LAUSR

The realization of large-scale and high-density gaps with the size as small as possible is crucial for designing ultrasensitive surface-enhanced Raman scattering (SERS) substrates. As known, the ultra-thin alumina mask (UTAM) surface nanopatterning technique allows to fabricate periodic nanoparticle (NP) arrays with 5-nm gaps among the NPs, however, it still faces a significant challenge to realize the reliable distribution of nanogaps over large area, because of the unavoidable collapse of UTAM pore wall during the traditional one-step homothermal pore-widening process. Herein, an efficient two-step poikilothermal pore-widening process was developed to precisely control the pore wall etching of UTAM, enabling to effectively avoid the fragmentation of the UTAM and to finally obtain large-scale UTAM with the pore wall thickness of about 5 nm. As a result, large-scale NP arrays with high-density sub-5 nm and even smaller gaps between the neighboring NPs have been realized through applying the as-prepared UTAM as the nanopatterning template. These NP arrays with sub-5 nm gaps show ultrahigh SERS sensitivity and good reproducibility, which demonstrates the practical feasibility of this promising two-step pore-widening UTAM technique for the fabrication of high-performance active SERS substrates with large-scale ultrasmall nanogaps.