Fabrication of Si/Au Core/Shell Nanoplasmonic Structures with Ultrasensitive Surface-Enhanced Raman Scattering for Mono layer Molecule Detection

Nanoparticles of noble metals are typically plasmonic materials, but the pure metals have high nonirradiative ohmic losses at optical frequencies, leading to large absorption and unwanted heating effects. Additionally, spherical silicon nanoparticles (NPs) have a unique optical system with a high-refractive-index dielectric nanostructure. Combining these two components in one functional core/shell NP nanostructure of Si/M, where M represents a noble metal, to produce resonant optical electronic and magnetic responses has been rare. Herein, an approach for the assembly of Si/M core/shell NPs is developed on the basis of double-beam laser ablation in liquid, thereby fabricating a series of Si/M (M = Au, Ag, Pd, and Pt) core/shell NPs and characterizing the intense visible-light scattering modes from the as-fabricated Si/Au NPs as a nanoplasmonic structure. Dark-field optical measurements show that these Si/Au NPs have a strong electromagnetic response in the visible-light region, and the resonant frequencies can be modulated by NP size and morphology. The dispersed NPs are used as a highly sensitive surface-enhanced Raman scattering (SERS) active probe for detecting monolayer molecules, as proven herein using 4-MBT molecules. A SERS plasmonic enhancement factor of similar to 10(8) is found for these Si/Au NPs by correlating the SERS measurement with scanning electron microscopy analysis. These findings present the possibility of confining light in ubiquitous silicon-based semiconductor technologies and manipulating the optical properties of nontraditional plasmonic nanostructures, while also opening new perspectives. This technique can be extended to other noble metals to form similar structures and fabricate low-loss metamaterials and nanophotonic devices.