A highly-ordered close-packed metallic nanotube array for surface-enhanced Raman scattering

This study reports on a rhombic metallic nanotube array (MeNTA) for surface-enhanced Raman scattering (SERS) applications. The close-packed structure of the MeNTA is made of silver and comprises over one hundred million rhombic nanotubes per 1 cm². The space-efficient arrangement was developed using finite difference time domain simulations, and fabrication was performed using a top-down lithographic method developed for semiconductors, followed by sputtering at room temperature, making it suitable for SERS applications. Scanning electron microscopy images confirmed the highly ordered periodic structure of the rhombic MeNTA substrate. In experiments, the rhombic MeNTAs demonstrated excellent SERS effects in the detection of rhodamine 6G (R6G), crystal violet (CV), folic acid, malachite green, and methyl parathion. The detection limit for R6G was 10⁻¹¹ M, with an enhancement factor of 1.35 × 10⁸ and a relative standard deviation of 6.98%. The detection limit for CV was 10⁻¹² M, with an enhancement factor of 3.23 × 10⁸ and a relative standard deviation of 5.92%. The high reproducibility of our findings can be attributed to the uniformly dense distribution of the periodic MeNTA.