Carbon nanotubes are often grown by chemical vapor deposition on silicon substrates covered with an iron catalyst. Photoemission and scanning electron microscopy studies presented here reveal how the iron silicide interface phase formed at elevated temperatures influences the catalytic efficiency of the iron. Moreover, we will show how the deposition of a thin layer of dense titanium nitride between the silicon substrate and the iron catalyst effectively prevents the formation of the silicide phase and consequently improves the carbon nanotubes growth.

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Titanium aluminum nitride films (Ti 1Ϫx Al x N) have been deposited by reactive magnetron cosputtering. Elemental compositions of these films have been determined by core level photoelectron spectroscopy. Scanning electron microscopy reveals a columnar film growth. This is also reflected by the topography of film surfaces as studied by atomic force microscopy. By x-ray diffraction a crystalline atomic structure is revealed. Single phase samples can be obtained, consisting of the substitutional solid solution ͑Ti, Al͒N. Crystallites show preferential orientation. The optical properties of these films have been investigated by spectrophotometry in the UV-VIS-NIR wavelength range. Depending on the elemental composition, the optical constants vary from metallic to dielectric behavior. For film compositions with xϽ0.5 typical features are a tunable transmission maximum and reflection minimum in the visible spectral range, a high infrared reflection, and a low infrared absorption. Due to these optical properties, Ti 1Ϫx Al x N films are promising candidates for applications such as coatings for solar control windows and optical selective solar absorbers.

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