Integrating vertically aligned CNTs into devices by nano-catalyst inkjet printing and laser ablation

There is a need for direct-write patterning alternatives to support trends in low-volume and late-stage manufacturing of devices and integrating sensors directly to existing products or formed materials. This is particularly challenging when trying to take advantage of the sensing properties linked to vertically aligned carbon nanotube forests. The catalyst layer thickness is a critical parameter when growing these forests by chemical vapor deposition, as it determines the size of catalyst nano-islands that form and act as seeds for nanotube growth. Physical vapor deposition is a standard technique for catalyst deposition, with photolithography used across the literature to pattern layers of catalyst and enable device design. However, wide-area direct-write techniques face a major barrier in reliably controlling layer thickness to the nanoscale precision required. In this paper, we combine deposition of iron oxide nanoparticles by the direct-write technique of inkjet printing with material removal by laser ablation to deliver both patterning and fine control of the layer thickness. First, we show that there is an optimum printed layer thickness to ensure a good quality forest growth and second that laser ablation can be used to enhance, reduce, or stop this growth. Detailed analysis of the catalyst with AFM, sXRD, and electron microscopy shows that these controls stem from their influence over nano-island formation of the catalyst at the start of the CVD process. Finally, we demonstrate the potential for applications by fabricating a simple gas sensor with this hybrid approach.