Electronic fractal patterns in building Sierpinski-triangle molecular systems.

The Sierpinski triangle (ST) is a fractal mathematical structure that has been used to explore the emergence of flat bands in lattices of different geometries and dimensions in condensed matter. Here we look into fractal features in the electronic properties of ST flakes and molecular chains simulating experimental synthesized fractal nanostructures. We use a single-orbital tight binding model to study the fractal properties of the electronic states and the Landauer formalism to explore transport responses of the quasi 1D molecular chains. The self-similarity of the energy states is found comparing different ST orders and also amplifying the energy ranges investigated, for both flakes and quasi-1D systems. In particular, the results for the local density of states of the theoretical molecular chains proposed here exhibit quite similar spatial charge distribution of experimental STM reports. The analysis of the transport response of such all-carbon fractal molecular chains can be used as a guide to propose a variety of architectures in the synthesis of real new molecular chains.

Exploring the enhancement of the thermoelectric properties of bilayer graphyne nanoribbons.

Carbon materials are vital for sustainable energy applications based on abundant and non-toxic raw materials. In this scenario, carbon nanoribbons have superior thermoelectric properties in comparison with their 2D material counterparts, owing to their particular electronic and transport properties. Therefore, we explore the electronic and thermoelectric properties of bilayer α-graphyne nanoribbons (α-BGyNRs) by means of density functional theory, tight-binding, and the non-equilibrium Green's functions (NEGF) method. Our calculations indicate that Ab stacking is the most stable configuration regardless of the edge type. The band structure presents finite band gaps with different features for armchair and zigzag nanoribbons. Concerning the thermoelectric quantities, the Seebeck coefficient is highly sensitive to the width and edge type, while its room-temperature values can achieve a measurable mV K-1 scale. The electric conductance is found to increase due to layering, thus enhancing the power factor for α-BGyNRs compared with single nanoribbons. These findings therefore indicate the possibility of engineering such systems for thermal nanodevices.