Multifunctional CVD diamond window for Infrared imaging

At a Glance

Metadata	Details
Publication Date	2025-03-18
Journal	MRS Advances
Authors	R. Guillemet, Mane‐Si Laure Lee, Doriane Jussey, Elyess Traouli, Brigitte Loiseaux
Analysis	Full AI Review Included

Technical Documentation & Analysis: Multifunctional CVD Diamond Windows

Executive Summary

This research successfully demonstrates a multifunctional CVD diamond optical window leveraging metasurface technology and electrochemical activation for superior performance in harsh LWIR imaging environments.

LWIR Performance: Achieved enhanced transmission of 80-90% across the critical 8-14 µm Long-Wave Infrared (LWIR) band using subwavelength conical metasurfaces, representing a 20-30% gain over bare polished diamond.
Extreme Fluidic Resistance: The surface exhibits robust superhydrophobicity (Contact Angle ~160°) and effective antirain/antimist properties, preventing image degradation in wet conditions.
Mechanical Durability: Nanoscratch testing confirmed exceptional mechanical resistance, with full diamond structures withstanding vertical forces up to 5 mN and severe abrasion (40 frictions @ 10N) without breakage, significantly outperforming DLC-coated Germanium.
Active Self-Cleaning: Integration of a low-doped Boron-Doped Diamond (BDD) coating enables electrochemical antifouling. Contaminants (oil/gasoline) were completely removed within minutes using a low anodic current (100 mA/cm²).
Scalability: The fabrication methodology (nano-imprint lithography and RIE-ICP etching) is confirmed to be scalable and compatible with large-area and curved diamond surfaces.
Core Value Proposition: CVD diamond provides a single material solution combining outstanding optical, mechanical, and electrochemical properties for low-maintenance, 24/7 operation of optronics systems.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Material	CVD Diamond	N/A	Used for 2” optical window
Window Diameter	2	inches	Demonstrated functional size
Substrate Thickness	1	mm	As-purchased material
Initial Roughness (Ra)	< 15	nm	Average roughness on both faces
Operational Wavelength Range	8-14	µm	Long-Wave Infrared (LWIR)
Peak Transmission (Structured)	80-90	%	Double-sided structured window
Transmission Enhancement	20-30	%	Increase over bare polished diamond (~68%)
Metasurface Periodicity	~2	µm	Conical structures
Structure Aspect Ratio	> 1:4	N/A	High aspect ratio microstructuration
Superhydrophobicity	~160	°	Drop contact angle (DI or tap water)
BDD Coating Thickness	~100	nm	Applied for electrochemical antifouling
BDD Doping Level	~10¹⁸	at.cm^-3	Low doping to maintain IR transparency
Nanoscratch Resistance	5	mN	Maximum vertical force applied without structure breakage
Electrochemical Cleaning Current	100	mA/cm²	Anodic treatment for contaminant removal

Key Methodologies

The multifunctional diamond window was manufactured using a scalable process flow combining advanced lithography, plasma etching, and surface functionalization.

Substrate Acquisition: A 2” CVD diamond window (1 mm thick, Ra < 15 nm) was sourced as the base material.
Pattern Definition (Nano-imprint Lithography): A lithography step, based on nano-imprint lithography (NIL), was used to define the ~2 µm periodic conical patterns in a resist layer. NIL is noted for its scalability and compatibility with curved surfaces.
Hard Mask Transfer: The patterns were transferred into a Ni-based metallic hard mask deposited via sputtering.
Diamond Etching (RIE-ICP): Reactive Ion Etching - Inductively Coupled Plasma (RIE-ICP) using O₂ plasma was employed to achieve high aspect ratio microstructuration (> 1:4) in the diamond substrate.
Antifouling Layer Deposition: A thin (~100 nm) layer of low-doped Boron-Doped Diamond (BDD) was deposited via CVD to enable electrochemical self-cleaning properties.
Superhydrophobic Functionalization: An additional chemical functionalization step was carried out using C₄F₈ plasma to deposit a few nm thick Polytetrafluoroethylene (PTFE) layer, resulting in the ~160° contact angle.
Electrochemical Activation: Anodic treatment using a continuous current of 100 mA/cm² was applied to the BDD surface to generate oxidant radicals (OH*) for self-cleaning of oil/gasoline contaminants.

6CCVD Solutions & Capabilities

The successful replication and extension of this multifunctional diamond technology rely heavily on high-quality, large-area CVD diamond substrates and specialized processing capabilities. 6CCVD is uniquely positioned to supply the foundational materials and engineering support required for next-generation LWIR optics.

Research Requirement	6CCVD Solution & Capability	Technical Advantage for Replication/Extension
High-Quality Substrate	Optical Grade Polycrystalline Diamond (PCD)	We provide high-purity MPCVD PCD plates up to 125 mm in diameter, exceeding the 2” size used in the study, enabling larger format LWIR windows.
Specific Material Doping	Custom Boron-Doped Diamond (BDD)	We specialize in BDD growth, offering precise control over doping levels (e.g., 10¹⁸ at.cm^-3) and thickness (0.1 µm - 500 µm) necessary for optimal electrochemical antifouling without sacrificing IR transparency.
Substrate Dimensions	Custom Thicknesses and Substrates	We supply SCD and PCD wafers in the required 1 mm thickness, and offer robust substrates up to 10 mm thick for extreme mechanical applications or high-pressure environments.
Surface Preparation	Precision Polishing Services	Achieving the necessary low roughness for subsequent nano-imprint lithography is critical. We guarantee ultra-smooth surfaces: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
Hard Mask Integration	In-House Metalization Services	The RIE-ICP etching process requires a robust hard mask (e.g., Ni-based). 6CCVD offers internal deposition of key metals (Ti, W, Pt, Au, Cu) to facilitate complex microstructuring processes.
Engineering Expertise	PhD-Level Material Consultation	6CCVD’s in-house PhD team can assist engineers and scientists with material selection, doping optimization, and interface engineering for similar LWIR metasurface and antifouling projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 2″ full 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 µm 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

Tech Support

Original Source

DOI: https://doi.org/10.1557/s43580-025-01233-8