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Noble metal nanoparticles are since many years in the focus of extensive research. Unique optical properties caused by the excitation of resonant collective electron oscillations, the localized surface plasmon resonance (LSPR), have lead to a vast number of reported applications.
Here, we present results of a systematic investigation of the plasmonic properties of the novel nanoplasmonic material, Al. Supported Al nanodisks and nanoholes in extended Al films, fabricated by the hole-mask colloidal lithography (HCL) method [1], are used as a model system. We find very sharp LSPRs with extinction cross-sections and full-widths-at-half-maximum (FWHM) comparable to Ag structures with identical geometry. The resonances are spectrally tunable over the UV-VIS-NIR range for disks/holes with diameters D=35-500nm at constant height h=20nm. Excellent agreement with electrostatic spheroid theory (modified long wavelength approximation MLWA) in terms of spectral plasmon peak position, extinction cross-section and FWHM is found for the nanodisk case. The branching ratio between radiative and non-radiative LSPR-decay is obtained from direct measurements of the extinction and scattering cross-sections for a wide range of disk/hole diameters. These results are discussed in view of the native oxide shell thickness as well as of the weak interband transition in bulk Al at 1.5eV.
Based on these results we introduce a unique and very versatile novel materials characterization concept, by studying Al oxidation kinetics in situ and in real time by monitoring the related plasmonic response. By either using the plasmonic response from nanodisks with varying sizes or from nanoholes in an extended film, nanoparticle as well as bulk-like systems can be addressed by the same experimental method. We present a number of oxidation kinetics studies for Al nanodisks of different diameters (50nm, 110nm and 300nm) as well as for extended films (by nanoholes) in air and water environments.
[1] H. Fredriksson, Y. Alaverdyan, A. Dmitriev, C. Langhammer, D. S. Sutherland, M. Zäch and B. Kasemo, Advanced Materials, submitted |