Localized Surface Plasmon Resonance Spectroscopy of Triangular Aluminum Nanoparticles

The localized surface plasmon resonance (LSPR) of Al nanoparticles fabricated by nanosphere lithography (NSL) was examined by UV−vis extinction spectroscopy and electrodynamics theory. Al triangular nanoparticle arrays can support LSP resonances that are tunable throughout the visible and into the UV portion of the spectrum. Scanning electron microscope and atomic force microscope studies point to the presence of a thin native Al2O3 layer on the surface of the Al triangular nanoparticles. The presence of the oxide layer, especially on the tips of the nanotriangles, results in a significant red shift in the LSPR λmax. The refractive index (RI) sensitivity of the Al triangular nanoparticle arrays in bulk solvents was determined to be 0.405 eV/RIU. Theoretical results show that the oxide layer leads to a significant decrease in this RI sensitivity compared to unoxidized triangular nanoparticles of similar size and geometry. A comparison of Al, Ag, Cu, and Au triangular nanoparticles for a similar shape and geometry show that the LSPR λmax has the ordering Au > Cu > Ag > Al, while the full width at half-maximum satisfies Al > Au > Ag > Cu.