Silica Antireflective Coatings Research Articles

Robust anti-reflective silica nanocoatings: abrasion resistance enhanced via capillary condensation of APTES

Capillary condensation of APTES into silica anti-reflective coatings offers both excellent anti-reflective property and robust mechanical durability.

自组装法制备的亚波长纳米多孔二氧化硅薄膜

自组装法制备的亚波长纳米多孔二氧化硅薄膜

Sol-gel preparation of hydrophobic silica antireflective coatings with low refractive index by base/acid two-step catalysis.

Hydrophobic antireflective coatings with a low refractive index were prepared via a base/acid-catalyzed two-step sol-gel process using tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors, respectively. The base-catalyzed hydrolysis of TEOS leads to the formation of a sol with spherical silica particles in the first step. In the second step, the acid-catalyzed MTES hydrolysis and condensation occur at the surface of the initial base-catalyzed spherical silica particles, which enlarge the silica particle size from 12.9 to 35.0 nm. By a dip-coating process, this hybrid sol gives an antireflective coating with a refractive index of about 1.15. Moreover, the water contact angles of the resulted coatings increase from 22.4 to 108.7° with the increases of MTES content, which affords the coatings an excellent hydrophobicity. A "core-shell" particle growth mechanism of the hybrid sol was proposed and the relationship between the microstructure of silica sols and the properties of AR coatings was investigated.

Sol–gel silica antireflective coating with enhanced abrasion-resistance using polypropylene glycol as porogen

Silica antireflective (AR) coatings with high transmittance and enhanced abrasion-resistance were synthesized by sol–gel process using polypropylene glycol (PPG) as porogen. The effects of molecular weight of PPG and weight ratio of PPG to SiO2 on the refractive index and abrasion-resistance of the coating were systematically studied and compared with those of polyethylene glycol (PEG). Experimental data showed that the refractive index decreased with increasing the weight ratio to SiO2 and molecular weight of both PEG and PPG, but PPG was much more effective than PEG. In the case of same molecular weight, PPG modified coating has the higher porosity than PEG modified one. When the weight ratio of PPG to SiO2 is in a low level, the PPG-containing silica AR coatings exhibit the good abrasion-resistance. PPG is liquid at room temperature and the better solubility than PEG. These effective and economic AR coatings with enhanced abrasion-resistance have potential value in the field of solar thermal collectors.

Preparation of hydrophobic and abrasion-resistant silica antireflective coatings by using a cationic surfactant to regulate surface morphologies

Antireflective (AR) coatings were prepared in the process of the acid catalyzed sol–gel process by using tetraethylorthosilicate (TEOS) as silica precursor and cetyltrimethyl ammonium bromide (CTAB) as template. Acid-catalyzed silica AR coatings exhibited extremely strong adhesive forces with glass substrates and excellent abrasion-resistant property. The experimental results revealed that the regulation of the template concentrations in silica sols could not only improve the transmittance of coatings but also alter the surface morphology and roughness. To further improve hydrophobicity and minimize the conflict between roughness and transmittance, the target coating was designed as a bilayer coating, composed of a porous bottom layer acting as AR coating and a rough top layer providing applicable roughness. Trimethylchlorosilane (TMCS) treatment was finally used to obtain the hydrophobicity of the AR coatings. The results indicated that, the antireflection, hydrophobicity and abrasion-resistant property were successfully integrated in the bilayer AR coating, which showed 96.6% transmittance, 130° water contact angle and 5 H pencil hardness. Meanwhile, the multiple performances are very promising in the long practical application of solar collector covers.

