Optical Origin of Subnanometer Resolution in Tip-Enhanced Raman Mapping

Zhang, Chao; Chen, Baoqin; Li, Zhiyuan

doi:10.1021/acs.jpcc.5b02653

Cited by 88 publications

(98 citation statements)

References 40 publications

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“…Upon inclusion of the molecular selfinteraction, the size of the plasmonic field was found to be further reduced. 27 From current simulations, the size of the SCP seems to play the decisive role in the subnanometer Raman images. However, the increase in the nonlinear contribution to the total intensity is on the other hand an effective way to further improve the resolution of the Raman image.…”

mentioning

confidence: 77%

Theoretical Modeling of Plasmon-Enhanced Raman Images of a Single Molecule with Subnanometer Resolution

et al. 2015

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Under local plasmonic excitation, Raman images of single molecules can now surprisingly reach subnanometer resolution. However, its physical origin has not been fully understood. Here we report a quantum-mechanical description of the interaction between a molecule and a highly confined plasmonic field. We show that when the spatial distribution of the plasmonic field is comparable to the size of the molecule, the optical transition matrix of the molecule becomes dependent on the position and distribution of the plasmonic field, resulting in a spatially resolved high-resolution Raman image of the molecule. The resonant Raman image reflects the electronic transition density of the molecule. In combination with first-principles calculations, the simulated Raman image of a porphyrin derivative adsorbed on a silver surface nicely reproduces its experimental counterpart. The present theory provides the basic framework for describing linear and nonlinear responses of molecules under highly confined plasmonic fields.

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confidence: 77%

Theoretical Modeling of Plasmon-Enhanced Raman Images of a Single Molecule with Subnanometer Resolution

et al. 2015

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“…Here, we use the self‐consisted model of the near‐field interaction to take into account the depolarization related to the orientation of molecule symmetry axes. The TERS intensity in far‐field zone reads as

I_{TERS} ((), ν) ~ {|{bolde}_{s}^{T} {\overset{R}{true}}_{ν}^{*} {bolde}_{e}|}^{2},

where

{\overset{true\leftrightarrow}{R}}_{ν}^{*}

is a Raman tensor of the vibration mode ν modified by the optical near field of a tip‐substrate gap, e e and e s are the unit polarization vectors of the incident and scattered fields, and symbol ( g ) T stands for the transpose.…”

Section: Modelmentioning

confidence: 99%

Tip‐modified Raman tensor of a porphine molecule

Gazizov

Салахов

Kharintsev

2019

J Raman Spectroscopy

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It is well established that bringing a plasmonic tip into the proximity of a single molecule inevitably affects its state and vice versa. Due to the enhanced light–matter interaction, spectroscopic information on the molecule captured with tip‐enhanced Raman spectroscopy (TERS) can noticeably differ on that coming from standard far‐field Raman spectroscopy. In this work, we develop a theoretical approach for calculating Raman tensors of a single oblate molecule that takes near‐field depolarization effects into account. Generally speaking, a tip‐dressed molecule exhibits the modified polarizability and, therefore, the Raman tensors. It is reported that the TERS technique can be used to reconstruct Raman tensors of vibration modes of anisotropic single molecules. The symmetric and antisymmetric modes of the molecules nearby a plasmonic tip are enhanced differently. In order to unravel the Raman tensors, two near‐field depolarization factors are necessarily introduced for the oblate molecule. As an example, we consider a free base porphine molecule as a test molecule to demonstrate the enhancement of intensities of Raman bands assigned to different symmetries. Also, we demonstrate an experimental way how to measure the depolarization factors using an ensemble of randomly oriented molecules. We believe that our finding will be beneficial to the interpretation of TERS measurements of single molecules.

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“…Creation of an "atomic-scale hot spot" has also been proposed [48]. In addition, multiple elastic scattering of light between molecular dipoles adsorbed on the surface has been proposed to explain the improved signal intensity and TERS spatial resolution [49].…”

Section: Understanding Tersmentioning

confidence: 99%

Nanoscale Insights into Enhanced Raman Spectroscopy

Rzeznicka¹,

Horino²

2018

Raman Spectroscopy

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Enhanced Raman spectroscopies, such as surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS), are based on the amplification of intrinsically weak Raman signals of a molecule by metallic nanostructures. The main enhancement is attributed to electromagnetic enhancement. Chemical effects, such as formation of a surface complex, or a charge-transfer complex, co-adsorbed anion effect, also add to the enhancement of the signal. Using SERS, it has been difficult to study details of chemical enhancement and polarization effects due to limited optical resolution of the technique and usage of roughened metal surfaces. These obstacles were overcome with the development of the TERS technique. TERS has extended Raman spectroscopy into the nanoscale region. In this chapter, nanoscale insights into surface chemistry that lead to Raman signal enhancement are described. The effect of molecular binding and orientation as well as commonly used in SERS chloride activation of metal surfaces is discussed. Finally, we describe the future prospects of TERS and the challenges that keep us from harnessing the full potential of the technique.

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Optical Origin of Subnanometer Resolution in Tip-Enhanced Raman Mapping

Cited by 88 publications

References 40 publications

Theoretical Modeling of Plasmon-Enhanced Raman Images of a Single Molecule with Subnanometer Resolution

Theoretical Modeling of Plasmon-Enhanced Raman Images of a Single Molecule with Subnanometer Resolution

Tip‐modified Raman tensor of a porphine molecule

Nanoscale Insights into Enhanced Raman Spectroscopy

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