Browsing by Author "Chacham, Helio"
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Item Aerosol-printed MoS2 ink as a high sensitivity humidity sensor.(2022) Pereira, Neuma das Mercês; Rezende, Natália Pereira; Cunha, Thiago Henrique Rodrigues da; Barboza, Ana Paula Moreira; Silva, Glaura Goulart; Lippross, Daniel; Neves, Bernardo Ruegger Almeida; Chacham, Helio; Ferlauto, Andre Santarosa; Lacerda, Rodrigo GribelMolybdenum disulfide (MoS2) is attractive for use in nextgeneration nanoelectronic devices and exhibits great potential for humidity sensing applications. Herein, MoS2 ink was successfully prepared via a simple exfoliation method by sonication. The structural and surface morphology of a deposited ink film was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). The aerosol-printed MoS2 ink sensor has high sensitivity, with a conductivity increase by 6 orders of magnitude upon relative humidity increase from 10 to 95% at room temperature. The sensor also has fast response/recovery times and excellent repeatability. Possible mechanisms for the water-induced conductivity increase are discussed. An analytical model that encompasses two ionic conduction regimes, with a percolation transition to an insulating state below a low humidity threshold, describes the sensor response successfully. In conclusion, our work provides a low-cost and straightforward strategy for fabricating a highperformance humidity sensor and fundamental insights into the sensing mechanism.Item Apparent softening of wet graphene membranes on a microfluidic platfor.(2018) Ferrari, Gustavo Arrighi; Oliveira, Alan Barros de; Almeida, Ive Silvestre de; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Fernandes, Thales Fernando Damasceno; Meireles, Leonel Muniz; Silva Neto, Eliel Gomes da; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Lacerda, Rodrigo GribelGraphene is regarded as the toughest two-dimensional material (highest in-plane elastic properties) and, as a consequence, it has been employed/proposed as an ultrathin membrane in a myriad of microfluidic devices. Yet, an experimental investigation of eventual variations on the apparent elastic properties of a suspended graphene membrane in contact with air or water is still missing. In this work, the mechanical response of suspended monolayer graphene membranes on a microfluidic platform is investigated via scanning probe microscopy experiments. A high elastic modulus is measured for the membrane when the platform is filled with air, as expected. However, a significant apparent softening of graphene is observed when water fills the microfluidic system. Through molecular dynamics simulations and a phenomenological model, we associate such softening to a water-induced uncrumpling process of the suspended graphene membrane. This result may bring substantial modifications on the design and operation of microfluidic devices which exploit pressure application on graphene membranes.Item Charge and spin current rectification through functionalized boron nitride bilayers.(2022) Moraes, Elizane Efigenia de; Pinto, Alysson Alves; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Chacham, HelioRecent experiments have reported the transformation of few-layer hexagonal boron nitride (h-BN) into sp3 -bonded c-BN layers through the application of pressure. A proposed mechanism, based on calculations and experiments, is that the phenomenon is facilitated by BN surface functionalization with OH or H radicals. In the present work, we perform ab initio calculations of ballistic electron transport, between Au electrodes, across such functionalized structures. We find that the stabilization of sp3 binding at zero pressure occurs for partial H coverage (≈58%), whereas large OH coverages (>75%) are necessary. Regarding transport properties, we find that all functionalized BN bilayer films present current rectification, consistent with the experimental findings. Maximum rectification occurs for partial OH and H coverages. The films also show spin-dependent transport, where, for a window of values of applied bias, a single spin component contributes to the total current, characterizing a spin filter behavior. Our results indicate that functionalized BN bilayer films are promising materials for the development of electronic devices where both charge and spin degrees of freedom might be manipulated.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 Controlling the electrical behavior of semiconducting carbon nanotubes via tube contact.(2011) Barboza, Ana Paula Moreira; Carara, Sabrina Silva; Batista, Ronaldo Junio Campos; Chacham, Helio; Neves, Bernardo Ruegger AlmeidaItem Crystal reorientation and plastic deformation of single-layer MoS and MoSe under uniaxial stress.