Variation Of Transmittance Research Articles

Electrochemical properties of WO3 sol-gel thin films on indium tin oxide/poly(ethylene terephthalate) substrate

This work presents a study on the thin films of WO3 deposited on a flexible substrate as a possible application in a flexible electrochromic device. The films were prepared by the sol-gel method and deposited by a dip-coating technique on indium tin oxide/poly(ethylene terephthalate) (ITO/PET) and densified at 100 °C for 1 h. The films of WO3 were subjected to electrochemical, optical, structural, and morphological characterizations that pointed out the film, deposited with a withdrawal of 60 mm min−1, which showed the charge density in the insertion process of 32.86 mC cm−2. This film also presented the electrochemical stability during 200 cycles. The transmittance variation (ΔT555 nm) between colored and bleached states was 42.6% and the coloration efficiency (η) was 14.91 cm2 C−1. The X-ray diffraction (XRD) confirmed the amorphous structure of the films and the atomic force microscopy (AFM) the root mean-squared (RMS) roughness of 4.15 nm. All the results indicate that this film may be used as an active layer in a flexible electrochromic device.

Impedance-matched dielectric metasurfaces for non-discrete wavefront engineering

Metasurfaces can manipulate optical wavefronts by locally shifting the phase of incident light with metallic or dielectric optical nanoresonators that are generally arranged on a lattice with subwavelength spacing. However, such conventional metasurfaces inevitably generate a spatially discrete multi-level phase profile due to the spacing of their building blocks. This directly leads to an efficiency reduction and thus limits their capability. Here, we propose and demonstrate highly efficient transmissive metasurfaces with the ability to form a continuous phase profile. The proposed strategy relies on the fact that high-index dielectric nanobeams with gradually modulated widths can be interpreted to be a virtually impedance-matched material with spatial variations of its refractive index. By highly utilizing such features, one-dimensionally continuous, arbitrary phase profiles can be created in a simple manner with the width profile design. Since spatial transmittance variations can be minimized due to the impedance matching feature, this approach provides a nearly ideal phase profile for spatial light modulation with phase-only filtering operations. We demonstrate that this approach has the capability to improve the performance in various metasurface-based optical components, including polarization-dependent, large-angle beam deflectors and versatile multi-beam splitters. Considering that designing optical phases even in deep-subwavelength regimes is critical for free-space optics, the proposed approach will enable new classes of optical components with complex wavefront engineering.

The impact of thermal transmittance variation on building design in the Mediterranean region

Contrarily to what happens in northern European countries, buildings in the Mediterranean region are prone to overheating. Consequently, it is important to better understand the role that the thermal transmittance of the building envelope elements has on air-conditioning consumptions. This paper analyzes the effect of different U-values on building design in the Mediterranean area. 192000 residential buildings were randomly generated for sixteen distinct locations and the energy consumption was assessed for each. It was found that in northern Mediterranean locations, as U-values decreased, energy consumption also decreased. However, in warmer climates, low thermal transmittances tended to significantly increase energy consumption. Hence, the lower the latitude, the higher the U-values should be, in order to prevent increasing the cooling demands. Additionally, geometry-based indexes were correlated with the building’s energy performance. For high U-values, it was found that bigger buildings worsen the energy performance and larger windows tended to improve it. For low U-values, bigger north-facing windows were beneficial. There is an adequate interval of values for which the geometry has a lower impact, which is wider and higher for lower latitudes, thus meaning that not only does the building performance improve but architects are also freer to explore alternative designs.

Influence of canopy condensate film on the performance of solar chimney power plant

Presence of dust and/or condensate film affects the transmissivity of solar radiation through the transparent canopy/cover of solar collectors. This paper presents experimental investigation results of water vapor film condensate on the upper and lower surfaces of the canopy and how it affects solar chimney performance. The experimental measurements were carried out utilizing the solar chimney model, which has a collector of 7.0 m diameter and chimney of 6.5 m height above the collector. After 10 days of measurements and observation, radiation transmittance was considerably reduced from 7:30 a.m. until 10:30 a.m. due to the presence of condensate. Consequently, collector and solar chimney performance were influenced. A 9%–10% variation in solar radiation transmittance was found between dry and wet canopy. The condensate film required 2.0–3.0 h to evaporate. During the evaporation time (7:30 a.m. to 10:30 a.m.), the increase in the collector air temperature under wet canopy was 3.0 °C–5.0 °C less compared with that under dry canopy. Solar radiation from the sun until 10:30 a.m. was absorbed by the condensate film to evaporate. A delay was observed in the energy conversion processes from solar to thermal to kinetic, thereby delaying power generation. The presence of water condensate film reduced the hydrothermal performance of the solar chimney by two ways: by reducing the transmittance of solar radiation and by absorbing solar radiation from the water vapor particles to evaporate. An auxiliary heat source that supplies heat before sunrise is necessary to evaporate the condensate film and allow the solar chimney to operate early.

