GISAXS Study of the Alignment of Oriented Carbon Nanotubes Grown on Plain SiO2/Si(100) Substrates by a Catalytically Enhanced CVD Process

Despite the importance in the alignment of carbon nanotubes films to provide quite accurate emission centers for field emission, there are to our knowledge no quantitative study of the degree of alignment of CNTs films in the literature. Indeed SEM images provide a valuable qualitative impression of alignment in many reports but i) the images are only qualitative; ii) this is a local probe that can induce some misinterpretation about the true uniformity of the sample. Grazing Incidence Small Angle X-Ray Scattering (GISAXS) is well suited to get important structural information on the alignment and the correlation between nanostructures. In addition, we also investigate the alignment of CNTs by angular measurements of Auger electrons (C KVV transitions sensitive to the p electrons). In both cases the strong 1D anisotropic character of p electrons in oriented CNTs is spectroscopically probed. We have performed GISAXS experiments to get structural (orientation of the alignment mainly, but also size distribution and density) and correlation information (mutual alignment, presence of defects in the orientation) on nanostructures grown on plain SiO2 (thickness 2-8 nm)/Si(100) substrates after dispersion of a metallic catalytic islands. It is expected to get a sharp GISAXS signal if the nanotubes are perfectly aligned normal to the surface. The degree of the alignment of CNTs was studied according to growth parameters (substrate temperature, NH3 concentration, gas activation parameters, nature of the metal).