Construction of a Synergistic Etching System Based on Fe2O3–Si Highly Exothermic Reaction and Its Mechanism in Diamond Surface Etching

Abstract

The etching behavior, mechanism, and efficiency of diamond were systematically compared for the silicon-thermal method and direct etching using pure Fe powder or Fe₂O₃₂O₃ alone. XRD, SEM, and thermodynamic analyses showed that the silicon-thermal reaction system (Fe₂O₃–Si), owing to its strong exothermic effect (ΔH ≈ –1070 kJ mol^–1), generated an active high-temperature etching medium in situ, dominated by Fe and FeO and accompanied by the formation of silicates. Together, they created a dynamic etching environment described as “high-enthalpy-driven multiphase coupling catalysis-dissolution-migration”. The introduction of CaO further led to the formation of Ca₂SiO₄, which significantly enhanced the etching effect by stabilizing the FeO phase and improving mass transport, particularly inducing complex and deep etch morphologies on the diamond (111) planes and grain boundaries. Experiments demonstrated that the etching efficacy of the silicon-thermal method was significantly superior to the mild etching achieved by pure Fe or Fe₂O₃ alone. This research provides a new strategy based on silicon-thermal reduction for the efficient and deep surface processing of diamond.