Effect of hydrophobicity on the stability of sol–gel silica coatings in vacuum and their laser damage threshold

Silica antireflective coatings modified by hexamethyldisilazane (HMDS) were deposited on clean substrates (silicon wafer or K9 glass blanks) by sol–gel processing. The effects of HMDS on the contamination resistant capability and laser-induced damage threshold (LIDT) of coatings were investigated. Transmission electron microscopy revealed that a stable sol with uniformly distributed silica particles with an average particle size of about 15 nm was acquired by adding appropriate amount of HMDS into the standard SiO2 sol. With the modified sol the resultant coatings were hydrophobic and the contact angle for water increased with increasing amount of HMDS in the reaction mixture. Such increase in hydrophobicity was not the result of surface roughness. The antireflective properties were retained after HMDS-treatment and the maximum transmission values were above 99 %. The introduction of HMDS into silica sols had also increased the LIDT of coatings from 24.3 to 37.0 J cm−2 when the molar ratio of HMDS to tetraethoxysilane was 0.05:1. The increase in LIDT was attributed to the decrease of nodular defect and uniform microstructures of coatings as an effect of the HMDS modification. After some of the hydroxyl groups on the surface of the SiO2 particle were replaced by methyl groups, from which the SiO2 particle gained a water-repellent surface, the stability of coatings in vacuum was increased. The maximum transmission values of modified coatings decreased by only 0.25 % after storage under vacuum for 168 h. In contrast, the standard sol–gel silica coatings decreased about 2 % under similar conditions. The LIDT of modified coatings remained as high as 30.8 J cm−2, more than that of standard coatings stored for the same duration in air.

A novel route to prepare weather resistant, durable antireflective films for solar glass

Silica antireflective coatings by the base catalyzed sol–gel process show poor mechanical property. In this study, the base-catalyzed sol was modified by acid-catalyzed polysiloxane and nano-TiO2 sol. The single layer antireflective films were prepared using spray coating technology, the effects of transmission speed on the optical performance of the films were studied. The results show that the films derived from the modified sol have an excellent weather resistance. Its degradation of transmittance after damp-heat test is only 0.23%. The maximum transmittance of the antireflective solar glass with single layer coating is about 95.02% at 565nm wavelength, which is about 3.36% higher than the substrate glass. The adhesion of the film is 5B and the pencil hardness is equal or higher than 3H. High transmittance, good mechanical properties and excellent durability make the films be suited to solar glass.

Effect of ethylene glycol variation on silica antireflective coatings

A new type of sol-gel process addition of ethylene glycol has been developed. Sol-gel derived bulk and thin films were prepared from different compositions containing varying concentrations of ethylene glycol from 5% to 15% at constant water (H2O)/tetraethyl-orthosilicate (TEOS) ratio. Scanning electronic microscope (SEM) was carried out to monitor the effects of concentration of ethylene glycol on the internal environment of sol-gel materials. Sol-gel thin films, prepared by rotating coating technique were depicted uniform and cracked surface at rotating speed 2,000 r/min (high speed) and 800 r/min (low speed) respectively. It was shown that an antireflective film produced by incorporation of ethylene glycol in the precursor solution is a more effective method to effect the uniformly porous structures of SiO2 thin film on the glass substrate. The surface of the film on glass substrates is seen to exist in different conditions with different compositions of ethylene glycol.

