EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Diamond and graphene are carbon allotropes with starkly different electronic properties. Combining them into graphene-on-diamond heterostructures provides new perspectives for devices that will benefit from these complementary properties. Graphitization, in particular mediated by a metal catalyst, is a promising synthesis route. In the present work, nickel-catalysed graphitization of single crystalline diamond is studied using aberration-corrected transmission electron microscopy in combination with electron energy loss spectroscopy, Raman spectroscopy and electric transport measurements. Depending on different crystallographic orientations of the diamond surfaces, the morphology of the different phases (diamond, Ni, and graphite) as well as the atomic structure of their interfaces are systematically analysed. We propose competing atomistic processes of graphitization occurring at one- and two-dimensional contact sites of diamond and Ni. Laterally moving Ni nanoparticles etching surface steps of diamond convert it to graphite atomic layer by layer. This process dominates on (111) diamond surfaces remaining almost atomically flat during the diamond to graphite transformation. At (100) and (110) surfaces of diamond, two dimensional etching is prevailing by Ni nanoparticles drilling into the diamond substrate. The results obtained provide evidence at the nanoscale on the reaction rates of the catalytic etching. The (100) surface of diamond covered with the largest amount of well-crystallized graphite is the most reactive. Contrary to that, the (111) surface shows a rather high stability against catalytic etching. In the latter case, only a thin disordered graphite layer is formed yielding relatively low electric conductance.