Electrochromic and photoluminescence properties of cobalt oxide thin films prepared by spray pyrolysis

Cobalt oxide thin films were prepared by a facile spray pyrolysis technique, using a perfume atomizer with an aqueous solution of hydrated cobalt chloride salt with a molar concentration of 0.025 M as a source of cobalt. The films were deposited onto glass substrates at temperature of 350 °C. The structural, morphological, and electrochromic properties of the obtained films were studied. It was found from X-ray diffraction analysis that the films were polycrystalline in nature with spinel-type cubic structure and preferred orientation along [111] direction. The Scanning Electron Microscopy images revealed a porous structure with the average grain size around 200 nm. The cyclic voltammetry measurements revealed that Cobalt oxide thin film is an anodically coloring electrochromic material with a transmittance variation in the visible range of 31%, and a fast response time (about 2 seconds) and a good cycling stability. These electrochromic performances make cobalt oxide thin film an attractive material for using as an anodic electrochromic material in smart windows devices. The photoluminescence spectra exhibited a strong emission in the visible region confirming the good crystallinity properties of Co3O4 thin films.

Feature Fusion-Based Multi-Task ConvNet for Simultaneous Optical Performance Monitoring and Bit-Rate/Modulation Format Identification

We propose a novel feature fusion based multi-task convolutional neural network (ConvNet) for simultaneous bit-rate and modulation format identification (BR-MFI) and optical performance monitoring (OPM) in heterogeneous fiber-optic networks. The proposed multi-task ConvNet fuses the intermediate layers through the convolutional operation and then trains multi-task losses on the fused feature. In addition to traditional multi-task ConvNet's ability of the feature extraction and sharing, our multi-task ConvNet is able to capture both global and local information of phase portraits and has good performance on OPM and BR-MFI tasks in a short processing time (~51 ms). The simulation results of six signals (consisted of two bit-rates and three modulation formats) demonstrate the root-mean-square (RMS) errors of the optical signal-to-noise ratio (OSNR), chromatic dispersion (CD) and differential group delay (DGD) are 0.81 dB, 1.52 ps/nm and 0.32 ps, respectively. Meanwhile, the 100% classification accuracy can be obtained for BR-MFI. Besides, the effects of the fused feature shape, the location of feature extracted for fusion, the transmitter variations and fiber nonlinearity on the performance of the proposed technique are thoroughly investigated.

Surface Structures of Cosmetic Standard Poly Methyl Methacrylate UV Evaluation Plates and their Influence on the in vitro Evaluation of UV Protection Abilities of Cosmetic Sunscreens.

Cosmetic standard poly methyl methacrylate (PMMA) UV evaluation plates, i.e., roughened PMMA plates, are used in the EU and the US for the in vitro evaluation of UV protection abilities of sunscreen, such as in vitro UVA-PF and critical wavelength for the Broad-spectrum approval. In our previous studies, inhomogeneity in the thickness of a pseudo-sunscreen layer applied on a flat quartz plate was observed to alter UV transmission. Thus, the surface roughness of the standard plates should have a significant influence on the in vitro evaluation. In the present study, we have analyzed the surface structures of three cosmetic standard PMMA UV evaluation plates: Helioplates HD6 (Sa = 6 µm) and ISO plates (Ra = 2 and 5 µm). A decamethylcyclopentasiloxane and 2-propanol-mixed solvent solution of acrylsilicone resin was prepared, and the solution was added dropwise onto the plates. After the evaporation of the solvents, the plates were cut and the cross section was analyzed using SEM-EDS. The distribution of silicon atoms at the cross-section suggested that the maximum depth of penetrating of acrylsilicone resin was larger than Ra for all the standard plates, and the surface structure was significantly different for each standard plate. In addition, cracks into which the acrylsilicone resin deeply penetrated were observed on the surface of some plates. Clear-solution-type pseudo-sunscreen samples in which UV absorbers and acrylsilicone resin were dissolved were deposited on the standard roughened PMMA plates. It was observed that the addition of acrylsilicone resin drastically changed the net UV transmission. The degree to which the hollows of the roughened surface were filled with the pseudo-sunscreen samples determined the variation of UV transmittance.

