Pillar-cap shaped arrays of Ag/SiO2 multilayers after annealing treatment as a SERS—active substrate

Designed Growth of AgNP Arrays for Anti-counterfeiting Based on Surface-Enhanced Raman Spectroscopy Signals

Based on etched PS sphere arrays, the different growths of Ag nanoparticles with tunable LSPR are designed when SiO2-25 nm/Ag-30 nm/SiO2-100 nm sandwich nanocavity structures are annealed at 500 °C, including the hexagonal silver nanoparticle rings, circular silver nanoparticle rings, and aggregated silver nanoparticles. The uniformity of particle size and regularity of position generate enhanced electromagnetic field and good surface-enhanced Raman spectroscopy signals as confirmed by UV-vis observation and finite difference time domain method simulation. The developed nanostructures are effectively used as stable, nonreproducible, and markable anti-counterfeiting signs.

Confined growth of Ag nanoflakes induced by LSPR-driven carrier transfer in periodic nanopatterned arrays

The growth of metal nanostructures induced by surface plasmons has attracted widespread attention and provides a wide range of applications in the development of plasmonic nanochemistry, biosensors, photoelectrochemical coupling reactions, etc. Herein, a simple method is reported for the fabrication of Ag nanoflakes induced by the surface plasma on two-dimensional periodic nanopatterned arrays with the aid of 4-MBA molecules. The light radiation, molecules, and environmental gases are selected to track the formation mechanism of Ag nanoflakes. The in situ Raman observations and theoretical analyses confirm that small aromatic molecules with carboxyl groups play important roles in Ag nanoflake formation derived by localized surface plasmon resonance (LSPR)-driven carriers, which provide profound insights into the study of LSPR-driven carriers, participating in chemical reactions and the reconstruction of dense hot spots in nanogaps.

Manipulation and Applications of Hotspots in Nanostructured Surfaces and Thin Films

The synthesis of nanostructured surfaces and thin films has potential applications in the field of plasmonics, including plasmon sensors, plasmon-enhanced molecular spectroscopy (PEMS), plasmon-mediated chemical reactions (PMCRs), and so on. In this article, we review various nanostructured surfaces and thin films obtained by the combination of nanosphere lithography (NSL) and physical vapor deposition. Plasmonic nanostructured surfaces and thin films can be fabricated by controlling the deposition process, etching time, transfer, fabrication routes, and their combination steps, which manipulate the formation, distribution, and evolution of hotspots. Based on these hotspots, PEMS and PMCRs can be achieved. This is especially significant for the early diagnosis of hepatocellular carcinoma (HCC) based on surface-enhanced Raman scattering (SERS) and controlling the growth locations of Ag nanoparticles (AgNPs) in nanostructured surfaces and thin films, which is expected to enhance the optical and sensing performance.

Charge Transfer Tuned by the Surrounding Dielectrics in TiO₂-Ag Composite Arrays

TiO₂/Ag bilayer films sputtered onto a 2D polystyrene (PS) bead array in a magnetron sputtering system were found to form a nanocap-shaped nanostructure composed of a TiO₂-Ag composite on each PS bead, in which the Ag nanoparticles were trapped partially or fully in the TiO₂ matrix, depending on the TiO₂ thickness. X-ray Photoelectron Spectroscopy (XPS) results showed the opposite shifts of binding energy for Ti 2p and Ag 3d, indicating the transfer of electrons from metallic Ag to TiO₂ owing to the Ag-O-TiO₂ composite formation. UV-Vis absorption spectra showed the blue shifts of the surface plasma resonance peaks, and the maximum absorption peak intensity was obtained for TiO₂ at 30 nm. The surface-enhanced Raman scattering (SERS) peak intensity first increased and then decreased when the TiO₂ thickness changed. The observations of SERS, XPS, and UV-Vis absorption spectra were explained by the dependency of the charge-transfer process on TiO₂ thickness, which was ascribed to the changing dielectric properties in the metal/semiconductor system.