Figure 4

SERS enhancement factors (EF) of Au nanoislands and their SERS limit-of-detection.

a,b) Spatial distribution of SERS enhancement factors (EFs) at ~1069 cm⁻¹ of benzenethiol (BT) molecules at an excitation laser of 633 nm over an area of 4-inch glass substrate for (a) a single-step solid-state dewetting with t_1Au = 10 nm and (b) a repeated dewetting with t_1Au = 5, t_2Au = 5 nm. A expanded spatial map of SERS EFs at ~1069 cm⁻¹ were acquired at 1 mm intervals over an area of 1 cm² and has spatially averaged SERS EFs about ~10⁶ for 10 nm and ~10⁷ for t_1Au = 5 and t_2Au = 5 nm, demonstrating the excellent uniformity over a 4-inch substrate. The SEM images and numerically calculated electric field intensity distributions at excitation wavelength of 633 nm by using a three-dimensional finite difference time domain (3D-FDTD) method (upper left) and representative SERS spectra of BT molecules (upper right). (c-d) SERS limit-of-detection (LOD) of octopamine molecules with different concentrations. The LOD exhibits ca. 100 μM for (c) a single-step solid-state dewetting with t_1Au = 10 nm but increases down to 10 μM for (d) repeated dewetting with t_1Au = 5, t_2Au = 5 nm.