Dual-Scattering Near-Field Microscope for Correlative Nanoimaging of SERS and Electromagnetic Hotspots

Kusch, Patryk; Mastel, Stefan; Mueller, Niclas S.; Azpiazu, Nieves Morquillas; Heeg, Sebastian; Gorbachev, Roman; Schedin, F.; Hübner, Uwe; Pascual, José; Reich, Stéphanie; Hillenbrand, Rainer

doi:10.1021/acs.nanolett.7b00503

Cited by 52 publications

(63 citation statements)

References 62 publications

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“…Nanoscale mapping of the SERS intensity of the plasmonic dimers using a dual Raman-Rayleigh scattering scanning near-eld optical microscope shows that the SERS enhancement vanishes on top of the nanodiscs. 47 The presence of chemical enhancement at 638 nm should still lead to a strong and detectable 6T signal, which is clearly not the case in the measurements of Fig. 9.…”

Section: Chemical Enhancementmentioning

confidence: 69%

Plasmonic enhancement of SERS measured on molecules in carbon nanotubes

et al. 2017

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We isolated the plasmonic contribution to surface-enhanced Raman scattering (SERS) and found it to be much stronger than expected. Organic dyes encapsulated in single-walled carbon nanotubes are ideal probes for quantifying plasmonic enhancement in a Raman experiment. The molecules are chemically protected through the nanotube wall and spatially isolated from the metal, which prevents enhancement by chemical means and through surface roughness. The tubes carry molecules into SERS hotspots, thereby defining molecular position and making it accessible for structural characterization with atomic-force and electron microscopy. We measured a SERS enhancement factor of 10 on α-sexithiophene (6T) molecules in the gap of a plasmonic nanodimer. This is two orders of magnitude stronger than predicted by the electromagnetic enhancement theory (10). We discuss various phenomena that may explain the discrepancy (including hybridization, static and dynamic charge transfer, surface roughness, uncertainties in molecular position and orientation), but found all of them lacking in enhancement for our probe system. We suggest that plasmonic enhancement in SERS is, in fact, much stronger than currently anticipated. We discuss novel approaches for treating SERS quantum mechanically that appear promising for predicting correct enhancement factors. Our findings have important consequences on the understanding of SERS as well as for designing and optimizing plasmonic substrates.

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Section: Chemical Enhancementmentioning

confidence: 69%

Plasmonic enhancement of SERS measured on molecules in carbon nanotubes

et al. 2017

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“…The typical laser spot sizes in a Raman experiment are several hundred nanometers in diameter. Some of us recently introduced a SNOM for inelastically scattered light that measured a SERS hot spot 75 nm in diameter (lateral size perpendicular to the dimer axis) for gold dimers similar to those studied here [18]. As an alternative approach, we obtain an upper limit for the SERS hot spot by spatially mapping the Raman response of graphene on the dimer in real space.…”

Section: B Localization Of the Near-field Enhancementmentioning

confidence: 85%

“…Common techniques to characterize the spatial distribution of the local near-field of a SERS hot spot are electron energy loss spectroscopy [15], scattering optical near-field microscopy (SNOM), and dual s-SNOM for uncovered particles [16][17][18]. The far-field resonance, in contrast, is often investigated by dark-field spectroscopy measuring the elastically scattered light [19].…”

Section: Introductionmentioning

confidence: 99%

Graphene as a local probe to investigate near-field properties of plasmonic nanostructures

et al. 2018

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Light interacting with metallic nanoparticles creates a strongly localized near-field around the particle that enhances inelastic light scattering by several orders of magnitude. Surface-enhanced Raman scattering describes the enhancement of the Raman intensity by plasmonic nanoparticles. We present an extensive Raman characterization of a plasmonic gold nanodimer covered with graphene. Its two-dimensional nature and energy-independent optical properties make graphene an excellent material for investigating local electromagnetic near-fields. We show the localization of the near-field of the plasmonic dimer by spatial Raman measurements. Energy-and polarization-dependent measurements reveal the local near-field resonance of the plasmonic system. To investigate the far-field resonance we perform dark-field spectroscopy and find that near-field and far-field resonance energies differ by 170 meV, much more than expected from the model of a damped oscillator (40 meV).

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“…hot spots 1-10 nm) 16 , the methods are strictly separated into near and far-eld optical methods. Near-eld optical tip-based methods like s-SNOM-SERS 17 and functionalised TERS 18,19 or electron microscopy-based methods like PEEM 19 and STEM/EELS 20 as well as super resolution-imaging 16,21 enable nanoscale mapping of localised surface plasmon resonances (LSPRs) 20 , the electromagnetic eld enhancement [17][18][19] or of individual Raman bands 16,17,21 in hot spots and are important tools in fundamental research to study structural-functional relationships. Due to the high equipment expense, di cult handling and a low versatility these methods are however not common in applied analytical SERS research.…”

Section: Introductionmentioning

confidence: 99%

SERS background imaging – A versatile tool towards more reliable SERS analytics

Ebersbach

Münchberg

Freier

2020

Preprint

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Surface-enhanced Raman scattering (SERS) is a highly selective and sensitive straightforward analytical method, which is however not yet established in routine analysis due to a lack of reliability and reproducibility. To address this limitation, we show the distinct correlation of the ever-present but often neglected broad SERS background continuum with the SERS signal intensity of the analyte and how to exploit this correlation for an easy-to-handle, automatable and more reliable SERS measurement. First, fast and high-contrast imaging of the SERS substrate is performed for hot spot localisation utilizing the SERS background. Subsequently, highly enhanced SERS spectra are recorded at the centre of these spots. Furthermore, we correlate our SERS background imaging with other optical imaging modalities and electron microscopy to assess structure-property relationships. Monte Carlo simulations based on actual measurements illustrate the sampling error of a conventional SERS experiment and the advantages our method provides.

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Dual-Scattering Near-Field Microscope for Correlative Nanoimaging of SERS and Electromagnetic Hotspots

Cited by 52 publications

References 62 publications

Plasmonic enhancement of SERS measured on molecules in carbon nanotubes

Plasmonic enhancement of SERS measured on molecules in carbon nanotubes

Graphene as a local probe to investigate near-field properties of plasmonic nanostructures

SERS background imaging – A versatile tool towards more reliable SERS analytics

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