Heat Mirror Research Articles

Intermixing of metal oxide/Ag/metal oxide nanoscale multilayers prepared by rf reactive magnetron sputtering

This study mainly aims to evaluate the intermixing between layers during the deposition of dielectric/metal/dielectric nanoscale multilayer coatings. TiO2 and WO3 films as dielectric materials are developed using radio frequency reactive magnetron sputtering on unheated soda lime glass substrates. Ag films are grown using radio frequency argon sputtering. Auger electron spectroscopy and ultraviolet–visible–near infrared spectrometry are employed to estimate the degree of layer intermixing in TiO2/Ag, WO3/Ag, TiO2/Ag/TiO2 and WO3/Ag/WO3 films. The morphological properties are also investigated under a field emission scanning electron microscope and an atomic force microscope. The transmittance curves for bilayer films exhibited heat mirror effects significantly. However, multilayer films showed a little amount of heat mirror effects. Auger electron spectroscopy depth profiles confirmed a minor diffusion of Ag at the TiO2/Ag interface. However, significant interactions of WO3 with Ag were observed for the WO3/Ag film. Besides, severe intermixing and oxidation of Ag films were observed for the multilayer films.

Optimization of the Optical Performance of TiO<sub>2</sub>/Ag/TiO<sub>2</sub> Multilayers for Warm Climates

The optical performance of the heat mirror for warm climates was proposed, and a parameter Dx which equals the ratio of solar transmission to visible transmission was defined. To make the Dx as low as possible, the thicknesses of the films for TiO2/Ag/TiO2multilayers were optimized through computer simulation. A TiO2(140 nm)/Ag (16 nm)/TiO2(140 nm) structure optimized for 16-nm Ag has a maximum decrease in Dx value (from 0.75 to 0.51), which possesses excellent building energy efficiency.

Efficient Light Harvesting by Photosystem II Requires an Optimized Protein Packing Density in Grana Thylakoids

A recently developed technique for dilution of the naturally high protein packing density in isolated grana membranes was applied to study the dependence of the light harvesting efficiency of photosystem (PS) II on macromolecular crowding. Slight dilution of the protein packing from 80% area fraction to the value found in intact grana thylakoids (70%) leads to an improved functionality of PSII (increased antenna size, enhanced connectivity between reaction centers). Further dilution induces a functional disconnection of light-harvesting complex (LHC) II from PSII. It is concluded that efficient light harvesting by PSII requires an optimal protein packing density in grana membranes that is close to 70%. We hypothesize that the decreased efficiency in overcrowded isolated grana thylakoids is caused by excited state quenching in LHCII, which has previously been correlated with neoxanthin distortion. Resonance Raman spectroscopy confirms this increase in neoxanthin distortion in overcrowded grana as compared with intact thylakoids. Furthermore, analysis of the changes in the antenna size in highly diluted membranes indicates a lipid-induced dissociation of up to two trimeric LHCII from PSII, leaving one trimer connected. This observation supports a hierarchy of LHCII-binding sites on PSII.

Fabrication and Characterization of Multi-layer Heat Mirror with Photocatalytic Properties

A novel TiO2(5)/TiO2(buffer)/Ti(4)/Ag(3)/Ti(2)/TiO2(1) multi-layer film coating with corning glass is designed and fabricated by a dc magnetron sputtering method as a renovation of the well-known TiO2/Ti/Ag/Ti/TiO2 system in order to obtain a heat mirror system with photocatalytic properties due to sufficient thickness of the TiO2 layer. The outer TiO2 layer is fabricated in two steps, possibly claimed as two layers TiO2(5) and TiO2(buffer), among which the 70-nm-thick layer TiO2(buffer) deposited in poor oxygen effectively minimizes the oxidation toward its neighbor Ti(4) layer. The optimal total thickness of the TiO2(5) and TiO2(buffer) di-layer is found to be 300 nm to yield a highly photo-catalytic property of the film without affecting the optical properties considerably. This multi-layer film can transmit light of above 75–85% in the visible spectrum (380 ≤ λ ≤ 760 nm) and reflect radiation of above 90% in the infrared spectrum (λ ≥ 760 nm). Such multi-layer coatings are strongly recommended not only as promising transparent heat mirrors but also as photo-catalytic films for architectural window coatings.

