Visualization of Localized Intense Optical Fields in Single Gold−Nanoparticle Assemblies and Ultrasensitive Raman Active Sites

Imura, Kohei; Okamoto, Hiromi; Hossain, Mohammad Kamal; Kitajima, Masahiro

doi:10.1021/nl061650p

Cited by 227 publications

(217 citation statements)

References 37 publications

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“…To date, investigations of the optical properties of LSPR have largely relied on far-field spectroscopic techniques or numerical simulations. Several experimental approaches have been utilized to visualize the near field, including scanning photoionization microscopy, 16,17 scanning near-field optical microscopy, [18][19][20][21] nonlinear luminescence or fluorescent microscopy, 22,23 nonlinear photopolymerization 24,25 and near-field ablation of a substrate. [26][27][28][29] However, these approaches have practical limitations; specifically, both scanning photoionization microscopy and scanning near-field optical microscopy require a scanning process to acquire a near-field image, and their spatial resolution barely reaches the sub-50-nm level.…”

Section: Introductionmentioning

confidence: 99%

Direct imaging of the near field and dynamics of surface plasmon resonance on gold nanostructures using photoemission electron microscopy

et al. 2013

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Localized surface plasmon resonance (LSPR) can be supported by metallic nanoparticles and engineered nanostructures. An understanding of the spatially resolved near-field properties and dynamics of LSPR is important, but remains experimentally challenging. We report experimental studies toward this aim using photoemission electron microscopy (PEEM) with high spatial resolution of sub-10 nm. Various engineered gold nanostructure arrays (such as rods, nanodisk-like particles and dimers) are investigated via PEEM using near-infrared (NIR) femtosecond laser pulses as the excitation source. When the LSPR wavelengths overlap the spectrum of the femtosecond pulses, the LSPR is efficiently excited and promotes multiphoton photoemission, which is correlated with the local intensity of the metallic nanoparticles in the near field. Thus, the local field distribution of the LSPR on different Au nanostructures can be directly explored and discussed using the PEEM images. In addition, the dynamics of the LSPR is studied by combining interferometric time-resolved pump-probe technique and PEEM. Detailed information on the oscillation and dephasing of the LSPR field can be obtained. The results identify PEEM as a powerful tool for accessing the near-field mapping and dynamic properties of plasmonic nanostructures. Keywords: femtosecond laser; local field enhancement; near-field imaging; photoemission electron microscopy; surface plasmon resonance INTRODUCTION Because of the rapid development of nanofabrication techniques, metallic nanostructures that can exhibit localized surface plasmon resonance (LSPR) can be fabricated using several methods. The resonance frequency and amplitude of LSPR on metallic nanostructures are known to depend on the metal materials, shapes, and surrounding media. [1][2][3][4] In addition, the LSPR can confine optical fields in nanoscale space, leading to the so-called local field enhancement effect. These unique properties promote the application of LSPR in many fields, such as surface-enhanced Raman scattering, 5-8 sensing, 1,9,10 plasmonassisted photochemical reactions 4,11,12 and photocurrent generation. [13][14][15] To further understand the LSPR mechanism and to optimize the design of the plasmonic nanostructures for most applications, the near-field properties of the LSPR fields (especially the near-field distribution of the plasmonic nanostructures) must be determined. To date, investigations of the optical properties of LSPR have largely relied on far-field spectroscopic techniques or numerical simulations. Several experimental approaches have been utilized to visualize the near field, including scanning photoionization microscopy, 16,17 scanning near-field optical microscopy, 18-21 nonlinear luminescence or fluorescent microscopy, 22,23 nonlinear photopolymerization 24,25 and near-field ablation of a substrate. [26][27][28][29] However, these approaches have

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Section: Introductionmentioning

confidence: 99%

Direct imaging of the near field and dynamics of surface plasmon resonance on gold nanostructures using photoemission electron microscopy

et al. 2013

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“…Imura et al observed field enhancement in interstitial gaps between nanoparticles by aperture NSOM technique [37]. They investigated Raman spectra and two-photon-induced photoluminescence (TPI-PL) at single dimeric and trimeric aggregates of gold nanospheres by employing Ti:Saphhhire laser (λ = 785 nm).…”

Section: Gap Mode Enhancementmentioning

confidence: 99%

Imaging and spectroscopy through plasmonic nano-probe

Saito

Verma

2009

Eur. Phys. J. Appl. Phys.

