Change In Optical Transmission Research Articles

Roll-to-Roll Continuous Manufacturing Multifunctional Nanocomposites by Electric-Field-Assisted "Z" Direction Alignment of Graphite Flakes in Poly(dimethylsiloxane).

A roll-to-roll continuous process was developed to manufacture large-scale multifunctional poly(dimethylsiloxane) (PDMS) films embedded with thickness direction ("Z" direction) aligned graphite nanoparticles by application of electric field. The kinetics of particle "Z" alignment and chain formation was studied by tracking the real-time change of optical light transmission through film thickness direction. Benefiting from the anisotropic structure of aligned particle chains, the electrical and thermal properties of the nanocomposites were dramatically enhanced through the thickness direction as compared to those of the nanocomposites containing the same particle loading without electrical field alignment. With 5 vol % graphite loading, 250 times higher electrical conductivity, 43 times higher dielectric permittivity, and 1.5 times higher thermal conductivity was achieved in the film thickness direction after the particles were aligned under electrical field. Moreover, the aligned nanocomposites with merely 2 vol % graphite particles exhibit even higher electric conductivity and dielectric permittivity than those of the nonaligned nanocomposites at random percolation threshold (10 vol % particles), as the "electric-field-directed" percolation threshold concentration is substantially decreased using this process. As the graphite loading increases to 20 vol %, the aligned nanocomposites exhibit thermal conductivity as high as 6.05 W/m·K, which is 35 times the thermal conductivity of pure matrix. This roll-to-roll electric field continuous process provides a simple, low-cost, and commercially viable method to manufacture multifunctional nanocomposites for applications as embedded capacitor, electromagnetic (EM) shielding, and thermal interface materials.

Effects of ultraviolet nanosecond laser irradiation on structural modification and optical transmission of single layer graphene

Structural modifications and optical transmission change of single layer graphene (SLG) on transparent SiO2 substrate induced by nanosecond 355nm laser irradiation were systematically studied by scanning electron microscopy (SEM), laser-excited Raman, X-ray photon spectroscopy (XPS) and UV–vis transmission spectra. In this study, to avoid damage to graphene, the selected irradiation fluence was set to be smaller than the laser damage threshold of SLG. Laser-driven formation of nano-dots, carbon clusters and spherical carbon morphologies were clearly presented using SEM magnification images, and the formation mechanism of such structures were discussed. Raman spectra revealed formation of D' peak and the continuously increasing of ID/IG intensity ratio with the concurrent increase of laser fluence, indicating the increase in amount of structural defects and disordering in SLG. XPS results disclosed that the oxygen content in SLG increases with laser fluence. The formation and relative content increase of CO, COC and OCO bonds in SLG induced by laser irradiation were also revealed by XPS. Laser-driven micro-structure modifications of crystalline graphene to nano-crystalline graphene and photo-chemical reactions between graphene and O2 and H2O in air environment were suggested to be responsible for the Raman and XPS revealed modifications in SLG. It is worthy to point out that the above mentioned structural modifications only caused a slight decrease (<2% @ 550nm) in the optical transmittance of SLG. These results may provide more selections for the batch processing of large scale graphene aiming at modifying its structure and thus taiorling its properties.

Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo2O5.5+δ Thin Films.

Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo2O5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo2O5.5 (δ = 0) structure evidenced by aberration-corrected transmission electron microscopy. Moreover, the first-principles calculations reveal the origin and mechanism of optical transmittance enhancement in LaBaCo2O5.5 (δ = 0), which exhibits quite different energy band structure compared to that of LaBaCo2O6 (δ = 0.5). The discrepancy of energy band structure was thought to be the direct reason for the enhancement of optical transmission in reducing ambient. Hence, LaBaCo2O5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere.

