21. March 2017
›Bottom-up‹ synthesis of molecular, two-dimensional networks for electronic applications of the future
Scanning tunneling microscopy images of covalently bonded macro-cycles, one-dimensional and two-dimensional nanostructures produced by the polymerization of triphenylamine derivatives on an Au(111) surface. Image: Sabine Maier
EAM researchers have succeeded in covalently binding molecules on surfaces by means of hierarchical surface polymerization, thus enabling them to produce one-dimensional (1D) and two-dimensional (2D) planar nanostructures under controlled conditions. This was the first time it has been possible to show differences in electronic properties relative to the dimensionality of nanostructures. Programmed synthesis on surfaces is a seminal development when it comes to the precise generation of innovative nanomaterials for electronic applications.
Carbon is an essential building block in the development of innovative nanomaterials and electronic and optoelectronic applications such as flat screens. Defect-free, expanded one- and two-dimensional nanostructures are needed to construct these kinds of electronic and optoelectronic components. Using a so-called ‘bottom-up’ approach, in which small, appropriately designed molecular building blocks are employed to create surfaces, makes it possible to produce the required nanostructures without the need for solvents in high quality and with an accuracy down to individual atoms. This method represents the opposite of the ‘top-down’ methods used to date for the production of electronic components.
The geometric and electronic structures of such nanomaterials can be examined at the atomic level using a scanning tunneling microscope. In this case, the local band gaps of such covalently bonded networks were measured for the first time. These networks have a band gap of 2.5 eV and therefore belong to the class of organic semiconductors. Furthermore, it was also demonstrated that there is a sustained decrease in the band gaps between individual molecular building blocks with regard to the one- and two-dimensional organic structures created using the ‘bottom-up’ method. This is attributable to the increasing delocalization of electrons in the two-dimensional network, which is indicative of an effective charge transport. These insights represent significant progress towards the development of a method of programmed synthesis and characterization of covalently bonded two-dimensional networks that can be employed for the accurate production of innovative nanomaterials for electronic applications.
The research results achieved by a collaboration between teams from Experimental Physics (Prof. Sabine Maier), Organic Chemistry I (Prof. Milan Kivala) and Theoretical Chemistry (Prof. Andreas Görling) are the outcome of an EAM interdisciplinary project and Collaborative Research Center 953 ‘Synthetic Carbon Allotropes’.
Hierarchical on-surface synthesis and electronic structure of carbonyl-functionalized one- and two-dimensional covalent nanoarchitectures
Research Areas A2, B
Christian Steiner, Julian Gebhardt, Maximilian Ammon, Zechao Yang, Alexander Heidenreich, Natalie Hammer, Andreas Görling, Milan Kivala, Sabine Maier
Nat. Commun., 2017, 8, 14765