Publication of the month - May
Over at the OpTIC Technology Centre in St.Asaph, North Wales, the teams undertake the manufacture of complex large optical components, with OpTIC being the only UK manufacturer of these large components up to 2m diameter in the UK! The research and development team, in collaboration with industry, is leading the way in thin film coating, developing new products and processes for a wide range of industrial applications. A recent article in the Surface and Interfaces journal titled “Electron Beam Ion-Assisted Deposition of SiO₂–TiO₂ Broadband Antireflection Coatings: Substrate Temperature Effect on Optical Properties” talks about antireflection coatings being applied using electron beam ions and the analysis of their optical transmission. The research was undertaken in collaboration with colleagues at Bangor and Aberystwyth Universities, with our in-house research team comprising of Dr Omprakash Muthusamy, Dr Yasir Joya, Professor Richard Day, and Dr Chris Nyamayaro.
Antireflection coatings
Enhancing optical efficiency in technologies, such as high-performance solar panels and advanced lasers, involves maximising the volume of light that passes through the glass by reducing the light that is reflected away from the object. This is where the use of antireflection coatings comes into play, by adding thin layers to glass objects it enables more light to pass through instead of reflecting off, thus increasing efficiency.
This Study
In the article the team explain that antireflection coating made from layers of silicon dioxide (SiO₂) and titanium dioxide (TiO₂) are effective as they have high transparency, and the two materials bend light differently, meaning that they work in a complementary way to allow more light through. These materials are described as “non-toxic, earth-abundant, chemically and thermally stable, and low cost”. This multilayer antireflective coating can be applied using various deposition techniques and a method called electron beam ion assisted deposition was used during the study, which allows fine control over the layering, produces high quality, and is suited to industrial application.
The aim of the study was to clarify how the in-situ temperature of the glass object during coating regulates the surface microstructure and interfacial integrity during deposition, without the need for post processing treatments to achieve better optical transmission.
Findings
Testing (including adhesion and aging) of the reflective coating at various deposition temperatures found:
- The temperature of the object being coated with the antireflective coating plays a critical role in subsequent performance
- Optimal transmission and minimal reflection are achieved when the glass is heated to 160–180 °C during coating
- Temperatures above 200◦C led to reduced efficiency and defects
- Application between the temperatures of 160–180 °C produces antireflection results that are suitable for manufacturing high damage threshold laser optics and high-efficiency solar energy applications
- The surface remained smooth and dense at these temperatures, which supports effectiveness
- The wettability of the SiO₂–TiO₂ coatings were assessed and it was found that the coatings applied at the optimal temperatures of 160–180 °C can be suitable for self-cleaning purpose for solar cell, which can help maintain high transmission in real operating conditions.
In conclusion
Making changes to the coating temperature during manufacture, instead of using additional postproduction treatments, results in an efficient, cost-effective way to make clear and durable antireflection coatings for industry application. The research shows that applying the SiO₂–TiO₂ coatings, using electron-beam-ion assisted deposition with the object heated to the optimal window of 160–180 °C, yields strong results.