Laser-processing of VO2 thin films synthesized by polymer-assisted-deposition

We investigate a novel route for synthesis and laser-sintering of VO2 thin films via solution-based polymer-assisted-deposition (PAD). By replacing the traditional solvent for PAD (water) with propylene glycol, we are able to control the viscosity and improve the environmental stability of the precursor. The solution stability and ability to control the viscosity makes for an ideal solution to pattern simple or complex shapes via direct-write methods. We demonstrate the potential of our precursor for printing applications by combining PAD with laser induced forward transfer (LIFT). We also demonstrate large-area film synthesis on 4in. diameter glass wafers. By varying the annealing temperature, we identify the optimal synthesis conditions, obtaining optical transmittance changes of 60% at a 2500nm wavelength and a two-order-of-magnitude semiconductor-to-metal transition. We go on to demonstrate two routes for improved semiconductor-to-metal characteristics. The first method uses a multi-coating process to produce denser films with large particles. The second method uses a pulsed-UV-laser sintering step in films annealed at low temperatures (<450°C) to promote particle growth and improve the semiconductor-to-metal transition. By comparing the hysteresis width and semiconductor-to-metal transition magnitude in these samples, we demonstrate that both methods yield high quality VO2 with a three-order-of-magnitude transition.

On-Chip Mid-Infrared Photothermal Spectroscopy Using Suspended Silicon-on-Insulator Microring Resonators

Mid-infrared spectroscopic techniques rely on the specific ”fingerprint” absorption lines of molecules in the mid-infrared band to detect the presence and concentration of these molecules. Despite being very sensitive and selective, bulky and expensive equipment such as cooled mid-infrared detectors is required for conventional systems. In this paper, we demonstrate a miniature CMOS-compatible Silicon-on-Insulator (SOI) photothermal transducer for mid-infrared spectroscopy which can potentially be made in high volumes and at a low cost. The optical absorption of an analyte in the mid-infrared wavelength range (3.25–3.6 μm) is thermally transduced to an optical transmission change of a microring resonator through the thermo-optic effect in silicon. The photothermal signal is further enhanced by locally removing the silicon substrate beneath the transducer, hereby increasing the effective thermal isolation by a factor of 40. As a proof-of-concept, the absorption spectrum of a polymer that has been locally p...

Diamond single crystal-surface modification under high- fluence ion irradiation

The modification of (111) face of synthetic diamond has been studied experimentally for high-fluence 30 keV argon bombardment. It has been found that ion irradiation leads to the electrically conductive layer formation the sheet resistance of which decreases more than 100 times while changing the temperature of the irradiated diamond from 70 to 400 oC. This effect, as well as significant changes of optical transmittance after ion irradiation are associated with ion-induced structural changes of irradiated diamond obtained by the methods of Raman spectroscopy.

Semi-Solid Typed Ionic Conductor for Solid-State Electrochromic Approaches

Electrochromic (EC) phenomena are that their optical transmittance and/or reflectance change because of chemical reduction/oxidation processes occurred by the ions insertion and extraction when a potential is externally applied. In order to increase the ratio and speed of chemical reduction/oxidation processes, which are essential required property, there are many efforts to prepare the ionic conductors based on such as organic-solvents/liquids, ionic liquids, and polymer/gel. Although organic-solvent/liquid based ion conductors show better physical properties likely lower viscosity, density, and melting point helps easier ion mobility in medium, they exhibit low stability, high flammability, and low safety which limit the promising wide range application of EC devices (ECDs). Therefore instead of using organic-solvent/liquid based ion conductors, ionic liquids (ILs) are considered because of non-volatility, possibly makes choice and/or certainly increasing ion concentration, etc. In spite of these advantages, polymer and/or gel-typed ion conductors are only suitable in terms of the flexibility and scalability of ECDs. As their visco-elastic properties, polymer/gel-based ion conductors afford guaranteed good contact with the electrodes, and they also have simple processablity resulted in low production cost and better mechanical properties along with improved stability, reliability, and safety. Therefore, in the present work, polymer-based ion conductor is prepared and is optimized in order to obtain the efficient contrast ratio and switching speed for ECDs. In order to see the feasibility, the operation of polymer-based ion conductor introduced ECD fabricated on flexible substrate will be also presented. Acknowledgement This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (B0101-16-0133, The core technology development of light and space adaptable energy-saving I/O platform for future advertising service).

