Advantages of utilizing ultralow refractive index layers in optical coatings include broadband and wide angle
spectral performance. Ultralow refractive index films can be fabricated by chemical method and physical
vapor deposition. In the chemical method, ultralow refractive indices are controlled by sol-gel derived
nanostructures. In the physical method, ultralow refractive indices are obtained by self-shadowing nature in
oblique angle deposition. Techniques for ultralow refractive index silica formation and characterizations are
reviewed. Chemical, mechanical and optical properties of the ultralow refractive index silica are presented.
Optical coatings consisting of the ultralow refractive index silica layers are discussed in a spectral regime
from IR down to DUV.
SiO2 and SiO2-TiO2 composite nanoporous coating was successfully prepared via sol-gel method in this paper. By the
control of the different porosity of SiO2 coating and content of TiO2 in the mixture, the refractive index of the coatings
can be adjusted from 1.17 up to 2.20 continuously, which can be well matched with most of the optic materials used in
versatile detectors. Meanwhile, the thickness of the crack free SiO2 and SiO2-TiO2 nano-composite coatings can be easily
controlled by employing different experimental parameters. As a typical example, a coating with refractive index of 1.82
was prepared for a GaAs based IR detectors. In 2.5 - 6.0μm waveband, the maximum transmittance of GaAs substrate is
increased from 56% for uncoated sample to 94% for coated sample, which agrees with the theoretical results quite well.
In this paper, WO3 sol was prepared via the sol-gel method, and palladium chloride powder was dissolved in the sol in
different W: Pd molar ratios. Pd doped WO3 films were coated on silicon wafers and ordinary slide glasses by
dip-coating method. The grain distribution of WO3 sol doped with PdCl2 was measured by Laser Particle Size Analyzer.
Surface morphology and microstructure of WO3 films which doped or undoped with PdCl2 were analyzed by AFM,
which show that PdCl2 has an important effect on the structure of the WO3 films. The gasochromic properties of the films
are investigated by UV-Vis spectrophotometer. The WO3 films show good gasochromic properties. The effect of
concentration of PdCl2 on gasochromic kinetic process of WO3 films was investigated. Finally the modulation of the
light transmittance by the gasochromic films was discussed.
Good electrode materials play an important part in rechargeable Li batteries. In this paper, safe and inexpensive
vanadium pentoxide (V2O5) aerogel materials were used as cathode materials. We discussed preparation of the films and
lithium ion diffusion at the interface between the cathode and electrolyte by potential-step current transient technique and
digital simulations. The results showed that diffusion coefficient (DLi) of the V2O5 aerogel film was 9.18×10-14cm2/s and
exchange current was 12.5×10-6A at potential step 3.6~3.5VLi/Li+.
M-lines spectroscopy (MLS) is an accurate, to within 10-3-10-4, nondestructive technique for measuring optogeometric
parameters (refractive index and thickness) of thin planar step-index waveguide films. Two exciting polarizations can be
used and information about the film anisotropy derived. Usually, MLS uses only one wavelength, which may be
disadvantageous in some cases. We have developed an MLS setup that includes a set of lasers emitting in the range of
405 to 1550 nm to conduct multi-wavelength MLS (MWMLS). MWMLS offers an opportunity to obtain more detailed
optical information, e.g., index profiles and dispersion curves, especially important for sol-gel prepared waveguide thin
films that are relatively porous and whose structure depends on the annealing treatment. The paper presents a detailed
description of the MWMLS setup. By using sol-gel prepared waveguide thin films of Y2O3, HfO2:Eu3+, and TiO2, optical
measurements are exemplified. Proceeding from the measurements, the advantages and limitations of the method are
discussed.
