Influence of a top crust of entangled nanotubes on the structure of vertically aligned forests of single-walled carbon nanotubes

The time evolution of the growth process of vertically aligned single- walled carbon nanotubes ( or V- SWNTs) on a flat substrate was examined by scanning electron microscopy ( SEM), resonant Raman spectroscopy, and angle- resolved X- ray absorption near- edge structure ( XANES). This detailed characterization gives evidence for the growth of a thin layer ( crust) of randomly oriented single- walled carbon nanotubes during the first stages of the growth process. This crust is responsible for the unique forest- like morphology exhibited by this type of SWNT structure.