Three‐Mode Modulation Electrochromic Device with High Energy Efficiency for Windows of Buildings Located in Continental Climatic Regions

AbstractA sustainable use of energy in buildings demands energy‐efficient windows. A new design concept for electrochromic (EC) smart windows, easy to implement at the industrial level, is introduced here. It enables simultaneous control of visible and near‐infrared (NIR) solar radiation, thus contributing to reduce heating and cooling loads especially in buildings located in areas experiencing wide daily temperature ranges. The EC device comprises amorphous indium zinc oxide, a conducting oxide transparent in the visible and NIR spectral regions, as nonactive layer, and a sol–gel protonic ionic liquid‐doped di‐ureasil electrolyte displaying high transparency and proton conductivity. The device offers three voltage‐operated modes: bright hot (+3.0 V: transmittances of 70/83% at 555/1000 nm), semi‐bright warm (−2.0 V: transmittances of 37/35% at 555/1000 nm), and dark cold (−2.5 V: transmittances of 6/4% at 555/1000 nm). Its main figures of merit are: high switching efficiency (transmittance variations of 64/79% at 555/1000 nm), high optical density modulation (1.1/1.3 at 555/1000 nm), high optical contrast ratio in the visible region (lightness variation of ≈43), good cycling stability, and unprecedented coloration efficiency (−12538/−14818 cm2 C−1 and +2901/+3428 cm2 C−1 at 555/1000 nm), outstanding optical memory (transmittance variation loss of only 24% more than 4 months after coloration), and self‐healing ability following mechanical stress.

Plasmonic Ag nanowires sensitized ZnO flake-like structures as a potential photoanode material for enhanced visible light water splitting activity

Silver nanowires (AgNWs) functionalized ZnO flake-like (ZnO/AgNWs) morphological heterostructures were developed as a promising photoanode by facile RF magnetron sputtering and polyol methods. Herein, we demonstrate the role of rationally tailored AgNWs weight concentration (0, 0.03, 0.05 and 0.07g) on ZnO flake-like morphology for enhanced visible-light-driven photoelectrochemical (PEC) water splitting activity. From XRD studies, ZnO (002) facets were effectively influenced by the selective growth of Ag (111) facets. Notably, XPS studies reveal the strong correlation between AgNWs and ZnO, showing a significant red shift in Zn 2p and O 1s levels and blue shift in Ag 3d level. Whereas, surface hydroxyl groups (OH−) were originated on ZnO/AgNWs heterostructure, which acts as light trapping states. Interestingly, FESEM images comprise AgNWs distribution on ZnO flake-like morphology, which suggests AgNWs are most accessible networks at the interface of ZnO. As a result, we observed significant variation in the optical transmittance and matching band gap for strong visible light absorption. In conclusion, selective growth of AgNWs-0.05g on ZnO promoted the strong interface reaction kinetics with impressive photoconversion efficiency (0.38%). Thus, developing of unique flake-like/nanowire morphological features underlined to be crucial interest in energy conversion applications.

Bionic SiO2@Fc(COCH3)2 core-shell nanostructure for enhancing the electrochromic properties of ferrocene

