Precise 3D CNT array catalyst patterning using two-photon lithography for enhanced liftoff and scalability

Carbon nanotube arrays are promising for electron emission applications, where controlled spacing can enhance performance by reducing screening effects. Traditional lithography-based methods are frequently used to define CNT array catalyst structures. However, conventional lithography faces challenges in scalability and complexity, particularly when rapidly customizing designs and prototyping intricate patterns. This study addresses these issues by using a two-photon polymerization technique to enable fast, maskless, and precise patterning of CNT array catalyst regions. Two-photon lithography enables reproducible fabrication of micron scale structures without the need for complex masks, offering an alternative to conventional lithography methods. Two-photon lithography also facilitates 3D printability, which enables the easy addition of features to enhance both liftoff efficiency and the fabrication of intricate patterns. To optimize CNT catalyst patterning, a Design of Experiments approach was used using a full factorial experiment to study the effects of printing laser power and resolution size. Analysis of variance was used to investigate pattern quality with relation to critical dimension and laser power, aiding optimized manufacturing process and iterative testing of design. Scanning electron microscopy was used to verify critical dimensions and to classify printing defects. After inspection, Fe catalyst deposition was performed by sputtering, followed by wet etching of printed polymer, facilitating the liftoff process. Moving forward, these fabrication and optimization techniques offer a practical solution to address challenges in iteratively optimizing the geometry of CNT forest microstructures for specific applications. The process also addresses current issues in lithography, such as achieving finer resolutions, cost-efficiency, and the fabrication of arbitrarily complex 3D structures.