Iron-catalyzed selective thermochemical etching achieves planarization of polycrystalline diamond

A contact iron-catalyzed selective thermochemical etching technique is proposed for surface planarization of polycrystalline diamond (PCD) films. In the heating system consisted of C (diamond), Fe, O elements, the thermochemical etching of diamond areas contacted with Fe exhibits significant priority compared to areas uncontacted with Fe. With such pronounced selectivity, the in-situ observations confirm that the planarization of PCD is realized with pyramid-shaped protrusions in contact with Fe plate preferentially removed at the temperature of 1000, 1050 ℃. Fe₃C is detected on PCD surface and the decomposition of the metastable Fe₃C leads to the generation of graphite, which is the major route causing this selectivity. The atomic-scale mechanism of selectivity is investigated using multi-scale simulations. The iron element reduced energy barrier for oxidation reaction of diamond with O element, proving the selectivity properties of iron-catalyzed thermochemical etching. C atoms at top areas contacted with Fe atoms are activated into non-diamond structure by forming Fe₃C at diamond–Fe interface. As all the C atoms forming the protrusions are immersed in O atoms simultaneously, the activated C atoms contacted with Fe atoms were preferentially removed.