Facile fabrication of Au thin film substrates with crack-like nanogaps for surface-enhanced Raman spectroscopy

•Au thin films with crack-like nanogaps were deposited on Si wafers.•The process pressure and film thickness were optimized.•The film reflectance decreased and contact angle increased with the pressure.•Ideal SERS was obtained with the pressure of 13.3 Pa and film thickness of 215 nm.•The minimum detection concentration for three colorants is 2 μM. Surface-enhanced Raman spectroscopy (SERS) has the advantage of nondestructive, quick, and accurate detection of harmful substances. Among the methods used to fabricate SERS substrates, a conventional evaporation equipment can achieve nanostructure of various shapes and sizes by adjusting the process pressure. In this study, general thermal evaporation equipment was utilized to fabricate SERS substrates. Au thin films with nanogaps were deposited on bare Si wafers with different process pressures and film thicknesses to vary the shape and size of the nanogaps. The microstructure was observed through scanning electron microscopy and transmission electron microscopy. In addition, the contact angle and reflectance of the Au thin films were measured. As the process pressure increased, the light reflectance decreased and the contact angle of the film increased. The SERS effect was found to be influenced by the width, depth, and number of nanogaps, reflectivity, and contact angle of the thin films. Optimal performance was observed under a process pressure of 13.3 Pa and film thickness of 215 nm. Under these conditions, the 2 µM rhodamine 6 G, allura red AC, and sunset yellow FCF were detected, and the uniformity and reproducibility of the thin film were also confirmed over a 6-inch substrate.