Durability of polymeric encapsulation materials in a PMMA/glass concentrator photovoltaic system

AbstractThe durability of polymeric encapsulation materials was examined using outdoor exposure at the nominal geometric concentration of 500 suns. The results for 36‐month cumulative field deployment are presented for materials including: poly(ethylene‐co‐vinyl acetate), (EVA); polyvinyl butyral (PVB); ionomer; polyethylene/polyoctene copolymer (PO); thermoplastic polyurethane (TPU); poly(dimethylsiloxane) (PDMS); poly(diphenyl dimethyl siloxane) (PDPDMS); and poly(phenyl‐methyl siloxane) (PPMS). Measurements of the field conditions including ambient temperature and ultraviolet (UV) dose were recorded at the test site during the experiment. Measurements for the experiment included optical transmittance (with subsequent analysis of solar‐weighted transmittance, UV cut‐off wavelength, and yellowness index), mass, visual photography, photoelastic imaging, and fluorescence spectroscopy. While the results to date for EVA are presented and discussed, examination here focuses more on the siloxane materials. A specimen recently observed to fail by thermal decomposition is discussed in terms of the implementation of the experiment as well as its fluorescence signature, which was observed to become more pronounced with age. Modulated thermogravimetry (allowing determination of the activation energy of thermal decomposition) was performed on a subset of the siloxanes to quantify the propensity for decomposition at elevated temperatures. Supplemental, Pt‐catalyst‐ and primer‐solutions as well as peroxide‐cured PDMS specimens were examined to assess the source of the luminescence. The results of the study including the change in optical transmittance, observed failure modes, and subsequent analyses of the failure modes are described in the conclusions. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Correlations between Immobilizing Ions and Suppressing Hysteresis in Perovskite Solar Cells

Ion migration has been regarded as the major cause of photocurrent hysteresis. Here we use photoluminescence (PL) and optical images, combined with Galvanostatic measurement, to detect the ionic motion. We observe an irreversible PL and optical transmittance change after electric poling. By comparing a neat perovskite film with the sample coated by poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we found that PCBM effectively inhibits ionic motion near the surface of the perovskite.We further evidenced the donor–acceptor complex formed between PCBM and perovskite, implying the mechanism of inhibited ion migration by PCBM. We close by demonstrating that PCBM can also be introduced on the top of perovskite fim in an n–i–p TiO2 planar structure, to achieve an average 14% steady-state output over 2.3 × 105 s (∼64 h). This work highlights the importance of inhibiting ionic motion in perovskite solar cells.

Triphenylamine-based redox-active aramids with 1-piperidinyl substituent as an auxiliary donor: Enhanced electrochemical stability and electrochromic performance

A new triphenylamine-based diamine monomer 4,4′-diamino-4″-(1-piperidinyl)triphenylamine was synthesized and polymerized with various aromatic dicarboxylic acids via the phosphorylation polyamidation technique leading to a series of redox-active aromatic polyamides (aramids). All the aramids exhibit good solubility in many organic solvents and can be solution-cast into flexible and strong films with high thermal stability. Cyclic voltammograms of the polymer films on the indium-tin oxide (ITO)-coated glass substrate exhibit a pair of well-defined and reversible oxidation waves with very low onset potentials of 0.27–0.35V (vs. Ag/AgCl) in acetonitrile solution, with a strong color change from colorless neutral form to green and deep blue oxidized forms in the range of 0.75–1.20V. The optical transmittance change (Δ%T) at 636nm between the neutral state and the fully oxidized state is up to 83%.

Novel fabrication of an electrochromic antimony-doped tin oxide film using a nanoparticle deposition system

Novel deposition method of Antimony-doped tin oxide (ATO) thin films was introduced using a nanoparticle deposition system (NPDS) to fabricate an electrochromic (EC) device. NPDS is a dry deposition method that simplifies the ATO deposition process by eliminating the need for solvents or binders. In this study, an ATO EC layer was deposited using NPDS. The surface morphology and electrochemical and optical transmittance properties were characterized. The optical transmittance change in the ATO EC device was ∼35% over the wavelength range of 350–800nm, and the cyclic transmittance was stable. The ATO film deposited using NPDS, exhibited a coloration efficiency of 15.5cm2C−1. Therefore, our results suggest that ATO EC devices can be fabricated using a simple, cost-effective NPDS, which allows nanoparticles to be deposited directly without pre- or post-processing.

