GISAXS study of the alignment of oriented carbon nanotubes grown on plain SiO2/Si(100) substrates by a catalytically enhanced CVD process

We report a quantitative Grazing Incidence Small Angle X-Ray Scattering (GISAXS) study of the alignment of mutually oriented carbon nanotubes (CNTs) grown by a catalytically-activated, a plasma direct current and hot filaments-assisted (DC HF CCVD) process. Metallic catalytic (Co) islands were dispersed on plain SiO2 (5 nm thickness)/Si(100) substrates prior the growth of CNTs which can be considered as highly anisotropic 1D nanostructures. The GISAXS pattern analysis in the framework of the Distorted-Wave Born Approximation (DWBA) has been expanded to multilayered non-correlated surface science systems (non-correlated carbon nanotubes) and is based on the determination of carbon nanotubes density, characteristic lengths, atomic Co dispersion throughout the CNTs and roughnesses of the uncorrelated particles. Even dominated by envelope features of disordered objects, they provide noticeable information about CNTs films: both structural (orientation, size and length distribution) and correlation (density, mutual alignment) information. The results stand in rather good agreement with the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Moreover, the GISAXS patterns could only be satisfactorily reproduced by adding a mixed C-Co contribution between the pure carbon and the metallic cobalt let on top of the CNT, inferring that cobalt continuously fills the nanotube in the course of the growth and that the CNTs experience a large tendency toward mutual alignment. The effect of variable X-ray incidence angles has been investigated. With a weak addition of ammonia (from 1% to 3% of the gas mixture) the density has been found to decrease by more than one order of magnitude. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.