Reaction kinetics and temperature effects in syngas photo-initiated chemical vapor deposition on single-walled carbon nanotubes

Abstract

Photo-initiated chemical vapor deposition (PICVD) is a solvent-free process that can be used to produce thin films on a variety of substrates, with applications in fields ranging from biomedicine to optics and microelectronics. This study presents a kinetic analysis for this process using syngas (CO + H2) as a precursor for the surface treatment of single-walled carbon nanotubes (SWCNT) with average dimensions of 1.5 × 100 nm (diameter × length), and addresses the role of iron pentacarbonyl (Fe(CO)5), a photo-active contaminant found in CO. This work builds upon previously developed reaction schemes for PICVD, based mainly on surface characterizations, by coupling these analyses with gas-phase monitoring. This allows us to propose two separate reaction schemes for the gas and surface phase reactions and consider temperature effects. Online FTIR, offline GC-MS, and online GC characterized the gas phase, while for surface characterizations, XPS and TGA were used. Characterizations showed that a coating with a general formula of CnO3nFen was deposited, corresponding to 0.29 ± 0.04 mg carbon and 0.49 ± 0.03 mg iron on the SWCNT substrate over the course of treatment. The Fe(CO)5 was identified as the key reactant in syngas/PICVD reactions and was nearly completely consumed (94%). Mass balances derived from the gas phase characterization showed that Fe(CO)5 inputted to the plug flow reactor could potentially contribute all the amount of 0.49 ± 0.03 mg of Fe and 0.29 ± 0.04 mg of C to the coating on the SWCNT, indicating that syngas/PICVD can be optimized in the future to decrease gas throughput. Temperature did not show a significant effect in the case of PICVD. However, in the absence of ultraviolet light, its role becomes determinant, with rising temperatures causing more Fe deposition.