Light-scattering Properties Research Articles

Omnidirectional light harvesting enhancement of dye-sensitized solar cells decorated with two-dimensional ZnO nanoflowers

In this study, the chemical solution method was used to separately fabricate one-dimensional (1D) zinc oxide (ZnO) nanorods (NRs) and two-dimensional (2D) ZnO nanoflowers (NFs) on photoelectrodes for use in dye-sensitized solar cells (DSSCs). ZnO nanostructures (NSs) with different dimensions were grown on the photoelectrodes, and the effects of the NSs on the omnidirectional light-harvesting characteristics of the DSSCs and their bandgap were evaluated. The crystal structures and morphologies of the ZnO NSs were analysed using X-ray diffraction analysis and field-emission scanning electron microscopy, while their dye-adsorption characteristics were determined using an ultraviolet–visible–near infrared spectrometer. In addition, the finite-difference time-domain method was used to simulate the effects of the dimensions of the NSs on their light-scattering properties. The photoelectrodes with the ZnO NSs with different dimensions were then used to construct DSSCs, which were tested using electrochemical impedance spectroscopy as well as with a monochromatic incident photon-to-electron conversion efficiency measurement system and a solar simulator. Furthermore, with an increase in the incidence angle, the light-conversion efficiency of the 1D ZnO NRs reduced by 63.6% while that of the 2D ZnO NFs reduced only by 12%. Thus, DSSCs based on the 2D ZnO NFs are capable of capturing multidirectional incident light and hence ideal for use under scattered-light conditions.

Color generation from self-organized metalo-dielectric nanopillar arrays

Abstract Nanostructures composed of dielectric, metallic or metalo-dielectric structures are receiving significant attention due to their unique capabilities to manipulate light for a wide range of functions such as spectral colors, anti-reflection and enhanced light-matter interaction. The optical properties of such nanostructures are determined not only by the shape and dimensions of the structures but also by their spatial arrangement. Here, we demonstrate the generation of vivid colors from nanostructures composed of spatially disordered metalo-dielectric (In/InP) nanopillar arrays. The nanopillars are formed by a single-step, ion-sputtering-assisted, self-assembly process that is inherently scalable and avoids complex patterning and deposition procedures. The In/InP nanopillar dimensions can be changed in a controlled manner by varying the sputter duration, resulting in reflective colors from pale blue to dark red. The fast Fourier transform (FFT) analysis of the distribution of the formed nanopillars shows that they are spatially disordered. The electromagnetic simulations combined with the optical measurements show that the reflectance spectra are strongly influenced by the pillar dimensions. While the specular and diffuse reflectance components are appreciable in all the nanopillar samples, the specular part dominates for the shorter nanopillars, thereby leading to a glossy effect. The simulation results show that the characteristic features in the observed specular and diffused reflectance spectra are determined by the modal and light-scattering properties of single pillars. While the work focuses on the In/InP system, the findings are relevant in a wider context of structural color generation from other types of metalo-dielectric nanopillar arrays.

Spectrophotometry from Mars Hand Lens Imager goniometer measurements: Kimberley region, Gale crater

The light-scattering properties of surface materials on Mars are typically modeled using in situ spectrophotometric imaging sequences taken at multiple times of day to provide sufficient phase coverage. Herein, we report analyses of observations acquired at one time of day but under varying emission angles using the Mars Hand Lens Imager (MAHLI) on the robotic arm of the Mars Science Laboratory (MSL) rover as a goniometer. A multiple-viewpoint data set was acquired on Sol 544 by manipulating the arm to provide MAHLI images from 20 arm positions, all centered at the same location and from a near-constant distance of 1 m from the surface, permitting a phase angle coverage from ∼8 to 100°. From these images, we constructed a digital terrain model of the scene, and used it in combination with atmospheric scattering models to remove the diffuse components of radiance from surface units. Radiative transfer models using Hapke theory were conducted using the direct radiance components from specific rock and soil units. Despite the relatively limited number of observations, our modeled Hapke parameters were well-constrained for terrain types such as soils and certain types of rocks that were common within the scene, but the errors increased for rock types with fewer observations. Results from one-term and two-term Henyey-Greenstein phase functions show the soil units to be more backscattering than rocks, consistent with previous photometric studies of martian landing sites. Overall, we find that the MAHLI goniometer sequences can produce reasonable and consistent photometric results, providing a new and efficient means of acquiring spectrophotometric data by arm cameras on rovers such as MSL.

Estimation of Particle Size Distribution from Bulk Scattering Spectra: Validation on Monomodal Suspensions.