Although the properties of electrochromic materials (ECMs) have been enhanced using fabricated porous materials, the effect of materials porosity on such an enhancement remains unclear. Here, we report a novel ECMs with an adjustable pore hierarchy based on quasi-amorphous and ordered arrays of SiO2@Fc(COCH3)2. ECMs with different pore systems were generated by modifying Fc(COCH3)2 concentration and self-assembly temperature. The composition and core-shell structure of the SiO2@Fc(COCH3)2 nanospheres were confirmed through scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR) and EDX mapping. The influence of adjustable pore system on the electrochemical behavior was studied. Experimental results showed that the current density of the redox couple peaks of the quasi-amorphous porous SiO2@Fc(COCH3)2 films are considerably lower than those of the ordered porous films but are higher than those of the dense Fc(COCH3)2 films. At 550 nm, the transmittance variation of the quasi-amorphous porous SiO2@Fc(COCH3)2 film is 19%, whereas that of the ordered porous film is 35%. The coloration and bleaching times of the quasi-amorphous porous SiO2@Fc(COCH3)2 film are 17.1 s and 4.5 s, respectively, whereas those of the ordered porous film are only 16.5 s and 3.5 s, respectively. Furthermore, the porosities of the films are solved numerically by the finite-element method. For the ordered porous SiO2@Fc(COCH3)2 film, the porosity is 0.26, while the quasi-amorphous film became larger (0.31–0.41). This work is the first step in combining ferrocene derivative and colloidal crystal porous structures to develop a green, simple and efficient electrochromic process.

Stability of the Cu2ZnSnS4/TiO2 photocatalytic thin films active under visible light irradiation

The study investigates the long term stability and photocatalytic activity (up to 72 h) of the Cu2ZnSnS4/TiO2 thin film heterostructures, under simulated solar radiation, at low irradiance values (34 W/m2), using phenol and imidacloprid (c = 10 ppm) as testing pollutants. High removal efficiencies correspond to both phenol (73%) and imidacloprid (57%) after 72 h of irradiation, while mineralization occurs slower, with efficiencies up to 42% for phenol, and less than 10% for imidacloprid, in agreement with the pollutant chemical structure.The stability of the photocatalysts in the aqueous pollutant solutions is investigated using VIS transmittance spectra, scanning electron microscopy, atomic force microscopy while photocatalyst leaching was evaluated based on surface composition analysis and atomic absorption spectroscopy. The processes affecting the photocatalyst surface and composition were discussed and the results were correlated with TiO2 layer morphology and porosity and pollutants' structure; promising results are outlined as low variation in the layers transmittance (after 72 h of testing: ΔT600 < 15% for imidacloprid, ΔT600 < 30% for phenol).The results recommend the use of Cu2ZnSnS4/TiO2 thin film photocatalyst for large-scale applications, involving organic pollutants removal from wastewaters, even at very low concentrations.

Light-Induced Aggregation and Disaggregation of Stimuli-Responsive Latex Particles Depending on Spiropyran Concentration: Kinetics of Photochromism and Investigation of Reversible Photopatterning.

Light-controlling the physical and chemical properties of smart polymers by using photochromic compounds has been an interesting research subject. Incorporation of spiropyran (SP) on the surface of particles can induce photoswitchable aggregation/disaggregation to stimuli-responsive colloids. Herein, we developed a novel class of stimuli-responsive latex particles bearing SP with different contents (0, 0.5, 1, 3, and 5 wt %) by semicontinuous emulsifier-free emulsion copolymerization, which is able to change the particle size by light-induced aggregation/disaggregation in response to ultraviolet (UV) irradiation and visible light. The scanning electron microscopy images revealed the spherical morphology of the latex particles, with the size in the range of 400-900 nm. Light-induced aggregation and disaggregation of stimuli-responsive latex particles were investigated by dynamic light scattering and also confirmed by variation of transmittance during UV illumination time using ultraviolet-visible spectroscopy. The range of the light-induced shift in the particle size is about 200-600 nm (depending on the concentration of SP), where the reduction of transmittance upon UV irradiation (and conversely upon visible light) confirms the ability of latex particles for displaying reversible photoswitchable aggregation/disaggregation and also light-controlling the particle size. The kinetics of SP to merocyanine (MC) and MC to SP isomerizations were experimentally investigated and fitted by exponential equations. The photochromic latexes displayed remarkable photoswitchability and photofatigue resistant properties under alternating UV and visible light irradiation cycles. Additionally, these stimuli-responsive latexes displayed potential applications such as anticounterfeiting inks in erasable and rewritable writings on cellulosic papers for increasing safety in security documents.

