Editorial of the PCCP themed issue “Scanning tunneling microscopy: revealing new physical chemistry insight”

It has been 30 years since the invention of Scanning Tunnelling Microscopy (STM). STM allows scientists to directly image the nano-world at atomic resolution and has stimulated the development of a large family of probe-based microscopy. More importantly, STM has opened new avenues to explore the fascinating properties associated with nano-sized objects, and has fueled the growth of nanoscience and nanotechnology. As a powerful surface characterization technique, STM is particularly important for physical chemistry research of surfaces and interfaces.

The aim of the “Scanning tunneling microscopy: revealing new physical chemistry insight” themed issue, is to highlight the role of STM techniques at the interface of chemistry, physics, and material sciences, focusing especially on surface physical chemistry. The topics covered by the issue include single molecule science, surface physics and chemistry, supramolecular assembly on surfaces and interfaces, and molecular electronics.

One of the most fascinating features of STM is not only its ability to obtain the ultimate single molecular resolution, but also to locally probe the electronic properties of the atoms and molecules. It goes without saying that STM has motivated the development of single molecule science. In the perspective article by Wang, Hou, and coworkers (DOI: 10.1039/C3CP51446C), an overview of tip-assisted single molecule chemistry, such as the identification of specific orbitals or states of molecules on surfaces, tip-induced single-molecule manipulation, atomically resolved chemical reactions in photochemistry and tip-induced electroluminescence, has been given. One hot topic in single molecule science is molecular electronics and quantum transport through metallic nanocontacts. By employing the STM-based break junction technique, Mao et al. reported the observation of a multiple subatomic step-length when stretching single atom contacts (DOI: 10.1039/C3CP50473E).

Fundamental understanding of surface physical chemistry is of great importance for catalysis, electrochemistry, and many other application fields. The emergence of STM and other advanced surface characterization techniques provides powerful tools to understand surface and interface science. In this collection, Yang and Magnussen present quantitative studies of the diffusion process of adsorbates at electrodes under electrochemical control, using an in situ video STM at a temporal resolution of tens of milliseconds (DOI: 10.1039/C3CP51027A). Rosei et al. reported the structural characterization of submonolayer Zn on a Pd(111) surface, which is technically important for near-surface alloy heterogeneous catalysis (DOI: 10.1039/C3CP50793A).

The engineering of highly ordered molecular patterns on surfaces represents a prominent bottom-up approach for the fabrication of well-defined molecular architectures at surfaces, which is considered to be an important step towards next-generation molecule-based electronics. Chen et al. present a comprehensive review of supramolecular assemblies of binary nanostructures on graphite surfaces (DOI: 10.1039/C3CP00023K). Significant attention has been devoted to understanding and tailoring weak but appreciable non-covalent intermolecular interactions, such as hydrogen bonding (DOI: 10.1039/C3CP50891A), dipole–dipole interaction (DOI: 10.1039/C3CP50808K), and metal–ligand coordination interactions (DOI: 10.1039/C3CP50779C), in order to fabricate sophisticated 2D supramolecular assemblies. On the other hand, the phase transition of cobalt porphyrin adlayers on Au(100) surfaces highlights the important role of substrate structure and substrate–adsorbate interactions for supramolecular assembly (DOI: 10.1039/C3CP50797A). The delicate balance between different weak interactions may result in complicated polymorphs in the adlayers (DOI: 10.1039/C3CP50829C and DOI: 10.1039/C3CP51074C), which on the other hand, provides a great opportunity to understand the underlying driving forces of the self-assembly process. In addition, the processing conditions, such as concentration (DOI: 10.1039/C3CP51074C) and solvent (DOI: 10.1039/C3CP51586A), play an important role for the self-assembly process. The hierarchical 2D molecular assemblies, especially 2D nanoporous networks, provide interesting molecular templates to immobilize functional molecules in a spatially defined way (DOI: 10.1039/C3CP50371B).

In summary, the articles composing this themed issue provide a snapshot of the great impact of STM techniques to bring physical chemistry into the atomic and nano scale. With the burgeoning development of nanoscience and nanotechnology, “interface” and “molecular-level” have been more and more frequently seen as keywords in many emerging research fields. As a powerful and still developing technique, STM will continuously contribute to revealing the mechanism of the interface processes at an unprecedented molecular-level.

We wish to thank all the authors for their contributions to this special collection. We are particularly indebted to Philip Earis, Catherine Pridmore, Jane Hordern, and other editorial members for their hard work to make this collection possible.

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