The PECVD method combines electrical energy

The PECVD method combines electrical energy and heating to produce carbon nanotubes. The electricity is supplied to the substrates through powdered electrodes. Combining electricity and heat helps in dissociating more carbon atoms. The PECVD method has the advantage of producing carbon nanotubes at low temperatures which makes it possible to grow carbon nanotubes on polymers (Gunderson 10). The method also makes it possible to produce vertically aligned carbon nanotubes.

In the carbon vapor displacement system, a hydrocarbon precursor (mainly, ethylene, acetylene, or methane) is broken down into different reactive species in the reaction chamber. The hydrocarbon is subjected to temperatures ranging between 550⁰C and 1000⁰C. When the right operating temperature is achieved, the gas source is closed and the carbon source valve is opened. The presence of catalysts on substrates and high temperatures in the reaction chamber helps in the formation of carbon nanotubes. The main catalysts used in the carbon vapor deposition method are the transition metals, such as nickel, iron and cobalt. Carbon nanotubes can be produced at low temperatures through carbon vapor deposition (CVD). The method is also the most efficient in the production of Single-Walled Carbon Nanotubes (SWCNTs) and Multi-Walled Carbon Nanotubes (MWCNTs). Single-walled carbon nanotubes are usually produced at higher temperatures while production of the multi-walled carbon nanotubes occurs at lower temperatures.

During the production of carbon nanotubes using the CVD method, metallic and carbonaceous impurities are produced. Metallic impurities arise from residual catalysts, such as nickel, while carbonaceous impurities are by-products that arise from the reaction. The carbonaceous impurities are removed through oxidation. This is achieved using gas phase and liquid phase purification. Gas-phase purification uses high temperatures to eliminate carbonaceous impurities, whereas liquid phase purification involves the use of acidic solutions to wash the carbon nanotubes. Metallic impurities are removed by evaporation. The carbon vapor deposition (CVD) method has several advantages, such as producing hollow and uniform carbon nanotubes, forming highly aligned ensembles and lack of macroscopic defects.