Novel approach to low substrate temperature synthesis of carbon nanotubes

We present a novel approach, which will potentially allow for low-temperature-substrate synthesis of carbon nanotubes using direct-current plasma-enhanced chemical vapour deposition. The approach utilizes top-down plasma heating rather than conventional heating from a conventional substrate heater under the electrode. In this work, a relatively thick titanium layer is used as a thermal barrier to create a temperature gradient between the Ni catalyst surface and the substrate. We describe the growth properties as a function of the bias voltage and the hydrocarbon concentrations. The heating during growth is provided solely by the plasma, which is dependent only on the process conditions, which dictate the power density and the cooling of the substrate, plus now the thermal properties of the "barrier layer". This novel approach of using plasma heating and thermal barrier allows for the synthesis of carbon nanotubes at low substrate temperature conditions to be attained with suitable cooling schemes.</p

Growth kinetics changes of vertically aligned carbon nanostructures syntheslsed at low substrate temperatures

Carbon nanotubes and nanofibres are typically synthesised under substrate temperatures above 600°C. Here we investigate the influence of the substrate temperature and the plasma conditions on the growth of vertically aligned carbon nanostructures using Direct Current plasma Chemical Vapour Deposition, at temperatures below 550°C. These nanostructures are produced using a C 2H2 based plasma and nickel thin film as the catalyst. We found that preferential deposition of amorphous carbon takes place as the synthesis temperature is lowered below 500°C. However, lowering the carbon concentration in the gas feedstock (<2% cone.) allows for the nucleation of nanofibre-like structures, whilst balancing the buildup of amorphous carbon. This method allows for the synthesis of vertically aligned structures at low temperatures (around 230°C) without intentional heating, while still achieving reasonable average growth rates up to 27 nm/min. The only heating was provided by the plasma, which typically consumes ∼ 4 W/cm2. It was found that by varying the applied plasma bias during high temperature synthesis, we increased the growth rate up to 165 nm/min. Based on the observations of experimental process variations and the morphology of the synthesised structures, we propose a growth mechanism for such low temperature growth and examine the resulting morphology changes. © 2005 Materials Research Society