Observing the breathing of silica sol-gel-derived anti-reflection optical coatings

Vong, M. S. W.; Sermon, Paul A.

doi:10.1016/s0040-6090(96)09041-4

Cited by 42 publications

(21 citation statements)

References 58 publications

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“…Some bands due to PEG200 are obscured by the Si--O--and ethanol bands. The relative or//3 intensity of the bands associated with Si--O--Si and incorporated water decreased as the SIO2-10% PEG200 film was dried and aged at increasing temperatures, indicating the evolution of the silica structure [5]. In addition, the absorption bands due to PEG almost disappeared after heated at 703 K and no additional bands were detected during this maturation process.…”

Section: Ftirspectroscopymentioning

confidence: 93%

“…Thin oxide coatings of sols with suitably designed porosity and refractive index can as a result be manipulated to produce optimum optical [1] and catalytic [2,3] properties. Some [4] have approached this control for silica gels by pre-reacting a diol with tetraethylorthosilicate (TEOS), otherwise silica sol and gel properties can be controlled by a variation of the water 9 alkoxide ratio, catalyst concentration and dilution [5]. Polyethylene glycol (PEG, M.W.…”

Section: Introduction 2 Experimentalmentioning

confidence: 99%

“…Colloidal (3% w/w) silica sol was prepared from base (ammomium hydroxide) catalyzed hydrolysis/condensation of tetraethylorthosilicate (TEOS, 98% purity; Aldrich) in water (hplc grade) and ethanol (Aldrich) in the TEOS : HzO : C2HsOH : NH4OH molar ratio of 1 : 4 : 37 : 0.001 at ambient conditions [5]. The mixture was aged in a sealed polypropylene container for at least 7 days before drying at 313 K to form highly porous xerogels.…”

Section: Introduction 2 Experimentalmentioning

confidence: 99%

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Chemical modification of silica gels

Vong

Bazin

Sermon

1997

J Sol-Gel Sci Technol

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Abstract. Highly porous pure and polyethyleneglycol (PEG)-doped silica gels have been prepared from tetraethyl orthosilicate (TEOS) in ethanol using NH4OH base-catalysis. Addition of PEG to the SiO2-system increases the average particle size and most frequent pore diameter of the resultant gels while their total surface area decreases. The viscosity of the sol increases with PEG concentration and passes through a maximum with increasing molecular weight at PEG 200. Results obtained indicate a definite interaction of the polymer with SiO2 and that this interaction is not as a result of direct formation of Si--O-C linkage, but is more likely to be due to hydrogen bonding between the hydrated PEG and the Si--O--Si network. Structure-process correlations are considered.

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Section: Ftirspectroscopymentioning

confidence: 93%

Section: Introduction 2 Experimentalmentioning

confidence: 99%

Section: Introduction 2 Experimentalmentioning

confidence: 99%

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Chemical modification of silica gels

Vong

Bazin

Sermon

1997

J Sol-Gel Sci Technol

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“…The literature contains examples of AFM images of porous material, 263 -268 and of TEM images, 269,270 while a comparison of the two is also available. 271 Generally, the actual radius of the AFM tip is unknown, and therefore the lower detection limit for small pores is also unknown. Typically, this radius is >10 nm.…”

Section: Porositymentioning

confidence: 99%

“…Vong and Sermon investigated porous SiO 2 coatings from silica sols with different diameters of the colloid particles. 271 Sols with colloidal particles with average diameters of 17 nm resulted in porous coatings with particle diameters of 25 -30 nm. In porous coatings from sols with average diameters of 100 nm, the particle diameter did not change during annealing.…”

Section: Porositymentioning

confidence: 99%

Microscopy of Coatings

Rädlein¹

2000

Encyclopedia of Analytical Chemistry

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Fundamental research on films and the development and optimization of coatings are not possible without high‐resolution imaging. This article describes the advantages and disadvantages of the newly introduced scanning probe microscopy (SPM) in comparison with well‐established microscopy techniques with light and particles [e.g. scanning electron microscopy (SEM) and transmission electron microscopy (TEM)], which are limited by the diffraction limit, i.e. 200 nm for conventional light microscopy and 4 nm for SEM. This limit does not hold for SPM, which uses near‐field interactions for imaging. Thus, even simple atoms or molecules can be resolved on well‐ordered structures by scanning tunneling microscopy (STM) or atomic force microscopy (AFM). Both possess an extremely good height sensitivity of 0.02 nm. 1 In the constant‐height operation mode, AFM can detect vertical forces as low as 10 −15 –10 −4 N. Atomic resolution is not always possible or not always necessary for many practical applications; a lateral resolution of a few nanometers is sufficient. Besides the capability of achieving this value with ease, simple sample preparation, versatile environmental conditions and observation of reactions in situ are advantages of STM and AFM. Especially AFM has proved to be a useful technique for investigating coatings, because it is independent of conductivity and provides topographic data together with information on structure, local variations of mechanical properties and surface alterations in different media. However, some artifacts and restrictions have to be considered which can differ considerably from customary electron micrographs with comparable resolutions, such as onset overswing and tip convolution. Microscopy helps in solving coating problems according to substrate quality, nucleation, wettability, thickness, roughness, microstructure, crystal phases (texture, orientation), lateral and vertical homogeneity, density, porosity, interfaces, adhesion, hardness, stress, scratch and abrasion resistance, tribology, wear and corrosion. Practical examples of microscopy results on these questions are presented together with suitable preparation methods and interpretation of artifacts.

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