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 photoactive 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, off-line GC-MS and on-line 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 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.

Covalent functionalization of boron nitride nanotubes through photo‐initiated chemical vapour deposition

“…[36][37][38] Hydrogen and carbon monoxide, known as synthesis gas or syngas, can be excited in the presence of UV light and thus produce radicals or reactive species. [36][37][38][39] Syngas PICVD has been applied for the deposition of thin films on copper coupons [36] and silicon wafers. [37] It has also been used for the surface treatment of polymers such as high-density polyethylene (HDPE), polyethylene terephthalate (PET), [40] and polystyrenedivinylbenzene (PS-DVB).…”