from water vapor and other gases, and liquid water clouds on the radar signals of these channels are very similar, but the difference in O2 absorption is substantial. The surface pressure could be retrieved from the radar measured differential absorption optical depth of the atmosphere. The operational frequencies of the radar system are optimally selected, and the transmitted powers of the paired stronger and weaker O2 absorption channels are carefully distributed to balance the signal-to-noise ratios of these channels. Simulations of radar signals and pressure retrievals show that with an airborne system cruising at 10 km altitude, surface pressure measurements could achieve 1 mb accuracy within 1-s data processing. These pressure measurements would provide urgently needed supports in improving severe and general weather forecasts and gain unique knowledge on planetary boundary layer meteorology. Other advantages of this kind of high frequency radars would be their higher spatial resolution and increased potentials of small- or CubeSat applications.

Effects of copper oxide and sulfuric acid on the pyrolysis behavior of ammonium nitrate under thermal radiation experiments

Statistics have indicated that industrial accidents of ammonium nitrate were primarily caused by uncontrolled external fires where heating was dominantly controlled by radiation, and yet existing studies at milligram scale cannot fully simulate the real fire scenarios. To explore the pyrolysis behavior in typical fires, this study conducted thermal radiation experiments using pure ammonium nitrate, and its mixtures with copper oxide and sulfuric acid. Different from the pyrolysis process identified in milligram scale tests, the bench-scale pyrolysis of ammonium nitrate under radiation consisted of four stages. Pyrolysis structure model of each stage was built to reveal the differences in dominated thermal behavior. Results indicated that two additives had different thermo-chemical effects on pyrolysis of ammonium nitrate. Sulfuric acid accelerated the reaction rate of each stage by generating catalytic nitric acid; copper oxide reduced the number of reaction stages into three via surface absorptions. The time and mass loss rate of different stages were determined. Recommendations on effective emergency response were made to prevent the transition of slow decomposition into fast decomposition, and thus to intervene the fire-induced domino effect of ammonium nitrate. This study helps to understand the pyrolysis behavior of ammonium nitrate under fire exposure, and provides insights for pyrolysis modeling and firefighting in industry of interest.

Ignition of polymers under exponential heat flux considering both surface and in-depth absorptions

Analytical models addressing ignition of solids under constant heat flux have been developed in previous studies utilizing surface or in-depth absorption or combination of them. When encountering time-dependent heat flux, the majority of the studies focused on polynomial heat flux and surface absorption assumption. However, in-depth absorption also should be taken into account under time-dependent heat flux in analytical models especially for infrared translucent solids. In this work, an analytical model aiming at revealing the ignition mechanism of translucent polymers under exponential time-increasing heat flux is established considering both surface and in-depth absorptions. Critical temperature is employed as ignition criterion. Four typical non-charring polymers, polymethyl methacrylate (PMMA), polyoxymethylene (POM), polyamide 6 (PA 6) and polypropylene (PP), are utilized as the reference materials, and a numerical solver is employed to validate the analytical model. The results show that the developed analytical model provides accurate predictions of surface temperature and ignition time. Surface heat loss by convection and reradiation has little effect on surface temperature, ignition time and critical energy, but it affects the ignition heat flux greatly. Thermal penetration depth differs from the one under constant heat flux, and it gets smaller as the surface heat loss is considered. The ignition time, thermal penetration depth and critical energy decrease as the heat flux increasing rate gets larger. Meanwhile, the ignition heat flux for in-depth absorption is higher than that for surface absorption, and both increase with heat flux increasing rate. Furthermore, the linearity between ignition time and the squared critical energy, proposed in constant and linear heat flux scenarios, is also found valid under this exponential heat flux condition.

Evaluation of aging process of silicone rubber composite insulators with photothermal radiometry

Silicone rubber composite insulators are increasingly used in high-voltage power transmission and distribution grids. However, the aging of composite insulators is a serious safety issue of power systems. Understanding the aging mechanism of composite insulators is therefore of great importance. In this paper, a 3D photothermal radiometry (PTR) is employed to determine the thermal and absorption properties of silicone rubber composite insulators aged in natural environment. A 3D PTR model was developed to extract precisely the thermal diffusivity and absorption coefficients of the composite insulators. In this PTR model both surface and bulk absorptions were accounted for by taking into consideration the fact that a surface absorption of aged composite insulators would be created and changed by surface crazing, chalking, and contamination during aging process. By multi-parameter fitting the measured modulation frequency dependences of PTR amplitude and phase to this 3D PTR model, the thermal diffusivity, surface absorption, as well as bulk absorption coefficient of the composite insulators were extracted simultaneously. The comparisons between the thermal diffusivities, absorption characteristics of fresh and aged composite insulators indicated that aging caused significant decrease of thermal diffusivity and substantial increase of absorption of composite insulators, and the thermal diffusivity and absorption changes were aging level dependent. These experimental results demonstrated that both thermal and absorption properties may be useful parameters for evaluating the aging level and understanding the aging mechanism of silicone rubber composite insulators.

