Integrated nanowire plasmonics · 2University of Rochester, Center for Coherence and Quantum...
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Integrated nanowire plasmonics K. Goodfellow 1,2 , C. Chakraborty 2,3 , R. Beams 1 , L. Novotny 4 , and A. N. Vamivakas 1,2,3 1 University of Rochester, The Institute of Optics, 275 Hutchison Road, 14627, Rochester, NY, USA 2 University of Rochester, Center for Coherence and Quantum Optics, 14627, Rochester, NY, USA 3 University of Rochester, Materials Science, 14627, Rochester, NY, USA 4 ETH, Photonics Laboratory, Zurich, 8093 Zurich, Switzerland [email protected] Abstract – Atomically thin materials, such as graphene and transition metal dichalcogenides, offer an interesting platform to tailor nanoscale light-matter interaction. The ease with which these materials can be incorporated into optoelectronic devices has given rise to the emerging area of nano-optoelectronics. In this talk I will discuss some recent results on merging plasmonics and atomically thin materials as well as the possibility of exploiting atomically thin semiconductors for integrated quantum photonics applications. I. INTRODUCTION As silicon photonic integrated circuits have continued to mature, novel nanophotonic devices and nanomaterials are being explored for their potential in next-generation on-chip optical processing [1-3]. Particularly exciting is the possibility to engineer nanophotonic devices that both enhance light-matter interaction and support confined electromagnetic modes that can propagate in deeply subwavelength regions. Surface plasmon polaritons (SPPs), electromagnetic excitations that propagate along the interface between a metal and a dielectric, are a natural candidate for both integrated subwavelength light guiding and pronounced light-matter coupling. An exemplary system in this regard is silver (Ag) nanowires and the optical properties of individual Ag nanowires have been extensively studied. A step towards efficient and compact nanophotonic circuitry is the integration of plasmonic waveguides that couple directly to on-chip sources, detectors, and modulators. Initial steps have been made in coupling Ag nanowires with other nanostructures, such as quantum dots, fluorescent molecules and nitrogen- vacancy centers. Furthermore, near-field coupling between these nanostructures and the wire allows for plasmons to be generated anywhere along the wire, not just at the ends. Although there has been some investigation into graphene-nanowire hybrids for nanophotonic circuitry the vast potential for two-dimensional atomically thin materials in this realm is largely unexplored. Single-layer molybdenum disulfide (MoS 2 ), a semiconductor being explored for its photoluminescence, valley-selective properties, and potential as a transistor and photodetector, is an ideal choice to couple with nanoplasmonic circuitry. In this paper, we explore the nanophotonics of a MoS 2 /Ag nanowire hybrid structure. We demonstrate coupling between a single-layer MoS 2 flake and a single Ag nanowire. We show that a plasmon excited at the uncovered end of the nanowire can propagate and excite MoS 2 photoluminescence (PL), both by direct plasmon- to-exciton conversion along the wire and by absorbing photons rescattering from the end of the wire. We also demonstrate that MoS 2 excitons can decay to generate Ag-nanowire plasmons. Finally, we show it is possible for the Ag nanowire to serve a dual role as both a channel for MoS 2 excitation and subsequent extraction of the decaying MoS 2 excitons. II. NEAR-FIELD DETECTION OF OPTICAL PLASMONS Figure 1a presents an image of the fabricated MoS 2 /Ag nanowire device. The flake is electrically contacted enabling both photocurrent measurement and voltage biasing. A photon incident on the uncovered end of the nanowire generates a wire plasmon via scattering. Although there are several decay channels available to the plasmon, we study plasmons that propagate along the nanowire and induce a current in MoS 2 . Figure 1b presents an exemplary spatially-resolved photocurrent map, with highlighted regions representing the contact electrodes
Transcript of Integrated nanowire plasmonics · 2University of Rochester, Center for Coherence and Quantum...
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Integrated nanowire plasmonics
K. Goodfellow1,2, C. Chakraborty2,3, R. Beams1, L. Novotny4, and A. N. Vamivakas1,2,3
1University of Rochester, The Institute of Optics, 275 Hutchison Road, 14627, Rochester, NY, USA 2University of Rochester, Center for Coherence and Quantum Optics, 14627, Rochester, NY, USA
3University of Rochester, Materials Science, 14627, Rochester, NY, USA 4ETH, Photonics Laboratory, Zurich, 8093 Zurich, Switzerland
Abstract – Atomically thin materials, such as graphene and transition metal dichalcogenides, offer an interesting platform to tailor nanoscale light-matter interaction. The ease with which these materials can be incorporated into optoelectronic devices has given rise to the emerging area of nano-optoelectronics. In this talk I will discuss some recent results on merging plasmonics and atomically thin materials as well as the possibility of exploiting atomically thin semiconductors for integrated quantum photonics applications.
