Direct Laser Writing of Ferromagnetic Nickel Utilizing the Principle of Sensitized Triplet–Triplet Annihilation Upconversion

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Direct laser writing of ferromagnetic microstructures is of great interest for sensing and data storage in compact three-dimensional architectures. However, reliable direct laser writing of metallic, and even more so ferromagnetic, materials remains a major challenge. Here, we discuss a developed photoresist suitable to direct laser write ferromagnetic nickel based on sensitized triplet–triplet annihilation upconversion. By combining an in situ photochemical deoxygenation process with a sensitized triplet–triplet annihilation upconversion process and photoreduction of Ni2+ ions, the deposition of nickel-containing structures is enabled under ambient conditions. Using this approach, nickel-based structures are fabricated as a proof of concept. Scanning electron microscopy and EDX analysis indicate spatially confined deposition of nickel, while magnetic characterization by vibrating sample magnetometry and scanning NV magnetometry confirm ferromagnetic behavior of the printed structures. This work provides a possible route toward extending direct laser writing to metallic and especially ferromagnetic materials.