Water-assisted synthesis of carbon nanotubes: Acetylene partial pressure and height control

摘要

The effect of the partial pressure of acetylene on the height of carbon nanotube films synthesized by the water-assisted CVD ( WA-CVD) was studied. Initially, Fe (2 nm)/Al2O3( 15 nm) bilayers were deposited onto a silicon substrate and subjected to the WA-CVD to grow carbon nanotubes. The growth was carried out at 800 degrees C for a period of similar to 10 min using a mixture of acetylene/ argon gases with a water bubbling system. The partial pressure of acetylene was varied from similar to 5 to 95% while keeping the total pressure of the gas mixture constant. The height of the carbon nanotube film was measured using scanning electron microscopy. The analysis showed that the height of the film gradually increased from 800 +/- 15 nm to 1.4 +/- 0.002 mm as the partial pressure of the acetylene feedstock was sequentially increased from 5 to 40%. Thereafter, the height decreased gradually to 0.77 +/- 0.002 mm as the partial pressure of acetylene was further increased to 95%. These samples were subjected to X-ray photoelectron spectroscopy after removing the nanotube film from the surface. The analysis revealed that at a lower acetylene content surface oxidation is predominant, whereas in the higher acetylene content regime carbonization influenced the height of the carbon nanotube film. Details of the analysis are presented.