Diamond-based active antireflective optical windows with omniphobic properties – D-FACTO

In the D-FACTO project, we propose to design and fabricate active optical windows based on nanostructured diamond, combining anti-reflective, superhydrophobic, anti-icing and anti-fouling properties. This research project is motivated by the very promising results obtained within the framework of the ANR ASTRID F-MARS project (2019-2022), coordinated by Thales Research & Technology (TRT). In this project, TRT has already shown its capability to simulate and manufacture “multifunctional” windows with broadband anti-reflective and large incidence, superhydrophobic and anti-rain properties in the range of Visible, Midwave InfraRed. and Longwave InfraRed, by developing nanostructuration processes of glass, silicon and germanium respectively.
These optical windows aim to meet the needs of many optical and optronics systems used in civil and military fields: land and sea surveillance systems, airborne sensors for threat detection, autonomous train cameras, etc. However, the superhydrophobic nature of these windows, which is fundamental for some of these applications, does not protect these systems, for example, from the formation of various biofilms (marine, hydrocarbons, etc.), nor from the formation of frost.
The aim of the D-FACTO project is to extend the multifunctionality of these optical surfaces, by developing robust “active” diamond windows allowing them to be get anti-fouling and anti-ince properties, by using a low current. electrical, coupled (or not) with adequate surface functionalization. Indeed, diamond has intrinsic qualities of interest: in addition to having very good mechanical properties, it is transparent in the ranges from visible to LWIR and it is an excellent thermal conductor. Once doped, it has remarkable electrochemical properties, among which the capacity for electrochemical self-cleaning of its surface and therefore anti-fouling properties.
The work of the consortium, composed of two academic partners, CEA-LIST and ILV, and an industrialist (TRT), will first focus on the development of pre-industrial processes for producing optical windows based on synthetic diamond which will benefit from its optical, mechanical and physicochemical "flexibility" advantages for anti-fouling, anti-ince and anti-reflective applications. They will also focus on the understanding and optimizationof the phenomena involved in the self-cleaning and anti-icing mechanisms of these so-called "active" windows. The manipulation of surfaces by electrochemistry of diamond, or else by more conventional surface treatments, should make it possible to modulate its omniphobic capacities. The consortium will thus have various very original functionalization possibilities for optimal physicochemical adaptation.
Considering the state of the art, the challenges of the D-FACTO project are the following:
• to develop a large area (2-3 inches) process of diamond nanostructuring for anti-reflective applications in Vis, MWIR and LWIR.
• to characterize and optimize the growth of doped diamond by taking into account the application constraints (compliance with optical specifications, nature of the substrates in the case of diamond / silicon, diamond / germanium “hydride” windows, etc.).
• to optimize the physicochemical properties of the post-nanostructuring process diamond surface and to develop specific chemical engineering based on various surface treatments: “electroless” chemistry, electrochemical assistance, plasma process, etc.
• Set up a robust characterization methodology, able of combining fine wettability analysis and chemical analysis by photoemission or Auger emission of diamond, in order to guide the consortium in optimizing the functionalization of nanostructures.