A classical description of subnanometer resolution by atomic features in metallic structures

Abstract

Recent experiments have evidenced sub-nanometer resolution in plasmonic-enhanced probe spectroscopy. Such a high resolution cannot be simply explained using the commonly considered radii of metallic nanoparticles on plasmonic probes. In this contribution the effects of defects as small as a single atom found on spherical plasmonic particles acting as probing tips are investigated in connection with the spatial resolution provided. The presence of abundant edge and corner sites with atomic scale dimensions in crystalline metallic nanoparticles is evident from transmission electron microscopy (TEM) images. Electrodynamic calculations based on the Finite Element Method (FEM) are implemented to reveal the impact of the presence of such atomic features in probing tips on the lateral spatial resolution and field localization. Our analysis is developed for three different configurations, and under resonant and non-resonant illumination conditions, respectively. Based on this analysis, the limits of field enhancement, lateral resolution and field confinement in plasmon-enhanced spectroscopy and microscopy are inferred, reaching values below 1 nanometer for reasonable atomic sizes.

Nanoscale Chemical Imaging of Interfacial Monolayers by Tip‐Enhanced Raman Spectroscopy

“…When compressing the film at low pressure,aface-to-face stacking structure could be formed, and uniform hexagonal pores with as ize of circa 24.7 are expected ( Figure 1D). Note that this additional water layer could act as an insulating layer between the compound 1 ML and the Au(111) surface,w hich avoids interferences from moleculesubstrate interactions and makes for areasonable system for studying intermolecular interactions by TERS.A ccording to recent work, [22] the radius of the TERS enhanced region can be considerably smaller that the radius of the TERS probe. Note that this additional water layer could act as an insulating layer between the compound 1 ML and the Au(111) surface,w hich avoids interferences from moleculesubstrate interactions and makes for areasonable system for studying intermolecular interactions by TERS.A ccording to recent work, [22] the radius of the TERS enhanced region can be considerably smaller that the radius of the TERS probe.…”

PIP2 Phospholipid‐Induced Aggregation of Tau Filaments Probed by Tip‐Enhanced Raman Spectroscopy

“…[18] Interestingly,d espite the approximately 30 nm curvature radius of the TERS probe apex, the fiber characterization could be obtained with al ateral spatial resolution lower than 10 nm ( Figures S2 and S3);t his is probably because of the roughness of the metal coating and the formation of ametal nanoparticle at the apex, which is in line with recent reports where the possibility to reach subnanometer resolution was even demonstrated in the presence of defects at the noble metal tip end. [20] The geometry and the electromagnetic properties of this nanoparticle defines its TERS activity,which may change from one TERS probe to another. This dependence,i na ddition to the sensitivity of TERS signals to molecular orientation and gradient-field effects,e xplains the plethora of TERS signatures with variable intensities reported for protein (amyloid especially) fibers described in the literature, [18,[21][22][23][24][25] and for K18 + POPC:PIP 2 and K18 + HS fibers in this study.Because of this intrinsic intensity variability of TERS bands,areliable comparison between TERS features identifiable in the two samples often requires the statistical investigation of their relative abundance in the spectra.…”

Classical and ab Initio Plasmonics Meet at Sub-nanometric Noble Metal Rods

“…Thus, it has been recently shown that sub-nanometric inhomogeneities in field-enhancement patterns in plasmonic gaps [24][25][26] can be described, at least qualitatively, through classical optics calculations. On the other hand, the physical mechanisms behind the failure of classical predictions for the LSPR frequencies in compact nanoparticles (with sizes in the ∼ 1-3 nm range) are well understood.…”