Development of transparent heat mirrors based on metal oxide thin film structures

The aim of this work is the preparation of RF sputtered indium–tin oxide (ITO) thin films for application as transparent heat mirrors. The heat mirrors are important elements for the photothermal solar energy conversion. In combination with moderate spectral selectivity of the solar absorbers they could increase the efficiency of the solar collector. The optical properties of ITO and double-layer ITO with titanium dioxide (TiO 2) structures in the visible and infrared ranges were investigated. The films were deposited on glass substrates by RF sputtering technique. Tin-doped indium, as well as titanium targets was used. The influence of the In–Sn target composition and the deposition parameters on the film properties were studied. The films' surface morphology and structure were investigated by SEM, TEM and XRD, the composition was studied applying electron probe microanalyzer (EPMA). The thicknesses of the films were determined by the laser ellipsometry method. The measurements in the infrared range were performed on Fourier transform infrared spectrophotometer (FTIR). The single layer ITO structures showed reflectance in the infrared range not exceeding 50% at longer wavelengths. The double layer structures with TiO 2 under layer showed increased reflectance in the infrared range with high visible transmittance reaching 85%.

Transparent heat mirrors based on tungsten oxide–silver multilayer structures

Transparent heat mirrors based on tungsten oxide/silver three-layer structures were fabricated using thermal evaporation. The optical and morphological properties of the single layers were first investigated to serve as a basis for the fabrication of the heat mirrors. Only silver films with a thickness higher than 18 nm were found to be continuous. Subsequently, WO 3/Ag/WO 3 multilayers were deposited, where the WO 3 layers thickness was fixed at 35 nm, and the thickness of the silver layer was varied from 18 to 39 nm. The optical properties of the multilayers were measured over the visible and near infrared ranges. These multilayers exhibited the desired heat mirror behavior, namely the transmittance was largely confined to the visible range and the reflectance was diminished in that range. The maximum visible transmittance was 88.3% at 554 nm. Increasing the thickness of the silver films resulted in a decrease of the visible transmittance, with a corresponding increase in the infrared reflectance. Optimization of these two opposing trends was evaluated using a figure of merit, from which the best performance was obtained for multilayers with a silver layer of thickness of 24 nm.

Amplified radiative cooling via optimised combinations of aperture geometry and spectral emittance profiles of surfaces and the atmosphere

Net thermal radiation cooling, from surfaces at sub-ambient temperatures, to the night sky is amplified if the aperture to the sky is partially blocked with heat mirrors. The temperature at which radiation loss stagnates (the effective sky temperature) falls continuously as the aperture closes and is derived in terms of the aperture size and the spectral properties and temperatures of the atmosphere and of the emitting surface. Cooling surfaces must have high absorptance between 7.9 μm and 13 μm where the atmosphere is most transparent. The best response for the remainder of the Planck radiation spectrum surprisingly switches between two spectral extremes at a temperature which falls as the aperture gets smaller. A perfect absorber is best above this switch, while surfaces which reflect all of this radiation are best below it. A simple formula is presented for the cross-over temperature as a function of aperture size. With known material properties plus representative non-radiative heat gains a high emittance surface is generally better except when heat mirrors are not used. A known high emittance roof paint at 10° C below ambient, under a 45° aperture lined with shiny aluminium, can achieve a net output power near 135 W m −2 under a clear sky.

PHOTO-CATALYTIC TRANSPARENT HEAT MIRROR FILM TiO2/TiN/TiO2

Transparenet heat mirror thin films, having high transmittance in the visible region and high reflectance in the infrared region. TiO/TiN/TiO2 films prepared D.C reactive magnetron sputtering method on glass substrates, play role as transparent heat mirror. Besides, the top TiO2 layer has both photo-catalytic and anti-reflective properties. However, st ong thickness dependence of top layer on catalytic properties is a problem need to solve. The experiment shows optimum thickness in order to have good catalytic properties is above 350 nm. This report, we found relationship among thicknesses of films through calculating and experiment. Films prepared, have both catalytic and transparent heat mirror properties with the bottom Tio, layer thickness of 40-300 nm, the middle TiN layer thickness of 16-22 nm and the top TiO2 layer of above 350 nm.