Analytical prediction of heat transfer and ignition time of solids exposed to time-dependent thermal radiation

An analytical model was developed in this study to predict the heat transfer and ignition time of solids subjected to time-dependent thermal radiation (HF=atb). Both surface and in-depth absorptions, corresponding to opaque and translucent materials, were considered in the model and critical temperature was employed. The predictions of the new model fit well with the experimental and numerical results. The results show that for surface absorption the ignition time to the power of −(b+0.5) is proportional to a, and the reciprocal of square root of ignition time is linearly correlated with ignition HF. Furthermore, a critical ignition HF was found to represent the lower limit of ignition HF range, which is different with the critical HF at constant HF. While for in-depth absorption, the ignition time to the power of −(b+1) and −1 were linearly proportional to a/(b+1) and ignition HF, respectively. For translucent solids, the analytical model cannot be applied to constant HF but can provide relatively high accuracy in predicting ignition time under variable HF. Also, the effect of in-depth absorption coefficient on ignition time were addressed, and it was found that this important parameter exerts its influence on ignition process following the similar mechanism with that of constant HF.

Comparative study of surface and body absorptions for axisymmetric modeling of long pulsed laser heating material: theoretical model and mathematical solutions of temperature

In this article, we presented the comparative study of surface and body absorptions for axisymmetric modeling of long pulsed laser heating material. First, theoretical models of surface absorption is established based on the representation of heat source term through the surface boundary of material, and mathematical solutions of its homogeneous equation are obtained using separation of variables and Laplace transform method. Next, theoretical models of body absorption is established based on the representation of heat source term in the heat conduction equation, and mathematical solutions of its non-homogeneous equation are obtained using integral transform method. The presented methods are validated through modeling results of the surface absorption and body absorption model, respectively.

Background-free piezoresponse force microscopy for quantitative measurements

We report an effective method to remove the system-inherent background [Jungk et al., Appl. Phys. Lett. 91, 253511 (2007)] that is present in nominal piezoresponse force microscopy (PFM) setup. Control experiments performed in both ambient and ultrahigh vacuum environments indicate that the system-inherent background probably originates from the interactions between the modulation voltage and surface absorptions. By minimizing such interactions, background-free PFM results were obtained on glass, α-quartz, hexagonal ErMnO3, and periodically poled LiNbO3. The removal of background signal allows quantitative measurements of local intrinsic piezoelectric response with high sensitivity (≲0.1 pm/V).

Surface absorptions of H2S, HS and S on Fe(111) investigated by density functional theory

In this paper, the geometries and properties of H2S and its decomposition fragments adsorbed on Fe(111) surface are studied by means of the density functional theory based on generalized gradient approximation in wide ranges of coverage; the adsorption energy, work function, charge density difference, density of states, and charge population are calculated; the effect of coverage on surface adsorption is discussed; the adsorbability values of H2S, HS radical and S on Fe(111) are compared and analyzed. The results show that the force between absorbates and surface gradually weaken as the coverage increases, the interactions between the above-mentioned particles and Fe(111) are compared with each other: the magnitudes of their interactions are in the order of H2SxSy corrosion product films are easily formed, and the compactnesses of corrosion product films change with coverage variation. A study of the adsorbability values of various adsorbates in low index crystal plane indicates that the interactive force between adsorbates and Fe(111) surface is strongest, and that between the Fe(100) surface and Fe(110) is relatively weak, the difference in adsorption energy between them is not so much.

