Influence of Indium Nanoparticle Array Distributions on Deep-Ultraviolet Surface Plasmon Resonances

Noble metal nanoparticles (NPs) are often utilized as plasmonic materials, but their support of localized surface plasmon resonances (LSPRs) is limited to the visible to infrared regimes. In contrast, non-noble metal NPs are cheaper to synthesize and exhibit LSPRs extending from the IR to the UV spectral regions. Indium is of particular interest due to its potential as a low-loss, high-gain material with LSPRs tunable to the deep-UV range. To date, the plasmonic properties of In NPs with average NP diameter less than 20 nm have yet to be reported. Here, we present a computational-experimental approach to examine the influence of In nanoparticle (NP) array distributions on DUV surface plasmon resonances (SPR). Spectroscopic ellipsometry reveals that In NP arrays have negligible influence on Si absorptance for energies up to 6.4 eV. For energies beyond 6.4 eV, NP size distributions extracted from atomic-force micrographs are used as input into finite-difference time-domain (FDTD) simulations which predict absorptance enhancement with maxima at 7.95 ± 0.1 eV due to SPRs. SPR energy increases as the average NP diameter increases up to 12.5 nm but subsequently decreases beyond 12.5 nm, which can be attributed to intrinsic and extrinsic size-effects, respectively.