High energy carbon ions implantation: An attempt to grow diamond inside copper

This study is stimulated by recent reports"' which in- dicate that the heteroepitaxial growth of single crystalline diamond on copper is possible by implanting carbon ions which will diffuse to the copper surface, into a heated cop- per substrate or by applying laser annealing after carbon implantation. However, so far, the results of these two re- ports can not be reproduced in other laboratories3-" At normal temperature and atmospheric pressure, the nucle- ation of graphite is more favored than the nucleation of diamond because, under such conditions, graphite is the stable phase, whereas diamond is metastable.7 Therefore, any carbon contamination on the copper surface will be- come the nucleation center for graphite. Carbon has a very low solubility in solid copper.* Therefore, deep inside cop- per, carbon contamination is negligible if the material is of high purity. Proper annealing may provide favorable ther- modynamic conditions, mainly temperature and pressure, for the growth of diamond inside copper. We will discuss this point in more detail later in this letter. With high energy, the implanted carbon will be buried deep inside the copper. Meanwhile, the near-surface region of the substrate overlying the implanted layer will not be damaged severely. When heat treatment is applied, this less damaged region will regrow inwards from the surface. The region which is below the implanted layer will regrow out- wards. Such regrowth of copper is expected to be accom- panied by the segregation of carbon in the regrown region due to the low solubility of carbon. The segregated carbon will be sandwiched by the regrown copper on both sides, which has a relatively good crystalline structure. It is in- teresting to find out which phase of the implanted carbon will be in such a sandwiched environment. In this study, 1 MeV carbon ions generated from a 1.7 MeV tandem accelerator at the Texas Center for Super- conductivity at the University of Houston were implanted into a single-crystal copper with (100) orientation. RBS- channeling measurements showed that the Xmin value at the surface region was 4.7%, indicating that the copper sample had good crystalline quality. The total dose of the implan- tation was about 6.6X 1017 at/cm'. After carbon ion im-