The dynamic self-assembly of atoms and molecules into low-dimensional structures has been vigorously pursued for several decades: physicists, chemists and biologists have utilised this powerful technique for scientific exploration and the development of novel technologies at the nanoscale.
Of particular importance are methods for controlled self-assembly, where some form of direct manipulation is performed prior to self-assembly, allowing the creation of complex structures.
The strong covalent bonding that occurs on semiconductor surfaces has limited their use as substrates for controlled self-assembly to date.
Now, an international team including Dr Steven Schofield from the London Centre for Nanotechnology at University College London, and coworkers from the University of Newcastle, and the University of Sydney have developed a technique for the self-assembly of one-dimensional (1D) metal atom chains on silicon using organic molecules as a template.
The method, recently published in the Journal of the American Chemical Society, utilises individual organic adsorbates (benzonitrile) that are repositioned on the surface by direct manipulation using a scanning tunnelling microscope (STM) tip to form a template for the metal atom chain growth. Subsequent deposition of metal atoms (indium) to the surface results in the nucleation and growth of 1D metal atom “wires” in predefined surface locations.
Unlike previous demonstrations of 1D organic molecule chain growth on silicon [Lopinski et al. Nature 406, 48 (2000)] or the formation of 1D dopant wires in silicon [Schofield et al., PRL 91, 136104 (2003); Weber et al. Science 335, 64 (2010)], the method does not require the chemical passivation of the silicon surface to form a mask layer.
This technique is not only the first to allow the directed self-assembly of metal atoms into a 1D single atom wide chain on a clean silicon surface, but importantly it also provides the ability to form 1D single molecule junctions between a metal chain and an organic molecule on a surface. It is anticipated that this new technique will be applied to a wide variety of molecule/metal/semiconductor combinations with the potential to facilitate the much sought after goal of lateral single-molecule electronic junctions with known structural configuration.
Journal link: Guided self-assembly of metal atoms on silicon using organic-molecule templating, J. Am. Chem. Soc., 2012. DOI: 10.1021/ja3026399
Figure: A single atom wide metal atom chain (indium) templated on a silicon surface by benzonitrile adsorbates.
Authors: Daniel Belcher, Marian Radny, Steven Schofield, Phillip Smith and Oliver Warschkow