Photonic-Plasmonic Coupling of GaAs Single Nanowires to Optical Nanoantennas Alberto Casadei, †,¶ Emanuele F. Pecora, ‡,#,¶ Jacob Trevino, §,⊥,¶ Carlo Forestiere, ‡ Daniel Rü ffer, † Eleonora Russo-Averchi, † Federico Matteini, † Gozde Tutuncuoglu, † Martin Heiss, † Anna Fontcuberta i Morral, † and Luca Dal Negro* ,‡,§ † Laboratoire des Mate ́ riaux Semiconducteurs Ecole, Polytechnique Fé de ́ rale de Lausanne, 1015 Lausanne, Switzerland ‡ Department of Electrical and Computer Engineering & Photonics Center, Boston University, 8 Saint Mary Street, Boston, Massachusetts 02215, United States § Division of Materials Science and Engineering, Boston University, 15 Saint Mary’s Street, Brookline, Massachusetts 02446, United States * S Supporting Information ABSTRACT: We successfully demonstrate the plasmonic coupling between metal nanoantennas and individual GaAs nanowires (NWs). In particular, by using dark-field scattering and second harmonic excitation spectroscopy in partnership with analytical and full-vector FDTD modeling, we demonstrate controlled electromagnetic coupling between individual NWs and plasmonic nanoantennas with gap sizes varied between 90 and 500 nm. The significant electric field enhancement values (up to 20×) achieved inside the NW- nanoantennas gap regions allowed us to tailor the nonlinear optical response of NWs by engineering the plasmonic near-field coupling regime. These findings represent an initial step toward the development of coupled metal-semiconductor resonant nanostructures for the realization of next generation solar cells, detectors, and nonlinear optical devices with reduced footprints and energy consumption. KEYWORDS: Semiconductor nanowires, plasmonics, near-field optics, light coupling T he optical properties of semiconductor nanowires (NWs) are currently at the center of an intense research effort due to their potential applications in a number of nanoscale optoelectronic devices, such as tunable and enhanced light sources, 1-3 solar cells 4-8 and photodetectors, 9,10 optical switches, 11 and nonlinear devices and modulators. 12 NWs with engineered composition, size, and morphology offer the possibility to control the electronic structure and the linear and nonlinear optical properties of semiconductor materials. 13 Recently, the engineering of metal-semiconductor NWs that support distinctive structural resonances, such as the ones predicted by the classical Mie theory, 14 has been proven as a convenient pathway to enhance light-matter coupling. 15 Moreover, resonant metallic nanostructures supporting travel- ing or localized SSPs (i.e., collective oscillations of free electrons confined in one or more spatial dimensions at the nanoscale) have been thoroughly investigated as a powerful approach to manipulate optical radiation at the subwavelength scale. 16-20 In particular, plasmonic nanoparticle arrays and nanoantennas have shown the ability to strongly concentrate and increase the intensity of local electromagnetic fields over engineered nanoscale spatial domains and spectral band- widths. 21 However, although a significant amount of work has been devoted to understand and manipulate the optical responses of individual semiconductor NWs and plasmonic systems, little is currently known on their optical coupling regime and synergistic properties. Recently, colloidal arrays of plasmonic nanoparticles and lithographically defined metallic nanocylinders coupled to semiconductor NWs have been explored as novel metal-semiconductor interacting systems that enhance the optical response of their individual components. 22,23 The combination of the mature semi- conductor NWs platform with the nanoplasmonics technology could potentially open the way to novel technological applications that leverage strongly confined optical fields in order to manipulate the linear and nonlinear optical responses (i.e., scattering, absorption, emission, harmonic generation) of resonant semiconductor structures at the nanoscale. In particular, semiconductor NWs optically coupled to plasmonic nanoantennas with lithographically defined morphologies may become the basic building blocks for future high-efficiency solar cells, ultrafast optical switches, and modulators and nanoscale photodetectors with dramatically reduced energy consumption. In this paper, we investigate the resonant coupling of semiconductor NWs and plasmonic antennas. In particular, we Received: November 16, 2013 Revised: March 31, 2014 Published: April 17, 2014 Letter pubs.acs.org/NanoLett © 2014 American Chemical Society 2271 dx.doi.org/10.1021/nl404253x | Nano Lett. 2014, 14, 2271-2278