(2021) Alencar, Ananias Borges; Oliveira, Alan Barros de; Chacham, HelioWe investigate theoretically, through of first-principles calculations, the effect of the application of large in-plane uniaxial stress on single-layer of MoS2, MoSe2, and MoSSe alloys. For stress applied along the zigzag (zz) direction, we predict an anomalous behavior near the point fracture. This behavior is characterized by the reorientation of the MoS2 structure along the applied stress from zz to armchair due to the formation of transient square-lattice regions in the crystal, with an apparent crystal rotation of 30 degrees. After reorientation, a large plastic deformation ε = √3 − 1 remains after the stress is removed. This behavior is also observed in MoSe2 and in MoSSe alloys. This phenomenon is observed both in stress-constrained geometry optimizations and in ab initio molecular dynamics simulations at finite temperature and applied stress.Item 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 Edge-reconstructed, few-layered graphene nanoribbons : stability and electronic properties.(2017) Gonçalves, Juliana Aparecida; Nascimento, Regiane do; Matos, Matheus Josué de Souza; Oliveira, Alan Barros de; Chacham, Helio; Batista, Ronaldo Junio CamposWe report a first-principles study of edgereconstructed, few-layered graphene nanoribbons. We find that the nanoribbon stability increases linearly with increasing width and decreases linearly with increasing number of layers (from three to six layers). Specifically, we find that a threelayer 1.3 nm wide ribbon is energetically more stable than the C60 fullerene, and that a 1.8 nm wide ribbon is more stable than a (10,0) carbon nanotube. The morphologies of the reconstructed edges are characterized by the presence of five-, six-, and sevenfold rings, with sp3 and sp2 bonds at the reconstructed edges. The electronic structure of the few-layered nanoribbons with reconstructed edges can be metallic or semiconducting, with band gaps oscillating between 0 and 0.28 eV as a function of ribbon width.Item Estudo sobre fluxo de água em nanotubos de carbono e nitreto de boro hexagonal.(2018) Souza, Jarbas Ubiratan Vieira de; Batista, Ronaldo Junio Campos; Nascimento, Regiane do; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Chacham, HelioA Nanociência tem contribuído com várias áreas do conhecimento como biologia, física, química, etc. Sendo, então, uma importante área de estudo com impacto relevante. Dada essa afirmação, este trabalho teve foco no estudo de nanoestruturas, investigando propriedades dinâmicas de nanotubos constituídos de Carbono e Nitreto de Boro hexagonal, interagindo com moléculas de água em seu interior. Para estes fins, realizamos cálculos de dinâmica molecular com os potenciais empíricos: Lennard-Jones e Reaxff. Primeiramente, investigamos as propriedades dinâmicas de nanotubos de Carbono, com diversos diâmetros, interagindo com moléculas de água em seu interior. Onde posteriormente foi aplicado velocidade constante ao tubo, com o objetivo de observar a interação tubo/água a medida que o sistema atingisse equilíbrio. Assim, com auxílio de um modelo analítico foi possível extrair uma variável com unidade de medida de viscosidade (viscosidade aparente). Em seguida, foi feito o mesmo para nanotubos de nitreto de boro hexagonal, uma vez que poderíamos analisar a viscosidade aparente em ambos tipos de nanotubos com objetivo de compará-las. Foi então observado que a viscosidade em nanotubos compostos de carbono/água é maior que as apresentadas nos de h-BN/água. A velocidade constante de movimento do tubo na faixa de valor estudada, não influencia a viscosidade aparente em nenhum dos materiais em ambos potenciais. Com os resultados também conseguimos observar o comportamento da viscosidade na região cujos raios dos tubos variam de 4 a 14 angstroms (quiralidades (6,6), (9,9), (12,12), (16,16) e (20,20)).Item Graphene electromechanical water sensor : the Wetristor.(2019) Meireles, Leonel Muniz; Silva Neto, Eliel Gomes da; Ferrari, Gustavo Arrighi; Neves, Paulo A. A.; Gadelha, Andreij de Carvalho; Almeida, Ive Silvestre de; Taniguchi, Takashi; Watanabe, Kenji; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Campos, Leonardo Cristian; Lacerda, Rodrigo GribelA water-induced electromechanical response in suspended graphene atop a microfluidic channel is reported. The graphene membrane resistivity rapidly decreases to ≈25% upon water injection into the channel, defining a sensi-tive “channel wetting” device—a wetristor. The physical mechanism of the wetristor operation is investigated using two graphene membrane geometries, either uncovered or covered by an inert and rigid lid (hexagonal boron nitride multilayer or poly(methyl methacrylate) film). The wetristor effect, namely the water-induced resistivity collapse, occurs in uncovered devices only. Atomic force microscopy and Raman spectroscopy indicate substantial morphology changes of graphene membranes in such devices, while covered membranes suffer no changes, upon channel water filling. The results suggest an electromechanical nature for the wetristor effect, where the resistivity reduction is caused by unwrinkling of the graphene membrane through channel filling, with an eventual direct doping caused by water being of much smaller magnitude, if any. The wetristor device should find useful sensing applications in general micro- and nanofluidics.Item Graphene nanoencapsulation action at an air/lipid interface.