Effects of catalyst configurations and process conditions on the formation of catalyst nanoparticles and growth of single-walled carbon nanotubes

The synthesis of well-aligned and type-enriched semiconducting single-walled carbon nanotubes (sc-SWCNTs) with high quality by means of catalytic chemical vapour deposition (CCVD) on wafer-level are essential prerequisites for the implementation of nanodevices for sensor and electronic applications. In particular, the Co-Mo bilayer catalyst system is promising due to its ability to grow semiconducting enriched SWCNTs by CCVD. However, there is still a gap in understanding how to adjust catalyst properties aiming further improvements in SWCNTs film composition and morphology. In particular, surface morphological evolution during catalyst conditioning as well as its impact on SWCNT growth are not clearly understood. Here we present a systematic investigation on effects of catalyst support layer, catalyst preparation conditions, catalyst type and composition as well as gas composition for catalyst treatments on the size of catalyst nanoparticles (NPs) and the properties of CCVD grown SWCNTs. We show that H-2 treatment favors the formation of small catalyst NPs with narrow size distribution in the case of Al2O3 support layer. Moreover, we correlate the growth rates, quality of SWCNTs structures and sc-SWCNTs content with the Co-Mo catalyst morphological evolution.