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Multiphoton photoelectron emission microscopy of single Au nanorods: combined experimental and theoretical study of rod morphology and dielectric environment on localized surface plasmon resonances.

Multiphoton photoelectron emission microscopy of single Au nanorods: combined experimental and... Multiphoton photoelectron emission from individual Au nanorods deposited on indium tin oxide (ITO) substrates is studied via scanning photoionization microscopy, based on femtosecond laser excitation at frequencies near the rod longitudinal surface plasmon resonance (LSPR). The observed resonances in photoemission correlate strongly with plasmon resonances measured in dark field microscopy (DFM), thus establishing a novel scheme for wavelength-resolved study of plasmons in isolated metallic nanoparticles based on highly sensitive electron counting methods. In this work, we explore experimental and theoretical effects of (i) morphology and (ii) aspect ratio (AR) for longitudinal plasmon resonance behavior in Au nanorods. A quasilinear dependence between LSPR and aspect ratio (AR) is experimentally determined [Δλ≈ +100(10) nm/AR unit] for Au nanorods on ITO, in excellent agreement with the first principles value from finite element computer modeling [Δλ = +108(5) nm/AR unit]. Interestingly, however, LSPR values for larger vs. smaller diameter rods (w≈ 20 nm and 10 nm) are systematically red-shifted [ΔE≈-0.03(1) eV; Δλ≈ +15(5) nm at λ≈ 800 nm], indicating that electromagnetic retardation effects must also be considered for highest accuracy in LSPR position. To augment these results, the influence of the dielectric environment on the rod LSPR has been explored both experimentally and numerically. In particular, detailed finite-element simulations for ITO supported Au nanorods are found to yield plasmon resonances in near quantitative agreement (ΔE≈±0.04 eV) with experiment, with residual differences arising from uncertainty in the refractive index of the ITO thin film. Furthermore, the results indicate that plasmon resonance predictions based on infinitely thick ITO substrates are reliable to a few meV for film thicknesses larger than approximately twice the rod width. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical chemistry chemical physics : PCCP Pubmed

Multiphoton photoelectron emission microscopy of single Au nanorods: combined experimental and theoretical study of rod morphology and dielectric environment on localized surface plasmon resonances.

Physical chemistry chemical physics : PCCP , Volume 15 (26): -10588 – Jan 16, 2014

Multiphoton photoelectron emission microscopy of single Au nanorods: combined experimental and theoretical study of rod morphology and dielectric environment on localized surface plasmon resonances.


Abstract

Multiphoton photoelectron emission from individual Au nanorods deposited on indium tin oxide (ITO) substrates is studied via scanning photoionization microscopy, based on femtosecond laser excitation at frequencies near the rod longitudinal surface plasmon resonance (LSPR). The observed resonances in photoemission correlate strongly with plasmon resonances measured in dark field microscopy (DFM), thus establishing a novel scheme for wavelength-resolved study of plasmons in isolated metallic nanoparticles based on highly sensitive electron counting methods. In this work, we explore experimental and theoretical effects of (i) morphology and (ii) aspect ratio (AR) for longitudinal plasmon resonance behavior in Au nanorods. A quasilinear dependence between LSPR and aspect ratio (AR) is experimentally determined [Δλ≈ +100(10) nm/AR unit] for Au nanorods on ITO, in excellent agreement with the first principles value from finite element computer modeling [Δλ = +108(5) nm/AR unit]. Interestingly, however, LSPR values for larger vs. smaller diameter rods (w≈ 20 nm and 10 nm) are systematically red-shifted [ΔE≈-0.03(1) eV; Δλ≈ +15(5) nm at λ≈ 800 nm], indicating that electromagnetic retardation effects must also be considered for highest accuracy in LSPR position. To augment these results, the influence of the dielectric environment on the rod LSPR has been explored both experimentally and numerically. In particular, detailed finite-element simulations for ITO supported Au nanorods are found to yield plasmon resonances in near quantitative agreement (ΔE≈±0.04 eV) with experiment, with residual differences arising from uncertainty in the refractive index of the ITO thin film. Furthermore, the results indicate that plasmon resonance predictions based on infinitely thick ITO substrates are reliable to a few meV for film thicknesses larger than approximately twice the rod width.

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ISSN
1463-9076
DOI
10.1039/c3cp44385j
pmid
23417070

Abstract

Multiphoton photoelectron emission from individual Au nanorods deposited on indium tin oxide (ITO) substrates is studied via scanning photoionization microscopy, based on femtosecond laser excitation at frequencies near the rod longitudinal surface plasmon resonance (LSPR). The observed resonances in photoemission correlate strongly with plasmon resonances measured in dark field microscopy (DFM), thus establishing a novel scheme for wavelength-resolved study of plasmons in isolated metallic nanoparticles based on highly sensitive electron counting methods. In this work, we explore experimental and theoretical effects of (i) morphology and (ii) aspect ratio (AR) for longitudinal plasmon resonance behavior in Au nanorods. A quasilinear dependence between LSPR and aspect ratio (AR) is experimentally determined [Δλ≈ +100(10) nm/AR unit] for Au nanorods on ITO, in excellent agreement with the first principles value from finite element computer modeling [Δλ = +108(5) nm/AR unit]. Interestingly, however, LSPR values for larger vs. smaller diameter rods (w≈ 20 nm and 10 nm) are systematically red-shifted [ΔE≈-0.03(1) eV; Δλ≈ +15(5) nm at λ≈ 800 nm], indicating that electromagnetic retardation effects must also be considered for highest accuracy in LSPR position. To augment these results, the influence of the dielectric environment on the rod LSPR has been explored both experimentally and numerically. In particular, detailed finite-element simulations for ITO supported Au nanorods are found to yield plasmon resonances in near quantitative agreement (ΔE≈±0.04 eV) with experiment, with residual differences arising from uncertainty in the refractive index of the ITO thin film. Furthermore, the results indicate that plasmon resonance predictions based on infinitely thick ITO substrates are reliable to a few meV for film thicknesses larger than approximately twice the rod width.

Journal

Physical chemistry chemical physics : PCCPPubmed

Published: Jan 16, 2014

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