SERS Enhancement of CoSe₂ Nanocages via Biphase Junction Strategy

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 CoSe₂ nanocages are constructed by biphase junction strategy to improve CT efficiency. Electron localization function (ELF) simulations demonstrated that the orthorhombic phase (o-CoSe₂) exhibits higher electron delocalization compared to the cubic phase (c-CoSe₂) due to its metallicity, facilitating interfacial CT. The phase composition of CoSe₂ is modulated by changing the dosage of Se, where reduced Se content increases the o-CoSe₂ phase fraction and metallicity, albeit at the expense of reduced dispersion and surface adsorption sites. Optimizing these competing factors, CoSe₂-140 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 CoSe₂ 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.