Real time monitoring of fs laser annealing on indium tin oxide

In this study, a set of time-resolved pump-probe systems for the real-time monitoring of femtosecond (fs) laser annealing of ITO substrates is established. A pump beam is used as the light source for thermal annealing, and a probe beam is used to monitor the transmittance variation of ITO in real time. Measurement results show that with increasing machining energy, the transmittance variation detected by the probe beam gradually increases. When the laser energy is small, the transmittance changes arithmetically. When the laser energy is sufficient to complete the modification of ITO, the transmittance variation rises suddenly and sharply, indicating that the thermal annealing modification has been completed in the irradiated area. Then, the laser source is shut down to achieve real-time monitoring. Degenerate and non-degenerate pump-probe experimental results indicate that the 400-nm probe beam is more sensitive than the 800-nm probe beam in measuring curve variation because the variation in the ITO transmission spectrum in the 400-nm wave band is greater than that in the 800-nm wave band. Electron backscatter diffraction analysis indicates that the crystallographic directions of ITO after laser annealing are consistent. This shows that the ITO changed from non-crystallized to crystallized after being irradiated by the pump beam, confirming the thermal annealing modification.

Graphene based tunable broadband far-infrared absorber

We present the tunable graphene based complimentary hexagonal circular array absorber for far infrared frequency range. Proposed absorber structure is analysed for different chemical potentials of graphene. Absorber structure is also analysed and compared in terms of their absorption, transmittance, reflectance and phase variation. Modulation depth of the absorption is achieved 85% for 0.5eV graphene chemical potential. Maximum bandwidth of 4.55 THz is achieved for 250 μm small hexagon circular radius. It is also observed that bandwidth of the operation is increased with higher chemical potential. The proposed tunable absorber can be used for the various applications like THz sensor, absorber, modulator and polarizer over far infrared frequency.

A novel designed high strength and thermoresponsive double network hydrogels cross-linked by starch-based microspheres

A new kind of nanocomposite double network (DN) hydrogels consisting of starch-based microspheres cross-linked oligo (ethylene glycol) methyl ether methacrylate) (POEGMA) as soft network and diethylene glycol dimethacrylate (DEGMA) cross-linked poly(2-(2-methoxyethoxy) ethyl methacrylate (PMEO2MA) as brittle network (named POEGMA/PMEO2MA DN hydrogels) were synthesized by a two-step free radical polymerization. The chemical structure of DN hydrogels was characterized by 1H NMR, the temperature sensitive properties were measured by the lower critical solution temperature (LCST) tested by UV-Vis spectrophotometer as a function of temperature, the mechanical properties were measured by tensile test. The LCST showed only one transition at 20.2 °C measured by the transmittance variation as a function of the ambient temperature from 5 to 70 °C. The fracture toughness and the hysteresis behaviors were also tested and showed that they were affected by the content of starch-based microspheres cross-linker in the soft POEGMA network, the content of small-molecular cross-linkers and monomer concentration in the brittle PMEO2MA network. They are related to perfect network and physical adherence and entanglements between microspheres and the networks brought by AAS microspheres, the increment of “sacrifice bond” brought by DEGMA and polymer chains entanglement brought by MEO2MA. These studies will provide theoretical support for the future research of DN hydrogel and macromolecular microspheres cross-linked hydrogel.

Quantification of the Transparency of the Transparent Soil in Geotechnical Modeling

An indispensable process of geotechnical modeling with transparent soils involves capturing and analyzing images, in which favorable transparency is required for optical measurements. This paper proposes an objective framework for quantification of transparency in transparent soil based on its transmittance. Specifically, transparent soil with fused quartz serves as the soil sample for the detection of transmittance, and transmittance’s impact on imaging quality in geotechnical modeling with transparent soil is investigated through an evaluation function of image clarity. According to the results of research about transparent soil with fused quartz, viewing depth and refractive index matching are the dominant factors that affect variations in transmittance of transparent soil, and the variations of transmittance are subjected to exponential decay regarding viewing depth or refractive index matching based on the theoretical modeling’s function of curve fitting. Moreover, experimental results indicate that imaging quality of geotechnical modeling with transparent soil is enhanced with increasing transmittance, and imaging quality shows a remarkable improvement when transmittance is greater than 90%.

