Probing the Structure of Single-Molecule Surface-Enhanced Raman Scattering Hot Spots

Camden, Jon P.; Dieringer, Jon A.; Wang, Yingmin; Masiello, David J.; Marks, Lawrence D.; Schatz, George C.; Duyne, Richard P. Van

doi:10.1021/ja8051427

Cited by 872 publications

(844 citation statements)

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“…5a-c. In other words, the thinner Ag samples (10 nm and 30 nm) employed here contain more 'hot spots' , which are known to favour the generation of the strong plasmon fields, as often demonstrated in the SERS measurements 20,21 . The lack of a sufficient number of 'hot spots' in the thick Ag film (100 nm) thus makes it incapable of producing nonlinear electron scattering.…”

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confidence: 85%

Nonlinear inelastic electron scattering revealed by plasmon-enhanced electron energy-loss spectroscopy

Liu

Zhang

et al. 2014

Nature Phys

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Electron energy-loss spectroscopy is a powerful tool for identifying the chemical composition of materials [1][2][3][4][5] . It relies mostly on the measurement of inelastic electrons, which carry specific atomic or molecular information. Inelastic electron scattering, however, has a very low intensity, often orders of magnitude weaker than that of elastically scattered electrons. Here, we report the observation of enhanced inelastic electron scattering from silver nanostructures, the intensity of which can reach up to 60% of its elastic counterpart. A home-made scanning probe electron energy-loss spectrometer 6 was used to produce highly localized plasmonic excitations, significantly enhancing the strength of the local electric field of silver nanostructures. The intensity of inelastic electron scattering was found to increase nonlinearly with respect to the electric field generated by the tip-sample bias, providing direct evidence of nonlinear electron scattering processes. Figure 1a gives a schematic drawing of the scanning probe electron energy-loss spectroscopy (SP-EELS) technique used in this study, the details of which can be found elsewhere 6 . Briefly, it consists of a tip-sample system and a toroidal electron energy analyser (TEEA). The experimental arrangement is sketched in Fig. 1b. A tip made from a 0.42 mm tungsten wire by electrochemical etching is approached to a distance of micrometres from the grounded sample surface, which is prepared by evaporating a 30 nm thin film of Ag on freshly cleaved highly ordered pyrolytic graphene (HOPG). Silver structures with dimensions of tens of nanometres are observed on the sample surface, as illustrated in the inset of Fig. 1b. Electrons are field-emitted from the tip when a negative tip voltage V t of hundreds of volts is applied, and surface plasmon resonance (SPR) of the Ag nanostructures is excited by the field-emission electrons under a strong electric field introduced by the tip-sample bias. The backscattered electrons from the sample surface are collected and analysed by the TEEA. In this way the electron energy-loss spectroscopy (EELS) under a certain tip-sample distance and tip voltage can be acquired.It should be mentioned that EELS has been applied for decades to detect surface plasmons 1,7-14 , and in combination with a scanning transmission electron microscope (STEM) it is capable of mapping the spatial variation of SPRs at the nanoscale 11-14 . The energy-loss feature of Ag systems has been studied extensively by EELS, including low-energy backscattering EELS (refs 1,10) and high-energy transmission EELS (refs 11,13,14). A typical EELS spectrum of Ag nanostructures is shown in Fig. 1c, which was obtained at a tip-sample distance of 114 µm with a tip voltage of −246 V and a sample current of 10 pA. The energy-loss peak located at about 3.7 eV is associated with the SPR excitation of Ag. Our spectrum is in excellent agreement with those reported by Palmer's group, who also used scanning probe electron spectroscopy to investigate the EELS of Ag sur...

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confidence: 85%

Nonlinear inelastic electron scattering revealed by plasmon-enhanced electron energy-loss spectroscopy

Liu

Zhang

et al. 2014

Nature Phys

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“…[1][2][3] The close approach (i.e., within 2.5 times the particle diameter) of two nanoparticles leads to interaction of their localized surface plasmon resonances. This interaction has been exploited in a number of applications, including surface-enhanced Raman spectroscopy (SERS) to allow the detection of single molecules, [4][5][6][7][8] the Universal Plasmon Ruler which has been used to measure the distance between two metal nanoparticles in biological systems, [9][10][11][12] and in optoelectronics where the near field coupling of nanoparticles spaced less than two diameters apart results in the transmission of light energy down a nanoparticle chain [13][14][15][16][17] or through an array. 18 This near field interaction between nanoparticles is highly distance-dependent and has been described using an electromagnetic analogue of molecular orbital theory, the plasmon hybridization model, which highlights the asymmetry introduced by dimer formation.…”