Optimization of ZnS/Ag/ZnS Multilayer Thin Film Systems for Heat Mirror Applications

Optimization of ZnS/Ag/ZnS Multilayer Thin Film Systems for Heat Mirror Applications

An Investigation of Titanium‐Vanadium Nitride Phase Space, Conducted Using Combinatorial Atmospheric Pressure CVD

AbstractThe technique of combinatorial atmospheric pressure (AP)CVD, a recent addition to the growing number of combinatorial materials methods, is used to form twelve members of the TixV1‐xN alloy series with 0.29 < x < 0.94. This series of compounds has a rock‐salt structure with TiN and VN as the end members. The twelve phases, which have potential use as heat mirror coatings, are all synthesized in a single experiment. The structure and properties of the materials are investigated using powder X‐ray diffraction (XRD) and electron probe microanalysis (EPMA). The optical properties are considered using visible‐IR spectroscopy (IRS), which allows the suitability of the films as solar control coatings to be investigated and optimized as a function of composition.

Preparation of RF reactively sputtered indium-tin oxide thin films with optical properties suitable for heat mirrors

Technologies are discussed for preparing and characterizing indium-tin oxide (ITO) thin films with properties appropriate for usage as heat mirrors in solar thermal collectors. The samples were prepared by means of radio frequency (RF) reactive sputtering of indium-tin targets in oxygen. The technological parameters were optimized to obtain films with optimal properties for heat mirrors. The optical properties of the films were studied by visible and infra-red (IR) spectrophotometry and laser ellipsometry. The reflectance of the films in the thermal IR range was investigated by a Fourier transform infra-red (FTIR) spectrophotometer. Heating of the substrates during the sputtering and their post deposition annealing in different environments were also studied. The ultimate purpose of the present research being the development of a technological process leading to low-cost ITO thin films with high transparency in the visible and near IR (0.3-2.4 μm) and high reflection in the thermal IR range (2.5-25 μm), we investigated the correlation of the ITO thin films structural and optical properties with the technological process parameters - target composition and heat treatment.

TiO2/TiN/TiO2 heat mirrors by laser ablation of single TiN target

Titanium oxide (TiO2) and titanium nitride (TiN) multilayered films grown by pulsed laser deposition (PLD) technique have been tested as a heat mirror, which have a high transmittance in the visible region and a high reflectance in the infrared. Three layer TiO2/TiN/TiO2 heat mirrors were grown on Corning glass substrates ablating single TiN target. Switching of TiO2-to-TiN layers composition was achieved by changing gas atmosphere (oxygen-to-nitrogen). Grown TiO2/TiN/TiO2 heat mirrors are highly transparent in visible (above 60% at 525nm), opaque in infrared (10% at 2600nm) and in the range from 400 nm to 2600 nm they possess almost the same properties as films prepared using two targets: TiO2 and TiN. XPS confirms similarity of chemical composition of multilayered TiO2/TiN films prepared by single TiN and two TiO2 and TiN targets techniques. Furthermore, multifunctional self cleaning properties of TiO2/TiN heat mirrors are expected through the precise control of the composition of the top TiO2 layer operating as a photocatalyst.

The Effect of Film Thickness on the Suitability of Titanium Oxynitride (TiNxOy, x + y = 1) Films as Heat Mirrors – Formed by the Atmospheric Pressure CVD of TiCl4 and NH3

AbstractFilms of titanium oxynitride are assessed for their potential as heat mirror coatings on window glass, as a function of the film thickness. The coatings are deposited from the atmospheric pressure (AP) chemical vapor reaction of TiCl4 and ammonia. The heat mirror properties are evaluated using transmission and reflection spectroscopy. The composition of the samples is determined by X‐ray photoelectron spectroscopy (XPS), and the thickness of the films by scanning electron microscopy (SEM). These results suggest that an effective heat mirror can be formed by a 100 nm thick coating of titanium oxynitride, which has a transmission of 49 % in the visible (610 nm), and a reflection of 46 % in the near infrared (1320 nm).

