In Situ Probing of Electron Beam-Assisted Oxidation Dynamics in Diamond via Environmental TEM

Diamond is widely considered for high-temperature applications in extreme environments due to its exceptional hardness, thermal conductivity, and chemical inertness. However, its performance is limited by surface oxidation when exposed to high-temperature oxidative environments. Here, we comprehensively investigate the surface oxidation failure of diamond nanoneedles under oxygen atmosphere, electron beam irradiation and thermal activation. The dynamic oxidation process is monitored by spherical aberration-corrected environmental transmission electron microscopy (ETEM). Our results reveal an anisotropic oxidation behavior, where the reaction front preferentially propagates along the {111} and {001} through progressive degradation. This crystallographic selectivity highlights inherent differences in surface stability and reactivity among diamond facets. Initially, a continuous amorphous carbon coating layer provides protection to the diamond surface by acting as a diffusion barrier. However, once the layer thins below a critical threshold (∼10.2 ± 0.5 nm), it undergoes topological fragmentation, exposing the diamond to anisotropic oxidation, which proceeds preferentially along the (111) and (001) planes. Additionally, we demonstrate that the oxidation rate is significantly enhanced by the synergy of localized electronic excitation and thermal effects, which effectively lowers the activation energy barrier. These atomic-scale insights establish a mechanistic foundation for designing oxidation-resistant diamond coatings and provide experimentally accessible routes for validating and translating ETEM-derived mechanisms into engineering practice.