| 1. |
- Li, Zhipeng, et al.
(author)
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Multiple-Particle Nanoantennas for Enormous Enhancement and Polarization Control of Light Emission.
- 2009
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 3:3, s. 637-642
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Journal article (peer-reviewed)abstract
- We investigate the light emission from dipolar emitters located within nanoparticle antennas. It is found that the enormous emission enhancement can reach nearly a million fold. For multinanoparticle antennas, the polarization of the emissions strongly depends on the geometry of the antennas, the emitted wavelengths, and the dielectric functions of surrounding media. It is shown that a polarization nanorotator, which modulates the emission polarization on the nanometer scale, can be readily realized by varying either the geometry or surrounding media of nanoparticle antennas.
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| 2. |
- Shegai, Timur, et al.
(author)
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Managing light polarization via plasmon-molecule interactions within an asymmetric metal nanoparticle trimer
- 2008
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In: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 105:43, s. 16448-16453
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Journal article (peer-reviewed)abstract
- The interaction of light with metal nanoparticles leads to novel phenomena mediated by surface plasmon excitations. In this article we use single molecules to characterize the interaction of surface plasmons with light, and show that such interaction can strongly modulate the polarization of the emitted light. The simplest nanostructures that enable such polarization modulation are asymmetric silver nanocrystal trimers, where individual Raman scattering molecules are located in the gap between two of the nanoparticles. The third particle breaks the dipolar symmetry of the two-particle junction, generating a wavelength-dependent polarization pattern. Indeed, the scattered light becomes elliptically polarized and its intensity pattern is rotated in the presence of the third particle. We use a combination of spectroscopic observations on single molecules, scanning electron microscope imaging, and generalized Mie theory calculations to provide a full picture of the effect of particles on the polarization of the emitted light. Furthermore, our theoretical analysis allows us to show that the observed phenomenon is very sensitive to the size of the trimer particles and their relative position, suggesting future means for precise control of light polarization on the nanoscale.
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| 3. |
- Shegai, Timur, 1982, et al.
(author)
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Raman spectroelectrochemistry of molecules within individual electromagnetic hot spots
- 2009
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:40, s. 14392-14398
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Journal article (peer-reviewed)abstract
- The role of chemical enhancement in surface-enhanced Raman scattering (SERS) remains a contested subject. We study SERS spectra of 4-mercaptopyridine molecules excited far from the molecular resonance, which are collected from individual electromagnetic hot spots at concentrations close to the single-molecule limit. The hot spots are created by depositing Tollen's silver island films on a transparent electrode incorporated within an electrochemical cell. Analysis of the intensity of the spectra relative to those obtained from individual rhodamine 6G molecules on the same surface provides a lower limit of ?3 orders of magnitude for the chemical enhancement. This large enhancement is likely to be due to a charge transfer resonance involving the transfer of an electron from the metal to an adsorbed molecule. Excitation at three different wavelengths, as well as variation of electrode potential from 0 to -1.2 V, lead to significant changes in the relative intensities of bands in the spectrum. It is suggested that while the bulk of the enhancement is due to an Albrecht A-term resonance Raman effect (involving the charge transfer transition), vibronic coupling provides additional enhancement which is sensitive to electrode potential. The measurement of potential-dependent SERS spectra from individual hot spots opens the way to a thorough characterization of chemical enhancement, as well to studies of redox phenomena at the single-molecule level.
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