Change In Optical Transmission Research Articles

Infrared transition properties of vanadium dioxide thin films across semiconductor-metal transition

Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray diffraction (XRD), atom force microscopy (AFM), and Fourier transform infrared spectrum (FTIR) were employed to measure the crystalline structure, surface morphology, and infrared optical transmittance. The phase transition properties were characterized by transmittance. The results show that the annealed vanadium oxide thin film is composed of monoclinic VO2, with preferred orientation of (011). The maximum of transmittance change is beyond 65% as the temperature increases from 20 to 80°C. The reversible changes in optical transmittance against temperature were observed. The change rate of transmittance at short wavelength is higher than that at long wavelength at the same temperature across semiconductor-metal phase transition. This phenomenon was discussed using diffraction effect.

Optical, structural and electrochromic properties of nickel oxide films produced by sol–gel technique

Nickel oxide films have been deposited from nickel acetate precursor using a sol–gel dip coating method, onto glass and conducting fluorine doped tin oxide (FTO) glass substrate. The direct energy gap ( E gd) values for the 2–10 layered films are in the range of 3.62 eV–3.72 eV. X-ray diffraction (XRD) analysis reveals that films consisting of 2–6 layers are amorphous, while films consisting of 8–10 layers are poly-crystalline with cubic grains of around 12 nm–20 nm and preferential growth along the (1 1 1) and (2 0 0) planes. Fourier Transform Infrared (FTIR) spectrum confirms the formation of Ni–O. Electrochromic properties of the nickel oxide coatings were studied using cyclic voltammetric (CV) technique. The 8 layered NiO films exhibit the anodic/cathodic diffusion coefficient of 16.7/5.73 × 10 −13 cm 2/s and the change in optical transmission is Δ T 630nm = 53% with a photopic contrast ratio of 2.87.

Geometric confinement effects on the metal-insulator transition temperature and stress relaxation in VO2 thin films grown on silicon

VO2 undergoes a sharp metal-insulator transition at ∼67 °C with several orders of change in conductivity and optical transmittance. Understanding and control of the properties of vanadium oxide layers grown on technologically relevant substrates such as Si (100) single crystals is therefore of great interest. In this work, we show tunability of metal-insulator transition temperature as well as recoverable stress in VO2 thin films grown on Si substrate by introducing nanoscale atomic layer deposited HfO2 interfacial layers with no degradation in the resistance ratio. For a confined VO2 film, the metal-insulator transition temperature is suppressed by ∼16 °C and the recoverable stress is 150 MPa, compared to 400 MPa for a bare film. These observations are further correlated with in situ variable temperature measurement of stress changes occurring during the phase transition. Structural and microstructural studies on the various samples have been carried out by x ray diffraction and cross-sectional transmission electron microscopy. The strategy of tuning the metal-insulator transition characteristics by nanoscale interfacial dielectrics is of broader relevance in design of programmable materials and integration into solid state devices for electronics.

Combined light and electron scattering for exploring hydrogen in thin metallic films

We present a method, combining optical transmission with electrical resistance, to study the hydrogen uptake in thin transition metal films. The change in optical transmission is used to determine the hydrogen concentration, while the change in resistance serves as an indicator for the ordering of hydrogen. We identify phase boundaries and regions of high and low orders as well as changes in the ordering temperature. As a demonstration of this approach we compare the hydrogen uptake of 50 and 10 nm single-crystal vanadium films. The ordered phase is found to be extended to higher temperatures in the thinner sample.

Thermo-optical response of layered Bi nanostructures produced by pulsed laser deposition

This work reports optical transmission changes in layered Bi nanostructures (NSs) upon heating–cooling cycles up to temperatures above the melting temperature. The nanostructured films prepared by pulsed laser deposition consist of Bi NSs with different characteristic sizes that are organised in layers and embedded in an amorphous Al 2O 3 host. The spectral dependence of the optical transmission as well as its changes upon heating are reported. The combination of Bi NSs layers with more than one characteristic size allows controlling the width of the melting–solidification transition. Eventually, it is shown how a multiple temperature thermo-optical film can be designed and prepared.