A particle size distribution (PSD) estimation method based on light-scattering properties was validated on experimental visible/near-infrared scattering spectra of polystyrene suspensions, with a nominal particle size ranging from 0.1 to 12 μm in diameter. On the basis of μs and g spectra extracted from double integrating sphere measurements, good PSD estimates were obtained for particles ≥1 μm. The particle volume fraction estimates in the case of μs were close to the target concentrations, although influenced by small baseline fluctuations on the spectra. For submicrometer particles, on the other hand, the non-oscillating μs spectra lack discriminating power, resulting in erroneous PSD estimates. The reduced scattering coefficient spectra (μs') were found less useful for particle size estimation as they lack a characteristic shape, causing an over- or underestimation of the distribution width. In summary, the estimation routine proved to deliver PSD estimates in line with the reference measurements for micrometer-sized or larger particles based on their μs and g scattering spectra. Additional validation on more polydisperse samples forms the next step before going to bimodal PSD estimates.

Light scattering from volcanic-sand particles in deposited and aerosol form

The light-scattering properties of volcanic sand collected in Iceland are studied here to characterize the sand particles and develop a reference for future remote-sensing observations. While such sand is common in Iceland, the smaller-size fraction can be readily transported by winds and found in the atmosphere at distant locations. The sand appears dark when deposited on a surface due to the high optical absorption of the material. Therefore, atmospheric regions containing such particles during a dust storm may absorb sunlight considerably, causing redistribution of solar energy. Here, we measure the angular scattered-light intensity and degree of linear polarization from the sand. This is done with two experimental apparatuses, the Cosmic Dust Laboratory (CoDuLab) at the Institute de Astrofísica de Andalucía (IAA) and the goniospectropolarimeter (FIGIFIGO) at the Finnish Geospatial Research Institute (FGI). Two scattering-scenarios of practical interest for remote-sensing applications are considered: (1) single sand-particles suspended in aerosol as an optically thin cloud, and (2) the same particles deposited on a substrate. We also model the measurements with the discrete dipole approximation to estimate the complex-valued refractive index m, where we find that m ≈ 1.6 + 0.01i at λ = 647 nm. Lastly, we present a comparative analysis of the polarimetric response of the sand particles with that reported in the literature for carbon-soot, another highly absorbing atmospheric contaminant.

A Divide-and-Conquer Strategy for Quantification of Light Absorption, Scattering, and Emission Properties of Fluorescent Nanomaterials in Solutions.

Optical properties of fluorescent materials including their UV-vis absorption, scattering, and on-resonance fluorescence activities are strongly wavelength-dependent. Reported herein is a divide-and-conquer strategy for experimental quantification of fundamental optical constants of fluorescent nanomaterials including their UV-vis absorption, scattering, and on-resonance-fluorescence (ORF) cross-section spectra and ORF fluorescence and light scattering depolarization spectra. The fluorophore UV-vis extinction spectrum is first divided into a blue and a red wavelength region. The UV-vis extinction cross-section spectrum in the blue wavelength region is decomposed into its absorption and scattering extinction spectra straightforwardly using the established polarized resonance synchronous spectroscopic technique. In its red wavelength region, however, the fluorophores can be simultaneous photon absorbers, scatterers, and anti-Stokes-shifted, on-resonance, and Stokes-shifted fluorescence emitters under the resonance excitation and detection conditions. A polarized anti-Stokes'-shifted, on-resonance, and Stokes'-shifted spectroscopic method is developed for quantifying fluorophore absorption, scattering, one-resonance fluorescence (ORF) cross-section spectra, and scattering and ORF fluorescence depolarization spectra in this wavelength region. Example applications of the presented techniques were demonstrated with fluorescent polystyrene nanoparticles, fluorescent quantum dots, and molecular fluorophores Rhodamine 6G and Eosin Y.

Recent Advances in the Optimization of Organic Light-Emitting Diodes with Metal-Containing Nanomaterials.

Metal-containing nanomaterials have attracted widespread attention in recent years due to their physicochemical, light-scattering and plasmonic properties. By introducing different kinds and different structures of metal-containing nanomaterials into organic light-emitting diodes (OLEDs), the optical properties of the devices can be tailored, which can effectively improve the luminous efficiency of OLEDs. In this review, the fundamental knowledge of OLEDs and metallic nanomaterials were firstly introduced. Then we overviewed the recent development of the optimization of OLEDs through introducing different kinds of metal-containing nanomaterials.

