Electron and X‑ray Focused Beam-Induced Cross-Linking in Liquids:

Toward Rapid Continuous 3D Nanoprinting and Interfacing using Soft Materials

Modern additive fabrication of three-dimensional (3D) micron to centimeter size constructs made of polymers and soft materials has immensely benefited from the development of photocurable formulations suitable for optical photolithography,holographic,and stereolithographymethods. Recent implementation of multiphoton laser polymerization and its coupling with advanced irradiation schemes has drastically improved the writing rates and resolution, which now approaches the 100 nm range. Alternatively, traditional electron beam lithography and its variations such as electron-beam chemical lithography, etc. rely on tightly focused electron beams and a high interaction cross-section of 0.1−10 keV electrons with the matter and have been routinely used for complex patterning of polymer resists, self-assembled monolayers, and dried gel films with up to a few nanometers accuracy.

Similarly, a significant progress has been made in deep X-ray lithography, direct writing with zone plate focused X-ray beams for precise, and chemically selective fabrication of high aspect ratio microstructures. Reduced radiation damage within the so-called “water window” has spurred wide biomedical X-ray spectroscopy, microscopy, and tomography research including material processing, for example, gels related controlled swelling and polymerization inside live systems, particles encapsulations,and high aspect ratio structures fabrication.The potential of focused X-rays for additive fabrication through the deposition from gas-phase precursors or from liquid solutions is now well recognized and is becoming an active area of research.

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Image: The electron/X-ray beam gelation in liquid polymer solution through a SiN ultrathin membrane. Varying the energy and focus of the soft X-rays smaller or larger excitation volumes and therefore finer or wider feature sizes and patterns can be generated.