水氨或/和六甲基二硅氮烷表面处理碱催化二氧化硅增透膜结果的对比研究

Aiming at the shortcoming that base-catalyzed quarter-wave silica antireflective coatings,prepared by sol-gel method,are porous and therefore low environment-resistant,water/NH3vapor and/or hexamethyldisilazane vapor were utilized to modify the surface of these coatings to obtain high hydrophobicity and abrasion-resistance.Otherwise,comparison between different modified results from single vapor and combined vapors,were carried out to show the changes of coatings’physical properties and microstructures after different surface modifications and the influence of the treated order of combined vapors to the result coatings.According to the investigations,some conclusion can be drawn that water-ammonia vapor treatment facilitates the cross-link between hydroxyl groups in coatings,which reduces the film thickness,strengthens the abrasion-resistance,and simultaneously maintains the high transmittance;hexamethyldisilazane vapor treatment introduces methyl groups into coatings,making the polarity of coating surface and the interaction between particles decreased obviously,leading to poorer abrasion-resistance but fortunately,distinctly improved hydrophobicity;when coatings are treated by water-ammonia combined hexamethyldisilazane vapor,the water-ammonia vapor firstly strengthens the abrasion-resistance and meanwhile reduces the amount of hydroxyl groups which hindered the later hexamethyldisilazane vapor treatment,finally obtaining AR coatings with good abrasion-resistance and a certain extent of hydrophobicity;when coatings are treated by hexamethyldisilazane combined water-ammonia vapor,the hexamethyldisilazane vapor obviously improves the hydrophobicity but weakens the effect of water-ammonia vapor,resulting in a slight weaker abrasion-resistance compared to that after single water-ammonia vapor treatment.

Effect of Different Temperatures on Fabricating Silica Antireflective Coatings

Based on TEOS system and sol-gel process, together with catalysts, Antireflective coating films prepared by sol—gel on glass substrate have been processed by furnace thermal annealing (FA). the refractive index and thinkness of SiO2 film is exactly controlled. The films are characterized by ellipsometer and SEM respectively. The effect of different temperatures in these processions are found and discussed

Quantum State in Fabricating Silica Antireflective Coatings

Based on TEOS system and sol-gel process, together with catalysts, Antireflective coating films prepared by sol—gel on glass substrate have been processed by rapid thermal annealing (RTA). the refractive index and thinkness of SiO2 film is exactly controlled. The films are characterized by ellipsometer and SEM respectively. The quantum states in these processions are found and discussed.

Effect of Speed on Silica Antireflective Coatings by Dipping Coating

Sol-gel thin films prepared by dipping coating technique, sol–gel derived bulk were prepared from constant water (H2O)/tetraethyl-orthosilicate (TEOS) ratio, dipping coating were carried out at different dipping speed 100mm/min, 200mm/min, 300mm/min, 400mm/min, 500mm/min respectively. The films are characterized by ellipsometer and SEM respectively. The experimental results show the thickness of films are become bigger and bigger with the dipping speed increasing.The refractive index change is not obvious.

A simple route to prepare crack-free thick antireflective silica coatings with improved antireflective stability

In this study, a simple route was proposed to prepare crack-free thick antireflective (AR) silica coatings with improved abrasion resistance and AR stability. Using tetraethylorthosilicate (TEOS) as precursor and hydroxyl-terminated polydimethylsiloxane (PDMS) as modifier, silica AR coatings were prepared by sol–gel process with dip-coating method. It is found that the addition of PDMS extends the adjustable range of sol viscosity, and allows the preparation of thick coatings by a simple route. PDMS prevents the thick AR coating from cracking and enhances its abrasion resistance due to the enhanced particle-to-particle bond strength and the reduced stress inside the film. The hydrophobicity of the coating is also improved by the introduction of hydrophobic methyl groups, and the measured water contact angle increases from 23.4° to 75.3°. Thick crack-free AR coatings with good abrasion resistance and antireflective stability can be prepared by this simple route.

A review of contamination-resistant antireflective sol–gel coatings

Sol–gel derived silica antireflective (AR) coatings have been widely used as the optical components for high peak power laser systems because of their excellent optical properties and high laser-induced damage thresholds. However, the sol–gel derived coatings have a high surface area that is more susceptible to be contaminated by absorption of trace amounts of water vapor and other volatile organic compounds from the environment. In this paper, the major approaches to fabricate contamination resistant sol–gel derived silica AR coatings have been extensively reviewed. Different approaches, including solution-phase and vapor-phase silanization, ammonia–water vapor treatment and fluorine modification have been discussed. The optical properties and laser-induced damage thresholds of modified coatings have also been evaluated. The improved sol–gel AR coatings have been shown to possess superior contamination resistance to work in vacuum systems compare to the traditional sol–gel AR coatings.

