Real space chemical analysis of two structurally very similar components, that is, regioisomers lies at the heart of heterogeneous catalysis reactions, modern-age electronic devices, and various other surface related problems in surface science and nanotechnology. One of the big challenges in surface chemistry is to identify different surface adsorbed molecules and analyze their chemical properties individually. Herein, we report a topological and chemical analysis of two regioisomers, trans-and cis-tetrakispentafluorophenylporphodilactone (trans-and cis-H 2 F 20 TPPDL) molecules by highresolution scanning tunneling microscopy, and ultrahigh vacuum tip-enhanced Raman spectroscopy (UHV-TERS). Both isomeric structures are investigated individually on Ag(100) at liquid nitrogen temperature. Following that, we have successfully distinguished these two regioisomeric molecules simultaneously through TERS with an angstrom scale (8 Å) spatial resolution. Also, the two-component organic heterojunction has been characterized at large scale using high-resolution two-dimensional mapping. Combined with time-dependent density functional theory simulations, we explain the TERS spectral discrepancies for both isomers in the fingerprint region.

Two-dimensional boron monolayers (i.e., borophene) hold promise for a variety of energy, catalytic, and nanoelectronic device technologies due to the unique nature of boron–boron bonds. To realize its full potential, borophene needs to be seamlessly interfaced with other materials, thus motivating the atomic-scale characterization of borophene-based heterostructures. Here, we report the vertical integration of borophene with tetraphenyldibenzoperiflanthene (DBP) and measure the angstrom-scale interfacial interactions with ultrahigh-vacuum tip-enhanced Raman spectroscopy (UHV-TERS). In addition to identifying the vibrational signatures of adsorbed DBP, TERS reveals subtle ripples and compressive strains of the borophene lattice underneath the molecular layer. The induced interfacial strain is demonstrated to extend in borophene by ∼1 nm beyond the molecular region by virtue of 5 Å chemical spatial resolution. Molecular manipulation experiments prove the molecular origins of interfacial strain in addition to allowing atomic control of local strain with magnitudes as small as ∼0.6%. In addition to being the first realization of an organic/borophene vertical heterostructure, this study demonstrates that UHV-TERS is a powerful analytical tool to spectroscopically investigate buried and highly localized interfacial characteristics at the atomic scale, which can be applied to additional classes of heterostructured materials.

Tip-enhanced Raman spectroscopy (TERS), a cutting-edge near-field spectroscopic tool, provides invaluable chemical insight with impressive spatial resolution in chemistry-related fields such as molecular and catalytic systems, surface science, two-dimensional materials, and biochemistry. High-resolution TERS, in particular, which has advanced exceptionally in the last five years, provides a unique opportunity to scrutinize single molecules individually. Here, this perspective places emphasis on the basic concepts and recent experimental findings of this state-of-the-art research and concludes with a glimpse of future prospects.

In order to fully characterize interfacial systems at the smallest scales, advanced analytical surface techniques have to be employed to render a complete picture of molecular assemblies. In this study, we carried out ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) experiments on subphthalocyanine (SubPc) molecules, which are self-assembled on a Ag(100) substrate. The UHV STM experiments were complemented by tip-enhanced Raman spectroscopy (TERS), surface-enhanced Raman spectroscopy (SERS), and density functional theory (DFT) calculations. The TERS spectrum shows a high signal intensity (>600 ADU·mW–1·s–1) due to piezo-driven in-vacuo excitation and collection lenses with large numerical apertures (NA = 0.4). A new two-dimensional molecular superstructure of SubPc was discovered to consist of two distinct molecular binding configurations, both of which interact relatively weakly with the underlying metallic substrate as revealed by high-signal-to-noise enhanced Raman spectra. Our results demonstrate the necessity of advanced Raman techniques such as TERS when precisely probing molecule–molecule and molecule–substrate interactions.

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