Exploring the structure and properties of new graphene-like polymers

(Nanowerk News) A team of scientists from Siberian Federal University (SibFU) together with foreign colleagues described the structural and physical properties of a group of two-dimensional materials based on polycyclic molecules called circulenes. The possibility of flexible design and variable properties of these materials make them suitable for nanoelectronics.
The results are published in the Journal of Physical Chemistry C ("Strong Topological States and High Charge Carrier Mobility in Tetraoxa[8]circulene Nanosheets").
properties of new graphene-like polymers
Among three types of nanosheets, only two demonstrate semiconducting properties exhibiting 1.37 and 1.84 eV direct band gaps, while another one is found to be a semimetal, which hosts strong topological states and enhances the band gap (∼87 meV) induced by spin–orbit coupling (SOC) that exceeds by several orders of magnitude that gap in graphene. (© ACS)
Circulenes are organic molecules that consist of several hydrocarbon cycles forming a flower-like structure. Their high stability, symmetricity, and optical properties make them of special interest for nanoelectronics especially for solar cells and organic LEDs.
The most stable and most studied tetraoxa[8]circulene molecule could be potentially polymerized into graphene-like nanoribbons and sheets. The authors have published the results of simulations proving this possibility. They also described properties and structure of the proposed materials.
"Having only one building block - a tetraoxa[8]circulene molecule - one can create a material with properties similar to those of silicon (a semiconductor traditionally used in electronics) or graphene (a semimetal) depending on the synthesis parameters.
However, the proposed materials have some advantages. The charge carrier mobility is about 10 times higher compared to silicon, therefore, one could expect higher conductivity," says the main author of the study Artem Kuklin, research associate at the department of theoretical physics of Siberian Federal University.
Having the equilibrium geometries and tested their stability, the scientists discovered several stable tetraoxa[8]circulene-based polymers. The difference between them lied in the type of coupling between the molecules resulting in different properties. The polymers demonstrate high charge carrier mobility.
This property was analyzed by fitting of energy zones near bandgap - a parameter represented by separation of empty and occupied electronic states. The mechanical properties exhibit that the new materials 1.5-3 times more stretchable than graphene.
The authors also emphasized existence of topological states in one of the polymers caused by spin-orbit coupling, which is not typical for light elements-based materials. The materials possessed such kind of properties are insulators in the bulk but can conduct electricity on the surface (edges).
"The proposed nanostructures possess useful properties and may be used in various fields, from the production of ionic sieves to elements of nanoelectronic devices. Further we plan to develop this topic and modify our compounds with metal adatoms to study their magnetic and catalytic properties. We would also like to find a research group that could synthesize these materials," concludes Artem Kuklin.
Source: Siberian Federal University
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