We have performed 120 keV carbon-ion implantations into copper at high doses (5 x 10(17) cm(-2)) and high temperatures (973 K less than or equal to T less than or equal to 1273 K) acid characterized the microstructure of the surface layer formed by this process. This study reinvestigates the possibility of producing thin diamond films by the so-called carbon-ion-implantation-out-diffusion method. The basic mechanisms of the carbon layer growth are not well understood and we propose a model where the segregation of C atoms and the preferential sputtering of Cu atoms would play an important role. In order to examine the validity of such a hypothesis we have investigated the influence of both the ion flux and the temperature. For all experimental conditions we observe the formation of a uniform graphite layer (turbostratic graphite) with a more- or less-pronounced texture along the (0001) direction. We have identified in the graphite layer a high density of graphitic shelled micrograins ("fullerene onions") but the presence of diamond has never been detected. Our results are in agreement with some previous studies on this subject that were not able to reproduce the first results claiming that diamond formation is possible by this method. It is suggested that a higher C ion flux or the presence of impurities in the copper substrate could be favourable for such a mechanism of diamond growth.