Vibrational and electronic excitations in gold nanocrystals

Bayle, Maxime; Combe, Nicolas; Sangeetha, N.; Viau, Guillaume; Carles, R.

doi:10.1039/c4nr02185a

Cited by 41 publications

(85 citation statements)

References 53 publications

(92 reference statements)

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“…In particular, the background follows Bose statistics and that comforts unambiguously its interpretation as inelastic scattering by electron-hole pair excitations [14,17,19,20,22,43]. In particular, Portales et al have exactly drawn the same conclusions by analyzing Raman scattering by Ag-NCs embedded in SiO 2 but elaborated within a very different technique [17].…”

Section: A Stokes and Anti-stokes Electronic Raman Scatteringmentioning

confidence: 70%

“…11(a)] and ligands. When the laser excitation is tuned from λ i = 532 to 638 nm, near the maximum of the LSPR wavelength (λ LSPR 630 nm [20]), one notes in Fig. 11(b) that the response of all excitations displays a similar enhancement, but that the corrected intensity of the inelastic signal does not goes to zero at zero-frequency shift.…”

Section: E Plasmon-resonant Raman Scattering Versus Hot Luminescencementioning

confidence: 99%

“…The link between SERS and background signal is evidenced by the same resonant behavior versus excitation wavelength [20,29], the same dependence on tip-sample distance in TERS experiments [5], and same time dependence for the blinking phenomenon [27]. Until now, no model has been proposed to quantitatively analyze the whole spectral shape of the background and in particular its correlation with the surface geometry.…”

Section: Introductionmentioning

confidence: 99%

“…In particular, this maximum occurs at the free surface of the bilayer [19]. To enhance the interaction between electrons in the M-NCs and polaritons in the dielectric, it is thus particularly relevant to place these NCs at the near vicinity of this free surface [19,20]. As a consequence, two techniques have been used: either (a) low-energy implantation of Ag + ions leading to the formation of a single plane of Ag-NCs embedded at few nanometer distance beneath the free surface [37], or (b) deposition on this surface of assemblies of colloidal Au-NCs.…”

Section: B Optical Measurements: Original Setup and Proceduresmentioning

confidence: 99%

“…It has been observed that the shape of this signal is related to the size of the metal particles [16], and a linear dependence of the frequency of its maximum intensity versus the inverse of the size of silver nanocrystals (Ag-NCs) has been demonstrated [17]. More recently, the background dependence on local morphology and surface roughness has been once more underlined [18], and a direct link between the line shape of the background and the mean diameter of the NCs assembly has been put forward using a phenomenological approach [19,20].…”

Section: Introductionmentioning

confidence: 99%

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Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

et al. 2015

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Since the discovery of surface-enhanced Raman scattering (SERS) 40 years ago, the origin of the "background" that is systematically observed in SERS spectra has remained questionable. To deeply analyze this phenomenon, plasmon-resonant Raman scattering was recorded under specific experimental conditions on a panel of composite multilayer samples containing noble metal (Ag and Au) nanoparticles. Stokes, anti-Stokes, and wide, including very low, frequency ranges have been explored. The effects of temperature, size (in the nm range), embedding medium (SiO 2 , Si 3 N 4 , or TiO 2 ) or ligands have been successively analyzed. Both lattice (Lamb modes and bulk phonons) and electron (plasmon mode and electron-hole excitations) dynamics have been investigated. This work confirms that in Ag-based nanoplasmonics composite layers, only Raman scattering by single-particle electronic excitations accounts for the background. This latter appears as an intrinsic phenomenon independently of the presence of molecules on the metallic surface. Its spectral shape is well described by revisiting a model developed in the 1990s for analyzing electron scattering in dirty metals, and used later in superconductors. The g s factor, that determines the effective mean-free path of free carriers, is evaluated, g expt s = 0.33 ± 0.04, in good agreement with a recent evaluation based on time-dependent local density approximation g theor s = 0.32. Confinement and interface roughness effects at the nanometer range thus appear crucial to understand and control SERS enhancement and more generally plasmon-enhanced processes on metallic surfaces.

