Abstract
We describe a new material system based on alloys of gallium and platinum that is well-suited for ultraviolet (UV) plasmonics. Although gallium has previously been shown to be useful for such studies, creating a continuous, pinhole-free thin film has been technically challenging. For example, when vacuum deposition techniques are used, gallium forms as isolated spherical nanoparticles on a wide variety of substrates. We demonstrate that when a platinum wetting layer is deposited first on a substrate followed by a thick gallium layer, a Ga-Pt alloy thin film is formed near the interface. The excess surface gallium can then be removed using a focused ion beam (FIB), exposing the alloy film. Ellipsometry measurements show that the alloy largely retains the dielectric properties of solid gallium throughout the UV, although the properties of the two diverge somewhat in the visible. We fabricate periodic subwavelength aperture arrays in the alloy thin film and observe enhanced optical transmission resonances that are sharper in the UV than in the visible. The patterned films appear to be stable over time periods exceeding six months based on optical measurements.
Highlights
The field of plasmonics has grown tremendously in recent years, with demonstrations of device technologies relevant to a broad range of research topics that include physics, chemistry, materials science, engineering and bioscience [1,2,3,4]
The relevance of plasmonics for the UV spectral range arises from the fact that a wide variety of excitations may be found within this region that can be used to understand the structural, conformational and kinetic properties of materials
It should be noted that the observed composition is dependent upon the sample geometry and beam spread within the transmission electron microscope (TEM)
Summary
The field of plasmonics has grown tremendously in recent years, with demonstrations of device technologies relevant to a broad range of research topics that include physics, chemistry, materials science, engineering and bioscience [1,2,3,4]. The success of this approach relies fundamentally on using metals with dielectric properties that allow for strong enhancement of the electromagnetic field, while minimizing propagation losses. This alleviates a significant issue that would exist for pure Ga thin films: processing steps that require that the temperature go above 30° C would cause Ga to melt, making the retention of metal nanostructuring difficult
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