Abstract
Abstract Carbon nanotubes (CNTs) have been synthesized from Ar-CH4 mixtures using rf-plasma enhanced chemical vapor deposition (rf-PECVD) at 500°C. Reduction gases such as H2 and NH3 were found unnecessary for carbon nanotube formation compared to thermal CVD. The relationship between the growth of CNTs and the plasma condition in PECVD has been investigated by in situ self bias measurement. Plasma conditions were controlled by changing the interelectrode distance, rf power and the applied substrate negative bias. By increasing the interelectrode distance and rf power, the spatial density of CNTs was on a rise as a result of the increase in ions density and self bias. As the applied substrate negative bias increased, the spatial density of CNTs decreased possibly due to the positive ions over bombarding effect.
Highlights
Plasma enhanced CVD (PECVD) has been recognized as one of the viable fabrication techniques of carbon nanotubes (CNTs) to produce vertically aligned nanotubes on patterned substrates at relatively low temperature [1,2,3,4]
The present paper focuses on the influence of the plasma condition on the surface morphology of CNTs using in situ self-bias plasma diagnostics
It was found that reduction gases such as H2 and NH3 were not necessary for carbon nanotube formation during PECVD compared to thermal CVD
Summary
Carbon nanotube was synthesized in a homemade rfPECVD reactor, as shown in Fig. (a). A gas showerhead at the upper electrode was utilized to keep the growth of CNTs uniform. The process for the growth of CNTs consists of three steps: (1) heat treatment; (2) Ar plasma pretreatment and (3) Ar-CH4 plasma treatment. Ar gas was introduced into the chamber and maintained at 0.9 Torr with a flow rate of 100 sccm when the synthesis temperature reached 500qC. Ar plasma was introduced at 30 W for 5 min to pretreat the catalyst. CH4 gas was introduced into the chamber and kept at 1 Torr, initiating the synthesis process. The higher mobility of the electrons than that of the ions in the plasma creates a sheath next to the electrodes with an excess of ions. The surface morphology of CNTs under different plasma conditions was characterized by scanning electron microscopy (SEM)
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