Omnidirectional light‐harvesting enhancement of dye‐sensitized solar cells with ZnO nanorods

In this work, the chemical solution method was used to prepare one-dimensional (1-D) ZnO nanorod (NR) photoelectrodes, which were subsequently used in dye-sensitized solar cells (DSSCs). The effects of ZnO NRs on the omnidirectional light-harvesting performance of DSSCs were investigated by growing ZnO NRs with varying lengths as photoelectrodes. On the basis of field-emission scanning electron microscopy and ultraviolet (UV)–vis-near infrared (NIR) spectroscopy measurements on the ZnO NR photoelectrodes of varying lengths, it was observed that the dye adsorption and light-scattering properties of NRs are affected by their length. In addition, DSSCs were prepared using ZnO NRs of varying lengths. These DSSCs were examined via electrochemical impedance spectroscopy, monochromatic incident photon-to-electron conversion efficiency measurements, and solar simulations to measure their photovoltaic efficiencies, carrier lifetimes, and device characteristics in omnidirectional antireflection measurements. The highest photovoltaic efficiency between these DSSCs was 0.33%. Omnidirectional antireflection measurements were performed on DSSCs with different ZnO NR lengths, and it was observed that the smallest change in efficiency between angles of incidence of 0° and 60° was 23%. Therefore, the light-scattering properties of ZnO NR photoelectrodes improve the omnidirectional antireflection light capture characteristics of DSSCs.

A shape model of internally mixed soot particles derived from artificial surface tension

Abstract. To retrieve the physical properties of aerosols from multi-channel ground-based and satellite measurements, we developed a shape model of coated soot particles and created a dataset of their optical properties. Bare soot particles were assumed to have an aggregate shape, and two types of aggregates with different size–shape dependences were modeled using a polyhedral Voronoi structure. To simulate the detailed shape properties of mixtures of soot aggregates and adhered water-soluble substances, we propose a simple model of surface tension derived from the artificial surface potential. The light-scattering properties of the modeled particles with different volume fractions of water-soluble material were calculated using the finite-difference time-domain method and discrete-dipole approximation. The results of the single-scattering albedo and asymmetry factors were compared to those of conventional internally mixed spheres (i.e., effective medium spheres based on the Maxwell-Garnett approximation and simple core-shell spheres). In addition, the lidar backscattering properties (i.e., lidar ratios and linear depolarization ratios) of the modeled soot particles were investigated. For internally mixed soot particles, the lidar backscattering properties were sensitive to the shape of the soot particles and the volume mixing ratio of the assumed water-soluble components. However, the average optical properties of biomass smoke, which have been reported from in situ field and laboratory measurements, were difficult to explain based on the individually modeled particle. Nonetheless, our shape model and its calculated optical properties are expected to be useful as an alternative model for biomass smoke particles in advanced remote sensing via multi-channel radiometer and lidar measurements.

A low-cost bench-top research device for turbidity measurement by radially distributed illumination intensity sensing at multiple wavelengths

Presented here is a new bench-top research device for the measurement of the optical turbidity of natural sediment-laden water samples. This prototype device employs 18 unique angular measurement positions and a variety of user-selectable LED light sources. The motivation for this project was the need to generate more parameter-rich data sets pertaining to the light-scattering properties of natural sediment suspensions, and to address the issues raised by Kitchener et al. (2017) concerning the inconsistent calibration methodologies currently employed to quantify suspended sediment concentration (SSC) by optical turbidity measurement. The mechanical design comprises re-purposed waste plastic materials and 3D-printed parts. The active light-source control and monitoring hardware and firmware executes on the open-source Arduino embedded microcontroller platform. The modular light sensors plug into any of the angular measurement positions, providing a 0–5 V nominal output signal, which is readable by the user's choice of data-acquisition system. The device will facilitate the highly detailed characterization of suspended sediment samples, providing 18 voltage output channels for analysis by the user. The precise calibration of the light sensors is by the use of neutral density (ND) filters in conjunction with light-source electrical current measurements, providing light-source intensity values as required. The empirical data provided by existing turbidity meters are acquired using incommensurate methodologies, and therefore they are not cross-comparable. A new methodology, described here, facilitates the cross-comparability of turbidity measurements.

Three-Dimensional Bicontinuous BiVO4/ZnO Photoanodes for High Solar Water-Splitting Performance at Low Bias Potential.

