Towards new levels for stacking of sol-gel functional coatings

Abstract

High optical performance coatings prepared by a liquid deposition process have been studied with focus on the parameters playing a role on the layer stacking ability. During the development of multilayer optical coatings, defects such as cracks, scattering and a refractive index gradient could appear. In order to understand the origins of these limitations, the investigation was performed on colloidal stacks of single and multi-materials. This study has rendered it possible to define the main process parameters as well as the physical and chemical parameters of the suspensions influencing the stacking capacity. This work is a first step to obtaining evidence of a relationship between the thin film microstructure induced by deposition conditions and the ability to achieve sol-gel thick films with good optical (homogeneous) and mechanical (crack-free) properties.

Sol–Gel Route Toward Efficient and Robust Distributed Bragg Reflectors for Light Management Applications

“…In that regard, liquid processes have recently become increasingly studied owing to their simplicity, scalability and low cost compared to more traditional, vacuum‐based deposition approaches. In particular, sol–gel processing is a simple and scalable technique well known for its flexibility to engineer a variety of microstructured compounds, including DBRs, with tunable properties …”

“…Moreover, each layer deposited necessitates sometimes long annealing steps at elevated temperatures, which impacts the simplicity, scalability and cost of the process . The use of porous layers as the low‐index materials, thanks to colloidal nanoparticles, or with polymeric sol and sacrificial surfactant pore templates, has alleviated in part these limitations by allowing for a larger index contrast thanks to very low index layers, which resulted in DBRs requiring less bi‐layers to exhibit good optical performance. These strategies have so far relied on open porosity with mesoscale feature size, which have brought great improvement to the field of liquid based optical coatings, but still suffer from a number of limitations: first, the open porosity network gives rise to inter‐diffusion during the high index layer deposition.…”

Improvement on contamination resistance to volatile organics and moisture of sol–gel silica antireflective coating for 351 nm laser system by structural modulation with fluorinated compounds

“…Due to certain intrinsic characteristics that ensure high LIDT and transmittance, sol-gel coatings are widely employed in these transmission optic components. [2][3][4][5][6][7][8] Specic porosity in these sol-gel coatings is necessary to obtain desirable refractive index, in which the micro-pores among particles play a major role. However, the sol-gel coating can easily adsorb organic contaminants and moisture in the environment, due to its porous structure and enormous surface hydroxyls.…”

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A new silica antireflective (AR) coating with excellent spectral stability and laser-induced damage threshold (LIDT), which are crucial characteristics in high-powered laser systems, was prepared using the sol-gel method. First, aided by 2,2,3,3,4,4,5,5,6,6,7,, crosslinking among silica particles was facilitated. Thus high and adjustable inter-particle porosity was obtained and hence the refractive indices of the coatings were modulated.

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