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The influence of nano-structure and composition of the substrate on the properties of carbon nanotubes (CNTs) is presented. The samples are obtained following a sequential in situ deposition routine. First, TiNxOy films are grown on a crystalline silicon substrate. Immediately, dispersed nickel catalyst particles are deposited on the film. The non-stoichiometric TiNxOy films and Ni particles are grown by ion beam sputtering of Ti and Ni targets, respectively. Soon after that, the CNTs are grown by feeding acetylene gas into the chamber and maintaining the substrate at 973 K. In situ x-ray photoelectron spectroscopy allows compositional and structural analysis in all the stages of the sample growth process. The CNTs are further studied by scanning and transmission electron microscopy techniques, showing different population densities, sizes and diameters as a function of the oxygen content in the TiNxOy films. The results show that oxygen influences the surface diffusion mobility of the precursor carbon atoms involved in the growth of nanotubes suggesting the inhibition of catalyst particle coarsening. It is concluded that, in addition to acting as a diffusion barrier between the catalyst particles and the silicon support, the TiNxOy films modify the growth kinetics of the CNTs. [ABSTRACT FROM AUTHOR]