Combinatorial Printing of Iron and Cobalt Reactive Inks to Produce Magnetic Amorphous and Nanocrystalline Metals

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 in 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 reactive ink produced fully amorphous iron and the cobalt reactive 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 the local composition and the correlated atomic structure. Triiron dodecacarbonyl and dicobalt octacarbonyl are used as the iron and cobalt metal precursors, respectively, because these zerovalent 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 the 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.