Mechanistic role of nitrogen in anisotropic air-based EBIE of diamond

Elucidate the exact mechanistic role of nitrogen radicals generated by secondary-electron–induced dissociation of N2 during electron beam–induced etching (EBIE) of (100)-oriented diamond in air, particularly in producing anisotropic etch features with (111)-faceted pits. Determine whether nitrogen contributes by forming stable surface intermediates or by altering local reaction pathways and quantify its influence relative to oxygen radicals.

Background

The study demonstrates that EBIE of diamond in air is predominantly driven by low-energy secondary electrons that dissociate O2 and N2, generating radicals that chemisorb and form volatile species enabling etching. Under air, long exposures produce anisotropic inverse-pyramidal pits bounded by (111) facets on (100)-oriented diamond, unlike the isotropic morphologies typically reported for pure oxygen atmospheres.

The authors suggest a synergistic role between oxygen and nitrogen radicals in producing this anisotropy and note that nitrogen may affect surface chemistry by forming intermediates or modifying reaction pathways. However, the precise mechanistic contribution of nitrogen to anisotropic etching remains unresolved.