Fe/Cu(1 0 0)––a test case for the understanding of epitaxially grown magnetic thin films

The chemical desorption of carbon and nitrogen-containing species from the growth surface was investigated for the deposition of fullerene-like carbon nitride (FL CNx) thin solid films by reactive magnetron sputtering of a carbon target in a N2-containing atmosphere. The desorption of mainly C2N2 was suppressed by decreasing the substrate temperature for various N2 fractions in the discharge stepwise from 873 K down to cryogenic temperatures of 153 K. This approach enabled us to quantify the film-forming flux by determining the carbon and nitrogen incorporation rates by elastic recoil detection. The incorporation of both, carbon and nitrogen, was found to increase substantially at lower substrate temperatures, whereas this effect is most pronounced for the higher N2 fractions. In turn, a modified Arrhenius-type rate equation was applied to extrapolate the total flux of the elements as well as their respective activation energies of desorption for the series at higher N2 fractions. The reasonable fit indicates that the desorption process is mainly determined by the surface diffusion rate of adsorbed CxNy species as well as their structure and total number. The extrapolated fluxes of carbon and nitrogen atoms arriving as preformed species at the growth surface scaled strongly with the availability of N2 in the discharge, while the obtained activation energies of 0.05–0.17 eV point towards a saturation of the process at elevated temperatures. Furthermore, the constant C/N ratio found in the film-forming flux leads to the notion that most of the nitrogen incorporated originates from preformed species instead of N atoms or ions. The FL structure evolution has to be seen as a sensitive interplay between the type and magnitude of preformed CxNy species in the deposition flux and the selectiveness of the preferential etching by means of the chemical desorption.