Effect of temperature of annealing on optical, structural and electrochromic properties of sol–gel dip coated molybdenum oxide films

The sol–gel dip-coating method is used for the preparation of MoO 3 thin films. The 6 layered MoO 3 films were prepared and annealed at various temperatures in the range of 200–350 °C. The band gap value for MoO 3 films were calculated from optical absorption measurements and it is in the range of 3.55–3.73 eV. XRD spectrum reveals (0 2 0) is the major diffraction plane for the films prepared above 250 °C, which reveals the formation of MoO 3 in α-orthorhombic phase. The films prepared at 200 °C and 250 °C exhibits amorphous nature. The FTIR spectrum confirms the presence of Mo–O–Mo and Mo O bonds. Nanorods were observed in the SEM images in the case of MoO 3 films prepared above 250 °C. The films prepared at 250 °C exhibit maximum anodic diffusion coefficient of 9.61 × 10 −11 cm 2/s. The same film exhibits the change in optical transmission of 58.4% at 630 nm with the optical density of 0.80.

Enhanced electrochromism in cerium doped molybdenum oxide thin films

Abstract Cerium (5–15% by weight) doped molybdenum oxide thin films have been prepared on FTO coated glass substrate at 250 °C using sol–gel dip coating method. The structural and morphological changes were observed with the help of XRD, SEM and EDS analysis. The amorphous structure of the Ce doped samples, favours easy intercalation and deintercalation processes. Mo oxide films with 10 wt.% of Ce exhibit maximum anodic diffusion coefficient of 24.99 × 10 −11 cm 2 /s and the change in optical transmittance of (Δ T at 550 nm) of 79.28% between coloured and bleached state with the optical density of (ΔOD) 1.15.

Hydrogen absorption by metallic thin films detected by optical transmittance measurements

The hydrogen absorption by bilayers of Pd/Nb and Pd/Ti, grown on glass substrates, was studied by measuring changes in optical transmittance and reflectance in the visible range (wavelengths between 400 nm and 1000 nm) of the films at hydrogen pressures between 3.99 × 10 2 and 4.65 × 10 4 Pa. The electrical resistance of the films was also measured during absorption to correlate with the optical data. All the films were grown by a controlled sputtering technique in high vacuum. Pd films ranging in thickness between 4 nm and 45 nm were also characterized when the films were exposed to a hydrogen pressure. The resistance and transmittance of all the Pd samples increased with the uptake of hydrogen until saturation occurred. For Pd/Ti bilayers, fast uptake of hydrogen was deduced from a transmittance increase, indicating hydrogen absorption in the Ti layer. In the case of the Pd/Nb bilayer, a decrease in transmittance was observed, indicating that hydrogen was not absorbed in the Nb layer. The transmittance decrease could be explained by a reduction of Nb native oxide by the hydrogen at the surface.

Electrochromic properties of Ni(V)O x films deposited via reactive magnetron sputtering with a 8V–92Ni alloy target

NiO x has been extensively used as complementary counter electrochromic (EC) layer in smart windows. Reactive sputter deposition for obtaining NiO x layer using metallic Ni targets has been very often considered, however, the ferromagnetic property of metallic Ni failed to be applied by conventional magnetron enhancement, particularly when considering large-area deposition. To overcome this, 8 at.% V is alloyed into Ni target for eliminating the ferromagnetism, and Ni(V)O x films are deposited via the reactive magnetron sputter technique in this study. Microstructure and the related EC properties were investigated. Experimental results show that the sputtering erosion of the non-ferromagnetic Ni(V) target surface becomes controllable as opposed to the pure Ni target. The Ni(V)O x film deposited at the working atmosphere of 1.33 Pa and oxygen flow ratio of 40% exhibits the highest optical transmission change (colored to bleached). The half device assembled with a 200 nm-thick film presents the shortest response time (3 s for coloring, 2 s for bleaching) and the greatest optical transmittance change in visible region (69.5% for bleached, 42.0% for colored). This study demonstrates that alloying 8 at.% V as a de-ferromagnetiser in Ni target does not observably affect the electrochromic properties of deposits.

