Numerical analyses of the ultraviolet and visible plasmonic spectra measured from hemispherical gallium nanostructures on dielectric substrates reveal that resonance frequencies are quite sensitive to illumination angle and polarization in a way that depends on nanostructure size, shape, and substrate. Large, polarization-dependent splittings arise from the broken symmetry of hemispherical gallium nanoparticles on sapphire substrates, inducing strong interactions with the substrate that depend sensitively on the angle of illumination and the nanoparticle diameter.

Liquid Ga nanoparticles have been deposited on sapphire substrates at room temperature. The optical evolution of Ga nanoparticle surface plasmon resonance during deposition has been characterized by in situ real-time spectroscopic ellipsometry to control and tune the plasmon resonance photon energy. The existence of both longitudinal and transverse modes for spheroidal Ga nanoparticles supported on a sapphire substrate is demonstrated and the dependence of the longitudinal and transverse plasmon energies on particle size is discussed. Stability of the Ga surface plasmon resonance to air exposure and high temperature is also demonstrated.

Self-assembled arrays of hemispherical gallium nanoparticles deposited by molecular beam epitaxy on a sapphire support are explored as a new type of substrate for ultraviolet plasmonics. Spin-casting a 5 nm film of crystal violet upon these nanoparticles permitted the demonstration of surface-enhanced Raman spectra, fluorescence, and degradation following excitation by a HeCd laser operating at 325 nm. Measured local Raman enhancement factors exceeding 10(7) demonstrate the potential of gallium nanoparticle arrays for plasmonically enhanced ultraviolet detection and remediation.

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...