The influence of argon dilution on the formation of carbon nanotubes in anodic aluminum oxide pores

The effect of argon on the growth of carbon nanotubes (CNTs) in anodic aluminum oxide (AAO) pores was investigated. A thin layer of Co was electrodeposited at the bottom of pores. The CNTs were grown using hot filament chemical vapour deposition by decomposing a mixture of C₂H₂:H₂ on a tungsten filament. Argon was used as diluent to this mixture and its content was varied keeping C₂H₂:H₂ ratio constant. It was observed that the Ar content affects the growth, density and morphology of the CNTs. Ultra-high resolution field emission microscopic (UHR-FESEM) and transmission electron microscopic (TEM) observation shows fine tubular multi-wall structure with diameter of ~20 nm. Two prominent Raman peaks are observed at 1330 cm^-1 (D band) and 1600 cm^-1 (G band). The ratio of peak intensities (I_D/I_G) was decreased from 2.0 to 0.83 with increasing argon content, indicating that the amount of disordered/amorphous carbon decreased with increasing ratio of Ar. Photoelectron spectroscopic results indicated that when the Ar-content is below 70%, the C 1s peak is centered at 284.4 eV and above this, a shift is observed towards a lower binding energy, centered at 283.8 eV. The effect of C₂ dimer as a dominant growth species is discussed.