Synthesis and properties of new aromatic polyamides with redox‐active 2,4‐dimethoxytriphenylamine moieties

AbstractA new triphenylamine‐based diamine monomer, 4,4′‐diamino‐2″,4″‐dimethoxytriphenylamine (2), was synthesized from readily available reagents and was reacted with various aromatic dicarboxylic acids to produce a series of aromatic polyamides (4a–h) containing the redox‐active 2,4‐dimethoxy‐substituted triphenylamine (dimethoxyTPA) unit. All the resulting polyamides were readily soluble in polar organic solvents and could be solution cast into tough and flexible films. These polymers exhibited good thermal stability with glass transition temperatures of 243–289 °C and softening temperatures of 238–280 °C, 10% weight loss temperatures in excess of 470 °C in nitrogen, and char yields higher than 60% at 800 °C in nitrogen. The redox behaviors of the polymers were examined using cyclic voltammetry (CV). All these polyamides showed two reversible oxidation processes in the first CV scan. The polymers also displayed low ionization potentials as a result of their dimethoxyTPA moieties. In addition, the polymers displayed excellent stability of electrochromic characteristics with coloration change from a colorless neutral state to green and blue‐purple oxidized states. These anodically coloring polyamides showed high green coloration efficiency (CE = 329 cm2/C), high contrast of optical transmittance change (ΔT% = 84% at 829 nm), and long‐term redox reversibility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3392–3401, 2010

New tensiographic approach to surface studies of protein kinetics showing possible structural rearrangement of protein layers on polymer substrates

An application of optical tensiography is described for studying protein adsorption/desorption/crystallisation processes. This paper concentrates on investigating the physics of the surface kinetics and associated crystallisation processes of the serum protein BSA. The measurements show changes in optical transmission caused by the development of protein layers on surfaces inside a liquid drop. Various absorption mechanisms are evaluated and a physical explanation suggested for the results involving changes in optical scattering as the structure of the protein layers develops. It is shown that tensiography provides a powerful real-time method for monitoring protein adsorption processes on a solid substrate that gives new insights into protein kinetics on these substrates. The study reveals results that are in agreement with earlier work showing multilayer structures and perhaps rearrangement of complex protein layer structures. Finally, consideration is briefly given to potential applications and most importantly the experimental development of this new tensiographic approach for improved real-time absorption measurements of proteins on solid substrates.

Innovative design for optical porous silicon gas sensor

A simple system for the detection of analytes in the atmosphere employing a freestanding nanostructured porous silicon optical microcavity was designed and built. The system is based on the measurement of optical transmittance changes as a function of the incidence angle of a monochromatic laser beam. Using a matrix formalism and effective medium theories we calculate the optimal conditions for the system so as to obtain the best sensitivity of the sensor. We tested the system over a detection area of the porous silicon microcavity of 100 μm 2 with isopropyl alcohol vapor diluted in a N 2 stream. With the system proposed we were able to detect changes in the concentration of isopropyl alcohol as small as 1 ppm, which is equivalent to a change in the effective refractive index of about 3 × 10 −6. The response time is very fast, lower than 0.5 s.