Effect of Catalytic Time Variation on Silica Antireflective Coatings

Based on TEOS system and sol-gel process, together with catalysts, the microstructure of SiO2 particles in the sol is exactly controlled. The films are characterized by ellipsometer and SEM respectively. The experimental results show that adjusting catalytic time can effectively effect the uniformly porous structures of SiO2 thin film on the glass substrate.

Preparation of antireflective coatings with high transmittance and enhanced abrasion-resistance by a base/acid two-step catalyzed sol–gel process

Antireflective (AR) coatings with high transmittance and enhanced abrasion-resistance were prepared by a base/acid two-step catalyzed sol–gel process using tetraethylorthosilicate (TEOS) as precursor. These AR coatings exhibit both high transmittance and enhanced abrasion-resistance when the mole ratio of acid-catalyzed silica to base-catalyzed silica was 0.5. The experimental results revealed that the acid-catalyzed silica was covalently bonded to base-catalyzed silica particles, which greatly increased the abrasion-resistance. Hexamethyldisiloxane (HMDS) treatment was further used to improve the hydrophobicity of the AR coatings. The water contact angles of pure silica AR coatings and AR coatings treated with 16% HMDS were 21.3° and 72.5°, respectively, indicating a significant increase in hydrophobicity. FTIR spectra revealed the existence of –Si (CH 3) 3 after HMDS treatment, showing that the hydroxyl groups of AR coatings were replaced by –OSi (CH 3) 3, affording the AR coatings treated with HMDS excellent environmental resistance.

Sol-Gel Processing by Organic Polymer Addition for Silica Antireflective Coatings

Based on TEOS system and sol-gel process together with catalysts and organic polymer, the microstructure of SiO2 film is controlled. The films are characterized by ellipsometer and SEM respectively. The experimental results show an antireflective film produced by incorporation of organic polymer in the precursor solution is a more effective method of effect the uniformly porous structures of SiO2 thin film on the glass substrate.

Sol−Gel Preparation of PDMS/Silica Hybrid Antireflective Coatings with Controlled Thickness and Durable Antireflective Performance

Thick silica antireflective (AR) coatings with controlled thickness and durable AR performance were prepared by a base-catalyzed sol−gel process using tetraethyl orthosilicate (TEOS) as precursor and hydroxyl-terminated polydimethylsiloxane (PDMS) as a modifier. The addition of PDMS greatly increased the controllable viscosity range of the silica sol but did not obviously affect the particle size. This phenomenon is attributed to a “compulsive aggregation” process of the sol, which involves the formation of “PDMS bridges” between silica particles in the sol. The mechanism of “PDMS bridge” formation is proposed based on sol viscosity, sol particle size changes, and FTIR identification. The increased controllable viscosity range provided a convenient way to prepare AR coatings with controlled thickness and therefore with controlled wavelength of maximum transmittance. The introduction of PDMS into the silica sol also increased the hydrophobicity and hence the durability of the AR coatings in wet environments.

含氟有机硅改性多孔二氧化硅减反膜

含氟有机硅改性多孔二氧化硅减反膜

Effect of oil vapor contamination on the performance of porous silica sol-gel antireflection-coated optics in vacuum spatial filters of high-power neodymium glass laser

The effect of oil vapor contamination on sol-gel porous silica antireflection (AR) coatings deposited on optics used in vacuum spatial filters of high-power lasers is experimentally studied. The contamination results in the reduction of laser-induced damage threshold (LIDT) and the increase in reflectivity of the AR coatings. In comparison, the silica coatings treated with ammonia and hexamethyl-disilazane (HMDS) show almost no increase of reflectivity, and their LIDT value reduces only marginally at the wavelength of laser operation. It is found that the decrease in LIDT of the coatings exposed to oil vapors occurs due to higher absorption of the laser light, as evidenced from the increase in the imaginary part of the refractive index of the coatings.