Size-controlled gallium nanoparticles deposited on sapphire are explored as alternative substrates to enhance Raman spectral signatures. Gallium's resilience following oxidation is inherently advantageous compared to silver for practical ex vacuo, non-solution applications. Ga nanoparticles are grown using a simple, molecular beam epitaxy-based fabrication protocol, and by monitoring their corresponding surface plasmon resonance energy through in situ spectroscopic ellipsometry, the nanoparticles are easily controlled for size. Raman spectroscopy performed on cresyl fast violet (CFV) deposited on substrates of differing mean nanoparticle size represents the first demonstration of enhanced Raman signals from reproducibly tunable self-assembled Ga nanoparticles. Nonoptimized aggregate enhancement factors of ~80 were observed from the substrate with the smallest Ga nanoparticles for CFV dye solutions down to a dilution of 10 ppm.Gallium, a standard metal used for optoelectronic devices, represents an alternative plasmonic material with attributes superior to traditional nanostructured silver and gold. Here we present the first demonstration of plasmonic Ga nanoparticle (NP) substrates for surface-enhanced Raman scattering. We have previously demonstrated that the Ga NP SPR is minimally redshifted and not quenched when exposed to air. 2 The Ga SPR remains stable and protected once oxidized even after over a year of air exposure. Conversely, Ag oxidizes excessively and becomes quenched within 36 hours of air exposure. 6 In addition the Ga plasmon mode's remarkable thermal stability from 80K 7 to 873K 2 foreshadows Ga's advantageous use for applications in thermally harsh and diverse environments. Given these promising and unique attributes, we demonstrate room temperature-deposited, tunable, plasmonic Ga nanoparticles and their applicability to surface-enhanced Raman scattering (SERS).The Raman enhancement and longevity of Ga NPs substrates were tested using the standard Raman dye Cresyl fast violet (CFV). Ga NPs were grown by molecular beam epitaxy on inert, sapphire substrates to mitigate fluorescence interference in Raman measurements typically observed with glass substrates, but can be deposited on a wide variety of solid supports. 2 By adjusting the deposition time at a fixed beam flux, we modified the mean NP diameter and, therefore, tuned the surface plasmon resonance of three Ga NPs/sapphire substrates to (i) 2.9eV, (ii) 1.96eV, or (iii) 1.58eV, respectively, as shown in the pseudoextinction coefficient, , measured by in situ spectroscopic ellipsometry 2, 8 (figure 1).Substrates were half metallized and half unmetallized for direct comparison between the Ga NPs' influence and the bare sapphire. A 1μL volume of 100ppm CFV in ethanol was dropwise placed on fully oxidized Ga NPs/sapphire substrates and dried for approximately 15 minutes to ensure complete EtOH evaporation and to minimize the distance between the CFV molecules and the metal NP surfaces.CFV and sapphire possess distinct, strong, and wel...

The role of graphene in enabling deoxidation of silver nanostructures, thereby contributing to enhance plasmonic properties and to improve the temporal stability of graphene/silver hybrids for both general plasmonic and meta‐materials applications, as well as for surface enhanced Raman scattering (SERS) substrates, is demonstrated. The chemical mechanism occurring at the graphene–silver oxide interface is based on the reduction of silver oxide triggered by graphene that acts as a shuttle of electrons and as a kind of catalyst in the deoxidation. A mechanism is formulated, combining elements of electron transfer, role of defects in graphene, and electrochemical potentials of graphene, silver, and oxygen. Therefore, the formulated model represents a step forward from the simple view of graphene as barrier to oxygen diffusion proposed so far in literature. Single layer graphene grown by chemical vapor deposition is transferred onto silver thin films, a periodic silver fishnet structure fabricated by nanoimprint lithography, and onto silver nanoparticle ensembles supporting a localized surface plasmon resonance in the visible range. Through the study of these nanostructured graphene/Ag hybrids, the effectiveness of graphene in preventing and reducing oxidation of silver plasmonic structures, keeping silver in a metallic state over months at air exposure, is demonstrated. The enhanced and stable plasmonic properties of the silver‐fishnet/graphene hybrids are evaluated through their SERS response for detecting benzyl mercaptane.

Self-assembled monolayers (SAMs) derived of 4-methoxy-terphenyl-3'',5''-dimethanethiol (TPDMT) and 4-methoxyterphenyl-4''-methanethiol (TPMT) have been prepared by chemisorption from solution onto gold thin films and nanoparticles. The SAMs have been characterized by spectroscopic ellipsometry, Raman spectroscopy and atomic force microscopy to determine their optical properties, namely the refractive index and extinction coefficient, in an extended spectral range of 0.75-6.5 eV. From the analysis of the optical data, information on SAMs structural organization has been inferred. Comparison of SAMs generated from the above aromatic thiols to well-known SAMs generated from the alkanethiol dodecanethiol revealed that the former aromatic SAMs are densely packed and highly vertically oriented, with a slightly higher packing density and a absence of molecular inclination in TPMT/Au. The thermal behavior of SAMs has also been monitored using ellipsometry in the temperature range 25-500 degrees C. Gold nanoparticles functionalized by the same aromatic thiols have also been discussed for surface enhanced Raman spectroscopy applications. This study represents a step forward tailoring the optical and thermal behavior of surfaces as well as nanoparticles.