(247c) Catalyst-Support Interactions and Their Influence in Water-Assisted Carbon Nanotube Carpet Growth

The growth and catalyst morphological changes occurring for thin Fe layers deposited on Al₂O₃, MgO, TiN, and ZrO₂ using water-assisted chemical vapor deposition are compared. The growth behaviors of the catalyst substrates were evidently different, with Al₂O₃/Fe supporting high-quality carbon nanotube (CNT) carpet growth and showing the highest activity and longest lifetime. The TiN/Fe catalyst also supported CNT carpet growth, albeit with much lower activity, shorter lifetime, and lower CNT quality while MgO/Fe and ZrO₂/Fe did not support CNT carpet growth under standard growth conditions. Studies using a combination of atomic force microscopy and X-ray photoelectron spectroscopy revealed a general correlation between the catalyst behavior (activity and lifetime) and the evolution of the catalyst (Ostwald ripening and subsurface diffusion rates).  Analysis of MgO/Fe and ZrO₂/Fe catalyst systems raise interesting questions related to additional chemical interactions between the substrate and catalyst that could influence nucleation and CNT growth. This work provides a step toward understanding the challenges that arise in engineering efficient CNT growth processes on a desired substrate.