Preparation and properties of RF sputtered indium–tin oxide thin films for applications as heat mirrors in photothermal solar energy conversion

In the present research, in order to deposit indium–tin oxide (ITO) thin films the method of RF reactive sputtering was used. Sputtering of two types indium–tin targets in the presence of oxygen as reactive gas was made. The technological parameters were optimized to obtain films with good quality on different substrates. The films' microstructure was studied by TEM and SAED. To identify the optical properties of the films the methods of infrared spectrometry and laser ellipsometry were used. UV–VIS spectrophotometry showed the high visible transmittance of the RF sputtered ITO films. Heating of the substrates during the films sputtering and their post deposition thermal treatment also were studied. The ultimate goal of the present research activities was to develop new technological processes leading to low-cost, highly effective optical coatings for application in photo thermal solar energy conversion and utilization.

Magnetic and Optical Properties of Isolated Magnetite Nanocrystals

Following preparation of isolated nano-sized magnetite particles in a low-concentration dispersant solution, this study investigated the magnetic and optical properties. Magnetic measurements indicated that the magnetite nanoparticles exhibited perfect superparamagnetism above the blocking temperature. Optical measurements revealed that the magnetic films exhibited good transmittance in the visible region and excellent UVB absorption. It has potential for use in optical applications (UVB-cut), such as sunglasses, heat mirror film and others.

Thermodynamic evaluation of the In–Sn–O system

Thermodynamic evaluation of the In–Sn–O system was made, because indium-tin-oxide (ITO) system is used for instance in transparent electrodes for display devices, transparent coatings for solar energy heat mirrors and window films in n–p heterojunction solar cells. The thermodynamic data is limited, so the phase diagram for In–Sn–O system is somewhat tentative.

05/02285 Spectrally selective laminated glazing consisting of solar control and heat mirror coated glass: preparation, characterization and modelling of heat transfer

05/02285 Spectrally selective laminated glazing consisting of solar control and heat mirror coated glass: preparation, characterization and modelling of heat transfer

Optical properties of metal-dielectric multilayers in the near UV region

Metal-dielectric multilayers have versatile optical properties that can be used in many applications. The special properties of metal films in the near UV region are analyzed in terms of the d-band contribution to the plasma oscillation. The important parameters that determine the multilayer optical properties such as skin depth dependence on the wavelength and the thickness of silver films have been calculated. The morphology of silver films on titanium dioxide has been observed by TEM. The results indicate that an optimal thickness exists for near UV transparency, and that may be related to the resonance of voids and interface enhanced resonance-tunneling transmission of semi-continuous silver films. A special heat mirror with high transparency in the near UV region was designed and fabricated according to the optimal thickness of silver; it has been found to exhibit sound optical properties.

High-rate and low-temperature synthesis of TiO2, TiN, and TiO2∕TiN∕TiO2 thin films and study of their optical and interfacial characteristics

Using a newly developed pulsed dc sputtering source with unbalanced magnetrons, we deposited advanced inorganic functional thin films such as TiO2, TiN, and TiO2∕TiN∕TiO2 on glass at 200°C at rates 3 to 4 times greater than those deposited by conventional dc sputtering. The TiO2(101) and TiN(100) thin films were stoichiometric and polycrystalline but highly oriented. The TiO2 films showed high transmittances (90%) in the visible range. The TiN films showed very high reflectances (70%) in the infrared region. However, both transmittance and reflectance are strongly influenced by the thickness and surface roughness. Multilayer films of TiO2∕TiN∕TiO2 were also deposited on glass, and exhibited good optical properties. The best transmittances (85%) and reflectances (80%) were obtained with a thin film with TiO2(370nm)∕TiN(22nm)∕TiO2(450nm)∕glass structure. The high IR reflectance suggests the as-grown multilayer film can be used as a heat mirror.

Low-emissivity coating of amorphous diamond-like carbon/Ag-alloy multilayer on glass

Transparent low-emissivity (low-e) coatings comprising dielectrics of amorphous diamond-like carbon (DLC) and Ag-alloy films are investigated. All films have been prepared by dc magnetron sputtering. An index of refraction of the DLC film deposited in a gas mixture of Ar/H 2 (4%) shows n = 1.80 + 0.047 i at 500 nm wavelength. A multilayer stack of DLC (70 nm thick)/Ag 87.5Cu 12.5-alloy (10 nm)/DLC (140 nm)/Ag 87.5Cu 12.5-alloy (10 nm)/DLC (70 nm) has revealed clear interference spectra with spectra selectivity. This coating performs low emittance less than 0.1 for black body radiation at 297 K, exhibiting a transparent heat mirror property embedded in DLC films.