Molecular-Scale Chemical Imaging of the Orientation of an On-Surface Coordination Complex by Tip-Enhanced Raman Spectroscopy

Abstract

Metal–organic coordination structures at interfaces play an essential role in many biological and chemical systems. Understanding the molecular specificity, orientation, and spatial distribution of the coordination complexes at the nanometer scale is of great importance for effective molecular engineering of nanostructures and fabrication of functional devices with controllable properties. However, fundamental properties of such coordination systems are still rarely studied directly. In this work, we present a spectroscopic approach on the basis of tip-enhanced Raman spectroscopy (TERS) to investigate cobalt­(II) tetraphenyl-porphyrine coordination species on the scale of a single molecule under ambient conditions. Coordination species anchored on gold surfaces modified with pyridine thiol self-assembled monolayers can be spectroscopically distinguished and mapped with ca. 2 nm resolution. In addition, in combination with density functional theory simulations, the adsorption configuration and molecular orientation of the coordination complexes are also revealed using TERS imaging.

Visualizing On-Surface Decomposition Chemistry at the Nanoscale Using Tip-Enhanced Raman Spectroscopy

“…Furthermore, taking advantage of the spectral differences between 4-PyS-SH and 4-PyS, spatial resolution of the high-resolution TERS image can be estimated. Since the thermal drift of our system is 0.02–0.03 nm/s under laser illumination at ambient conditions, a relatively short spectral acquisition time of 1 s was chosen to minimize the influence of drift Figure c and Figure S6 display the TERS images of the 890 cm –1 signal of 4-PyS-SH on 4-PyS-functionalized Au(111) samples prepared with different immersion times.…”

Progress of tip-enhanced Raman scattering for the last two decades and its challenges in very recent years

“…53 Moreover, of particular note is that during 2019-2021, a number of studies focused on chemical imaging with a resolution of a few angstroms (the chemical imaging of a single molecule or a single bond) were reported. 16,17,39,[54][55][56] They are significantly different from TERS imaging studies before 2018, where the resolution was only at the nanometer level. Angstrom-resolved TERS microscopy, especially with the new scanning Raman picoscopy (SRP) methodology, can be used for visually constructing the chemical structure in real space and the determination of structural and chemical heterogeneities of surface species at the single-bond limit.…”

“…Moreover, due to a large gradient field effect, it allows IR-active modes to emerge in the spectra of adaptive tip-enhanced nanospectroscopy. Molecular-scale chemical imaging of the orientation of an on-surface coordination complex by TERS was reported by Cai et al 55 In this investigation, STM-TERS was employed to create the chemical imaging of a "single molecule" under ambient conditions. Cobalt(II) tetraphenylporphyrin coordination species anchored on gold surfaces modified with pyridine thiol self-assembled monolayers can be spectroscopically identified and mapped with an approximately 2 nm resolution.…”

“…12,57,58 A "single molecule" can be investigated and mapped under ambient conditions. 55 Intramolecular and intermolecular interactions of single molecules can also be visualized. [59][60][61] Moreover, a new sideillumination EC-TERS setup has been proposed, and the investigations using EC-TERS have been developed rapidly.…”

Can Light Alter the Yield of Plasmon-Driven Reactions on Gold and Gold–Palladium Nanoplates?

“…Experimental evidence recently reported by our and other research groups suggests that the electrostatic potential may determine rates and yields of plasmon-driven reactions. − Specifically, Jain’s group showed that reduction of carbon dioxide on gold nanoparticles yields a broad spectrum of hydrocarbons including methane, ethane, and ethylene as well as propane and propene. , Sungju and Jain discovered that relative yield of these reaction products could be altered by light intensity used to catalyze this reaction . Our group used tip-enhanced Raman spectroscopy (TERS), a modern analytical technique that demonstrates single-molecule sensitivity and Angstrom spatial resolution, − to investigate a relationship between rates of plasmon-driven processes and light intensity. ,, In TERS, the metalized scanning probe is brought in the close proximity to the sample surface. , Next, the probe is illuminated by light, which generates high electric field (electrostatic potential) in the tip–sample junction. , As was discussed above, the electrostatic potential triggers plasmon-driven reactions in the molecular analytes present directly under the tip. Simultaneously, high local density of the electric field enhances Raman scattering from the molecules present under the tip. , Thus, TERS allows to perform and simultaneously monitor plasmon-driven transformations at the nanoscale. − Using TERS, Li and co-workers found that an increase in the light intensity increases rates of 4-nitrobenzenethiol (4-NBT) to p , p ′-dimercapto­azobisbenzene (DMAB) on both AuNPs and Au@PdNPs .…”