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

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. Spitzen‐Forschung: Eine experimentelle und theoretische Studie von Grenzflächenmonolagen auf molekularer Ebene mittels TERS‐Bildgebung und DFT‐Rechnungen unter Berücksichtigung von Dispersionskorrekturen und Oberflächenauswahlregeln wird vorgestellt. Anhand der Rechnungen werden π‐π‐Stapelung und Flexibilitäten in der Molekülorientierung als Ursache für die Differenzen in den TERS‐Spektren der LB‐Monoschicht postuliert.