Localized plasmonic fields of nanoantennas enhance second harmonic generation from two-dimensional molybdenum disulfide
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Research Letter
Localized plasmonic fields of nanoantennas enhance second harmonic generation from two-dimensional molybdenum disulfide Gregory T. Forcherio, MicroElectronics-Photonics Program, University of Arkansas, Fayetteville, AR 72701, USA; Sensors & Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, MD 20783, USA Luigi Bonacina, and Jean-Pierre Wolf, Applied Physics Departement, Université de Genève, Genève 1211, Switzerland D. Keith Roper, MicroElectronics-Photonics Program, University of Arkansas, Fayetteville, AR 72701, USA; Ralph E. Martin Department of Chemical Engineering, University of Arkansas, Fayetteville, AR 72701, USA Address all correspondence to G. T. Forcherio at [email protected] (Received 30 May 2018; accepted 5 July 2018)
Abstract Frequency-dependence and magnitude of second harmonic generation (SHG) from ∼4 × 105 nm2 molybdenum disulfide (MoS2) monolayers was examined in presence of single 150 nm plasmonic gold@silica shell@core nanoantenna monomer and dimers. Quantitative agreement between discrete dipole approximation-calculated fields and measured SHG enhancements was found. SHG from MoS2 was enhanced up to 1.88 × upon deposition of a plasmonic nanoantenna-dimer with 170 nm gap, reaching maximal normalized SHG conversion efficiency of 0.0250%/W. Pump losses attributable to plasmonic damping, e.g., scattering and/or hot-electron injection into MoS2, were apparent. Linear and nonlinear optical activity of MoS2 and nanoantenna controls were compared with literature values.
Introduction Transition metal dichalcogenide (TMD) monolayers are promising optoelectronic platforms because of their direct bandgap near 2 eV and 102 pm/V second-order nonlinear susceptibility, χ(2). Interfacing monolayer TMD with metal nanoantennas offers additional degrees of freedom in design of optoelectronics via surface plasmon light manipulation. Examination of optoelectronic processes in nanoantenna-TMD heterostructures has to date focused on linear optical operations, where polarization, P, responds linearly to the excitation field Eω at a frequency ω according to χ(1). As examples, far-field optical absorption and scattering activity,[1] 10–1000 × enhanced TMD absorption/emission,[2] photoluminescence (PL) quenching,[3] and 11–38% efficient plasmonic hot electron transport[4,5] have been reported. Extraordinary second harmonic generation (SHG) and frequency mixing have been measured from two-dimensional (2D) TMD arising from the secondorder nonlinear contribution to P that scales with E2v according to their large χ(2).[6–10] Although SHG and third harmonic generation (THG) have been demonstrably augmented 60–1700 × by plasmonic fields in many nanomaterial heterostructures,[11–17] such activity remains largely unexplored for nanoantenna-TMD systems. Fryett et al. first reported 200 × enhancement of SHG from a sub-region of mechanically-exfoliated monolayer tungsten diselenide (WSe2) by a linearly-polarized Si cavity photonic crystal, after deconvoluting SHG from background PL bands.[10
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