| 1. |
- Fang, Yurui, 1983, et al.
(author)
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Plasmon Enhanced Internal Photoemission in Antenna-Spacer-Mirror Based Au/TiO2 Nanostructures
- 2015
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:6, s. 4059-4065
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Journal article (peer-reviewed)abstract
- Emission of photoexcited hot electrons from plasmonic metal nanostructures to semiconductors is key to a number of proposed nanophotonics technologies for Solar harvesting, water splitting, photocatalysis, and a variety of optical sensing and photodetector applications. Favorable materials and catalytic properties make systems based on gold and TiO2 particularly interesting, but the internal photo emission efficiency for visible light is low because of the wide bandgap of the semiconductor. We investigated the incident photon-to-electron conversion efficiency of thin TiO2 films decorated with Au nanodisk antennas in an electrochemical circuit and found that incorporation of a Au mirror beneath the semiconductor amplified the photoresponse for light with wavelength lambda = 500-950 nm by a factor 2-10 compared to identical structures lacking the mirror component. Classical electrodynamics simulations showed that the enhancement effect is caused by a favorable interplay between localized surface plasmon excitations and cavity modes that together amplify the light absorption in the Au/TiO2 interface. The experimentally determined internal quantum efficiency for hot electron transfer decreases monotonically with wavelength, similar to the probability for interband excitations with energy higher than the Schottky barrier obtained from a density functional theory band structure simulation of a thin Au/TiO2 slab.
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| 2. |
- Hakonen, Aron, 1970, et al.
(author)
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Dimer-on-mirror SERS substrates with attogram sensitivity fabricated by colloidal lithography.
- 2015
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:21
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Journal article (peer-reviewed)abstract
- Nanoplasmonic substrates with optimized field-enhancement properties are a key component in the continued development of surface-enhanced Raman scattering (SERS) molecular analysis but are challenging to produce inexpensively in large scale. We used a facile and cost-effective bottom-up technique, colloidal hole-mask lithography, to produce macroscopic dimer-on-mirror gold nanostructures. The optimized structures exhibit excellent SERS performance, as exemplified by detection of 2.5 and 50 attograms of BPE, a common SERS probe, using Raman microscopy and a simple handheld device, respectively. The corresponding Raman enhancement factor is of the order 10(11), which compares favourably to previously reported record performance values.
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| 3. |
- Shao, Lei, 1987, et al.
(author)
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Gold Nanorod Rotary Motors Driven by Resonant Light Scattering
- 2015
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 9:12, s. 12542-12551
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Journal article (peer-reviewed)abstract
- Efficient and robust artificial nanomotors could provide a variety of exciting possibilities for applications in physics, biology and chemistry, including nanoelectromechanical systems, biochemical sensing, and drug delivery. However, the application of current man-made nanomotors is limited by their sophisticated fabrication techniques, low mechanical output power and severe environmental requirements, making their performance far below that of natural biomotors. Here we show that single-crystal gold nanorods can be rotated extremely fast in aqueous solutions through optical torques dominated by plasmonic resonant scattering of circularly polarized laser light with power as low as a few mW. The nanorods are trapped in 2D against a glass surface, and their rotational dynamics is highly dependent on their surface plasmon resonance properties. They can be kept continuously rotating for hours with limited photothermal side effects and they can be applied for detection of molecular binding with high sensitivity. Because of their biocompatibility, mechanical and thermal stability, and record rotation speeds reaching up to 42 kHz (2.5 million revolutions per minute), these rotary nanomotors could advance technologies to meet a wide range of future nanomechanical and biomedical needs in fields such as nanorobotics, nanosurgery, DNA manipulation and nano/microfluidic flow control.
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| 4. |
- Verre, Ruggero, 1985, et al.
(author)
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Directional Light Extinction and Emission in a Metasurface of Tilted Plasmonic Nanopillars
- 2016
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 16:1, s. 98-104
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Journal article (peer-reviewed)abstract
- Plasmonic optical antennas and metamaterials with an ability to boost light-matter interactions for particular incidence or emission angles could find widespread use in solar harvesting, biophotonics, and in improving photon source performance at optical frequencies. However, directional plasmonic structures have generally large footprints or require complicated geometries and costly nano-fabrication technologies. Here, we present a directional metasurface realized by breaking the out-of-plane symmetry of its individual elements: tilted subwavelength plasmonic gold nanopillars. Directionality is caused by the complex charge oscillation induced in each individual nanopillar, which essentially acts as a tilted dipole above a dielectric interface. The metasurface is homogeneous over a macroscopic area and it is fabricated by a combination of facile colloidal lithography and off-normal metal deposition. Fluorescence excitation and emission from dye molecules deposited on the metasurface is enhanced in specific directions determined by the tilt angle of the nanopillars. We envisage that these directional metasurfaces can be used as cost-effective substrates for surface-enhanced spectroscopies and a variety of nanophotonic applications.