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Abstract. This article is a comprehensive review of the subject of near-field nano imaging and spectroscopy by surface plasmon polaritons induced on a metallized probe. The emphasis of the review is on fundamental aspects of plasmon enhancement and near-field spectroscopy, which are categorized as optical antenna structures, polarization properties in near-field, resonance frequency of surface plasmons, etc. Most recent studies that contribute to the understanding and interpretation of these phenomena are highlighted. Applications of near-field optics as newly established analytical tools for biology, materials sciences and plasmonic superlenses are included in the article.

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“…We applied nearfield imaging to assembled gold nanoparticles and succeeded in experimental visualization of localized enhanced optical fields for the first time. 25,26 I felt that this finding might also stimulate a novel research area, as in the standing wave observation of a single nanoparticle mentioned above, and made some efforts to develop the study. As a result we have derived some guidelines for the structures of nanoparticle assemblies to get efficient field enhancement.…”

Section: Introductionmentioning

confidence: 97%

“…Figure 9 shows near-field two-photon excitation images for gold nanosphere dimers using a femtosecond Ti:sapphire laser (wavelength 780 nm) as an excitation source. 25,26 In this measurement the system is illuminated by the near-field radia- AWARD ACCOUNTS Bull. Chem.…”

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confidence: 99%

Nanooptical Studies on Physical and Chemical Characteristics of Noble Metal Nanostructures

Okamoto¹

2013

Bulletin of the Chemical Society of Japan

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Studies on physical and chemical properties of noble metal nanostructures, mainly by near-field optical microscopy and spectroscopy, are described. Near-field optical microscopy provides optical observation methodology with a spatial resolution in nanometer regime beyond the diffraction limit of light. We developed near-field imaging systems equipped with various light sources including ultrashort pulsed lasers, which enables advanced nonlinear and ultrafast near-field measurements as well as conventional near-field imaging. In particular, near-field two-photon excitation imaging was shown to provide a convenient tool to visualize the enhanced optical fields in the vicinities of metal nanostructures. With these methods we demonstrated that nanoscale optical field structures in metal nanostructures can be directly visualized. For single noble metal nanoparticles, such as gold nanorods as typical examples, plasmon standing wave functions were visualized. Ultrafast imaging revealed that sub-picosecond relaxation was reflected on the plasmon wave function images through thermally induced dielectric function changes of the metal. In some cases optical field distribution features arising from the lightning rod effects were observed, depending on the resonance conditions of the incident wavelengths with the plasmon modes. We also found anomalous near-field transmission phenomenon for nanoapertures blocked by nanodisks near the plasmon resonance wavelengths, which arise from the efficient near-field to propagating-field conversion ability of the nanodisks. In assembled nanoparticles, enhanced optical fields at the gap sites between the particles were visualized, which elucidates experimentally the mechanism of surface-enhanced Raman scattering. The characteristic field distributions in many particle assemblies were also observed and analyzed. Through these studies, we established a valuable methodology to investigate optical and spectroscopic properties of metal nanostructures, and the information obtained is available only by optical measurements with high spatial resolution.

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Visualization of Localized Intense Optical Fields in Single Gold−Nanoparticle Assemblies and Ultrasensitive Raman Active Sites

Cited by 227 publications

References 37 publications

Direct imaging of the near field and dynamics of surface plasmon resonance on gold nanostructures using photoemission electron microscopy

Direct imaging of the near field and dynamics of surface plasmon resonance on gold nanostructures using photoemission electron microscopy

Imaging and spectroscopy through plasmonic nano-probe

Nanooptical Studies on Physical and Chemical Characteristics of Noble Metal Nanostructures

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