A photoanode capable of high-efficiency water oxidation at low bias potential is essential for its practical application for photocathode-coupled tandem systems. To address this issue, a photoanode with low turn-on voltage for water oxidation and high charge separation efficiency at low bias potential is essential. In this study, we demonstrate the photoanode of the BiVO4/ZnO three-dimensional (3D) bicontinuous (BC) structure. ZnO has a relatively cathodic flat-band potential, which leads to low turn-on potential; the BiVO4/ZnO 3D BC photoanode shows an onset potential of 0.09 V versus the reversible hydrogen electrode ( VRHE). Moreover, we achieve remarkably high charge separation efficiency at low bias potential (78% at 0.6 VRHE); this is attributed to the application of thin-film BiVO4 shells by high light-scattering properties of the 3D BC structure. As a result, the BiVO4/ZnO 3D BC photoanode generates a high water oxidation photocurrent of up to 3.4 ± 0.2 mA cm-2 (with CoPi catalyst coating). This photocurrent value is reproducible, and the photocurrent-to-O2 conversion efficiency is over 90%. To the best of our knowledge, this is the highest value among the values of the photocurrent at 0.6 VRHE in previous BiVO4-based heterojunction photoanodes.

Does orbital angular momentum have effect on laser's scattering by molecular atmosphere?

Lasers with orbital angular momentum (OAM) have potential applications in communication technology, manipulation of particles, and remote sensing. Because of its unusual light-scattering properties, the OAM laser's interaction with a molecular atmosphere must be studied to ensure that it is not lossy for communication or remote-sensing applications that involve its transmission through an atmospheric environment. In this study, the finite-difference time-domain (FDTD) method [21] is applied to calculate the light scattering of the purely azimuthal (the radial mode number is assumed to be zero) Laguerre–Gaussian (LG) beams with OAM by very small dielectric particles. Not like Lorenz-Mie solutions, the FDTD method can calculate for particles off the central axis of the LG beam. It is found that when the particles are very small, and the topological charge number of the OAM of a laser is not extremely large, the laser's OAM has little effect on the scattering phase function. This suggests that Rayleigh theory can be applied directly to calculate the light scattering by atmospheric molecules. The transmission of a laser beam with OAM in a molecular atmosphere is not different from that of a regular Gaussian beam.

Interpolating light-scattering properties of irregularly shaped, absorbing particles.

Success in developing remote-sensing methods is largely based on adequate modeling of target-particle shapes. In various terrestrial and cosmic applications, submicrometer- and micrometer-sized dust particles appear to have a highly irregular morphology. Light scattering by such irregularly shaped particles can be computed only with a numerical technique that, in practice, is a time-consuming approach, demanding significant computational resources. In this Letter, we discuss an efficient way to accelerate light-scattering computations through interpolation of the numerical results obtained at different levels of material absorption. We find a nonlinear dependence of reflectance, degree of linear polarization, and linear and circular polarization ratios on the imaginary part of refractive index Im(m). Over the range of ΔIm(m)=0.05, the dependence can be satisfactorily described with a cubic polynomial function, whose determination requires exact computations at four different values of Im(m). The light-scattering characteristics at other intermediate values of Im(m) can be inferred with great accuracy via interpolation.

Hollow organosilica beads as reference particles for optical detection of extracellular vesicles

Background The concentration of extracellular vesicles (EVs) in body fluids is a promising biomarker for disease, and flow cytometry remains the clinically most applicable method to identify the cellular origin of single EVs in suspension. To compare concentration measurements of EVs between flow cytometers, solid polystyrene reference beads and EVs were distributed in the first ISTH-organized interlaboratory comparison studies. The beads were used to set size gates based on light scatter, and the concentration of EVs was measured within the size gates. However, polystyrene beads lead to false size determination of EVs, owing to the mismatch in refractive index between beads and EVs. Moreover, polystyrene beads gate different EV sizes on different flow cytometers. Objective To prepare, characterize and test hollow organosilica beads (HOBs) as reference beads to set EV size gates in flow cytometry investigations. Methods HOBs were prepared with a hard template sol-gel method, and extensively characterized for morphology, size, and colloidal stability. The applicability of HOBs as reference particles was investigated by flow cytometry with HOBs and platelet-derived EVs. Results HOBs proved to be monodisperse with a homogeneous shell thickness. Two-angle light-scattering measurements by flow cytometry confirmed that HOBs have light-scattering properties similar to those of platelet-derived EVs. Conclusions Because the structure and light-scattering properties HOBs resemble those of EVs, HOBs with a given size will gate EVs of the same size. Therefore, HOBs are ideal reference beads with which to standardize optical measurements of the EV concentration within a predefined size range.

