Watching carbon nanotubes grow

The growth of carbon nanotubes by chemical vapor deposition (CVD) is followed and characterized by performing field-emission microscopy directly in a modified CVD reactor, where the hydrocarbon gas is introduced at a partial pressure below ${10}^{\text{−2}}\hspace{0.17em}\mathrm{mbar}$ and a high voltage is applied between the heated substrate and a phosphor screen. This allows us not only to detect a field-emission current that increases with the length of the nanotubes, but also to observe the growth of the individual emitters by following the evolution of their field-emission patterns on the phosphor screen. Nanotubes grow after an activation time of a few s and reach a length of 5–10 μm in typically 10 s. We deduce a growth rate in the range 1–10 μm/s that increases with the gas pressure.