Nanoelectrical analysis of single molecules and atomic-scale materials at the solid/liquid interface

Abstract

Evaluating the built-in functionality of nanomaterials under practical conditions is central for their proposed integration as active components in next-generation electronics. Low-dimensional materials from single atoms to molecules have been consistently resolved and manipulated under ultrahigh vacuum at low temperatures. At room temperature, atomic-scale imaging has also been performed by probing materials at the solid/liquid interface. We exploit this electrical interface to develop a robust electronic decoupling platform that provides precise information on molecular energy levels recorded using in situ scanning tunnelling microscopy/spectroscopy with high spatial and energy resolution in a high-density liquid environment. Our experimental findings, supported by ab initio electronic structure calculations and atomic-scale molecular dynamics simulations, reveal direct mapping of single-molecule structure and resonance states at the solid/liquid interface. We further extend this approach to resolve the electronic structure of graphene monolayers at atomic length scales under standard room-temperature operating conditions.T he elemental properties of carbon nanostructures are environment dependent. Interpreting the synergism between electronically active nanomaterials and their local chemical domain is pivotal to both scientific and technological interests. Scanning probe microscopy operated at cryogenic conditions with functionalized metal tips 1,2 in combination with inorganic decoupling platforms 3,4 is a widely adopted technique to examine the intramolecular structure of organic materials. In addition to probing matter under ultrahigh-vacuum conditions, scanning tunnelling microscopy (STM) operated at the solid/liquid interface 5-11 has previously been demonstrated to record real-time molecular dynamics 7,12-14 , register ultrafast chemical reactions 8,15 , probe the structure of supra-molecular architectures [16][17][18] and chemical-fieldeffect transistors 19 , and perform spectral analysis of molecules 6,13,20 and real-space visualization of biomolecules 5 at room temperature. It would be highly attractive to capitalize on principal findings from these two research disciplines to probe the precise electronic states in liquids and quantitatively describe the functionality of single molecules and two-dimensional nanostructures. The experimental challenge lies in addressing the electrochemical congestion present at the solid/liquid electrical interface at room temperature, which stems from the high mobility of organic molecules on metals, the dynamics of the solvent that serves as a liquid sheath and the detrimental effects of the metallic platform due to mixing of metal bands with discrete molecular electronic states 21 . A potential strategy is to employ nonpolar, highly viscous liquid sheaths with low affinity towards the substrate and to engineer a spacer layer 3,22,23 that electrically disconnects the organic material of interest from metal-induced perturbations. The bottom-up construction of the spac...

Templated bilayer self-assembly of fully conjugated π-expanded macrocyclic oligothiophenes complexed with fullerenes

“…Control over the self-assembly of molecular structures on a solid surface is of particular interest towards three-dimensional (3D) engineering of supramolecular materials1 and designing of molecular electronic devices234. Hydrogen-bonding is the most versatile, yet specific type of weak interaction to engineer two-dimensional (2D) self-assembled networks56 due to the high level of control at the molecular level78 and the potential applications9.…”

Graphene wrinkle effects on molecular resonance states

“…Immediately following the spray-deposition step the sample was blow dried using N 2 gas in a fume cupboard and then fixed on a metal disk (purchased from Ted Pella, Inc) for AFM or placed within a custom-built Teflon based liquid-cell sample holder filled with a thin layer of silicone oil for STM measurements. The silicone oil film protects the organic architecture from ambient contamination 70 and ensures stable STM imaging 71,72 and spectroscopy. 70,73 AFM was conducted on a Dimension V AFM system operated in tapping mode under standard laboratory conditions with a HI-RES tip (Cr-Au coating) with tip radius of <2 nm purchased from µMasch Co. Ltd. STM was performed in constant-current mode at room-temperature using a Veeco Scanning Tunnelling Microscope, Nanoscope IIIa, Multimode (Scanner model: E-Scanner) located in a noise-free laboratory.…”

“…The silicone oil film protects the organic architecture from ambient contamination 70 and ensures stable STM imaging 71,72 and spectroscopy. 70,73 AFM was conducted on a Dimension V AFM system operated in tapping mode under standard laboratory conditions with a HI-RES tip (Cr-Au coating) with tip radius of <2 nm purchased from µMasch Co. Ltd. STM was performed in constant-current mode at room-temperature using a Veeco Scanning Tunnelling Microscope, Nanoscope IIIa, Multimode (Scanner model: E-Scanner) located in a noise-free laboratory. A mechanically cut Au wire (0.25 mm, Good Fellow GmbH) was used as the STM probe.…”

“…To avoid tip artefacts the Au tip was calibrated by measuring standard reference differential conductance spectra acquired over blank Au (111) and graphene. 70 Image processing was performed using Gwyddion 2.39 freeware (http://gwyddion.net).…”

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

“…Previously, we were unable to measure clearly the LUMO-derived resonance states of a C 60 molecule which was directly adsorbed on Au(111) due to substrate induced hybridisation of molecular energy levels 24 (right hand inset schematic in Fig. 2d).…”