Facet-Dependent Oxidative Fabrication of Diamond Determined by Operando Scanning Electron Microscopy

Diamond crystals hold promising applications in electronics and optics but are particularly challenging in controlled fabrication. Current diamond machining is primarily achieved through surface oxidation. However, knowledge remains limited to microscale oxidation dynamics, impeding the development of precision diamond fabrication. This work uses a self-developed operando system to unravel the oxidation dynamics on diamond microcrystals under a high-temperature, oxygen-rich atmosphere. After precise sampling by a focused ion beam, oxidation-induced surface atomic structure as well as reaction intermediates were further analyzed using high-resolution transmission electron microscopy and electron energy loss spectroscopy. Diamond initially transforms into amorphous carbon, subsequently reacting with oxygen and forming CO₂, leading to material removal and formation of oxidation pits with distinct geometries. The growth of these pits is influenced by the crystal symmetry of diamond, thereby demonstrating the characteristic morphologies of facet-dependence. The microstructural dynamics disclosed in this research provide new insights into precision oxidative diamond fabrication.