Congratulations to Collin for publishing his first, first-author paper. Collin worked extremely hard on this paper. It was supposed to be a simple paper showing how to print iron using an iron-carbonyl reactive ink and it morphed into an amazing paper showing that amorphous metals can be printed using a mixture of metal carbonyls and primary-amine solvents (octylamine in this case). For this work, Collin developed two new reactive inks, one using tri-iron dodecarbonyl to print amorphous iron and another using dicobalt octacarbonyl to print nanoparticle cobalt within an amorphous cobalt matrix. He demonstrated that the amorphous iron and nanocrystalline cobalt can be patterned and showed that the amorphous phases are stabilized by a mix of un-decomposed carbonyls and trapped or complexed solvents. This is extremely exciting work that not only demonstrates two new reactive inks, but that we can print amorphous and nanocrystalline magnetic materials at reasonably low temperatures using reactive inks.
Abstract: Reactive inks are an attractive method to selectively pattern metallic features with minimal post processing. While significant progress has been made developing silver and copper reactive inks for printed electronics, less progress has been made developing metal reactive inks with properties suitable for structural or magnetic applications. To address this gap, this work introduces particle-free iron and cobalt metal reactive inks to print magnetic iron and cobalt metals. Interestingly, structure analysis of the printed reactive inks showed that the iron ink produced fully amorphous iron and the cobalt ink produced nanocrystals dispersed in an amorphous matrix. This work also demonstrates two combinatorial methods of printing these inks: by mixing the two inks together to produce amorphous iron-cobalt alloys and by spatially patterning the iron and cobalt monometallic inks to achieve control over both local composition and the correlated atomic structure. Triiron dodecacarbonyl and dicobalt octacarbonyl are used as the iron and cobalt metal precursors because these zero-valent metal complexes directly decompose to metal and carbon monoxide gas. The printed metals’ elemental and chemical compositions were evaluated using energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and Mössbauer effect spectroscopy showing that the amorphous phases are likely stabilized by either remnant carbonyl bonds from incomplete decomposition of the metal carbonyl or residual octylamine solvent interacting with the metal atoms. Additional characterization includes resistivity measurements to verify metallic conductivity, nanoindentation to quantify hardness, and magnetometry studies to quantify magnetic performance. As a demonstration, the Fe and Co reactive inks were sequentially printed in a combinatorial, layer-by-layer manner to produce a vertically graded iron and cobalt line as well as a matrix of nanocrystalline cobalt dots on an amorphous iron film. Overall, this work introduces a method to directly print continuous, amorphous, magnetic, and structural alloys at moderate temperatures from a particle-free reactive ink.