Printing gel-like catalysts for the directed growth of multiwall carbon nanotubes

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Microcontact printing is used to transfer an Fe(III)-containing gel-like catalyst precursor from a hydrophilized elastomeric stamp to a substrate. The catalytic pattern activates the growth of multiwall carbon nanotubes using chemical vapor deposition of acetylene. Our results show that the choice of the catalyst is of extreme importance. Most of the aqueous and ethanolic Fe(III) inks used give rise to drying effects on the stamp surface, which lead to the formation of islands of the catalyst within the pattern. To avoid these shortcomings, we developed a catalyst precursor, which has better performance on the stamp and as a catalyst on the substrate. Simple aging of the ethanolic Fe(III) ink results in a polymerized gel-like catalyst, which can be printed homogeneously on the substrate with excellent contrast. Changing the concentration of the catalyst in the ink allows the density of the carbon nanotubes in the film to be tuned. A scanning anode field emission microscope was used to investigate the microscopic field emission properties of the samples. The emission images reproduce the topographical contrast nicely and prove the high quality of the patterning process.