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

Abstract

We report an investigation of interfacial fluorinated hydrocarbon (carboxylic-fantrip) monolayers by nanoscale imaging using tip-enhanced Raman spectroscopy (TERS) and density functional theory (DFT) calculations. By comparing TERS images of a sub-monolayer prepared by spin-coating and a π-π-stacked monolayer on Au(111) in which the molecular orientation is confined, specific Raman peaks shift and line widths narrow in the transferred LB monolayer. Based on DFT calculations that take into account dispersion corrections and surface selection rules, these specific effects are proposed to originate from π-π stacking and molecular orientation restriction. TERS shows the possibility to distinguish between a random and locked orientation with a spatial resolution of less than 10 nm. This work combines experimental TERS imaging with theoretical DFT calculations and opens up the possibility of studying molecular orientations and intermolecular interaction at the nanoscale and molecular level.

Synthetic 2D Polymers: A Critical Perspective and a Look into the Future

“…Based on this work, Shao et al. have recently applied a combined TERS and density functional theory (DFT) approach to the carboxylic fantrip monomer 12 ( Figure a), synthesized by the King group, and the corresponding polymer 2DP12 . Monomer 12 was spread at an air–water interface to a dense monolayer and subsequently irradiated so as to affect dimerization between the anthracene units of neighboring monomers, which were believed to pack in antiparallel fashion within ftf ‐stacks.…”

“…b) Tip‐enhanced Raman spectrum of the monomer monolayer (purple) and the polymer monolayer (green) with the two signals highlighted in red, which are decisive for the structural claim that 2DP12 is in fact a 2D polymer and not just a covalently cross‐linked monolayer. Reproduced with permission 61b. Copyright 2017, Wiley‐VCH.…”

Two-dimensional Polymers in Microscopy and Spatially Resolved Vibrational Analysis – A Review

“…covalent sheets by mapping an edge of the 2D-polymer with a pixel size of 125 × 125 nm 2 and explaining the preferential formation of dianthracene bridges via [4 + 4]-cycloadditions from the resulting spectra. [13] Several subsequent reports from our laboratory have strengthened the view that ambient TERS is indeed suitable for the chemical identification and characterization of monolayers, including covalently bound sheets such as 2D-polymers, [12,22,36,37] where the appearance of characteristic bands in the Raman spectrum hints at the formation or absence of covalent bonds between monomer molecules (see Fig. 3).…”

Structural Characterization of a Covalent Monolayer Sheet Obtained by Two‐Dimensional Polymerization at an Air/Water Interface

“…To confirm that the observed excimer fluorescence stems exclusively from a monomer, the excitation spectrum of the monomer monolayer on quartz was recorded (see Figure S5). A previous TERS study also shows face‐to‐face stacking of 1 . The occurrence of excimer emission is a reliable indication for polymerizability ,…”