Plasmonic Sensing of Heat Transport at Solid–Liquid Interfaces

We report experimental studies of interfacial heat transport for a system of Au nanodisks supported on fused silica substrates, coated by hydrophilic and hydrophobic self-assembled monolayers, and immersed in water–ethanol mixtures and solutions of a nonionic surfactant, hexyl-β-d-glucoside in water. The Au nanodisks are abruptly heated by a sub-picosecond optical pulse; time-resolved changes in the temperature of the Au nanodisk and the liquid near the nanodisk/liquid interface are monitored by measurements of transient changes in optical transmission. The interface thermal conductance G of nanodisks coated with a hydrophilic self-assembled monolayer (SAM) of sodium 3-mercapto-1-propanesulfonate varies over the range 90 < G < 190 MW m–2 K–1 as the composition of the liquid mixture is changed from pure ethanol to pure water. With increasing hexyl-β-d-glucoside concentration in water, the interface thermal conductance of hydrophilic nanodisks decreases from 190 MW m–2 K–1 to 130 MW m–2 K–1 as the concentra...

Investigating the light stability of solid-solution-based AgCl-AgBr and AgBr-TlI crystals

For the development of mid-infrared fiber-optical elements, one needs light-stable, flexible materials that are transparent within this spectral band. Solid solutions of silver and monadic thallium halides prove to be the most suitable crystalline media for these needs. We study the light stability variation of high-purity AgCl1?xBrx (0≤x≤1) and Ag1?xTlxBr1?xIx (0≤x≤0.05) crystals by measuring the optical transmission change as functions of the composition and UV exposure time. The former is executed in a broad spectral range from 6500?350 cm?1, within which we choose three wavelengths to trace the transmission change. For thallium-monoiodide-containing samples, an effect is observed that we assumed to be translucence.

Highly redox‐stable and electrochromic aramids with morpholinyl‐substituted triphenylamine units

ABSTRACTA novel morpholinyl‐substituted, triphenylamine‐based diamine monomer, namely 4,4′‐diamino‐4″‐(4‐morpholinyl)triphenylamine, was synthesized and polymerized with various aromatic dicarboxylic acids via the phosphorylation polyamidation reaction leading to a series of electroactive aromatic polyamides (aramids). All aramids were readily soluble in polar organic solvents and could be solution cast into tough and flexible films with high thermal stability. Cyclic voltammograms of the aramid films on the indium‐tin oxide‐coated glass substrate exhibited a pair of reversible oxidation waves with very low onset potentials of 0.36 − 0.41 V (vs. Ag/AgCl) in acetonitrile solution. The polymer films showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency, high contrast ratio, and rapid switching time. The optical transmittance change (Δ%T) at 650 nm between the neutral state and the fully oxidized state is up to 90%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1289–1298

Nano-Welding of Ag Nanowires Using Rapid Thermal Annealing for Transparent Conductive Films.

Ag nanowire (NW) films obtained by the spraying the Ag NWs on the substrates were nano-welded by rapid thermal annealing (RTA) process and the effect of RTA process on the change of sheet resistance and optical transmittance of the Ag NW films was investigated. The increased number of Ag NW sprays on the substrate decreased the sheet resistance but also decreased the optical transmittance. By the annealing for 60 sec in a nitrogen environment to 225-250 degrees C, the sheet resistance of Ag NW film could be decreased to about 50%, even though it was accompanied by the slight decrease of optical transmittance less than 5%. The decrease of sheet resistance was related to the nano-welding of the Ag NW junctions and the slight decrease of optical transmittance was related local melting of the Ag NWs and spreading on the substrate surface. Through the nano-welding by RTA process, the Ag NW film with the sheet resistance of -20 Ω/sq. and the optical transmittance of 93% could be obtained.

