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

Abstract 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 Cu ₂ O@amorphous Fe ₂ O ₃ (a‐Fe ₂ O ₃ ) 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 Cu ₂ O and a‐Fe ₂ O ₃ , which can concentrate electrons within the a‐Fe ₂ O ₃ shell and reduce the recombination probability of charge carriers. Meanwhile, the amorphous phase of a‐Fe ₂ O ₃ provides abundant defect states for promoting the substrate‐molecule interactions. The density functional theory calculations show that Cu ₂ O@a‐Fe ₂ O ₃ heterostructure possesses an obviously increased density of states near the Fermi level than Cu ₂ O and a‐Fe ₂ O ₃ alone. In addition, the amorphous phase of a‐Fe ₂ O ₃ 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 Cu ₂ O@a‐Fe ₂ O ₃ heterostructure ≈10 times and ≈20 times larger enhancement factor for methylene blue than pure Cu ₂ O and a‐Fe ₂ O ₃ , respectively. This work can provide new insights into the rational design of the ultrasensitive CM‐based SERS platforms for practical applications.