Revealing the impact of catalyst phase transition on carbon nanotube growth by in situ Raman spectroscopy.

The physical state of the catalyst and its impact on the growth of single-walled carbon nanotubes (SWNTs) is the subject of a long-standing debate. We addressed it here using in situ Raman spectroscopy to measure Fe and Ni catalyst lifetimes during the growth of individual SWNTs across a wide range of temperatures (500-1400 °C). The temperature dependence of the Fe catalyst lifetimes underwent a sharp increase around 1100 °C due to a solid-to-liquid phase transition. By comparing experimental results with the metal-carbon phase diagrams, we prove that SWNTs can grow from solid and liquid phase-catalysts, depending on the temperature.

In situ evidence for chirality-dependent growth rates of individual carbon nanotubes.

Chiral-selective growth of single-walled carbon nanotubes (SWNTs) remains a great challenge that hinders their use in applications such as electronics and medicine. Recent experimental and theoretical reports have begun to address this problem by suggesting that selectivity may be achieved during nucleation by changing the catalyst composition or structure. Nevertheless, to establish a rational basis for chiral-selective synthesis, the underlying mechanisms governing nucleation, growth, and termination of SWNTs must be better understood. To this end, we report the first measurements of growth rates of individual SWNTs through in situ Raman spectroscopy and correlate them with their chiral angles. Our results show that the growth rates are directly proportional to the chiral angles, in agreement with recent theoretical predictions. Importantly, the evidence singles out the growth stage as responsible for the chiral distribution-distinct from nucleation and termination which might also affect the final product distribution. Our results suggest a route to chiral-selective synthesis of SWNTs through rational synthetic design strategies based on kinetic control.

On the development of a confocal Rayleigh-Brillouin microscope.

This Note illustrates how a confocal microscope may be modified to conduct Rayleigh-Brillouin mapping experiments that yield very useful information on the mechanical properties of interfacial materials in small volume elements. While the modifications to the microscope are quite straightforward, they do entail significant changes in the optical design. The instrument described herein consists of an argon ion laser equipped with an actively stabilized intercavity etalon that serves as the excitation source for a modified Zeiss LSM 310 confocal laser scan microscope. The optics of the microscope were reconfigured to enable interfacing of the microscope with a tandem triple-pass Fabry-Perot interferometer. This instrument enables three-dimensional Rayleigh-Brillouin spectral mapping of samples at micron spatial resolution. The performance of the instrument and its ability to perform both lateral and depth scans of the acoustic phonon velocity and, hence, the longitudinal modulus across bonded polymer/polymer and polymer/ceramic interfaces are illustrated and discussed.