Crystal Structure, Surface Topography, Surface Morphology and Optical Properties of DC Magnetron Sputtered VO2 Thin Films using VO2 Target

Vanadium dioxide (VO2) thin films were deposited at room temperature on Corning 2947 glass substrates by direct current (DC) magnetron sputtering with a high purity VO2 target. Crystal structure, surface topography, surface morphology and optical properties of the deposited VO2 thin films were investigated. The deposited films exhibited a single orientation of (110) with a crystallite size of 41.3 nm as confirmed by the X-ray diffraction analysis and Scherrer formula, respectively. From the surface topography analysis, the film surface had root mean square surface roughness of ~6.8 nm and consisted of round-shaped grains. Similarly, from the surface morphology analysis, spherical-like grains were observed on the surface of the deposited VO2 thin films with estimated average grain size of 34.2 nm. The deposited thin films showed high transmittance and low reflectance in the visible and near-infrared wavelength regions at room temperature. In addition, from the optical transmittance against temperature measurements, only a few transmittance variation and a slight change in hysteresis loop were detected during heating and cooling between room temperature and 100 °C. Hence, the deposited VO2 thin films were found to exhibit lack of phase transition.

A facile method for the preparation of W-doped VO2 films with lowered phase transition temperature, narrowed hysteresis loops and excellent cycle stability

We present a facile method to prepare W - doped VO2 films with lowered phase transition temperature (Tt), narrowed hysteresis loops width (ΔTt) and excellent cycle stability. The W - doped VO2 films have been obtained by inorganic sol - gel method. And W dopant is introduced by pouring melt V2O5 into ammonium tungstate solution. The properties of the samples are measured by XRD, XPS, SEM and transmittance spectra. The Tt is reduced from 73 °C to 20 °C along with the ΔTt narrowed from 10 °C to 4 °C as W dopant increasing from 0 to 3.2 at%. Besides, no obvious attenuation is observed on crystal structure, variation of transmittance (ΔT2000nm), Tt and ΔTt for W - doped VO2 films after 550 alternate heating and cooling cycles, while the pure VO2 films show obvious degradation. Since the surface morphology has no obvious changes after 550 cycles, it suggests that the W dopant induced distorted crystal structure strengthen the cycle stability of W - doped VO2 films. These encouraging results show great potential and understanding of VO2 films for practical applications.

AC detection of directivity of fluorescence from a minute particle using TAS chip incorporated with radially arranged light-waveguides

In this paper, we attempt to drastically improve the S/N ratio of detected fluorescence signals from the resin-based optical TAS chip by applying AC-modulated laser power for irradiation on a fluorescent substance attached micro-particles at a frequency of approximately 1 MHz. We also try to precisely optimize both the drive frequency and voltage of the optical scanner (light switch) which utilizes optical fiber’s resonance characteristics, in order to completely suppress variation of apparent transmittance of radially arranged light waveguides for laser power irradiation. Through these countermeasures, we successfully obtained high-quality fluorescence signal waveforms corresponding to angular scanning irradiation on 5-μm diameter resin particles. The high-quality signal waveforms also ensured that “directivities” of fluorescence with high reproducibility were obtained under conditions of a wider range of particle running velocity in a TAS chip.

VO2-based thermally active low emissivity coatings

Vanadium dioxide is one of the likeliest candidates for future smart window applications due to its self-regulating nature and potentially simple implementation. However, the material is plagued with multiple drawbacks which need to be addressed before its commercialization. Amongst these, its low luminous transmittance has been the subject of many studies. In the present work, we propose to integrate a VO2 film into a traditional silver-containing low emissivity coating architecture. We first model and discuss the theoretical performance of such a coating in comparison with more standard configurations and demonstrate that the addition of silver offers many advantages for thin VO2 coatings; mainly an increase of luminous transmittance due to the presence of antireflective coatings while maintaining a high solar transmittance variation vs. temperature. The latter is shown to be the result of a displacement of the maximum transmission variation to lower wavelengths where the solar intensity is higher. We then fabricate prototype samples which confirm the predicted performance. Indeed, a silver-containing sample based on the following architecture Si3N4 [57 nm] | VO2 [27 nm] | Ag [11 nm] | Si3N4 [66 nm] is shown to possess the unique combination of a high luminous transmittance of 58.2% in its low temperature state, a solar transmittance variation of 7.1% with the added benefit of a low emissivity of 10%.