| Metadata | Details |
|---|
| Publication Date | 2025-03-18 |
| Journal | MRS Advances |
| Authors | R. Guillemet, ManeâSi Laure Lee, Doriane Jussey, Elyess Traouli, Brigitte Loiseaux |
| Analysis | Full AI Review Included |
- Multifunctional Window Demonstrated: A 2-inch Chemical Vapor Deposition (CVD) diamond optical window was successfully manufactured, integrating five key functionalities for LongWave Infrared (LWIR) imaging systems (8-14 ”m).
- Enhanced Optical Performance: Achieved high double-sided transmission of 80-90% across the LWIR band, representing a significant 20-30% transmission gain compared to flat polished diamond (~68%).
- Superior Fluidic Properties: The nanostructured surface, functionalized with PTFE, exhibited superhydrophobicity (contact angle ~160°), providing effective antirain and antimist behaviors for clear imaging in wet conditions.
- Extreme Mechanical Resistance: The full diamond microstructures showed exceptional resilience during nanoscratch testing, resisting vertical forces up to 5 mN with only minor blunting and no structural breakage.
- Active Self-Cleaning (Antifouling): Integration of a Boron-Doped Diamond (BDD) coating enables electrochemical activation (100 mA/cm2 anodic current), allowing the window to self-clean from oil and gasoline contamination within minutes.
- Scalable Manufacturing: The process relies on nano-imprint lithography (NIL) and plasma etching, making the technology compatible with large-scale production and curved optical surfaces.
| Parameter | Value | Unit | Context |
|---|
| Substrate Material | CVD Diamond | N/A | Purchased from Coherent Corp. |
| Window Diameter | 2 | inches | Full optical component size |
| Window Thickness | 1 | mm | Substrate thickness |
| Operational Wavelength | 8-14 | ”m | LongWave Infrared (LWIR) range |
| Double-Sided Transmission | 80-90 | % | Structured diamond performance |
| Transmission Increase | 20-30 | % | Gain over flat polished diamond |
| Structure Period | ~2 | ”m | Conical metasurface geometry |
| Structure Aspect Ratio | > 1:4 | Ratio | Height to period |
| Water Contact Angle | ~160 | ° | Superhydrophobicity (after PTFE coating) |
| Mechanical Load Resistance | Up to 5 | mN | Vertical force applied during nanoscratch (no breakage) |
| Diamond Hardness | 100 | GPa | Intrinsic diamond hardness |
| BDD Coating Thickness | ~100 | nm | Boron-doped diamond layer for antifouling |
| BDD Doping Level | ~1018 | at.cm-3 | Low absorption in IR range |
| Electrochemical Cleaning Current | 100 | mA/cm2 | Continuous anodic treatment |
- Substrate Acquisition and Preparation: A 2-inch, 1 mm thick CVD diamond window was used as the base material, selected for its broadband optical transmission (Visible to LWIR) and mechanical properties.
- Pattern Definition (Nano-Imprint Lithography): Patterns for the metasurface (~2 ”m period) were defined in a resist layer using scalable nano-imprint lithography (NIL), followed by transfer into a sputtered Ni-based metallic hard mask.
- Diamond Etching: High aspect ratio microstructuration was achieved using Reactive Ion Etching - Inductively Coupled Plasma (RIE-ICP) with O2 plasma, creating conical structures with an aspect ratio greater than 1:4.
- Superhydrophobic Functionalization: A chemical functionalization step involving C4F8 plasma was used to deposit a few nm thick Polytetrafluoroethylene (PTFE) layer, resulting in a water contact angle of ~160°.
- Antifouling Layer Deposition: A ~100 nm layer of Boron-Doped Diamond (BDD) was deposited on the nanostructured window to enable electrochemical properties, specifically the production of highly oxidant radicals (OH*) for cleaning.
- Optical and Fluidic Testing: Transmission was measured using Fourier-Transform Infrared Spectroscopy (FTIR). Fluidic properties (antirain/antimist) were assessed by implementing the window in front of a LWIR camera during water spraying and mist growth (at 5 °C).
- Mechanical Testing (Nanoscratch): Mechanical resistance was evaluated using nanoscratch testing (KLA G200 nanoindenter) under vertical loads up to 5 mN, comparing the failure mechanisms of full diamond structures against DLC-coated germanium.
- Electrochemical Cleaning Test: Contaminated BDD-coated windows (oil/gasoline mix) were cleaned using an anodic treatment with a continuous current density of 100 mA/cm2, monitored by SEM to confirm contaminant removal.
- Defense and Surveillance Optronics: Essential for protecting high-performance LWIR imaging systems (e.g., cameras, sensors) operating in visually degraded or harsh environments (dust, sand, chemical agents).
- Maritime and Coastal Monitoring: Enables 24/7 operation by eliminating the need for mechanical wipers, offering inherent antirain and antimist capabilities crucial for naval applications.
- Aerospace and UAV Imaging: Provides robust, lightweight windows for airborne sensors requiring high mechanical resistance against erosion and impact, coupled with high IR transmission.
- Industrial Inspection and Monitoring: Use in industrial settings where optical windows are frequently exposed to oil, fuel, or chemical contamination, leveraging the BDD self-cleaning function for low maintenance.
- High-Power Laser Systems: Diamondâs superior thermal conductivity and broad optical transmission make these structured windows suitable for high-power IR applications where thermal management is critical.
View Original Abstract
Abstract Diamond is well known for its outstanding thermal, electrical, and mechanical properties, but is also of great interest for optical and imaging applications. Imaging systems offer increasing performances, with high functionalities and technicity, but are often exposed to harsh or visually degraded environments. In this paper, we exploit some of the multiple physical properties of chemical vapor deposition (CVD) diamond and demonstrate the feasibility of diamond-based metasurface multifunctional windows for infrared spectral range, throughout different configurations. The resulting 2Ⳡfull diamond optical window provides imaging systems with several functionalities, including antireflective optical properties with an enhanced transmission up to 80-90% in the 8-14 ”m spectral range, high mechanical resistance, superhydrophobicity, antirain, and antimist behaviors. Moreover, the electrochemical activation of a boron-doped diamond-based window leads to self-cleaning properties, thus paving the way for the imaging system to low maintenance operations and 24/7 operation. Graphical abstract