Ultrafast charge transfer in mixed-dimensional WO3-x nanowire/WSe2 heterostructures for attomolar-level molecular sensing

Abstract

Developing efficient noble-metal-free surface-enhanced Raman scattering (SERS) substrates and unveiling the underlying mechanism is crucial for ultrasensitive molecular sensing. Herein, we report a facile synthesis of mixed-dimensional heterostructures via oxygen plasma treatments of two-dimensional (2D) materials. As a proof-of-concept, 1D/2D WO_3-x/WSe₂ heterostructures with good controllability and reproducibility are synthesized, in which 1D WO_3-x nanowire patterns are laterally arranged along the three-fold symmetric directions of 2D WSe₂. The WO_3-x/WSe₂ heterostructures exhibited high molecular sensitivity, with a limit of detection of 5 × 10⁻¹⁸M and an enhancement factor of 5.0 × 10¹¹ for methylene blue molecules, even in mixed solutions. We associate the ultrasensitive performance to the efficient charge transfer induced by the unique structures of 1D WO_3-x nanowires and the effective interlayer coupling of the heterostructures. We observed a charge transfer timescale of around 1.0 picosecond via ultrafast transient spectroscopy. Our work provides an alternative strategy for the synthesis of 1D nanostructures from 2D materials and offers insights on the role of ultrafast charge transfer mechanisms in plasmon-free SERS-based molecular sensing.

2D materials are promising substrates for surface-enhanced Raman scattering (SERS)-based molecular sensing, but their performance is usually inferior to their plasmonic counterparts. Here, the authors report the synthesis of 1D/2D WO_3-x/WSe₂ heterostructures, showing high molecular sensitivity associated to ultrafast charge transfer timescales of ~1 ps.