Background
Nanostructuring ultrahard materials like sapphire is challenging due to their inherent hardness and chemical stability, which complicate the precise modification and removal of material. Traditional approaches such as multilayer masking, low-power dry etching, and direct ultrafast laser processing have struggled to achieve the fine, dense features necessary for advanced functionalities, as these methods often lead to incomplete material removal or uncontrolled modification below the surface. Recent research has explored the use of near-field focusing techniques with dielectric microspheres to generate photonic nanojets that alter the material’s crystallinity and facilitate selective etching, but controlling the focal depth and ensuring complete removal of the laser-modified regions remain significant challenges, requiring careful optimization of parameters like microsphere size and process conditions.
Technology overview
Dielectric microspheres, placed on a sapphire substrate, are used as focusing lenses to concentrate ultrafast laser beams into photonic nanojets that locally alter the sapphire’s crystallinity, converting crystalline regions into amorphous or polycrystalline states. These modified areas become more susceptible to selective chemical etching with hydrofluoric acid, allowing the precise removal of material to form nanostructures.
By adjusting the size of the microspheres—from approximately 9 μm down to 1.18 μm—the process controls the focus depth and the resulting nanostructure dimensions, enabling the fabrication of features ranging from deep, wider holes to shallow, densely packed nanostructures with diameters as small as 190 nm. Finite-difference time-domain simulations are used to predict the intensity thresholds and etch profiles, achieving close agreement with experimental measurements and demonstrating the technique’s ability to create finely controlled nanostructures on ultrahard sapphire surfaces.
Benefits
- Enhanced precision in nanofabrication: The method uses dielectric microspheres for near-field laser focusing, producing nanostructures with controllable feature sizes (e.g., 190 nm to 510 nm diameters) that outperform conventional multilayer masks and low RF power dry etching in resolution and density.
- Superior process adaptability for ultra-hard materials: By converting crystalline sapphire regions to amorphous and polycrystalline states, the invention effectively overcomes sapphire’s inherent hardness and chemical resistance—challenges that have limited traditional ultrafast laser modification techniques.
- Optimized chemical etching efficiency: The laser-modified zones are engineered to enhance susceptibility to hydrofluoric acid etching, ensuring precise removal of target areas, which represents an improvement over earlier approaches that struggled with etchant penetration due to deep nanojet focal points.
- Robust mechanical and functional performance: The concave nanostructures created offer enhanced scratch resistance, fracture resistance, anti-glare, anti-fog, and self-cleaning properties, providing superior performance compared to standard nanostructuring methods that lack such tailored surface functionalities.
Applications
- High-performance optical and protective surface coatings: The invention enables the creation of sapphire surfaces with anti-glare, self-cleaning, anti-fogging, and enhanced scratch resistance, ideal for consumer electronics, architectural glass, and automotive applications.
- Aerospace and defense component fabrication: The nanostructuring method produces ultra-durable sapphire with tailored optical and mechanical properties, making it well-suited for optical windows, sensors, and other critical components in space and defense markets.