SiO2/ZrO2 gel films were derived from Zr-butoxide modified chemically with β-diketones and then mixed with Tetraethyl orthosilicate via Sol-Gel process. The obtained gel films showed an absorption band, in characteristic of the π-&pi* transition of chelate ring at around 334 nm, and its refractive index was changed from 1.463~1.647. The Si-O-Zr, Zr-O bands were detected by FTIR. The result indicated that SiO2 and ZrO2 integrated uniformly in the films on micro molecule magnitude. The negative tone gel films were irradiated with high pressure mercury lamp through mask and then leached in ethyl alcohol. The above process gave uniform surface-relief gratings of periods at 2.0μm. The present study had proved that the photosensitive gel films were versatile for the fabrication of micro optical devices
Optical and hydrophobic nano-porous silica films with low refractive index were prepared by means of a two-step acid-catalyzed method and sol-gel process using surfactant CH3 (CH2) 15 N(CH3)3 Br (CTAB)as template, with a simple dip-coating procedure. Methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were co-hydrolyzed in different molar ration and were used as precursors. The process was optimized by varying MTES / TEOS ration, sol aging, thermal treatment and dip-coating conditions to obtain good optical films with low refractive index. The infrared spectra of the films thus obtained indicated that they become hydrophobic with the introduction of the methyl groups. Contact angle values for optical hydrophobic films prepared are greater than 120 degree supplementing the result. The refractive indices and thickness of optical films are about 1.12-1.21 and about 300-440 nm according to different MTES / TEOS ration of 0.2-0.8 using CTAB (2.5 wt%)at 400 degree thermal treatment by Ellipsometry. AFM of the films provide an estimate of the root-mean-square roughness of the surface to be 312(pm). The optical transmittance spectra and mechanical intensity measurement results showed that the films have good optical and mechanical properties. As a result, the moisture-resistant ability of the films was highly improved and the mechanical intensity was improved too.
Sol-Gel optical film was widely used in high power laser system with the development of its preparation technique. Ultraviolet treating is an effective method to solidify the film and improve its performance. In this paper, optical films were deposited on K9, silica glass and silicon wafer substrates by Sol-Gel spin-coating method and ultraviolet light source was produced by 1000W high-pressure mercury lamp to irradiate these optical films. SEM, AFM, IR and ellipsometer were used to characterize the structure and optical properties of the films. Mechanical property of films was measured by pencil hardness-testing device. Laser damage threshold of films was measured by a Q-switched Nd:YAG high power laser whose wavelength was 1064nm and its pulse width 15ns. The results show that UV-irradiation can improve the mechanical property and increase the refractive index of the films. The nodules on the film surface can be changed into pits by UV-irradiation process so the laser damage threshold of Sol-Gel thin films increased. The laser damage threshold of ZrO2 single-layer film added with PVP reaches 50.6J/cm2 (1064 nm, 1 ns) after UV-irradiation process. It was found that UV-irradiation is an effective method to avoid infiltrating between the layers and improve the homogeneity of the multilayer films. The reflection of 5 layers of ZrO2/SiO2 multi-layer films is increased more than 10% after UV-irradiation treatment.
A sol-gel coating of transparent optically variable is introduced in this paper. The plastic films coated with titanium dioxide using sol-gel process were embossed to form special patterns in micrometer scales. AFM, SEM, ellipsometer and electrophotometer were used to characterize the TiO2 coating and the transparent optically variable. The results show that the titania coating has nano-porous structure and the refractive index is about 1.9. The diffraction efficiency of the transparent optically variable coating is about 2.0%.
Hydrophobic organic-inorganic silica hybrid films were prepared by means of a two-step acid-catalyzed method and sol-gel process using surfactant as template. Methyltriethoxysilane(MTES) and tetraethoxysilane(TEOS) were co-hydrolyzed in different molar ration and were used as precursors. Addition MTES in TEOS precursors produces a decrease of Si-OH and Si-O- surface content. The infrared spectra of the films thus obtained indicated that they become hydrophobic with the introduction of the methyl groups. Contact angle instrument was also used to supplement the result. Contact angle values for hydrophobic hybrid films are greater than 120° . The refractive indices and thickness of hydrophobic hybrid films are about 1.22-1.24 and about 270-300nm The Optical transmittance spectra and mechanical intensity measurement results showed that the films have good optical and mechanical properties.
Low-density silica thin films having densities ρ of 0.574-0.957(g/cm3 )and refractive indices n of 1.12-1.20 and porosities ∏ of 61%-77% as well as dielectric constants k of 1.92-2.54 were prepared by a two-step sol-gel process at ambient pressure, with a simple dip-coating procedure, which take the wet gel through solvent exchange and reaction with trimethylchlorosilane(TMCS) without any supercritical drying. The process was optimized by varying the dilution, aging, organic substitution, organic modification, heat treatment and dip-coating conditions. Ellipsometer was used to determine refractive index and thickness of films. Atomic force microscopy (AFM) used to observe the microstructure and surface of thin films. Infrared spectroscopy and anti-reflectance measurement was carried out too. Abrasion-resistant properties were tested by the methods suggested by Floch et.al .
