Observations of the synthesis of straight single wall carbon nanotubes directed by electric fields in an Environmental Transmission Electron Microscope

We report here observations in real time of the aligning effect of electric fields during the synthesis of carbon nanotubes in an environmental transmission electron microscope (ETEM). Growths took place using C₂H₂ as precursor gas at ∼10⁻⁴ mbar, a temperature of ∼700 °C and within a micro-capacitor incorporated in a specifically-designed heating micro-chip. Individual nanotubes are easily resolved as they appear as extremely straight lines growing parallel to the electric field. These nanotubes are predominantly Single Wall Carbon Nanotubes (SWNTs). Owing to the very good alignment of nanotubes in the object plane of the microscope we can obtain unprecedented excellent determination of the nanotubes’ growth rates and follow them dynamically. Constant growth rates are observed in most cases but other behaviours are observed such as growth rate acceleration. For low applied voltages the growing nanotubes can cross the gap and connect to the opposite electrode although some are destroyed by mechanical failure or during the contact. For high applied fields and positive biasing allowing Field Emission (FE), the growth is limited within the gap as FE can occur during growth leading to new saturation or destruction processes. These different mechanisms are presented as well as the observed balance between electrostatic and adhesion forces.