Multi-walled carbon nanotubes (MWCNTs) grown directly on tetrahedral amorphous carbon (ta-C): An interfacial study

• We show that synthesis of MWCNTs on top of ta-C layer at low temperatures is possible by using Al/Co/Fe trimetallic catalyst
• Detailed TEM analyses reveal the complex interfacial structure of the hybrid material
• It is shown that the ta-C layer is fully graphitized during the synthesis
• Possible reasons leading to the observed behavior are discussed in considerable detail

In this paper we present the results on the microstructure of a novel carbon hybrid material consisting of multi-walled carbon nanotubes (MWCNTs) grown on the top of tetrahedral amorphous carbon (ta-C) thin films on Si substrates with Ti adhesion promotion layer on top. It is shown here that: (i) the synthesis of the MWCNTs on top of ta-C layer at low temperatures is possible by using Al/Co/Fe trimetallic catalyst, (ii) the catalytic particles formed and used in the growth of MWCNTs form an FeCo alloy during the activation step, (iii) in addition to the catalytic particles, Fe-silicides with variable amount of dissolved Co are formed on both sides of the Ti adhesion layer and therefore it can be concluded that all species (Co, Fe and Si) diffuse during the formation of the silicides, (iv) Ti adhesion layer remains almost unaffected by the growth process and in particular no significant TiSi2 or TiCx layer formation takes place, (v) the MWCNT that are grown on top of ta-C are not well oriented and appear to have high defect densities and (vi) ta-C layer is fully replaced by a graphitic layer during the growth of MWCNTs.