No abstract

Wavelet decompositions of Raman spectra were investigated with respect to their usability for spike removal and denoising of the raw data. It could be shown that those operations should be performed sequentially. Suppression of spikes is not straightforwardly possible by wavelet transformation; however, the wavelet transform may be used to recognize the spikes by their first level detail coefficients. Spike locations could be projected from the details to the approximations and, further, to appropriate locations of the original spectrum. After spike recognition, those regions will be replaced by interpolated values. To complete processing, denoising is performed with the despiked spectrum by repeated application of wavelet transform methods.

No abstract

No abstract

Hard amorphous carbon (ta-C) films were implanted with 20 keV N+ ions with different fluences up to 6×1017/cm2 at different substrate temperatures. The nitrogen content of the films was monitored in situ using elastic recoil detection analysis. A characteristic temperature dependence is observed for the maximum achievable [N]/[C] composition ratio, with a drop of the saturation level from the room-temperature value of 0.35 to 0.17–0.12 above 150 °C. It is shown that the higher nitrogen retention at room temperature is correlated with the formation of N2-containing gas bubbles which are not present in samples implanted with high fluences at elevated temperatures. From residual-gas analyses it is found that nitrogen is reemitted from the films mainly as N2 when saturation occurs. Double-implantation experiments with spatially separated N14 and N15 implanted regions, respectively, indicate that the N–N molecule recombination observed at large implantation fluences occurs inside the films and not at the surface. Significant changes of the microstructure of the films are found with increasing implantation fluences. Inside the implanted near-surface region of several 10 nm thickness the density of the material decreases from 3.0 to about 1.7 g/cm−3. Graphitic clusters are identified in samples implanted up to saturation at 400 °C, using cross-section transmission electron microscopy. A basic approach to modeling the nitrogen saturation and release at large fluences is presented. Both nitrogen release and structural modification processes are interpreted as a tendency towards thermodynamic equilibrium which may constitute a strong driving force against the synthesis of nitrogen-rich hard C:N materials, compared to other nitride phases.