Reconciling results of MOCVD of a CNT composite with equilibrium thermodynamics

Composition and microstructure of the composite films can be tailored by controlling the CVD process parameters if an appropriate model can be suggested for quantitative prediction of growth. This is possible by applying equilibrium thermodynamics. A modification of such standard modeling procedure was required to account for the deposition of a hybrid film comprised of carbon nanotubes (CNTs), metallic iron (Fe⁰), and magnetite (Fe₃O₄), a composite useful for energy storage. In contrast with such composite nature of the deposits obtained by inert-ambient CVD using Fe(acac)₃ as precursor, equilibrium thermodynamic modeling with standard procedure predicts the deposition of only Fe₃C and carbon, without any co-deposition of Fe and Fe₃O₄. A modification of the procedure comprising chemical reasoning is therefore proposed herein, which predicts simultaneous deposition of FeO_1-x, Fe₃C, Fe₃O₄ and C. At high temperatures and in a carbon-rich atmosphere, these convert to Fe₃O₄, Fe and C, in agreement with experimental CVD. Close quantitative agreement between the modified thermodynamic modeling and experiment validates the reliability of the modified procedure. Understanding of the chemical process through thermodynamic modeling provides potential for control of CVD process parameters to achieve desired hybrid growth.