Numerical modeling of carrier gas flow in atomic layer deposition vacuum reactor: A comparative study of lattice Boltzmann models

This paper characterizes the carrier gas flow in the atomic layer deposition (ALD) vacuum reactor by introducing Lattice Boltzmann Method (LBM) to the ALD simulation through a comparative study of two LBM models. Numerical models of gas flow are constructed and implemented in two-dimensional geometry based on lattice Bhatnagar–Gross–Krook (LBGK)-D2Q9 model and two-relaxation-time (TRT) model. Both incompressible and compressible scenarios are simulated and the two models are compared in the aspects of flow features, stability, and efficiency. Our simulation outcome reveals that, for our specific ALD vacuum reactor, TRT model generates better steady laminar flow features all over the domain with better stability and reliability than LBGK-D2Q9 model especially when considering the compressible effects of the gas flow. The LBM-TRT is verified indirectly by comparing the numerical result with conventional continuum-based computational fluid dynamics solvers, and it shows very good agreement with these conventional methods. The velocity field of carrier gas flow through ALD vacuum reactor was characterized by LBM-TRT model finally. The flow in ALD is in a laminar steady state with velocity concentrated at the corners and around the wafer. The effects of flow fields on precursor distributions, surface absorptions, and surface reactions are discussed in detail. Steady and evenly distributed velocity field contribute to higher precursor concentration near the wafer and relatively lower particle velocities help to achieve better surface adsorption and deposition. The ALD reactor geometry needs to be considered carefully if a steady and laminar flow field around the wafer and better surface deposition are desired.

A TRANSMISSION SPECTRUM OF TITAN'S NORTH POLAR ATMOSPHERE FROM A SPECULAR REFLECTION OF THE SUN

Cassini/VIMS T85 observations of a solar specular reflection off of Kivu Lacus (87.?4N 241.?1E) provide an empirical transmission spectrum of Titan's atmosphere. Because this observation was acquired from short range (33,000?km), its intensity makes it visible within the 2.0, 2.7, and 2.8 ?m atmospheric windows in addition to the 5 ?m window where all previous specular reflections have been seen. The resulting measurement of the total one-way normal atmospheric optical depth (corresponding to haze scattering plus haze and gas absorption) provides strong empirical constraints on radiative transfer models. Using those models, we find that the total haze column abundance in our observation is 20% higher than the Huygens equatorial value. Ours is the first measurement in the 2-5 ?m wavelength range that probes all the way to the surface in Titan's arctic, where the vast majority of surface liquids are located. The specular technique complements other probes of atmospheric properties such as solar occultations and the direct measurements from Huygens. In breaking the degeneracy between surface and atmospheric absorptions, our measured optical depths will help to drive future calculations of deconvolved surface albedo spectra.

High spectral resolution atmospheric radiative transfer: Application of the equivalence theorem

This paper introduces several new variations of the equivalence theorem of Irvine [1964] which may increase the speed and accuracy of spectral radiative transfer models that calculate spectral radiance or flux. Using this theory, spectral gaseous, cloud, and surface absorptions are accommodated by integrating or summing over photon path length and scattering probability density functions (pdfs) after the completion of the multiple‐scattering calculation. This procedure can be performed for absorption coefficients at any spectral resolution within a wavelength interval in which scattering properties of the atmosphere can be considered constant. This technique eliminates the need to run the multiple‐scattering portion of a model more than once for each interval in lieu of integration and/or summation. If this procedure can be performed efficiently, dramatic increases in model speed may be realized. Also, because absorption coefficient spectral resolution can be extremely fine, the need for approximations or parameterizations is eliminated, increasing model accuracy. Unlike the original derivation, the new version of the gaseous absorption equation allows the use of complex model scattering atmospheres. An approximation is introduced which allows the use of gas profiles which vary in the vertical. Because employment of the complete theory requires a relatively large amount of computer memory, a pdf approximation is introduced to make it tractable. Validation of each relation is presented using a Monte Carlo model simulating shortwave flux. An example of shortwave flux transmitted through a three‐dimensional model atmosphere obtained from the Monte Carlo/equivalence theorem (MC/ET) model is shown along with an analysis of the effect of constant scattering property wavelength interval size on the resulting broadband flux.

Deconvolution and measurement of bulk and surface optical absorptions in Ti:Al2O3 crystals using photopyroelectric interferometry

The extension of our earlier single-layer (monolithic) photopyroelectric (PPE) interferometric theory to include surface and bulk optical absorptions has allowed the measurement of both bulk absorption coefficient and surface absorptance in one single experiment. Based on purely thermal-wave interferometry, the thermal-wave cavity lengths of a PPE interferometer were scanned using pairs of Ti: sapphire crystals with appropriate combinations of figure of merit, surface polish, and thickness. In the conventional single-ended (noninterferometric) PPE technique, the surface reflectivity, surface absorptance, and bulk absorption coefficient are always coupled together. However, PPE destructive interferometry provides a method for extracting highly precise values of one of these optical parameters, without the requirement of equally precise knowledge of the values of the others.

