Influence of different hydrocarbons on the height of MWCNT carpets: Role of catalyst and hybridization state of the carbon precursor

Abstract The length of multi-walled carbon nanotubes (MWCNT) has a particular relevance for a wide range of application. To that end, in an aerosol assisted chemical vapour deposition process MWCNT carpets with different heights were synthesized on an oxidized silicon substrate by using ferrocene as Fe-catalyst precursor and some hydrocarbons with different hybridization state. By variation of the synthesis temperature from 600 °C up to 900 °C, for every used hydrocarbon different carpet heights were measured depending on the temperature. Cyclohexane generated the highest MWCNT carpets and for all carbon precursor the maximum carpet height was measured at 850 °C. To elucidate this, the thermal decomposition of the used hydrocarbons was discussed and the corresponding main decomposition products methane, ethene and benzene were identified. Subsequently, these substances were directly used in a second chemical vapour deposition equipment to simulate the growth mechanism by the intermediate carbon precursors. It was found, that with comparable content of carbon in the gas phase, ethene is much higher efficient for growing high MWCNT carpets than methane. Moreover, benzene was figured out to be also an adequate carbon precursor under specific gas phase conditions, explaining the carpet heights when using toluene and xylene.