Constructing a Type-II Cu

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.