Carbon aerogels derived from organic sol-gel process and supercritical drying are novel porous materials with interconnect structures and higher electrical conductivity, which are considered to be ideal electrode materials for supercapacitors and rechargeable batteries. The objective of the research was to synthesize carbon aerogel films at ambient conditions. Resorcinol formaldehyde (RF) and carbon aerogel films have been produced with extremely high RC ratio (molar ratio of resorcinol to catalyst) followed by subcritical drying. The structure of the porous films was investigated using electron scanning microscope. The specific surface area was measured by using nitrogen adsorption and electrical conductivity was measured with four-probe method. It was found that with extremely high RC ratio, the porous structure of RF and carbon aerogel films can be controlled from micro to macro porous at ambient conditions. With respect to the application as electrodes for full cells, carbon aerogel films with different porous structures on the two surfaces have been also obtained through optimizing the sol-gel process.
The application of sol-gel thin films on the transparent hologram is introduced in this paper. The plastic films coated with titanium dioxide using sol-gel process were embossed to form special patterns in micrometer scales and thus the transparent holographic thin films were made. AFM, SEM, ellipsometer and electrophotometer were used to characterize the TiO2 coating and the transparent hologram. The results show that the titania coating has nano-porous structure and the refractive index of the titanium dioxide coating is about 1.9. The diffraction efficiency of the titanium dioxide derived transparent holographic thin film is about 2.0%.
A new method to strengthen nano porous broadband anti- reflectance silica films is described. Silica sols were made from TEOS with a base/acid two-step catalytic process. Properties of silica films deposited with a dip-coat method are characterized with AFM, SEM, spectrophotometer and abrasion test. Experimental results show that an average reflectance of a glass coated with the nano porous silica films is less than 1% in the visible region; and that the two-step catalysis obviously strengthens the films. Finally, the strengthening mechanism of the films is discussed.
ZrO2 thin films were prepared by sol-gel technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO2 at room temperature synthesized by hydrothermal process from inorganic precursor (ZrOCl2 (DOT) 8 H2O). By adding a soluble organic binder PVP to the suspension prior to application, it substantially increased the coating refractive index and the abrasion- resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions were investigated. Multilayer highly reflective dielectric coatings were also elaborated by laying down quarterwave- thick alternating coatings of the binder-aided zirconia and silica, which was prepared with the sol-gel process from TEOS. Laser damage thresholds of 20 and 18 J/cm2 (1064 nm, 1 ns) were achieved for single ZrO2-PVP coating and ZrO2-PVP/SiO2 multilayers respectively.
Sol-gel spin-coating technique was applied to produce tantalum pentoxide thin films. Pseudo-ternary phase diagrams were used to outline the sol-solution stability and the optimal Ta2O5 thin films formation regions of Ta(OC2H5)5-C2H5OH- CH3COOH-H2O system. Forbidden band gap of Ta2O5 thin film was calculated and found to be Eg equals 3.7 ev. Room temperature cyclic voltammetric measurements clearly revealed a protonic conductor behavior for Ta2O5 thin films.
We present some physical parameters that affect the deposition of TiO2 films by the sol-gel method. A set of solutions with different TiO2 concentrations has been prepared. After synthesis of a set of TiO2 films by spin coating at different spinning speeds, the films were annealed at different temperatures. The viscosities of the start solutions were measured by a viscometer. The thickness of the films and their refractive index were measured by a monochromatic ellipsometer. The results showed that the thickness is decreasing exponentially with increasing spinning speed and decreasing linearly with temperature according to the relation d(nm) equals 104 - 0.125 T( degree(s)C) + 322e-S/900. The thickness of the films ranges from 56 to 129 nm. The refractive index is decreasing with the spinning speed and increasing with the temperature according to the relation n equals 1.791 + 6.107X10-4T( degree(s)C) + 1.733e-S/600. The refractive index of the prepared films ranges from 1.89 to 2.125 depending on annealing temperature and spinning speed. The viscosity of the start solutions increased with increasing the TiO2 concentration and the aging time. One week, after preparing the solutions the viscosity was found to be in the range of 1.4 to 4.4 mPa.s depending on the concentrations.
TiO2 nanoparticle thin films are fabricated via sol-gel process followed by dip and spin coating technique, using Ti(OC4H9)4 as raw material. A complexing agent is used in order to form a stable sol. Experiments show that the colloidal particles in the sols are relatively large under basic catalyst conditions, while under acidic conditions, the colloidal particles are only about several nanometers. The properties and structures of the films are studied. The films are normally homogenous and crack-free. TEM shows that the films are composed of nanoparticles with a certain porosity. Under the thermal treatment of 80 degrees Celsius, the porosity and thickness of the film decrease while the refractive index increases from the original 1.70 to the final 1.89. When the temperature of the thermal treatment goes up, the size of the nanoparticles increases and crystallization occurs.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.