Fingerprinting Electronic Molecular Complexes in Liquid

Bottom-Up Self-Assembled Supramolecular Structures Built by STM at the Solid/Liquid Interface

One of the lines of research on organic devices is focused on their miniaturization to obtain denser and faster electronic circuits. The challenge is to build devices adding atom by atom or molecule by molecule until the desired structures are achieved. To do this job, techniques able to see and manipulate matter at this scale are needed. Scanning tunneling microscopy (STM) has been the selected technique by scientists to develop smart and functional unimolecular devices. This review article compiles the latest developments in this field giving examples of supramolecular systems monitored and fabricated at the molecular scale by bottom-up approaches using STM at the solid/liquid interface.

Polymer-Nanocarbon Topological and Electronic Interface

The electronic structure of semiconducting carbon nanotubes selected through polymer functionalization is routinely verified by measuring the spectral van Hove singularity signature under ultraclean vacuum conditions. Interpreting the effect of unperturbed polymer adsorption on the nanotube energetic bands in solvent media is experimentally challenging owing to solvent molecular crowding around the hybrid complex. Here, a liquid-based scanning tunneling microscope and spectroscope operating in a noise-free laboratory is used to resolve the polymer-semiconducting carbon-nanotube-underlying graphene heterostructure in the presence of encompassing solvent molecules. The spectroscopic measurements highlight the role of polymer packing and graphene landscape on the electronic shifts induced in the nanotube energy bands. Together with molecular dynamics simulations, our experimental findings emphasize the necessity of recording physicochemical and electronic properties of liquid-phase solubilized hybrid materials in their native state.

Motion of Fullerenes around Topological Defects on Metals: Implications for the Progress of Molecular Scale Devices

Research on motion of molecules in the presence of thermal noise is central for progress in two-terminal molecular scale electronic devices. However, it is still unclear what influence imperfections in bottom metal electrode surface can have on molecular motion. Here, we report a two-layer crowding study, detailing the early stages of surface motion of fullerene molecules on Au(111) with nanoscale pores in a n-tetradecane chemical environment. The motion of the fullerenes is directed by crowding of the underlying n-tetradecane molecules around the pore fringes at the liquid-solid interface. We observe in real-space the growth of molecular populations around different pore geometries. Supported by atomic-scale modeling, our findings extend the established picture of molecular crowding by revealing that trapped solvent molecules serve as prime nucleation sites at nanopore fringes.

A robust molecular probe for Ångstrom-scale analytics in liquids

Traditionally, nanomaterial profiling using a single-molecule-terminated scanning probe is performed at the vacuum–solid interface often at a few Kelvin, but is not a notion immediately associated with liquid–solid interface at room temperature. Here, using a scanning tunnelling probe functionalized with a single C₆₀ molecule stabilized in a high-density liquid, we resolve low-dimensional surface defects, atomic interfaces and capture Ångstrom-level bond-length variations in single-layer graphene and MoS₂. Atom-by-atom controllable imaging contrast is demonstrated at room temperature and the electronic structure of the C₆₀–metal probe complex within the encompassing liquid molecules is clarified using density functional theory. Our findings demonstrates that operating a robust single-molecular probe is not restricted to ultra-high vacuum and cryogenic settings. Hence the scope of high-precision analytics can be extended towards resolving sub-molecular features of organic elements and gauging ambient compatibility of emerging layered materials with atomic-scale sensitivity under experimentally less stringent conditions.

Single-molecule-terminated scanning probes typically operate under ultra-high vacuum conditions at low temperatures. Here, the authors show that tips functionalized with C₆₀ can image single-layer graphene and MoS₂ with high definition in a liquid environment at room temperature