Fabrication of triangular Au/Ag nanoparticle arrays with sub-10 nm nanogap controlled by flexible substrate for surface-enhanced Raman scattering

Abstract

Large-area ordered nanoparticle arrays have shown great potential as surface-enhanced Raman scattering (SERS) substrates. The preparation methods of metal nanogap with width greater than 10 nm are relatively mature. In contrast, nanomanufacturing methods for sub-10 nm still face challenges in realizing controllable and reproducible features. Herein, a series of triangular Au/Ag nanoparticle arrays (noted as Au/Ag NPAs) with sub-10 nm gap were prepared by utilizing stress-induced local cracking and high expansion coefficient of flexible polydimethylsiloxane (PDMS). The triangular tip-connected Au/Ag NPAs were firstly prepared by depositing Au and Ag films on home-made polystyrene (PS) templates, then gaps with precise size (3 nm, 5 nm, 7 nm, 9 nm and 11 nm) were achieved by controlling the temperature of flexible PDMS, and finally transferred to the silicon wafers using as SERS substrates. The results showed that when the prepared triangular Au/Ag NPAs with 3 nm nanogap were used as reliable SERS substrates, the relative standard deviation of Raman intensity at 621 cm−1 mode of Rhodamine 6G (R6G) with concentration of 10–6 M was 2.3%, indicating excellent uniformity. The approach showed good controllability and repeatability for SERS analysis, exhibiting good application prospect in surface trace detection.