Carbon nanotube growth inhibition in floating catalyst based chemical vapor deposition and its application in flexible circuit fabrication

Site selective growth of vertically aligned carbon nanotubes (VACNTs), using floating catalyst based chemical vapor deposition (FC-CVD), can be achieved by proper use of carbon nanotube growth inhibitors. Here, we present a detailed study on the inhibition properties of Au and Pt thin films in ferrocene catalyzed FC-CVD. Elemental composition and chemical state analysis, at different depths of the growth substrates, were performed using X-ray photoelectron spectroscopy. Propensity of Fe to diffuse into the growth substrate was stronger in the case of Pt coated SiO₂ as compared to Au coated or pristine SiO₂ substrates. Increase in catalyst concentration or decrease in film thickness resulted in a loss of inhibition action of Au, whereas inhibition action of Pt was unaffected. Diffusion of C, Si, Cr and O in Au were different from that in Pt. Our data provides new insights into growth inhibition processes and explains some of the contradictions in previously published reports. The inhibitor based FC-CVD technique was used to make flexible VACNT/polymer circuits, suitable for bio-electronic applications. Electrical sheet resistance, electrochemical double layer capacitance, and charge storage capacity of the VACNT/polymer films, were found to be approximately 135 Ω/□, 1 mF/cm² and 19 mC/cm², respectively.