DEFIS - Departamento de Física
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Navegando DEFIS - Departamento de Física por Assunto "2D materials"
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Item B–C–N diamondol-like compounds : stability trends and electronic properties.(2022) Pinto, Allan Kleyton Muniz; Pontes, João Guilherme de Moraes; Matos, Matheus Josué de Souza; Mazzoni, Mário Sérgio de Carvalho; Azevedo, Sérgio André FontesIn this work we apply first principles calculations to investigate the stability trends of mixed boron, nitrogen and carbon diamondol-like compounds. Several distinct geometric models are tested by varying the stoichiometry and position of boron and nitrogen dopants. We verify the special stability of a complete boron nitride compound – the bonitrol –, and we show that carbon substitutions in the bonitrol structure may also lead to stable systems. The electronic characterization of the resulting compounds indicates a rich phenomenology, with metallic, semimetallic, half-metallic and semiconducting behaviors.Item Compression induced modification of boron nitride layers : a conductive two-dimensional BN compound.(2019) Barboza, Ana Paula Moreira; Matos, Matheus Josué de Souza; Chacham, Helio; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Mazzoni, Mario Sergio de Carvalho; Neves, Bernardo Ruegger AlmeidaThe ability of creating materials with improved properties upon transformation processes applied to conventional materials is the keystone of materials science. Here, hexagonal boron nitride (h-BN), a large bandgap insulator, is transformed into a conductive two-dimensional (2D) material – bonitrol – that is stable at ambient conditions. The process, which requires compression of at least two h-BN layers and hydroxyl ions, is characterized via scanning probe microscopy experiments and ab initio calculations. This material and its creation mechanism represent an additional strategy on the transformation of known 2D materials into artificial advanced materials with exceptional propertiesItem Crystal-oriented wrinkles with origami-type junctions in few-layer hexagonal boron nitride.(2015) Oliveira, Camilla Karla Brites Queiroz Martins de; Gomes, Egleidson Frederik do Amaral; Prado, Mariana C.; Souza, Thonimar Vieira de Alencar; Nascimento, Regiane do; Moreira, Leandro Malard; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Chacham, Helio; Paula, Ana Maria de; Neves, Bernardo Ruegger AlmeidaUnderstanding layer interplay is the key to utilizing layered heterostructures formed by the stacking of different two-dimensional materials for device applications. Boron nitride has been demonstrated to be an ideal substrate on which to build graphene devices with improved mobilities. Here we present studies on the morphology and optical response of annealed few-layer hexagonal boron nitride flakes deposited on a silicon substrate that reveal the formation of linear wrinkles along well-defined crystallographic directions. The wrinkles formed a network of primarily threefold and occasionally fourfold origami-type junctions throughout the sample, and all threefold junctions and wrinkles formed along the armchair crystallographic direction. Furthermore, molecular dynamics simulations yielded, through spontaneous symmetry breaking, wrinkle junction morphologies that are consistent with both the experimental results and the proposed origami-folding model. Our findings indicate that this morphology may be a general feature of several two-dimensional materials under proper stress-strain conditions, resulting in direct consequences in device strain engineering.Item Liquid phase exfoliation of talc : effect of the medium on flake size and shape.(2023) Sousa, Samuel M.; Morais, Helane Lucia Oliveira de; Santos, Joyce Cristina da Cruz; Barboza, Ana Paula Moreira; Neves, Bernardo Ruegger Almeida; Pinto, Elisângela Silva; Prado, Mariana de CastroIndustrial applications of nanomaterials require large-scale production methods, such as liquid phase exfoliation (LPE). Regarding this, it is imperative to characterize the obtained materials to tailor parameters such as exfoliation medium, duration, and mechani- cal energy source to the desired applications. This work presents results of statistical analyses of talc flakes obtained by LPE in four different media. Talc is a phyllosilicate that can be exfoliated into nanoflakes with great mechanical properties. Sodium cholate at two different concentrations (below and at the critical micelar concentration), butanone, and Triton-X100 were employed as exfoli- ation medium for talc. Using recent published statistical analysis methods based on atomic force microscopy images of thousands of flakes, the shape and size distribution of nanotalc obtained using the four different media are compared. This comparison high- lights the strengths and weaknesses of the media tested and hopefully will facilitate the choice of the medium for applications that have specific requirements.Item Universal deformation pathways and flexural hardening of nanoscale 2D-material standing folds.(2018) Chacham, Helio; Barboza, Ana Paula Moreira; Oliveira, Alan Barros de; Oliveira, Camilla Karla Brites Queiroz Martins de; Batista, Ronaldo Junio Campos; Neves, Bernardo Ruegger AlmeidaIn the present work, we use atomic force microscopy nanomanipulation of 2D-material standing folds to investigate their mechanical deformation. Using graphene, h-BN and talc nanoscale wrinkles as testbeds, universal force–strain pathways are clearly uncovered and well-accounted for by an analytical model. Such universality further enables the investigation of each fold bending stiffness κ as a function of its characteristic height h 0. We observe a more than tenfold increase of κ as h 0 increases in the 10–100 nm range, with power-law behaviors of κ versus h 0 with exponents larger than unity for the three materials. This implies anomalous scaling of the mechanical responses of nano-objects made from these materials.