Experimental and theoretical study on the facet-dependent SERS activity of α-Fe2O3 films

Abstract

Semiconductors have attracted great attention for surface-enhanced Raman scattering (SERS) applications due to their rich variety, adjustable band structure, good chemical stability, and biocompatibility. However, their intrinsic weak SERS activity limited the further development of semiconductor substrates. Here, the α-Fe₂O₃ films with high { $1\overline{1}0$} and { $110$} facet exposure ratios were fabricated through an electrodeposition method with the existence of NH₄Cl and CH₃COONa. The α-Fe₂O₃{ $1\overline{1}0$} and α-Fe₂O₃{ $110$} films show excellent SERS properties with enhancement factor of 4.155×10³ and 5.481×10³, as well as the relatively low limit of detection down to 2 × 10⁻⁷ M for 4-nitrobenzenethiol. Meanwhile, the lower relative standard deviation values (<10%) confirm the well uniformity of as-prepared substrates. Ultraviolet photoelectron spectroscopy analysis reveals that the α-Fe₂O₃{ $110$} possesses the lower work function, which could guarantee the efficient interfacial charge transfer between substrates and probe molecules. Moreover, first principles calculations further indicates that the charge transfer efficiency on { $110$} facet can be effectively improved, and thus significantly enhance the SERS activity of α-Fe₂O₃. The current study provides a strategy for the fabrication and application of semiconductor-based SERS substrates.