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| 5. |
- Verre, Ruggero, 1985, et al.
(author)
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Optical Magnetism and Plasmonic Fano Resonances in Metal Insulator-Metal Oligomers
- 2015
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:3, s. 1952-1958
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Journal article (peer-reviewed)abstract
- The possibility of achieving:,Optical magnetism at visible- frequencies using plasmonic nanostructures has recently been a,subject of great interest, The,concept is based on designing that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonanees are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader Magnetic response can be,realized in plasmonic pentamers,constructed from metal insulator-metal (MINI) sandwich particles, Each MIM unit acts as 2 magnetic meta atom and the optical magnetism is rendered quasi broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamets exhibit multiple Fano resonances and a broad subradiant spectral window- that signals the magnetic interaction and a hierarchy of coupling effects in these intricate thee-dimensional nanoparticle oligomers.
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| 6. |
- Yang, Zhong-Jian, 1986
(author)
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Coherent Energy Transfers between Orthogonal Radiant and Weakly Radiant Plasmonic Nanorod Resonators
- 2015
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:46, s. 26079-26085
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Journal article (peer-reviewed)abstract
- The coherent couplings between plasmon modes have attracted significant research interest recently as they can dramatically modify the lightmatter interactions and have many applications such as sensor and metamaterial. In this work, the energy transfer properties in a radiant and weakly radiant plasmon mode coupled system are investigated in the time domain. The phase difference between the two modes is found to vary from p to 0 with wavelength, and it is about p/2 near the resonance. The plasmon energy transfers back and forth between the two modes, and the transfer cycles increase with the coupling strength. Therefore, the system can undergo from enhanced absorption to Fano resonance phenomena on the optical spectra. Furthermore, the total energy transfer efficiency from the radiant plasmon mode to the weakly radiant one is also studied, and it shows a FOrster resonance energy transfer (FRET)-like behavior.
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| 7. |
- Yang, Zhong-Jian, 1986, et al.
(author)
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Plasmonic Fano resonances in metallic nanorod complexes
- 2014
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 6:10, s. 4985-4997
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Journal article (peer-reviewed)abstract
- Plasmonic Fano resonances (FRs) in nanostructures have been extensively studied in recent years. Nanorod-based complexes for FRs have also attracted much attention. The basic optical properties and fabrication technology of different kinds of plasmonic nanorods have been greatly developed over the last several years. The mutipole plasmon resonances and their flexible adjustment ranges on nanorods make them promising for FR modifications and structure diversity. In this paper, we review some recently studied plasmonic nanorod based nanostructures for FRs, including single nanorods, dimers, mutipole rods and nanorod-nanoparticle hybrids. The corresponding applications of the FRs are also briefly discussed. This journal is © the Partner Organisations 2014.
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| 8. |
- Yang, Zhong-Jian, 1986, et al.
(author)
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Role of material loss and mode volume of plasmonic nanocavities for strong plasmon-exciton interactions
- 2016
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In: Optics Express. - : The Optical Society. - 1094-4087 .- 1094-4087. ; 24:18, s. 20373-20381
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Journal article (peer-reviewed)abstract
- We investigate the role of material loss and mode volume of plasmonic nanostructures on strong plasmon-exciton coupling. We find that the field enhancement, and therefore loss, is not important for the magnitude of the Rabi splitting as such, but instead it is determined by the mode volume. Nevertheless, for reaching true strong coupling condition, that is, coupling greater than any dissipation, it is important to compromise losses. We also show that using such popular geometries as a dimer of two spheres or bow-tie nanoantennas, does not allow compressing the mode volume much in comparison to a single nanoparticle case, except for very narrow gaps, but rather it allows for efficient extraction of the mode out of the metal thus making it more accessible for excitons to interact with. Even more efficient mode extraction is achieved when high refractive index dielectric is placed in the gap. Our findings may find practical use for quantum plasmonics applications. (C) 2016 Optical Society of America
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| 9. |
- Yang, Zhong-Jian, 1986, et al.
(author)
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Ultimate Limit of Light Extinction by Nanophotonic Structures
- 2015
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:11, s. 7633-7638
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Journal article (peer-reviewed)abstract
- Nanophotonic structures make it possible to precisely engineer the optical response at deep subwavelength scales. However, a fundamental understanding of the general performance limits remains a challenge. Here we use extensive electrodynamics simulations to demonstrate that the so-called f-sum rule sets a strict upper bound to the light extinction by nanostructures regardless their internal interactions and retardation effects. In particular, we show that the f-sum rule applies to arbitrarily complex plasmonic metal structures that exhibit an extraordinary spectral sensitivity to size, shape, near-field coupling effects, and incident polarization. The results may be used for benchmarking light scattering and absorption efficiencies, thus imposing fundamental limits on solar light harvesting, biomedical photonics, and optical communications.
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