SERS Enhancement of CoSe 2 Nanocages via Biphase Junction Strategy

Abstract Semiconductor substrates hold significant promise in surface‐enhanced Raman scattering (SERS) owing to their excellent selectivity and stability, but their SERS activity is hampered by inefficient interfacial charge transfer (CT). Here, the CoSe 2 nanocages are constructed by biphase junction strategy to improve CT efficiency. Electron localization function (ELF) simulations demonstrated that the orthorhombic phase (o‐CoSe 2 ) exhibits higher electron delocalization compared to the cubic phase (c‐CoSe 2 ) due to its metallicity, facilitating interfacial CT. The phase composition of CoSe 2 is modulated by changing the dosage of Se, where reduced Se content increases the o‐CoSe 2 phase fraction and metallicity, albeit at the expense of reduced dispersion and surface adsorption sites. Optimizing these competing factors, CoSe 2 ‐140 achieved optimal SERS performance, enabling the trace detection of carcinogenic p‐aminoazobenzene (PAAB) with a limit of detection (LOD) of 5 × 10 −8   m . These biphase junction CoSe 2 nanocages exhibited excellent homogeneity, long‐term stability, and resistance to acids/alkalis, demonstrating their potential for practical applications in complex environments. This work established a generalizable biphase junction engineering for amplifying electron delocalization in semiconductor SERS substrates, providing critical insights for designing high‐performance semiconductor SERS substrates through crystallographic phase regulation.