(92b) Physicochemical Properties of Engineered Catalyst Supports and Implications for Growth of Carbon Nanotube Carpets
Catalysts supported on alumina have been widely heralded for their unparalleled efficiency in the growth of high-quality carbon nanotube (CNT) carpets via CVD with hydrocarbon precursors. However, some important applications of CNT carpets require carpets to be grown directly on specific substrates. Thus, there is significant interest in understanding the properties of a good catalyst substrate and how to create and maximize these properties in inactive substrates. The recent transformation of an inactive catalyst substrate (c-cut sapphire) to an active substrate for CNT carpet growth via ion beam bombardment provides an excellent model system for this study (Nano Lett. 2014, 14, 4997). The properties of pristine and ion beam damaged sapphire substrates are probed using a combination of contact angle measurements and X-ray reflectivity (XRR). The contact angle data are analyzed using the van Oss-Good-Chaudhury model and the Young-Dupre equation, enabling the determination of the acid-base properties of the substrates. For the XRR data, a Fourier analysis of the interference pattern allows extraction of layer thickness while the atomic density and interfacial roughness are extracted by analyzing the amplitude of the interference oscillations. The results show interesting correlations between the physicochemical properties of the catalyst substrate and the activity of Fe catalyst during CNT carpet growth. Detailed discussion of the implications of the structural and acid-base properties of the pristine and engineered substrates in CNT carpet growth are presented.