Open AccessLinear and nonlinear optical characterization of self-assembled, large-area gold nanosphere metasurfaces with sub-nanometer gaps
Author(s) -
Jake Fontana,
Mauricio Maldonado,
Nicholas A. Charipar,
Scott A. Trammell,
Rafaela Nita,
Jawad Naciri,
Alberto Piqué,
Banahalli R. Ratna,
Anderson S. L. Gomes
Publication year - 2016
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.24.027360
Subject(s) - optics , nanometre , materials science , characterization (materials science) , nonlinear optics , nonlinear system , refractive index , nanotechnology , optoelectronics , physics , laser , quantum mechanics
We created centimeter-scale area metasurfaces consisting of a quasi-hexagonally close packed monolayer of gold nanospheres capped with alkanethiol ligands on glass substrates using a directed self-assembly approach. We experimentally characterized the morphology and the linear and nonlinear optical properties of metasurfaces. We show these metasurfaces, with interparticle gaps of 0.6 nm, are modeled well using a classical (without charge transfer) description. We find a large dispersion of linear refractive index, ranging from values less than vacuum, 0.87 at 600 nm, to Germanium-like values of 4.1 at 880 nm, determined using spectroscopic ellipsometry. Nonlinear optical characterization was carried out using femtosecond Z-scan and we observe saturation behavior of the nonlinear absorption (NLA) and nonlinear refraction (NLR). We find a negative NLR from these metasurfaces two orders of magnitude larger (n 2,sat = -7.94x10 -9 cm 2 /W at I sat,n2 = 0.43 GW/cm 2 ) than previous reports on gold nanostructures at similar femtosecond time scales. We also find the magnitude of the NLA comparable to the largest values reported (β 2,sat = -0.90x10 5 cm/GW at I sat,β2 = 0.34 GW/cm 2 ). Precise knowledge of the index of refraction is of crucial importance for emerging dispersion engineering technologies. Furthermore, utilizing this directed self-assembly approach enables the nanometer scale resolution required to develop the unique optical response and simultaneously provides high-throughput for potential device realization.