Low-temperature synthesis multiwalled carbon nanotubes by microwave plasma chemical vapor deposition using CH4-CO2 gas mixture

Vertically aligned carbon nanotubes (CNTs) with multiwalled structures were successfully grown on a Fe-deposited Si substrate at low temperatures below 300 degreesC by microwave plasma chemical vapor deposition using of a CH4-CO2 gas mixture. The low temperature would be beneficial for reducing the diameter of CNTs but it will also decrease the growth rate on the substrate. The low-temperature growth of CNTs was achieved by decreasing both the microwave power and the total gas pressure. The constituents of the gas mixture are also key factors in chemical vapor deposition. After deposition, the microstructure morphology of CNTs was observed by using scanning electron microscope and high-resolution transmission microscope. The results showed that even at low temperature a high yield of carbon nanotubes with a high emission current density and a small diameter is obtained. Vertically aligned multiwalled CNTs with a diameter about 12 nm were investigated by scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM).