Estudo computacional sobre o transporte elétrico e térmico em materiais à base de carbono

Abstract

The emergence of nanotechnology catalyzed a well-established trend in electronics: miniaturization. The pursuit of increasingly smaller and more efficient devices led to the development of a promising field known as molecular electronics. The first work in this area was presented by Aviram and Ratner in 1970, when they proposed that a molecule could function as a current rectifier. Building on these ideas, several studies have been conducted in the search for new nanoelectronic devices, and it is within this framework that the present work was developed. In this study, the potential of graphene-based materials as molecular junction devices for applications in molecular electronics was investigated. The analysis was conducted considering extended systems composed of a pyrene molecule as a conductive wire and graphene and aza-nanographene as electrodes. The transmission spectra, conductances, and Seebeck coefficients for each system were calculated using a computational approach that combined Landauer-Büttiker scattering theory and Density Functional Theory. The results obtained at the B3LYP-D3/6-31G(d) level show that the investigated systems exhibit conductances of the same order of magnitude as those measured and calculated for devices composed of metallic materials (10−3 to 10−5 ). The calculated conductance values (G/G0) of 6,20 × 10−4 and 1,80 × 10−5 for the graphene-based and aza-graphene-based systems, respectively, indicate that the graphene system has a conductance approximately 10 times higher than that of the aza-graphene system. The calculations of the thermoelectric coefficients for the analyzed systems indicate that the graphene-based material is more efficient than the aza-graphene material in converting thermal energy into electrical energy. The values obtained at 60 K were 45 and 400 (µ𝑉.𝐾 −1 ) for the aza-graphene and graphene systems, respectively. These values are of the same order of magnitude as those measured for gold based metallic aterials. The results also indicate that the transport mechanisms for the two systems are of different natures. In the case of the graphene system, the transport is predominantly mediated by the LUMO orbital, while in the aza-graphene device, the transport is associated with the HOMO orbital. These findings highlight the dependence of electrical and thermal transport properties on the molecular structure and chemical nature of the constituents. Results obtained from chemical modifications made by the insertion of the 𝑁𝑂2 group in specific positions of the pyrene (conductive wire) indicate an increase in conductivity compared to the unmodified system. The overall analysis of the obtained data suggests that both investigated carbon-based materials are potential candidates as thermoelectric materials.