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Section: A Stokes and Anti-stokes Electronic Raman Scatteringmentioning

confidence: 70%

Section: E Plasmon-resonant Raman Scattering Versus Hot Luminescencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: B Optical Measurements: Original Setup and Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

et al. 2015

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Surface‐Enhanced Raman Spectroscopy Characterization of Salt‐Induced Aggregation of Gold Nanoparticles

2017

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Low-frequency (< 300 cm À1 )v ibrational interactions between gold surfaces and dissolved halidesi nw ater werei nvestigated by surface-enhanced Ramans pectroscopy (SERS). Experiments with NaF,N aCl, NaBr,a nd NaI salts indicate that the Raman shifts of the Au-X À SERS bandsc orrelate with the bond strength of the corresponding covalent interaction. These lowfrequency SERS bands open up new meanst oi nvestigate the aggregation of nanoparticles in aqueous environments.Herein we illustrate that aggregationo fg old nanoparticles and their interactions with dissolved halidesc an be studied by surface-enhanced Ramans pectroscopy (SERS). Raman spectroscopy detects inelastically scattered photons that result from induced dipole interactions. [1] Only avery smallfraction of the incident photons are scattered inelastically,t hus leading to characteristically weak Ramans ignals. [2] Although elemental gold inelastically scatters incident photons and is thus Raman active, the resulting signal is generally too low to be detectable under typical laser intensities and acquisition times. Halides such as F À ,C l À ,B r À ,a nd I À undergo strong interactions with the gold surface. [3] These electron rich interactions can produce as trongR amans ignal if located in closep roximityt oa no ptical enhancer (such as an oblem etal surface with nano-topographical features). [4] Noble metal nanoparticles such as gold nanoparticles (AuNPs)e nhancev ibrational Raman bands due to surface plasmon effects. [5] Individual AuNPs provide negligible enhancement. However,a ss hown herein, nanoparticle aggregation induced by salt addition enables electromagnetic coupling within AuNP aggregates that gives rise to nano-structural 'hotspots' that exhibit higherSERS enhancements than individual nanoparticles. [6] To date, there have only been limited studies examining the SERS activity of Au-X À (where X À is a halide)i nteractions because they give rise to Raman bands with low wavenumber (< 300 cm À1 )v ibrational modes. [7] However,t his low frequency range contains valuable information about the relative bond-energies of halide-metal interactions. [4,[7][8] We first utilized SERS to characterize the interaction between gold and dissolved aqueous halides. 2D scans of NaX droplets on ac ommercial gold SERS substrate (Klarite )w ere collected as described in the SI. Briefly,a liquots of NaX salts (X = F, Cl, Br, I) were deposited and dried on the Klarite surface. Ac onfocal Ramans pectrometer was then rastered across the substrate to produce a2 Dm ap. Maps obtained for as eries of NaX salts illustrate that the Au-X À interactions are readily detectible via SERS ( Figure 1A). We note that solution phase Au-X À interactions do not generate sufficient signal for them to be detectable by conventionalR amans pectroscopy.T he Ramans ignal intensity is proportionalt ot he scattering path length, and for surfaceinteractions, such path lengths are generally very short, resultingi na10 5 fold signal loss relative to bulk samples. [9] The SERS substrate not o...

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Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au₃₈(PET)₂₄ and Au₃₈₋_xAg_x(PET)₂₄

Krishnadas

Baghdasaryan

Kazan

et al. 2021

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Distinct Raman spectroscopic signatures of the metal core of atomically precise, ligand‐protected noble metal nanoclusters are reported using Au38(PET)24 and Au38−xAgx(PET)24 (PET = 2‐phenylethanethiolate, ‐SC2H4C6H5) as model systems. The fingerprint Raman features (occurring <200 cm−1) of these clusters arise due to the vibrations involving metal atoms of their Au23 or Au23−xAgx cores. A distinct core breathing vibrational mode of the Au23 core has been observed at 90 cm−1. Whereas the breathing mode shifts to higher frequencies with increasing Ag content of the cluster, the vibrational signatures due to the outer metal‐ligand staple motifs (between 200 and 500 cm−1) do not shift significantly. DFT calculations furthermore reveal weak Raman bands at higher frequencies compared to the breathing mode, which are associated mostly with the rattling of two central gold atoms of the bi‐icosahedral Au23 core. These vibrations are also observed in the experimental spectrum. The study indicates that low‐frequency Raman spectra are a characteristic fingerprint of atomically precise clusters, just as electronic absorption spectroscopy, in contrast to the spectrum associated with the ligand shell, which is observed at higher frequencies.

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Vibrational and electronic excitations in gold nanocrystals

Cited by 41 publications

References 53 publications

Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

Surface‐Enhanced Raman Spectroscopy Characterization of Salt‐Induced Aggregation of Gold Nanoparticles

Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au₃₈(PET)₂₄ and Au₃₈₋_xAg_x(PET)₂₄

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Vibrational and electronic excitations in gold nanocrystals

Cited by 41 publications

References 53 publications

Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

Plasmon-resonant Raman spectroscopy in metallic nanoparticles: Surface-enhanced scattering by electronic excitations

Surface‐Enhanced Raman Spectroscopy Characterization of Salt‐Induced Aggregation of Gold Nanoparticles

Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au38(PET)24 and Au38−xAgx(PET)24

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Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au₃₈(PET)₂₄ and Au₃₈₋_xAg_x(PET)₂₄