Structure, vibrational modes, and surface electronic states of two-dimensional valentinite antimony oxide

We report a comprehensive study of two-dimensional (2D) valentinite antimony oxide (β-Sb2O3) exfoliated from its natural bulk form. The flakes exhibit well-defined morphology, low surface roughness, and preserved orthorhombic structure. Raman and infrared nano-spectroscopy reveal distinct vibrational modes, confirming the crystallinity and vibrational anisotropy of the material. Conductive atomic force microscopy shows dielectric breakdown at ⁓0.18 V/nm, consistent with insulating out-of-plane behavior. However, scanning tunneling spectroscopy reveals a near-zero surface gap at room temperature. First-principles calculations highlight strong surface band modulation, including full bandgap closure for specific surface terminations. These calculations also indicate a wide indirect bulk gap (⁓2.82 eV) while cathodoluminescence measurements reveal broad defect-related emission, yielding an estimated lower bound for the optical bandgap of approximately 3 eV. These results establish β-Sb2O3 as a unique 2D material with strong bulk-surface electronic contrast, offering potential for applications in wide-bandgap electronics, surface-state engineering, and optoelectronic nanodevices.