(2022) Ferrari, Gustavo Arrighi; Chacham, Helio; Oliveira, Alan Barros de; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Meireles, Leonel Muniz; Barboza, Ana Paula Moreira; Almeida, Ive Silvestre de; Neves, Bernardo Ruegger Almeida; Lacerda, Rodrigo GribelIn the present work, we apply a microfluidic channel platform to study mechanical and adhesion properties of suspended graphene in contact with oleic acid (a lipid). In the platform, one side of the suspended graphene, atop a window in a fluidic channel, is placed in contact with the lipid, and the mechanical response of graphene is experimentally accessed with an atomic force microscope probe. We observe a strong effect arising from the presence of oleic acid: the probe undergoes a large jump-to-contact effect, being pulled and partially encapsulated by graphene, in a phagocytosis-like phenomenon, until it penetrates 0.2 lm into graphene. In contrast, such encapsulation effect is neg- ligible in the absence of oleic acid in the channel, with probe penetration of less than 0.02 lm. The lipid-induced encapsulation effect is observed to occur concurrently with graphene delamination from the window walls. Molecular dynamics simulations and continuum mechanics analytical modeling are also performed, the latter allowing quantitative fittings to the experiments.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 Graphene/h-BN in-plane heterostructures : stability and electronic and transport properties.(2019) Nascimento, Regiane do; Moraes, Elizane Efigenia de; Matos, Matheus Josué de Souza; Prendergast, David; Manhabosco, Taíse Matte; Oliveira, Alan Barros de; Chacham, Helio; Batista, Ronaldo Junio CamposWe present a first-principles study of structural, electronic, and transport properties of in-plane Gr:BN heterostructures in the form of graphene stripes embedded in a BN matrix. In our calculations, we consider carbon, nitrogen, and boron chemical potentials that are consistent with growth conditions (gas sources and temperatures) at either nitrogen-rich or boron-rich environments. Interestingly, we find that structures with excess of B atoms can be energetically more stable than structures with excess of N atoms even in N-rich growth conditions. The general trend is that N-rich growth conditions favor B/N stoichiometric heterostructures, while B-rich growth conditions favor heterostructures with excess of B atoms at the graphene/BN junctions, such that only B−C bonds occur at both edges of a graphene stripe region embedded in BN. We also investigate the dependence of magnetic properties and the band gap magnitudes of graphene stripe regions embedded in BN with several structural characteristics. We find that graphene stripes with only one bond type (either B−C or N−C) at the graphene/BN edges always present metallic behavior, with zigzag-oriented stripes of this type presenting large magnetic moments. Finally, we obtain the characteristic I−V curves for systems formed by junctions of two graphene stripes embedded in BN, one of them terminated by C−N bonds and the other terminated by C−B bonds. We find that systems of this type should present rectifying behavior.Item High throughput investigation of an emergent and naturally abundant 2D material : clinochlore.(2022) Gonçalves, Raphaela de Oliveira; Guallichico, Luis Antonio Guallichico; Policarpo, Eduardo; Cadore, Alisson Ronieri; Freitas, Raul de Oliveira; Silva, Francisco Mateus Cirilo da; Teixeira, Veronica de Carvalho; Paniago, Roberto Magalhães; Chacham, Helio; Matos, Matheus Josué de Souza; Souza, Angelo Malachias de; Krambrock, Klaus Wilhelm Heinrich; Barcelos, Ingrid DavidPhyllosilicate minerals, which form a class of naturally occurring layered materials (LMs), have been recently considered as a low-cost source of two-dimensional (2D) materials. Clinochlore [Mg5Al(AlSi3)O10(OH)8] is one of the most abundant phyllosilicate minerals in nature, exhibiting the capability to be mechanically exfoliated down to a few layers. An important characteristic of clinochlore is the natural occurrence of defects and impurities which can strongly affect their optoelectronic properties, possibly in