Estudio químico-cuántico de los defectos producidos por las vacancias de oxígeno en los cristales de Titanato de plomo PbTiO3

Estudio químico-cuántico de los defectos producidos por las vacancias de oxígeno en los cristales de Titanato de plomo PbTiO

Estudio químico-cuántico de los defectos producidos por las vacancias de oxígeno en los cristales de Titanato de plomo PbTiO3

Estudio químico-cuántico de los defectos producidos por las vacancias de oxígeno en los cristales de Titanato de plomo PbTiO

Li and Na Diffusion in TiO2 from Quantum Chemical Theory versus Electrochemical Experiment

Diffusion of Li and Na ions in TiO2, anatase, has been studied using theor. (quantum chem. ab initio periodic Hartree-Fock and a modified semiempirical INDO) as well as electrochem. (chronocoulometry) methods. On the basis of the theor. calcns., the geometry of equil. and transition states for the impurities as well as the cryst. framework are analyzed and discussed. The calcd. activation energies for Li+ and Na+ diffusion were found to be only slightly higher than 0.5 eV by both theor. methods. The agreement of either theor. method with the electrochem. expts., 0.60 and 0.52 eV for Li+ and Na+, resp., is also remarkably good

Study of the electronic and structural properties of tin dioxide and armchair graphene nanoribbons

Scuola di Dottorato "Archimede" in Scienze, Comunicazione e Tecnologie, Indirizzo:Scienze e Tecnologiie Complessi, Ciclo XXVIII, a.a. 2015-2016This dissertation is focused on the study of the electrical and structural properties of two emerging materials, the tin dioxide (SnO2) and graphene, which have attracted the interest of the semiconductor-device community due to their extraordinary characteristics. The SnO2 has been studied by means of ab initio simulations (Vienna ab initio Simulation Package, VASP). Both n-type and p-type conductivities were investigated. The intrinsic n-type conductivity has been achieved through two schemes: the first one through the combination of oxygen deficiencies and interstitial atoms inside the SnO2 lattice, whereas in the second one, through the combination of interstitial and/or substitutional hydrogen atoms inside the SnO2 lattice. On the other hand, the p-type conductivity was achieved by codoping n-type SnO2 (from earlier configurations) with low concentrations of nitrogen and aluminum impurities. The performed theoretical studies, to a good extent, agree with the experimental results provided by our collaboration group at the National Central University, Jhong-Li (Taiwan). In prospective, these results confirmed that SnO2 is a promising candidate to replace indium in transparent conductive oxides (TCOs) used in photovoltaic, thin-film transistor, and transparent electronic applications. The theoretical study of graphene has been conducted by means of a tight-binding approach (Atomistic ToolKit simulation package, ATK): the electrical and structural properties of edge-defected armchair graphene nanoribbons (AGNRs) were studied. It was found that Stone-Wales defect (very common in carbon allotropes) placed at the edges of the AGNRs can spark an extra opening of the energy gap in graphene, in addition to that obtained through the quantum confinement of electrons. Moreover, an experimental study on the electrical properties of graphene was carried out at the Tyndall National Institute (Ireland) to understand the influence of multiple cleaning treatments on graphene field-effect transistor (GFET) devices. Debris from residual polymers that appeared during device fabrication was swept off the graphene surface without significantly degrading the electronic properties of the graphene flake. The results suggest that the unusual but extraordinary properties of these graphene allotropes can be considered as a very innovative booster for semiconductor devices, allowing the improvement of the scaling trend beyond that obtained with conventional materials.Università della Calabri