Two-dimensional materials can exhibit intriguing electronic properties that stem from their geometry. The best-known example is graphene’s Dirac cone that gives rise to massless electrons, which originates from the all-carbon hexagonal lattice. Two-dimensional conjugated polymers (2DCPs) can be considered as analogues of graphene, yet offering greater potential to design geometry and properties by carefully selecting their building blocks. Strikingly, 2DCPs on a kagome lattice (i.e. a trihexagonal tiling) can show both Dirac cones and flat bands, with highly-massive charge carriers.
Despite experimental efforts spanning more than a decade, the poor crystallinity of the synthesized polymers made the study of the electronic properties of 2DCPs a scientific niche reserved to theorists. A collaboration between the “Istituto di Struttura della Materia” of the Italian CNR three Canadian universities (INRS, McGill and Lakehead) realized the milestone of the synthesis of a long-range ordered 2D polymeric network, enabling the measurement of their Dirac cone and flat band features by angle-resolved photoelectron spectroscopy (ARPES). This achievement paves the way to study the intriguing electronic properties of this new class of materials, which make them promising for applications in future electronic and optoelectronic technologies.
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Image : a) Scanning tunneling microscope image of a highly-ordered polymeric network with the theoretical model superimposed b) second derivative of the ARPES map for the polymer on Au(111) along the ΓKM direction, where it is possible to observe the Dirac cone feature converging at a Dirac point (DP) around 0.55 eV; the theoretical calculated band structure is superimposed.