Navegando por Autor "Barbosa, Tiago Campolina"
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Item Graphene/h-BN heterostructures under pressure : from van der Waals to covale.(2019) Barboza, Ana Paula Moreira; Souza, Alan Custodio dos Reis; Matos, Matheus Josué de Souza; Brant, Juliana Caldeira; Barbosa, Tiago Campolina; Chacham, Helio; Mazzoni, Mário Sérgio de Carvalho; Neves, Bernardo Ruegger AlmeidaScanning probe microscopy and ab initio calculations reveal modifications on the electronic and structural properties of graphene/h-BN heterostructures induced by compression. Using AFM and EFM techniques, with charge injection being made in the heterostructures at different pressures, the charge injection efficiency monotonically decreases with increasing pressure for monolayer-graphene (MLG)+BN heterostructures, indicative of a conductor-insulator electronic transition. Bilayer-graphene (BLG)+BN and trilayer-graphene (TLG)+BN heterostructures show a non-monotonic behavior of charge injection versus pressure, indicative of competing electronic structure modifications. First-principle calculations of these systems indicate a pressure-induced van der Waals-to-covalent interlayer transition, where such interlayer covalent binding, in the presence of water molecules, results in a disordered insulating structure for the MLG + BN case, while it leads to an ordered conducting structure for both BLG + BN and TLG + BN heterostructures. These opposing effects may have a strong influence on graphene/h-BN-based electronic devices and their physics under pressurized environments.Item Investigation of spatially localized defects in synthetic WS2 monolayers.(2022) Rosa, Bárbara Luiza Teixeira; Fujisawa, Kazunori; Cruz, Joyce Cristina da; Zhang, Tianyi; Matos, Matheus Josué de Souza; Sousa, Frederico Barros de; Barbosa, Tiago Campolina; Fonseca, Lucas Lafetá Prates da; Ramos, Sérgio L. L. M.; Carvalho, Bruno Ricardo de; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Terrones, Mauricio; Moreira, Leandro MalardWhile the spatially nonhomogeneous light emission from synthetic WS2 monolayers is frequently reported in the literature, the nature of this phenomenon still requires thoughtful investigation. Here, we combine several characterization techniques (optical imaging, scanning probe and electron microscopy) along with density func- tional theory to investigate the presence of substitutional doping localized at narrow regions along the S zigzag edge of WS2 monolayers. We verified that photoluminescence quenching along narrow regions is not related to grain boundaries but to substitutional impurities of lighter metals at the W sites, which modify the radiative and nonradiative decay channels. We also found potential candidates for occupying the W site through ADF-STEM analysis and discussed their impact on photoluminescence quenching by performing density functional theory calculations. Our findings shed light on how atomic defects introduced during WS2 monolayer’s synthesis impact the crystalline quality and, therefore, the development of high-performance optoelectronic devices based on semiconducting 2D materials.