Photoelectrochemical Performance of Anatase TiO2 Thin Films Deposited by Self-Limiting Growth Techniques

Anatase photoanodes were deposited by self-limiting growth techniques at low temperature. The optical bandgap and flatband voltage of the as-deposited films agree with the values obtained from single crystal anatase. The donor density could be increased by both UV illumination and cathodic polarization in acidic solutions. Improvements in photocurrent scaled closely with changes in carrier concentration, with over 20-fold enhancements observed over the as-deposited films. The threshold potential for hydrogen intercalation was −0.6 V vs Ag/AgCl. At this level the carrier concentration could be manipulated with no change in optical transmission. At lower potentials irreversible changes are observed which are attributed to the reduction of the underlying indium tin oxide contact. In contrast, no changes were observed when fluorinated tin oxide was used as the contact layer.

Self-oscillating core/shell microgels: effect of a crosslinked nanoshell on autonomous oscillation of the core

We reported the effects of crosslinked nanoshells covering self-oscillating microgels on their oscillatory behaviors. We carried out seeded precipitation polymerization of N-substituted acrylamide derivatives using preformed, self-oscillating microgels as cores. The core/shell microgels obtained were characterized by dynamic light scattering. Oscillating behaviors were characterized by changes in optical transmittance. In addition, the characteristics (that is, induction period, oscillating period and waveform) of the oscillation of the core/shell microgels were compared with that of the parent core microgel to clarify the effect of the addition of a nanoshell on the autonomous oscillating behaviors of microgels. Effects of crosslinked nanoshells covering self-oscillating microgels on their oscillating behaviors were reported. We carried out seeded precipitation polymerization of N-substituted acrylamide derivatives using preformed, self-oscillating microgels as cores. The obtained core/shell microgels were characterized by dynamic light scattering. Thereafter, their oscillating behaviors were characterized by changes in optical transmittance. In this study, oscillating behaviors of core/shell microgels were compared with that of the parent core microgel to clarify the effect of nanoshell addition on the oscillating behaviors of microgels.

Magnetooptics of opal crystals modified by cobalt nanoparticles

Optical and magnetooptical properties of opal photonic crystals modified by Co nanoparticles have been investigated by modulation spectroscopy technique in the visible spectral range from 400 to 800 nm. The Co nanoparticles of 1 to 8 nm in size were formed by means of chemical reduction reaction inside synthetic opal crystals composed of regularly close-packed SiO2 spheres of diameter 250–300 nm. As it was estimated from the spectral shift of the stop band of photonic crystals, Co nanoparticles occupied up to several percent of void volume in opal crystal lattice. In the Faraday configuration, external magnetic field induced the change in optical transmission normalized to sample thickness 1 cm and magnetic field 1 T equal to 0.10–0.35 for Co-modified opal crystals in the spectral range under consideration. The fabricated hybrid structures can be considered as a possible prototype of magnetophotonic crystals. Keywords: magnetophotonic crystals, modulation spectroscopy

Electrically and thermally modulated optical properties of polymer dispersed chiral liquid crystal

The polymer dispersed chiral liquid crystals (PDCLCs) film was fabricated by photopolymerization induced phase separation (PIPS) of chiral liquid crystal (CLC)/polymerizable monomers/photoinitiator composites. The effects of the electrical and thermal modulation on optical rotation properties of PDCLCs film were investigated. The microsized liquid crystal droplets were resulted from the rapid polymerization of trifunctional monomers. The effects of the electrically and thermally modulated on realignment of liquid crystal director were investigated. It was found that the intensity of electric and thermal field influenced the alignment of liquid crystal droplets' director on PDCLCs film, and the electro-optical properties of the composites were affected accordingly. The principle of free energy minimum was used for explaining the change of optical rotation and transmittance of PDCLCs film with applying the voltage to the film. The dispersion and sizes of liquid crystal droplets were described by polarizing optical microscope (POM). POLYM. COMPOS., 31:1535–1540, 2010. © 2009 Society of Plastics Engineers

Effect of CuO on the Optical and Structural Properties of Phosphate Glass for Near-Infrard Filter