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confidence: 99%

Plasmon Coupling of Gold Nanorods at Short Distances and in Different Geometries

et al. 2009

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The experimentally determined scattering spectra of discrete, crystalline, gold nanorod dimers arranged side-to-side, end-to-end, at right angles in different orientations and also with longitudinal offsets are reported along with the electron micrographs of the individual dimers. The spectra exhibit both red-and blue-shifted surface plasmon resonances, consistent with the plasmon hybridization model. However, the plasmon coupling constant for gold dimers with less than a few nanometers separation between the particles does not obey the exponential dependence predicted by the Universal Plasmon Ruler equation. The experimentally determined spectra are compared with electrodynamic calculations and the interactions between the individual rod plasmons in different dimer orientations are elucidated.

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“…Linear molecular spectroscopies such as Raman and fluorescence have found their plasmonenhanced analogs in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence; both are now routinely realized in the extreme limit of singlemolecule detection; see, e.g., Refs. [7,8,9,10]. And plasmon-enhanced versions of n-wave mixing and hyperRaman scattering [11,12], as well as other nonlinear spectroscopies, are rapidly being explored as ultrasensitive probes of molecular structure complementary to those linear.…”

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confidence: 99%

On the linear response and scattering of an interacting molecule-metal system

Masiello

Schatz

2010

The Journal of Chemical Physics

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A many-body Green's function approach to the microscopic theory of plasmon-enhanced spectroscopy is presented within the context of localized surface-plasmon resonance spectroscopy and applied to investigate the coupling between quantum-molecular and classical-plasmonic resonances in monolayer-coated silver nanoparticles. Electronic propagators or Green's functions, accounting for the repeated polarization interaction between a single molecule and its image in a nearby nanoscale metal, are explicitly computed and used to construct the linear-response properties of the combined molecule-metal system to an external electromagnetic perturbation. Shifting and finite lifetime of states appear rigorously and automatically within our approach and reveal an intricate coupling between molecule and metal not fully described by previous theories. Self-consistent incorporation of this quantum-molecular response into the continuum-electromagnetic scattering of the molecule-metal target is exploited to compute the localized surface-plasmon resonance wavelength shift with respect to the bare metal from first principles.Ever increasing experimental interest in a variety of plasmon-enhanced molecular spectroscopies has provided impetus for the development of a corresponding assortment of theoretical descriptions of these phenomena [1,2,3,4,5,6]. Linear molecular spectroscopies such as Raman and fluorescence have found their plasmonenhanced analogs in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence; both are now routinely realized in the extreme limit of singlemolecule detection; see, e.g., Refs. [7,8,9,10]. And plasmon-enhanced versions of n-wave mixing and hyperRaman scattering [11,12], as well as other nonlinear spectroscopies, are rapidly being explored as ultrasensitive probes of molecular structure complementary to those linear. Conversely, spectroscopy of the plasmon itself, either localized to metal particles or propagating across metal surfaces [13], and embedded within a potentially resonant molecular environment [14,15] forms the basis for yet another promising direction of related research. Outside of the laboratory, the challenge remains to develop theories that are rich enough to describe the basic physics relevant to each, yet are simultaneously practical enough to implement numerically for real systems of current experimental interest.Here we present the first numerical implementation of a new and general many-body Green's function formalism that is capable of describing a variety of plasmonenhanced linear spectroscopies and apply it to model recent localized surface-plasmon resonance (LSPR) spectroscopy and molecular sensing experiments. LSPR spectroscopy is highly sensitive to the small refractive-index changes of the environment surrounding nanoscale metal particles and has been reported to detect the presence of as few as tens to hundreds of nearby molecules [16,17]. This sensitivity arises from the resonant coupling of incident light to the collective oscillation of conduction elect...

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Probing the Structure of Single-Molecule Surface-Enhanced Raman Scattering Hot Spots

Cited by 872 publications

References 15 publications

Nonlinear inelastic electron scattering revealed by plasmon-enhanced electron energy-loss spectroscopy

Nonlinear inelastic electron scattering revealed by plasmon-enhanced electron energy-loss spectroscopy

Plasmon Coupling of Gold Nanorods at Short Distances and in Different Geometries

On the linear response and scattering of an interacting molecule-metal system

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