Flexible Tuning of Shape and Arrangement of Au Nanoparticles in 2-Dimensional Self-Organized Arrays: Morphology and Plasmonic Response

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We report the fabrication of 2-dimensional arrays of Au nanoparticles (NPs) with flexibly tunable shape and arrangement, realized by deposition onto self-organized ridge-valley structures at the LiF(110) surface. Tuning the array fabrication conditions, the NP mean size, spacing, and aspect ratio could be controllably varied, allowing us to achieve a variety of 2-dimensional array morphologies. We discuss the consequences of the morphological tuning on the plasmonic response focusing on two particularly instructive cases: in-plane circular NPs arranged on a rectangular array and coherently aligned elongated ellipsoidal NPs laid on a square lattice. Comparing the data with model calculations allowed us to ascribe the optical birefringence of the arrays to the interplay of intrinsic and collective effects. The remarkably narrow width of the plasmonic resonance in these arrays is shown to arise as a consequence of the partial compensation of the dipolar coupling fields between neighboring nanoparticles.