technologically interesting ways. In the present work, we carry out a thorough investigation of the clinochlore structure on both bulk and 2D exfoliated forms, discussing its optical features and the influence of the insertion of impurities on its macroscopic prop- erties. Several experimental techniques are employed, followed by theoretical first-principles calculations considering several types of naturally-ocurring transition metal impurities in the mineral lattice and their effect on electronic and optical properties. We demonstrate the existence of requirements concerning surface quality and insulating properties of clinochlore that are mandatory for its suitable application in nanoelectronic devices. The results presented in this work provide important informations for clinochlore potential applications and establish a basis for further works that intend to optimize its properties to relevant 2D technological applications through defect engineering.Item Investigação de primeiros princípios de estruturas de carbono com ligações sp2 e sp3.(2016) Gonçalves, Juliana Aparecida; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Batista, Ronaldo Junio Campos; Chacham, Helio; Barboza, Ana Paula MoreiraAlótropos nanoestruturados de carbono têm atraído a atenção de muitos pesquisadores nas últimas décadas. Entre estes alótropos, o grafeno tem sido intensivamente investigado devido suas interessantes propriedades que podem levar a várias aplicações tecnológicas. Outro alótropo de carbono que tem sido muito estudado são os nanotubos de carbono (CNTs). Eles apresentam potencial para aplicações em nanotecnologia, eletrônica, óptica e outras áreas de ciências dos materiais. A combinação de tais materiais podem resultar em estruturas híbridas com novas propriedades interessantes ou eles poderiam melhorar as propriedades que impedem a sua real aplicação, como por exemplo a manipulação de uma única folha de grafeno. Neste trabalho, empregamos cálculos de Primeiros Princípios baseados na Teoria do Funcional da Densidade (DFT) dentro da Aproximação de Gradiente Generalizado (GGA), como implementado no programa SIESTA, para investigar nanoestruturas compostas por nanotubos de carbono, grafeno e fitas de grafeno de poucas camadas. Observamos que uma estrutura híbrida composta por 4 camadas de grafeno e um nanotubo de carbono (10,0) é a estrutura energeticamente mais estável entre aqueles que combinam tubo e algumas camadas de grafeno. A presença do tubo modifica a resistência mecânica do grafeno e tal estrutura híbrida é ferromagnética, apesar de ser feita de apenas átomos de carbono. Reconstruções de bordas foram observadas quando a estrutura híbrida foi esticada até o seu colapso, o que nos leva a investigar a estrutura de poucas camadas de bordas de grafeno. Um padrão no qual átomos das extremidades de algumas camadas de fitas grafeno formam pentágonos e heptágonos foi identificado. Com base em tal padrão, geramos fitas de grafeno com 3, 4, 5 e 6 camadas. No que diz respeito à estabilidade energética de tais estruturas, notou-se que elas são energeticamente mais estáveis do que nanotubos de carbono (10,0) e C60, os quais existem na natureza. Essas estruturas também têm características ferromagnéticas, que podem ser associadas com a presença de defeitos topológicos, heptágonos e pentágonos, e suas conexões sp2 e sp3.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.Item Modelos efetivos para separação solvente-soluto através de nanoestruturas : teoria e simulações computacionais.(2016) Vasconcelos, Cláudia Karina Barbosa de; Oliveira, Alan Barros de; Barbosa, Márcia Cristina Bernardes; Barboza, Ana Paula Moreira; Chacham, Helio; Matos, Matheus Josué de SouzaA escassez de água potável nos mais diversos países tem se mostrado um problema cada vez mais relevante. Estima-se que, atualmente, aproximadamente 748 milhões de pessoas no planeta não têm acesso à fontes de água potável. Sob esse aspecto, a dessalinização de água do mar tem se mostrado uma alternativa promissora, não apenas por 97% da água do planeta estar concentrada nos oceanos e mares mas também pelo fato do percentual de água obtido desta maneira ainda ser muito pequeno. Em especial, o processo de dessalinização da água através de nanoporos tem recebido grandes esforços científicos e tecnológicos. Apesar dos resultados animadores, um dos problemas encontrados é que o processo de dessalinização de água é tipicamente macro. Mesmo com o poder computacional disponível atualmente, é impossível simular este problema em escala-macro. Daí a importância de se procurar modelos mais simples e computacionalmente mais baratos. Nesse sentido, uma alternativa eficaz para a simulação computacional de fluidos complexos é a utilização dos potenciais efetivos do tipo caroço atenuado (core-softened