Solar-active photocatalytic tandems. A compromise in the photocatalytic processes design

The quest for Vis- or solar-active photocatalytic materials and working systems led to various solutions, aiming at high process efficiency, towards mineralization. This involves the pH-adjustment (supporting the pollutant adsorption on the photocatalyst) and the addition of electron trappers, as H2O2. While these may be effective on the process efficiency, they also can have photo-corrosion side effects, reducing the up-scaling potential.The paper presents a three-layered tandem system of SnO2/CuxS/TiO2, and proves its activity under artificial solar radiation in the phenol photodegradation. The effect of pH (3–9) is comparatively analysed considering the electrostatic interactions substrate – pollutant (based on pzc and pKa), the speciation of the oxidative species (particularly the pH-dependent equilibria) and the photocatalyst stability, evaluated based on changes in surface morphology and optical transmittance. The results show the need to optimize the photocatalytic process design with a compromise between the electrostatic attraction and the photo-corrosion conditions and outlines the neutral pH as best meeting the efficiency and stability prerequisites.

Active terahertz metamaterials based on the phase transition of VO2 thin films

Vanadium dioxide (VO2) thin films were prepared on single crystal sapphire substrates by pulsed laser deposition. VO2 films exhibited a significant resistivity drop (>104Ω-cm) and large optical transmittance change (>60%) in the near-infrared region across their semiconductor-to-metal transition. Hybrid metamaterial devices designed for the THz frequency regime were fabricated by combining double split-ring resonators (SRRs) with phase changing VO2 films. By changing the conductivity of VO2 via temperature, the behavior of the SRR gap was adjusted from capacitive to resistive in order to modulate the THz beam transmission at their resonance frequencies. A modulation efficiency greater than 50% was achieved at the magnetic resonance frequencies (0.3THz and 0.7THz) in these hybrid SRR–VO2 metamaterial devices.

Time-Resolved Investigations of the Cooling Dynamics of Metal Nanoparticles: Impact of Environment

Tunable two-color ultrafast pump–probe experiments are performed on colloidal metal nanospheres in water and ethanol, and the results are interpreted through a model including thermal dynamics in both the nanoparticle and its environment. Transient optical signals measured for gold nanoparticles in ethanol display a complex temporal response strongly dependent on the wavelength of the probe beam. We demonstrate that its origin is related to a large contribution of liquid environment transient heating to the optical response, in contrast to the usual assumption that optical transmission changes reflect the evolution of nanoparticle temperature only. Accounting for this contribution enables an accurate measurement of thermal conductances at gold–ethanol and gold–water interfaces. Moreover, the thermal dynamics of the solvent can be selectively probed through a specific choice of probe wavelength.

Photonic crystal thin-film micro-pressure sensors

We have engineered both the optical and mechanical behaviour of a suspended line defect photonic crystal waveguide to demonstrate an improved sensor response. Utilizing thinner than the conventional photonic crystal membrane increases the mechanical sensitivity and the dynamic range of the sensor. The mechanical sensitivity is also increased by optimizing the membrane pad connected to the core photonic crystal waveguide. The pad optimization also ensures maximum pad flatness under uniform pressure. The overall sensitivity obtained is as high as 6% optical transmission change per Pa of pressure.

Active control of all-fibre graphene devices with electrical gating.

Active manipulation of light in optical fibres has been extensively studied with great interest because of its compatibility with diverse fibre-optic systems. While graphene exhibits a strong electro-optic effect originating from its gapless Dirac-fermionic band structure, electric control of all-fibre graphene devices remains still highly challenging. Here we report electrically manipulable in-line graphene devices by integrating graphene-based field effect transistors on a side-polished fibre. Ion liquid used in the present work critically acts both as an efficient gating medium with wide electrochemical windows and transparent over-cladding facilitating light–matter interaction. Combined study of unique features in gate-variable electrical transport and optical transition at monolayer and randomly stacked multilayer graphene reveals that the device exhibits significant optical transmission change (>90%) with high efficiency-loss figure of merit. This subsequently modifies nonlinear saturable absorption characteristics of the device, enabling electrically tunable fibre laser at various operational regimes. The proposed device will open promising way for actively controlled optoelectronic and nonlinear photonic devices in all-fibre platform with greatly enhanced graphene–light interaction.