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We found that very high concentrations (up to 20% vol) of nitrogen in the ethanol/hydrogen gas mixture do not prejudice the diamond quality as determined by Raman spectroscopy. Nitrogen addition also increases the diamond growth rate, as was previously reported at low nitrogen concentrations. We observed that after a second heating cycle in air at temperatures between 300 and 673 K the electrical resistance versus temperature curves of the as-grown films presented a bulk semiconductor behavior. This stabilization was due to the oxidation of the as-grown hydrogenated surface. The electrical ionization energy Ed was found to be in the range of 1.62–1.90 eV corresponding to films produced with 0 to 20% vol nitrogen in the feed. The room temperature photoluminescence spectra of films produced at low nitrogen concentration suggest that Ed results from pure electronic transitions in the nitrogen-vacancy neutral defects; for samples produced with nitrogen concentrations in the range 15–20% vol the Ed values may be due to, among others, GR1 “vibronic” transitions and charged nitrogen-vacancy defects.

Our data demonstrate that multi-walled carbon nanotubes (MWCNTs) are internalized by macrophages, subsequently activating them to produce interleukin (IL)-12 (IL-12). This cytokine induced the proliferative response of T lymphocytes to a nonspecific mitogen and to ovalbumin (OVA). This increase in the proliferative response was accompanied by an increase in the expression of pro-inflammatory cytokines, such as interferon-gamma (IFNγ), tumor necrosis factor-alpha (TNFα) and IL-6, in mice inoculated with MWCNTs, whether or not they had been immunized with OVA. A decrease in the expression of transforming growth factor-beta (TGFβ) was observed in the mice treated with MWCNTs, whereas the suppression of the expression of both TGFβ and IL-10 was observed in mice that had been both treated and immunized. The activation of the T lymphocyte response by the pro-inflammatory cytokines leads to an increase in antibody production to OVA, suggesting the important immunostimulatory effect of carbon nanotubes.