Single-molecule imaging of activated nitrogen adsorption on individual manganese phthalocyanine.

An atomic-scale understanding of gas adsorption mechanisms on metal-porphyrins or metal-phthalocyanines is essential for their practical application in biological processes, gas sensing, and catalysis. Intensive research efforts have been devoted to the study of coordinative bonding with relatively active small molecules such as CO, NO, NH3, O2, and H2. However, the binding of single nitrogen atoms has never been addressed, which is both of fundamental interest and indeed essential for revealing the elementary chemical binding mechanism in nitrogen reduction processes. Here, we present a simple model system to investigate, at the single-molecule level, the binding of activated nitrogen species on the single Mn atom contained within the manganese phthalocyanine (MnPc) molecule supported on an inert graphite surface. Through the combination of in situ low-temperature scanning tunneling microscopy, scanning tunneling spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations, the active site and the binding configuration between the activated nitrogen species (neutral nitrogen atom) and the Mn center of MnPc are investigated at the atomic scale.

Self-assembly of binary molecular nanostructure arrays on graphite.

The controlled positioning and assembly of functional molecules into ordered nanostructures on surfaces depends on the interplay of multiple interactions on different strength and length scales. On metal surfaces, the relatively strong molecule-substrate interactions can constrain the molecules to adsorb in registry with the surface periodicity and lock them into specific adsorption sites. This can significantly reduce the structural tunability of the molecular nanostructure arrays formed. Inert graphite has a smooth potential-energy surface as well as relatively weak interfacial interactions with adsorbed molecules, and is therefore chosen as a supporting substrate for constructing molecular nanostructures with a high degree of controllability and tunability. The aim of this article is to highlight recent progress in the fabrication of self-assembled molecular nanostructures on inert graphite surfaces in ultra-high vacuum, with particular emphasis on the role of intermolecular interactions in the self-assembly process. We describe the formation of tunable two-dimensional (2D) binary molecular networks by directional and selective hydrogen bonding, as well as the templating effect of these 2D molecular networks, demonstrating the rational design and construction of long-range ordered 2D molecular nanostructures with desired functionality.

Reversible single-molecule switching in an ordered monolayer molecular dipole array.

Making electronic devices using a single molecule has been the ultimate goal of molecular electronics. For binary data storage in particular, the challenge has been the ability to switch a single molecule in between bistable states in a simple and repeatable manner. The reversible switching of single molecules of chloroaluminum phthalocyanine (ClAlPc) dipolar molecules within a close-packed monolayer is demonstrated. By pulsing an scanning tunneling microscopy tip, read-write operations of single-molecular binary bits at ~40 Tb/cm(2) (~250 Tb/in(2)) are demonstrated.

Rational design of two-dimensional molecular donor-acceptor nanostructure arrays.

The construction of long-range ordered organic donor-acceptor nanostructure arrays over microscopic areas supported on solid substrates is one of the most challenging tasks towards the realization of molecular nanodevices. They can also be used as ideal model systems to understand light induced charge transfer, charge separation and energy conversion processes and mechanisms at the nanometer scale. The aim of this paper is to highlight recent advances and progress in this topic. Special attention is given to two different strategies for the construction of organic donor-acceptor nanostructure arrays, namely (i) molecular self-assembly on artificially patterned or pre-defined molecular surface nanotemplates and (ii) molecular nanostructure formation steered via directional and selective intermolecular interactions. The interfacial charge transfer and the energy level alignment of these donor-acceptor nanostructures are also discussed.

One dimensional molecular dipole chain arrays on graphite via nanoscale phase separation.

Molecular dipole chain arrays of chloroaluminium phthalocyanine (ClAlPc) on the graphite surface have been investigated by scanning tunneling microscopy. The inter-chain spacing can be tuned by the co-adsorption of di-indenoperylene (DIP) via nanoscale phase separation.