Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and rapid detection technique that is used for detection of various analytes in trace quantities. We present a sensitive, large-area, and nanogap-rich SERS-active substrate by altering a thin gold (Au) film on the unpolished side of a single-side polished silicon wafer by repeated thermal deposition and annealing in an argon environment. The repeated thermal deposition and annealing process was compared on both sides of a one-side-polished silicon wafer; however, the rear side (etched/ unpolished side) demonstrated a more enhanced Raman signal owing to the larger effective area. The proposed substrate can be fabricated easily, having a high density of hotspots distributed uniformly all over the substrate. This ensures easy, rapid, and sensitive detection of analytes with a high degree of reproducibility, repeatability, and acceptable uniformity. The optimized substrate shows a high degree of stability with time when exposed to the ambient environment for a longer duration of 148 days. The reported substrate can detect up to 10 −11 M concentrations of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT), with limits of detection (LODs) of 1.22 and 1.26 ng/L, respectively. This work not only presents the efficient and sensitive SERS-active substrate but also shows the advantages of using the rear side of a one-side-polished silicon substrate as a SERS-active chip.

Simple ultrafast laser writing for the fabrication of hierarchical silicon nitride (a-SiNx:H) microstructures is demonstrated as an effective antireflection coating. A wide range of Si-rich to N-rich a-SiNx:H thin films, having varied optical band gap (2.32–5.94 eV) and refractive index (2.8–1.7) of wavelength-ordered (∼λ/4) thickness, are deposited using the plasma-enhanced chemical vapor deposition technique. The high-intensity femtosecond laser (800 nm, 120 fs, 1 kHz) interaction with a-SiNx:H films resulted in diverse nano-/microstructures with systematic width and depth born out of nonlinear light–matter interactions. These experimentally demonstrated the extremely disordered micro–nano structures over a large area of ∼ 1 cm2 that exhibit significant light trapping and absorption capabilities over a broad spectral region of 200–1000 nm. The extensive reduction of reflection losses from 30 to 2.8% from pre- to post-laser texturing is a favorable condition for broadband anti-reflective coatings for enhanced light harvesting from prefabricated photovoltaic devices.

Non-stoichiometric silicon nitride films were fabricated using PECVD technique and patterned by a femtosecond laser, with a uniform gold film of 10nm thickness deposited over it by sputtering technique to explore its potential as SERS substrate.

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Size of gold nano-islands and gap between them is engineered using repeated gold film deposition and then annealing in the presence of argon gas. Increase in the density of nano-islands resulted in better SERS performance.