Antireflective Reinforced nanostruCtures by HybrId TEChnologies – ARCHITEC

The ARCHITEC – Antireflective Reinforced nanostruCtures by HybrId TEChnologies – aims to improve antireflective (AR) optical coatings elaborated by Oblique Angle Deposition (OAD). This project follows Florian Maudet's PhD thesis work where ultra-high performance coatings were developed using gradient index multilayer stacks for applications in both the visible-SWIR [400-1800]nm and MWIR [3.5-5]µm spectral bands. The various solutions identified, although very efficient from an optical point of view (in terms of transmission) suffer from robustness problems. Thus, the main limitations of the current process are:
(i) the poor mechanical strength of nanostructured layers for vis-SWIR applications, where layer degradation is noticed during handling or cleaning steps,
(ii) chemical pollution within the nanostructured layers for MWIR applications, including oxidation of the semiconductors used, which leads to a decrease in optical transmission.
The ARCHITEC project proposes to address these issues through hybrid technologies by bringing together three partners whose core expertise are linked to innovations in the fields of materials science and optics, namely:
- the Ppna team at the Pprime Institute,
- the R&T team at SAFRAN Electronics and Defense,
- the SME RESCOLL.
The solutions considered in this project to overcome the problems identified involve the deployment of new deposition tools and post-deposition encapsulation processes.
The new deposition tools will allow samples to rotate and tilt in situ during OAD runs. Consequently, the development of complete stacks can be achieved in a single step, at constant temperature and without returning to atmospheric pressure, possibly improving the mechanical resistance of the treatments and significantly reducing pollution problems.
Moreover, the in situ control of inclination and rotation means that numerous and complex architectures can be obtained. The modification of the morphology of the columns towards chevrons is a solid approach to the mechanical reinforcement of the nanostructured layers.
Hybrid solutions for improving the mechanical resistance of deposits for visible-SWIR applications consist in reinforcing an AR stack structured by OAD via a Sol-Gel post-deposition, with high optical performance. This post-deposition, whether or not penetrating into the nanostructured layers, must be taken into account when developing the optical design. The Sol-Gel or aerogel solutions considered consist of:
(i) fill the pores of the porous structure to reinforce it without significantly altering the optical index of the structure,
(ii) apply a very thin surface layer to improve the resistance properties to mechanical aggression.
In addition, it is also planned to bring new functionalities to AR stacks through Sol-Gel layers such as anti-fouling, hydrophobicity and so on.
The improvement of the chemical robustness of nanostructured layers for MWIR applications consists in the addition of a dense surface layer via PVD included in the optical design. Another avenue explored will be the addition of an ultra-fine conformal and penetrating layer within structures even with a very high aspect ratio using Atomic Layer Deposition (ALD) technology.

The economic and societal benefits associated with the industrialization of the solutions developed under this project are significant from both a civil and military point of view.