| Description |
There has been great interest in the field of plasmonics over the last decade because plasmonics allows for sub-wavelength localization of light with corresponding increases in the magnitude of the electromagnetic field. Au and Ag are widely used in plasmonic applications in the visible range, but they are no longer appropriate in the ultraviolet (UV) range because of the interband transitions. For UV plasmonics, Al has been used as it exhibits plasma frequencies in the UV, with comparatively low losses. However, Al forms a very stable oxide film that makes device fabrication difficult. Thus, there exists a need to find metals that exhibit low loss through much of the ultraviolet spectral range. In this work, Mg and Mg alloys are explored as potential UV plasmonic materials as Mg has high plasma frequency and no interband transitions in the UV range. This research focused on the processing, structural characterization, and optical property evaluations of (i) pure nanostructured Mg films, (ii) Mg films with an Al seed layer, (iii) Mg-Al thin films, (iv) Mg-Ag thin films on quartz, (v) Mg thin films with nanohole arrays, and (vi) Mg nanotriangles on quartz/glass substrate. The films were prepared using magnetron sputtering. The surface morphology and the structure of Mg films were characterized using atomic force microscopy, scanning electron microscopy, stylus profilometry, and x-ray diffraction. The surface oxide layer on Mg was examined using x-ray photoelectron spectroscopy. Over all, Mg films showed improved localized surface plasmon resonance figure of merit (FOMLSP) compared to Al in portions of the UV spectrum. Increase in film thickness, presence of Al seed layer, and higher deposition rates improved optical performance of Mg films. The results showed that smooth and [0002] textured Mg films have low loss and improved FOMLSP. In case of Mg-Al alloys films, the FOMLSP curve blue shifted by about 40 nm for Mg rich Mg-Al alloy films and about 50 nm for Al rich Mg-Al alloy films when compared to pure Mg film. Mg nanostructures (nanotriangles and nanoholes) were fabricated using colloidal lithography. Mg nanohole fabrication proved to be a less challenging than fabricating nanotriangles. These structures were studied using transmission measurements. Both SPP and LSP resonances were blue shifted with decreasing hole diameter and there was an overall blue shift in extinction spectra with increasing film thickness. |