Theory of nonradiative decay dynamics in intensely pumped solid-state laser media via laser photothermal diagnostics

A rigorous analytical treatment of nonradiative deexcitation and thermal-conduction transient evolution in solid-state laser media, resulting from intense optical pumping with rectangular pulses from a time-gated laser source, is presented. This situation arises in rate-window photothermal detection from laser rods with bulk and surface absorptions, the latter being due to polishing during the manufacturing of the rod. Numerical simulations of the theory show that the surface nonradiative (optical-to-thermal) energy conversion term is likely to dominate even at absorptances on the order of 1%–2%. Therefore, polishing optimization appears to be necessary in order to minimize laser losses at the surfaces when laser rods are active in a resonator cavity. The present theory also provides physical insights into the very different nature of the bulk- and surface-originating heat-conduction transients, as well as on the profile of the superposition photothermal wave form and its dependence on the optical, thermal, and metastable-state relaxation parameters. As a prelude for input to the photothermal theory, a treatment of the excited-state dynamics of a typical laser manifold pumped by an intense laser beam, away from or near saturation, is developed, and the luminescence and photothermal energy source profiles are calculated analytically.

Surface and bulk absorption characteristics of chemically vapor-deposited zinc selenide in the infrared

<p>Chemically vapor-deposited zinc selenide exhibits outstanding properties in the infrared and has been established as a prime material for transmissive optics applications. Here we present and discuss data relating to the surface and the bulk absorption forward-looking infrared- (FLIR-) grade chemically vapor-deposited ZnSe, at wavelengths (2-20 µm) and temperatures (100-500 K) of current interest.</p><p>This investigation is based on both spectral emittance measurements and infrared transmission spectroscopy performed in the context of a systems development program. Surface effects can be detected at wavelengths of up to 14 µm and usually predominate at wavelengths of less than 8 µm. Fractional surface absorptions are temperature independent from approximately 200 to 400 K and can be fitted to a Fourier series, at wavelengths ranging from 3.5 to 13.5 µm. The bulk absorption coefficient (βv) is strongly dependent on temperature as well as wavelength, but it can be approximated by a bivariate polynomial expressin that yields recommended values. At wavelengths λ ≲ 10 µm, βv decreases with increasing temperature; it is shown that a wavelength-independent Debye-Waller factor provides a correct description of the temperature dependence, thus pointing to infrared-active localized modes. At wavelengths λ ≳ 14 µm, βv increases with temperature and exhibits temperature dependencies (T(1.7), T(2.6)) that reflect three- and four-phonon summation processes. Finally, an analysis of the temperature dependence of βv at 10.6 µm demonstrates that the intrinsic lattice dynamical contribution to bulk absorption at this wavelength should be close to 4 × 10(-4) cm(-1), in accord with the results of earlier laser calorimetry tests performed on exceptionally pure laser-grade chemically vapor-deposited ZnSe.</p>

Photopyroelectric deconvolution of bulk and surface optical-absorption and nonradiative energy conversion efficiency spectra in Ti:Al2O3 crystals

The extension of an earlier monolithic photopyroelectric spectroscopic model [A. Mandelis et al., Phys. Rev. B 48, 6808 (1993)] to include surface and bulk optical absorptions and the subsequent optical-to-thermal (nonradiative) energy conversion efficiencies associated with these sites has allowed the self-consistent determination of visible spectra of these quantities, using a very sensitive noncontact experimental configuration to obtain in-phase and quadrature photopyroelectric spectra of Ti:sapphire crystals of two thicknesses and figures of merit.

Photothermal displacement spectroscopy: An optical probe for solids and surfaces

We present a sensitive technique for determining the optical and thermal properties of solids, surfaces and thin films. This technique, photothermal displacement Spectroscopy, is based on the detection of the thermal expansion of a sample upon absorption of electromagnetic radiation. The technique is well suited for in situ ultrahigh vacuum studies and for experiments where wide temperature ranges are required. We show that surface and bulk optical absorption can be distinguished and that surface absorptions of αL=10−6/W of incident power can be measured. The theoretical basis of the signal generation is given, and excellent experimental and theoretical agreement is demonstrated. The implications of our findings to imaging and microscopy are discussed.