I. INTRODUCTION
As silicon photonic integrated circuits have continued to mature, novel nanophotonic devices and nanomaterials are being explored for their potential in next-generation on-chip optical processing [1-3]. Particularly exciting is the possibility to engineer nanophotonic devices that both enhance light-matter interaction and support confined electromagnetic modes that can propagate in deeply subwavelength regions. Surface plasmon polaritons (SPPs), electromagnetic excitations that propagate along the interface between a metal and a dielectric, are a natural candidate for both integrated subwavelength light guiding and pronounced light-matter coupling. An exemplary system in this regard is silver (Ag) nanowires and the optical properties of individual Ag nanowires have been extensively studied. A step towards efficient and compact nanophotonic circuitry is the integration of plasmonic waveguides that couple directly to on-chip sources, detectors, and modulators. Initial steps have been made in coupling Ag nanowires with other nanostructures, such as quantum dots, fluorescent molecules and nitrogen-vacancy centers. Furthermore, near-field coupling between these nanostructures and the wire allows for plasmons to be generated anywhere along the wire, not just at the ends. Although there has been some investigation into graphene-nanowire hybrids for nanophotonic circuitry the vast potential for two-dimensional atomically thin materials in this realm is largely unexplored. Single-layer molybdenum disulfide (MoS2), a semiconductor being explored for its photoluminescence, valley-selective properties, and potential as a transistor and photodetector, is an ideal choice to couple with nanoplasmonic circuitry. In this paper, we explore the nanophotonics of a MoS2/Ag nanowire hybrid structure. We demonstrate coupling between a single-layer MoS2 flake and a single Ag nanowire. We show that a plasmon excited at the uncovered end of the nanowire can propagate and excite MoS2 photoluminescence (PL), both by direct plasmon-to-exciton conversion along the wire and by absorbing photons rescattering from the end of the wire. We also demonstrate that MoS2 excitons can decay to generate Ag-nanowire plasmons. Finally, we show it is possible for the Ag nanowire to serve a dual role as both a channel for MoS2 excitation and subsequent extraction of the decaying MoS2 excitons.
II. NEAR-FIELD DETECTION OF OPTICAL PLASMONS Figure 1a presents an image of the fabricated MoS2/Ag nanowire device. The flake is electrically contacted enabling both photocurrent measurement and voltage biasing. A photon incident on the uncovered end of the nanowire generates a wire plasmon via scattering. Although there are several decay channels available to the plasmon, we study plasmons that propagate along the nanowire and induce a current in MoS2. Figure 1b presents an exemplary spatially-resolved photocurrent map, with highlighted regions representing the contact electrodes
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and the nanowire, from the device under zero external voltage bias. The single-layer MoS2 flake is only between the source and drain contacts. Apparent in the photocurrent map is direct photocurrent generation in the MoS2 flake and photocurrent when the far-field photons excite Ag nanowire optical plasmons at the uncovered end of the nanowire (solid box). Polarization dependence of the photocurrent indicates optical plasmons are being detected in the near-field with the MoS2 detector. It is interesting that the plasmon current is observed for the unbiased device indicating some potential energy landscape asymmetry resulting in a built-in electric field that can separate the plasmon generated carriers.
ACKNOWLEDGEMENT
The authors acknowledge support from the Institute of Optics, the U. S. Department of Energy (grant DE-FG02-05ER46207), the National Science Foundation IGERT program (DGE-0966089), the National Science Foundation (DMR-1309734) and the Swiss National Science Foundation (200021-149433). The sample used in this work was, in part, fabricated at the Cornell NanoScale Facility, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (Grant ECCS-0335765).
REFERENCES
[1] V. J. Sorger, R. F. Oulton, R.-M. Ma, and X. Zhang, MRS Bull. 37, 263 728 (2012). [2] K. Goodfellow, R. Beams, C. Chakraborty, L. Novotny and A. N. Vamivakas, “Integrated nanophotonics based on
nanowire plasmons and atomically-thin material”, Optica 1, 149 (2014). [3] C. Chakraborty, R. Beams, K. Goodfellow, G. Wicks, L. Novotny and A. N. Vamivakas, Optical antenna enhanced
graphene photodetector, Applied Physics Letters 105, 241114 (2014).
Figure 1. a) Image of lithographically patterned contacts on MoS2/Ag nanowire device just before metal evaporation. b) Photocurrent map of panel a) device.
