Recognition of chemical identity of organic adsorbates on solid surfaces at the nanoscale by molecular STM tips.

This paper reviews chemically selective imaging at the single-atom/molecule level by molecular STM tips. The molecular tips enable the recognition of a particular chemical species on the basis of chemical interactions with a sample molecule, including hydrogen-bond, metal-coordination, and charge-transfer interactions. The chemical selectivity can be tailored by designing functional groups of the tip molecules. Moreover, the rational design of the molecular tip allows sophisticated chemical recognition. The discrimination of DNA bases and chiral recognition on a single molecule basis are thereby achieved. The molecular tips also revealed rectified electron transmission within an electron donor-acceptor molecular pair. Self-assembled monolayers, carboxylated carbon nanotube, and conducting polymers can be utilized for the preparation of molecular tips. This technique may be coined "intermolecular tunneling microscopy" as its principle goes, and is of general significance for novel molecular imaging of chemical identities at the membrane and solid surfaces.