Constructing a Type‐II Cu ₂ O@amorphous Fe ₂ O ₃ Core–Shell p‐n Heterostructure for Highly Efficient Surface‐Enhanced Raman Scattering

Amorphous semiconductors have been proposed as ideal platforms for chemical mechanism (CM) based surface-enhanced Raman spectroscopy (SERS). Nevertheless, the high recombination rates of photo-generated excitons hinder further enhancement of their SERS performance. Here, a type-II Cu₂O@amorphous Fe₂O₃ (a-Fe₂O₃) core-shell p-n heterostructure is demonstrated as a novel platform for highly sensitive SERS detection. It is shown that a type-II p-n heterojunction is formed between Cu₂O and a-Fe₂O₃, which can concentrate electrons within the a-Fe₂O₃ shell and reduce the recombination probability of charge carriers. Meanwhile, the amorphous phase of a-Fe₂O₃ provides abundant defect states for promoting the substrate-molecule interactions. The density functional theory calculations show that Cu₂O@a-Fe₂O₃ heterostructure possesses an obviously increased density of states near the Fermi level than Cu₂O and a-Fe₂O₃ alone. In addition, the amorphous phase of a-Fe₂O₃ can efficiently strengthen the substrate-molecule interaction, enabling a larger static charge transfer between the substrate and molecules and hence an effectively increased polarizability tensor. These synergistic effects afford Cu₂O@a-Fe₂O₃ heterostructure ≈10 times and ≈20 times larger enhancement factor for methylene blue than pure Cu₂O and a-Fe₂O₃, respectively. This work can provide new insights into the rational design of the ultrasensitive CM-based SERS platforms for practical applications.