A robust molecular probe for Ångstrom-scale analytics in liquids.

Peter Nirmalraj,Andras Kis,Christos Dimitrakopoulos,Dumitru Dumcenco,Heike Riel,Damien Thompson,Bernd Gotsmann

doi:10.1038/ncomms12403

Abstract

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.

Highlights

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
The atomic-scale structure, extrinsic doping, bonding states and chemical composition can be precisely measured for single-atom-thick electronic materials from the two-dimensional (2D) form of carbon, graphene[6] to more recent transition metal dichalcogenides (TMDs)[7] with potential for triggering a new wave of 2D nanodevice technologies
A known alternative to vacuum to protect air-sensitive surfaces, is the liquid–solid interface in which a scanning tunnelling microscopy (STM) can be operated. This field of research has an almost 30-year history, from early reports on achieving atomic resolution on solid surfaces immersed in water[11], liquid nitrogen[12] and acidic solution[13] environments, observation of molecular dynamics[14], decoding molecular layer-underlying surface epitaxial relationship[15], capturing oxidation catalysis reactions[16] and in investigating through high-resolution STM images the supramolecular chemistry of molecules[17] and pattern formation during molecular self-assembly[18] at the liquid–solid electrical interface with a non-functionalized metal probe

Summary

Introduction

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. More recently it has been demonstrated that by terminating the apex of a scanning probe (including STM and AFM) with a single molecule, it is possible to further the limits of spatial resolution and enhance chemical contrast of the low-dimensional materials under study[19,20,21,22,23,24,25,26]. These single-molecule-terminated scanning probes have been mainly demonstrated to operate at UHV in a temperature scale ranging from 4 to 100 K (refs 20–22,25,27,28). We demonstrate that by engineering and operating a single-moleculeterminated Au STM probe in high-density liquids, it is possible to control random fluctuations of the molecule at the metal apex, maintain a clean interface protected from ambient contaminants thereby resulting in a robust single-molecular probe with prolonged lifetime

Methods

Results

Conclusion