Optical characteristics and structural changes depending on CuO content in phosphate glasses that are used in near-infrared (near-IR) filters were investigated. With phosphate glasses that contain 1-9 mol% CuO, changes in optical transmittance, optical absorption, and color coordinate were measured with a UV-VIS spectrophotometer. An XPS (X-ray photoelectron spectroscopy) analysis was performed to determine valence of copper ion that influences optical characteristics in near-IR filter glasses. Structural changes in glasses depending on CuO content were also analyzed by FT-IR (Fourier transform infrared) and Raman spectrophotometers. From the UV-VIS spectrophotometer results, strong absorption peaks at 220 & 900 nm were found and transmittance was decreased. The color coordinates of the glasses were shifted to the green color direction with CuO addition for increasing absorption of long wavelength range spectra, in spite of the amount of <TEX>$Cu^{2+}$</TEX>, which gives a blue color to glasses, and which was increased in XPS results. Also, structural de-polymerization of glasses with CuO addition were found by FT-IR and Raman results.

Optical, structural and electrochromic studies of molybdenum oxide thin films with nanorod structure

The MoO 3 thin films were prepared via sol–gel dip coating method on glass and FTO glass substrate. The optical and other properties of multilayered MoO 3 films with 2–10 layers were investigated. The MoO 3 films were studied using UV–Visible transmission, XRD, SEM, FTIR and Cyclic Voltammetry (CV) measurements. The band gap value for MoO 3 films was evaluated and in the range of 3.2 eV–3.72 eV. The XRD spectrum reveals that the crystallinity increases along the (020) and (040) planes with the increase in thickness. The SEM images showed the formation of nanorods upto six layers. The FTIR spectrum confirms the formation of MoO 3. The 6 layered films show the maximum anodic (spike)/cathodic (peak) diffusion coefficient of 18.84/1.701 × 10 −11 cm 2/s. The same film exhibits the change in optical transmission of 49% with the bleached/coloured state transmission of 62/13%.

Hydrogenography of Mg yNi 1− yH x gradient thin films: Interplay between the thermodynamics and kinetics of hydrogenation

We monitor the hydrogenation of PTFE/Pd-capped Mg y Ni 1− y H x gradient thin films using the change in optical transmission as a function of time, temperature and hydrogen pressure, to study the relation between kinetics and thermodynamics of hydrogenation of this multiphase hydride system. The interplay between kinetics and thermodynamics is used to extrapolate the hydrogenation equilibrium pressures via the H-absorption rate. Pressure–optical-transmission–isotherms determined independently at different temperatures provide a cross-check for the equilibrium pressure and the enthalpy of H-absorption. We find that the hydrogenation reaction is destabilized with respect to the Mg 2Ni → Mg 2NiH 4 reaction for Mg fractions close to the Mg 2Ni–Mg eutectic point. From a comparison with calculated enthalpies obtained from density functional theory, we conclude that the experimentally observed destabilization originates from the well-mixed microstructure around the eutectic point.

Fast temperature sensing using changes in extraordinary optical transmission through an array of subwavelength apertures

A fast, sensitive temperature sensor using changes in extraordinary optical transmission (EOT) through an array of nanoholes in a metallic film with a monochromatic collimated light source is analyzed and experimentally demonstrated. The device is composed of a dielectric material in contact with a metallic film with an array of nanoholes, (25 arrays per chip were treated as a single sensor), on a glass substrate. Although the present experiment used a volume of water in a test cell to demonstrate the phenomena, there are many configurations that implement this technology in a variety of applications. The fast response of the device is expected because it measures the average temperature of a thin layer of the dielectric material directly above the nanoholes, ~100 nm. The thermal response parameter of the nanohole array sensing region is ~108 times smaller and orders of magnitude faster than that of the reference thermistor. The increased speed and sensitivity of the nanohole array temperature sensor over the thermistor is observed in the reported data. The configuration of this temperature sensor was used for simplicity and to demonstrate that EOT effects can be used for temperature sensing.