Sensitivity enhanced photo-thermal borders detection in bio-phantoms enriched with gold nanoparticles

In the last decade diversity of applications in the fields of diagnostics and treatment for biomedical applications using gold nanoparticles (GNPs) as contrast agent sprang up. The strong optical absorption and scattering properties of the GNPs due to their localized surface plasmon resonance (LSPR) effect enables their use as contrast agents in these applications. The usage of the light-scattering properties of the GNPs in most imaging methods lead to background noise stems from light scattering from the tissue due to the same wavelengths of the illumination source and the GNPs’ scattering. In our previous works we presented a method to improve border detection of bio-phantoms enriched with GNPs leading for real-time complete tumor resection by using a modulated laser illumination, photo thermal imaging camera and the optical absorption of specially targeted GNPs. In this system the thermal camera detects the temperature field of the illuminated bio-phantoms. Although the surrounding area got heated the border location was detected at a precision of at least 0.5 mm through use of a simple post processing technique. In this paper, we present a continuation of our previous research with modified system of time sequence labelling (TSL) processing for improved border detection capable of operating and detecting borders at much lower signal to noise levels.

A European aerosol phenomenology – 6: scattering properties of atmospheric aerosol particles from 28 ACTRIS sites

Abstract. This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of σsp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, σsp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intra-annual variability. At mountain sites, higher σsp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher σsp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low σsp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high σsp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of σsp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of σsp are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.

Coating effect on light scattering by irregularly shaped particles

In this article, we study the impact of water coating on light scattering by irregularly shaped agglomerated debris particles. We compute light-scattering properties of three types of irregular particles, which simulate atmospheric particles before and after coating. We consider two types of the Junge size distributions over sub-micron range of rc. The coating is represented as deposition of same volume of material on original particles. We found that only the degree of linear polarization is sensitive to coating type, especially maximum value of the polarization that is typically acquired at side scattering. Behavior of the degree of linear polarization maximum appears in accordance with the Umov effect. The linear depolarization ratio at backscattering direction δl is insensitive to coating material, but it is dependent from particles size.

Ag nanoparticles for determination of bisphenol A by resonance light-scattering technique

Resonance light-scattering (RLS) technique was developed for studying the interaction of silver nanoparticles (Ag NPs) with bisphenol A. A simple and environmentally friendly method was developed to synthesize Ag NPs using cinnamon extract. Synthesized nanoparticles were characterized using various measurement techniques. The synthesized Ag NPs were nearly spherical, with the sizes ranging from 30 to 60 nm. Spectral analysis indicated that the cinnamon extract acted as the reducing and capping agents on the surface of Ag NPs. RLS technique was used as the detection method. Light-scattering properties of the synthesized nanoparticles in the presence or absence of bisphenol A was selected as the detection signal. Under the optimal conditions, the linear dynamic range and RSD were found to be 0.01–10.0 mg L−1 and 2.78% (n = 3), respectively. A limit of detection of 0.005 mg L−1 was obtained for the determination of bisphenol A. The obtained results showed successful application of the method for the analysis of bisphenol A in real samples.

Broadband Dielectric–Metal Hybrid Nanoantenna: Silicon Nanoparticle on a Mirror

We developed a broadband dielectric–metal hybrid nanogap resonator composed of a silicon nanoparticle (Si NP) and gold (Au) flat surface. We fabricate the nanogap resonator by depositing a monolayer of colloidal quantum dots (QDs) (∼2.8 nm in diameter) on a Au surface followed by dropping a diluted colloidal solution of Si NPs (∼150 nm in diameter). The QD monolayer acts as a precisely length-controlled nanogap as well as a light emitter to monitor the radiative properties of the nanogap resonator. We investigate the light-scattering properties of single-nanogap resonators experimentally and theoretically and found that the coupling of the Mie resonance of Si NPs with a Au surface effectively confines the electromagnetic field into the nanogap in a wider wavelength range than an all-metal nanogap resonator with a comparable size. Furthermore, we show that the resonance wavelength of the hybrid nanogap resonator is less sensitive to the gap length than that of the all-metal one. We demonstrate that the bro...

Optical Characterization of Mineral Dust and Soot Particles in the El Paso-Juarez Airshed

The light-scattering properties of mineral dust and soot particles in the El Paso-Juarez Airshed were analyzed using data from an acoustic extinctiometer and a laser particle counter in conjunction with a non-spherical scattering model for polydisperse and randomly oriented particles, the T-matrix model. The data selected correspond to days exhibiting a mean relative humidity (RH) less than 20% to avoid effects of possible aerosol hygroscopic growth. The inter-comparison for the selected days of the extinction and scattering coefficients results obtained using the T-matrix and the laser particle counter, with those obtained from an acoustic extinctiometer at a wavelength of 0.87 μm shows good agreement. In addition, the single-scattering albedo for this region is analyzed for the selected days. The methodology developed in this work can be used as a diagnostic tool to characterize mineral dust and soot particles, and the results of this study will provide a better understanding of the aerosol optical properties for the El Paso-Juarez Airshed.