Scanning-probe Raman spectroscopy with single-molecule sensitivity

Neacsu, Catalin C.; Dreyer, J.; Behr, Nicolas; Raschke, Markus B.

doi:10.1103/physrevb.73.193406

Cited by 244 publications

(244 citation statements)

References 27 publications

(21 reference statements)

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“…For the excited SPR state of the Ag nanostructure, the dipole moment is expected to be very large, and the local electric field (E 2 ) is enhanced enormously by the SPR oscillation. The combination of these two factors will result in a huge enhancement factor β, similar to the cases of surface-enhanced Raman spectroscopy (SERS; refs 20,21) and tip-enhanced Raman spectroscopy (TERS; refs [22][23][24][25]. In other words, the SPR peak of EELS should thus be significantly enhanced, and its transition probability should be quadratically dependent on the external field, as clearly confirmed by our experimental observations.…”

supporting

confidence: 61%

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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supporting

confidence: 61%

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

Liu

Zhang

et al. 2014

Nature Phys

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“…Raman polarisation behaviour and sudden temporal spectral changes supported the evidence that Raman signal was being detected from a single molecule [117]. About a decade later single molecule sensitivity on a length scale of 10 nm was reported using TERS [118,119]. Using AFM-TERS, Neacsu et al probed single molecules of malachite green adsorbed on a metal surface [118].…”

Section: Single Molecule Detectionmentioning

confidence: 73%

“…About a decade later single molecule sensitivity on a length scale of 10 nm was reported using TERS [118,119]. Using AFM-TERS, Neacsu et al probed single molecules of malachite green adsorbed on a metal surface [118]. The detection of an individual molecule was supported by the observation of temporal variations in the relative intensities of the peaks.…”

Section: Single Molecule Detectionmentioning

confidence: 91%

Tip-enhanced Raman spectroscopy: principles and applications

et al. 2015

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This review provides a detailed overview of the state of the art in tip-enhanced Raman spectroscopy (TERS) and focuses on its applications at the horizon including those in materials science, chemical science and biological science. The capabilities and potential of TERS are demonstrated by summarising major achievements of TERS applications in disparate fields of scientific research. Finally, an outlook has been given on future development of the technique and the mechanisms of achieving high signal enhancement and spatial resolution.

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“…This could explain the different results reported by two independent groups, in which the Raman spectra from similar molecules were very different. [10,11] The tips used by Neascu et al [11] have an apex diameter r ∼ 10 nm, while in the case of Domke et al, [10] r was >20 nm. This variety could cause a twofold difference in the field enhancement and consequently a fourfold difference in the heat generated by ohmic loss.…”

Section: Tip Sharpness Influences the Field Enhancementmentioning

confidence: 99%

Local field enhancement of an infinite conical metal tip illuminated by a focused beam

Zhang

Cui

Martin

2009

J Raman Spectroscopy

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We present a systematic numerical investigation of conical metal tips which are commonly used in tip-enhanced Raman spectroscopy (TERS). Different from previous studies, we focus on how the tip length and the illumination condition influence the local field enhancement at the tip apex, and provide a useful reference for real experiments. In particular, we show that the type of illumination has a dramatic influence on the field enhancement: a localized illumination spot -as used in experiments -producing a very different response than a plane wave illumination -as usually used in previous models. Also, the effect of the different geometrical parameters, such as the sharpness of the tip apex and the cone angle, provides guidance to optimize the tip design. Finally, we investigate the influence of the substrate and compare numerical data with results deduced from a simplified model, finding good agreement. This brings new insights into the enhancement mechanism of TERS.

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Scanning-probe Raman spectroscopy with single-molecule sensitivity

Cited by 244 publications

References 27 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

Tip-enhanced Raman spectroscopy: principles and applications

Local field enhancement of an infinite conical metal tip illuminated by a focused beam

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