potentials). Estes potenciais tem sido utilizados para investigar fluidos anômalos dando bons resultados na descrição de propriedades dinâmicas, termodinâmicas e estruturais desses fluidos. Devido à sua simplicidade, as simulações se tornam mais rápidas e tratamentos matemáticos se tornam possíveis. Baseado nesses potenciais, este trabalho propõe um modelo para a separação soluto solvente a partir de osmose reversa. O comportamento das partículas filtradas de solvente e as propriedades, tais como rejeição de soluto e fluxo volumétrico de solvente, foram comparadas com resultados prévios apresentados na literatura para modelos moleculares clássicos. O objetivo deste trabalho é o de dar os primeiros passos para o desenvolvimento de um modelo coarse-grained de dessalinização de água, onde a abordagem de problemas em escalas maiores, tanto em tempo quanto em tamanho, possam ser viáveis computacionalmente.Item Modifications in graphene electron states due to a deposited lattice of Au nanoparticles : density functional calculations.(2009) Carara, Sabrina Silva; Batista, Ronaldo Junio Campos; Chacham, HelioWe perform first-principles investigations of two-dimensional, triangular lattices of Au38 nanoparticles deposited on a graphene layer. We find that lattices of thiolate-covered nanoparticles cause electronic structure modifications in graphene such as minigaps, charge transfer, and new Dirac points, but graphene remains metallic. In contrast, for a moderate coverage of nanoparticles __0.2 nm−2_, a lattice of bare _noncovered_ Au nanoparticles may induce periodic deformations on the graphene layer leading to the opening of a band gap of a few tens of meV at the Dirac point, in such a way that a properly charged system might become a semiconductor.Item Nanomechanics of few-layer materials : do individual layers slide upon folding?(2020) Batista, Ronaldo Junio Campos; Dias, Rafael Freitas; Barboza, Ana Paula Moreira; Oliveira, Alan Barros de; Manhabosco, Taíse Matte; Silva, Thiago R. Gomes; Matos, Matheus Josué de Souza; Gadelha, Andreij de Carvalho; Rabelo, Cassiano; Cançado, Luiz Gustavo de Oliveira Lopes; Jorio, Ado; Chacham, Helio; Neves, Bernardo Ruegger AlmeidaFolds naturally appear on nanometrically thin materials, also called “2D materials”, after exfoliation, eventually creating folded edges across the resulting flakes. We investigate the adhesion and flexural properties of single-layered and multilayered 2D materials upon folding in the present work. This is accomplished by measuring and modeling mechanical properties of folded edges, which allows for the experimental determination of the bending stiffness (κ) of multilayered 2D materials as a function of the number of layers (n). In the case of talc, we obtain κ ∝ n 3 for n ≥ 5, indicating no interlayer sliding upon folding, at least in this thickness range. In contrast, tip-enhanced Raman spectroscopy measurements on edges in folded graphene flakes, 14 layers thick, show no significant strain. This indicates that layers in graphene flakes, up to 5 nm thick, can still slip to relieve stress, showing the richness of the effect in 2D systems. The obtained interlayer adhesion energy for graphene (0.25 N/m) and talc (0.62 N/m) is in good agreement with recent experimental results and theoretical predictions. The obtained value for the adhesion energy of graphene on a silicon substrate is also in agreement with previous results.Item Nanoporous graphene and H‑BN from BCN precursors : first-principles calculations.(2018) Dias, Rafael Freitas; Martins, Jonathan da Rocha; Chacham, Helio; Oliveira, Alan Barros de; Manhabosco, Taíse Matte; Batista, Ronaldo Junio CamposWe propose, based on results of first-principles calculations, that nanoporous graphene and h-BN might be efficiently produced from B–C–N layers as precursors. In our calculations, we find that the removal of the h-BN islands that naturally occur in BN-doped graphene, forming nanoporous graphene, requires less energy than if pristine graphene is used as a precursor. The same reduction ΔEf in pore formation energy is found for nanoporous h-BN obtained from graphene-doped BN as a precursor. ΔEf is found to increase linearly as a function of the number of B–C and N–C bonds at the island boundary, with the slope being nearly the same for either porous graphene or porous h-BN. This is explained by an analytical bond-energy model. In the case of porous graphene, we find that the pore formation energy would be further reduced by passivation by pyridinic and quaternary remnant nitrogen atoms at the pore edges, a mechanism that is found to be more effective than the passivation by hydrogen atoms. Both mechanisms for pore formation energy reduction should lead to a possibly efficient method for nanoporous graphene production.