Molecular Perturbation Effects in AFM-Based Tip-Enhanced Raman Spectroscopy: Contact versus Tapping Mode

Abstract

Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for nondestructive and label-free surface chemical characterization at nanometer length scales. However, despite being considered nondestructive, the interaction of the TERS probe used in the analysis can alter the molecular organization of the sample. In this study, we investigate the role of the atomic force microscopy (AFM) feedback (contact mode and tapping mode) on molecular perturbation in TERS analysis of soft samples using a self-assembled monolayer (SAM) of 2-chloro-4-nitrobenzene-1-thiol (Cl-NBT) as a test sample. Surprisingly, the tapping mode shows a consistently higher TERS signal resulting from a minimal perturbation of the Cl-NBT SAM compared to the contact mode. This study provides novel insights into the choice of the correct AFM-TERS operation mode for nanoscale chemical analysis of soft and delicate samples and is expected to expedite the growing application of TERS in this area.

Nanoscale Chemical Imaging of Human Cell Membranes Using Tip‐Enhanced Raman Spectroscopy

“…This is achieved by combining SPM and surface-enhanced Raman spectroscopy (SERS) to exploit the best of both worlds, i.e., the nanoscale spatial resolution of SPM and molecular specificity and sensitivity of SERS. [7] Over the last two decades, TERS has been successfully applied to characterize a variety of different samples, including heterogeneous catalysts, [8] two-dimensional (2D) materials, [9][10][11] polymer blends, [12] organic photovoltaic devices, [13] supported lipid membranes, [14] decomposition chemistry, [15] self-assembled organic monolayers, [16] solid-liquid interfaces, [17] and 2D reactive systems. [18,19] Compared to these applications, studying cell membranes is more challenging because of their chemical complexity, roughness, and low Raman crosssection of membrane components.…”

Nanoscale chemical imaging of human cell membrane using Tip-enhanced Raman spectroscopy

“…This is achieved by combining SPM and surface-enhanced Raman spectroscopy (SERS) to exploit the best of both worlds, i.e., the nanoscale spatial resolution of SPM and molecular specificity and sensitivity of SERS. [7] Over the last two decades, TERS has been successfully applied to characterize a variety of different samples, including heterogenous catalysts, [8] two-dimensional (2D) materials, [9][10][11] polymer blends, [12] organic photovoltaic devices, [13] supported lipid membranes, [14] decomposition chemistry, [15] selfassembled organic monolayers, [16] solid-liquid interfaces, [17] and 2D reactive systems. [18,19] Compared to these applications, studying cell membranes is more challenging because of their chemical complexity, roughness, and the low Raman crosssection of membrane components.…”

Selective Raman Enhancement with Electronic Sensitivity in Tip-Enhanced Raman Spectroscopy

“…11 Moreover, TERS of atomic point contact has attracted much attention recently. 12 A dramatic enhancement of TERS mediated by atomic point contact formation has been observed, resulting from the charge transfer between the tip and molecule. 13,14 As one of the important phenomena included in the chemical effect, the charge transfer leads to changes in the shape, spectral position, and intensity of Raman bands.…”

“…By further decreasing the tip–molecule gaps in the quantum tunneling regime, the vibrational modes of the planar molecule with angstrom-scale resolution have been imaged at the tip–molecule gaps of subatomic scale (∼2 Å) . Moreover, TERS of atomic point contact has attracted much attention recently . A dramatic enhancement of TERS mediated by atomic point contact formation has been observed, resulting from the charge transfer between the tip and molecule. , As one of the important phenomena included in the chemical effect, the charge transfer leads to changes in the shape, spectral position, and intensity of Raman bands. − A selective enhancement of specific Raman modes induced by a single silver atom has also been observed, depending on the charge distribution of the system .…”