Real-timein situRaman imaging of carbon nanotube growth

Abstract

In the quest for control over carbon nanotube synthesis in situ imaging has the potential to become a primary tool. Here, we show that global Raman imaging enables the observation of individual nanotubes and ensembles in real time, during growth. Individual nanotubes are detected even at 875 °C. Imaging and spectroscopy measurements of nanotube growth show distinct nucleation and growth phases. The first optical images of individual nanotubes captured during growth are presented.

The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

“…For the G band and RBM bands there is an initial exponential increase, a linear growth phase and a saturation phase and they Given that this involves sampling over a vast number of nanotubes this may have important implications. The RBM evolution, which represents only one specific diameter SWNT here, exactly tracks the G band evolution, which represents a large number of diameters, and would even include non-SWNT sp 2 carbon were it present in sufficient abundance to produce an appreciable signal. If one particular species of nanotube tracks the G band, it is probable that all nanotubes follow the G band.…”

“…After this, the bubbler was again bypassed, and the reactor purged at the growth temperature, and À nally the sample was cooled to room temperature. À Raman spectra were obtained from a home built Raman spectroscopy/GRI system [2,15]. The setup is illustrated in Fig.…”

“…With a beam splitter, as in Ref. [2], GRI data and Raman spectra were obtained simultaneously. However, because the catalyst was uniform, and the nanotube density very high (roughly ~10 to ~100 nanotubes/m 2 , as revealed by SEM imaging) the Raman image was uniform and contained no signiÀ cant spatial information other than À the illumination profile over 100 m scale distances.…”

“…An early spectroscopic study reported a linear increase in the G band signal during CVD using a zeolite/Fe Co-based catalyst and ethanol vapor as the carbon source [1]. In a combined Raman spectroscopy global Raman imaging (GRI) study, we were able to detect SWNTs as they formed in the reactor and to trace out the D and G band evolution [2]. This was for thin À lm À metal catalysts on silicon dioxide and using ethanol vapor as the carbon source.…”

“…For a more general discussion see Ref. [2]. Of special importance here are recent studies of dense forests of nanotubes, which are especially well suited to in situ observation.…”