Direct monitoring of plasmon resonances in a tip-surface gap of varying width

Abstract

We have studied the dependence of tip-enhanced Raman (TER) spectra composed of discrete Raman lines and an intense Lorentzian-shaped background on varying interparticle distance. For increasing tip-sample separation, we observe a remarkable blueshift of the background maximum that is ascribed to an energy shift of the localized surface plasmon resonance. In addition, we report on a steep background and Raman band intensity decrease within 5–10 nm tip retraction that highlights the underlying near-field enhancement mechanism of TER spectroscopy

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

“…The agreement with the model is excellent as shown in Figs 6,7,8,9, and 11(a). Our modeling of the electron-hole spectra contrasts with all previous attempts that do not consider the whole frequency range [5,21].…”

“…The impressive enhancement, up to 10 8 , of the vibrational fingerprint of molecules located at specific sites ("hot spots") on the surface of metallic particles is responsible of a further huge development of Raman spectrometry [2]. The possibilities of acquiring vibrational information down to a single molecule [3,4] and controlling a single hot spot with high spatial resolution using tip-enhanced Raman spectroscopy (TERS) [5][6][7][8] have led to new insights on local mechanisms at the origin of SERS. From the beginning, these mechanisms have been commonly referred to as electromagnetic (EM) [9] when due to local electromagnetic inductive effects, or chemical (CM) [10] when due to resonant charge transfer effects, the first one giving the largest contribution to the enhancement factor [11].…”

“…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.…”

Performing tip‐enhanced Raman spectroscopy in liquids

“…The increase in background signal intensity has been recently attributed to photons emitted from annihilated inelastically scattered localized surface plasmons. [54] The TER bands observed at 1576, 1073, 1023, 1000, and 690 cm −1 can be clearly assigned to PhS (for assignments see Table 2). The wavenumbers agree well with the vibrational spectra of PhS on Au surfaces and Ag thiophenolate salts.…”

Imaging and spectroscopy through plasmonic nano-probe

“…The resonance condition of surface plasmon is also affected by the gap distance. Pettinger et al reported [43] the dependence of TERS composed of discrete Raman lines and the intense Lorentzian-shaped background by varying tip-substrate gap in STM setup. Remarkable blue shift of the background, which means the energy shift of the localized surface plasmon resonance, was observed.…”