Browsing by Author "Neves, Bernardo Ruegger Almeida"
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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 Carbon nanotube-cellulose ink for rapid solvent identification.(2023) Cardoso, Tiago Amarante de Barros; Cunha, Thiago Henrique Rodrigues da; Moreira, Claudio Laudares; Barboza, Ana Paula Moreira; Santos, Ana Carolina dos; Pereira, Cíntia Lima; Silva, Vinícius Ornelas da; Neves, Bernardo Ruegger Almeida; Ferlauto, Andre Santarosa; Lacerda, Rodrigo GribelIn this work, a conductive ink based on microfibrillated cellulose (MFC) and multiwalled carbon nanotubes (MWCNTs) was used to produce transducers for rapid liquid identification. The transducers are simple resistive devices that can be easily fabricated by scalable printing techniques. We monitored the electrical response due to the interaction between a given liquid with the carbon nanotube–cellulose film over time. Using principal component analysis of the electrical response, we were able to extract robust data to differentiate between the liquids. We show that the proposed liquid sensor can classify different liquids, including organic solvents (acetone, chloroform, and different alcohols) and is also able to differentiate low concentrations of glycerin in water (10–100 ppm). We have also investigated the influence of two important properties of the liquids, namely dielectric constant and vapor pressure, on the transduction of the MFC-MWCNT sensors. These results were corroborated by independent heat flow mea- surements (thermogravimetric analysis). The proposed MFC-MWCNT sensor platform may help paving the way to rapid, inexpensive, and robust liquid analysis and identification.Item Charge transfer between carbon nanotubes on surfaces.(2015) Araujo, Karolline Aparecida de Souza; Barboza, Ana Paula Moreira; Fernandes, Thales Fernando Damasceno; Shadmi, Nitzan; Joselevich, Ernesto; Mazzoni, Mário Sérgio de Carvalho; Neves, Bernardo Ruegger AlmeidaThe charge transfer between neighboring single-walled carbon nanotubes (SWNTs) on a silicon oxide surface was investigated as a function of both the SWNT nature (metallic or semiconducting) and the anode/cathode distance using scanning probe techniques. Two main mechanisms were observed: a direct electron tunneling described by the typical Fowler–Nordheim model, and indirect electron transfer (hopping) mediated by functional groups on the supporting surface. Both mechanisms depend on the SWNT nature and on the anode/cathode separation: direct electron tunneling dominates the charge transfer process for metallic SWNTs, especially for large distances, while both mechanisms compete with each other for semiconducting SWNTs, prevailing one over the other depending on the anode/cathode separation. These mechanisms may significantly influence the design and operation of SWNT-based electronic devices.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 Controle de propriedades eletromecânicas de dicalcogenetos de metais de transição por microscopia de varredura por sonda.(2019) Bessa, Maurício Vasconcelos; Barboza, Ana Paula Moreira; Neves, Bernardo Ruegger Almeida; Barboza, Ana Paula Moreira; Souza, Thonimar Vieira de Alencar; Oliveira, Camilla Karla Brites Queiroz Martins deNeste trabalho serão apresentados resultados a respeito de propriedades eletromecânicas de Dicalcogenetos de Metais de Transição (TMDs - Transition Metal Dichalcogenides). Todas as medidas experimentais foram realizadas no Laboratório de Nanoscopia do Departamento de Física da UFMG. Cálculos por primeiros princípios previram que, a aproximação das camadas ou hidrogenação desses materiais poderia levar a diminuição do gap de energia dos mesmos. Utilizando técnicas de Microscopia de Varredura por Sonda foi possível verificar, experimentalmente, este resultado. Analisamos os efeitos produzidos pela aplicação de força compressiva e campo elétrico, em monocamadas e poucas camadas de TMDs. Observamos que os materiais apresentaram duas transições: a primeira ocorre em forças baixas (F < 200 nN), e é devida a hidrogenação da amostra. Já a segunda transição, ocorre em forças mais altas (F > 400 nN) e deve-se a aproximação das camadas dos TMDs estudados. A transição do comportamento semicondutor para o comportamento metálico, induzida pelo fechamento do gap em TMDs, é um processo reversível, dependente da força compressiva e do ambiente em que o experimento é realizado.Item 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 Corrosion, wear and wear–corrosion behavior of graphite-like a-C:H films deposited on bare and nitrided titanium alloy.(2013) Manhabosco, Taíse Matte; Barboza, Ana Paula Moreira; Batista, Ronaldo Junio Campos; Neves, Bernardo Ruegger Almeida; Muller, Iduvirges LourdesThis work presents a comparative wear, corrosion and wear–corrosion (the last one in a simulated physiological solution) study of graphite-like a-C:H (GLCH) films deposited on bare and nitrided Ti6Al4V alloy. Films, deposited by r.f. PACVD, presented low porosity and promoted high corrosion resistance. The friction coefficient of the films was very lowwith appreciablewear resistance at roomconditions. However, due to the simultaneous action of both load and the corrosive environment in wear–corrosion tests a marked reduction in the coating lifetime was observed. Unexpectedly, films deposited on the nitrided alloy presented a lifetime at least ten times shorter than that of films on bare alloy. We explain such a result in terms of film/substrate interaction. The weak GLCH/nitride alloy interaction facilitates fluid penetration between the film and the substratewhich leads to a fast film delamination. Such an interpretation is supported by force curve measurements, which show that the interaction between GLCH and nitrided alloy is four times weaker than that between GLCH and bare alloy.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 Electro-optical interfacial effects on a graphene/π-conjugated organic semiconductor hybrid system.(2018) Araujo, Karolline Aparecida de Souza; Cury, Luiz Alberto; Matos, Matheus Josué de Souza; Fernandes, Thales Fernando Damasceno; Cançado, Luiz Gustavo de Oliveira Lopes; Neves, Bernardo Ruegger AlmeidaThe influence of graphene and retinoic acid (RA) – a π-conjugated organic semiconductor – interface on their hybrid system is investigated. The physical properties of the interface are assessed via scanning probe microscopy, optical spectroscopy (photoluminescence and Raman) and ab initio calculations. The graphene/RA interaction induces the formation of a well-organized π-conjugated self-assembled monolayer (SAM) at the interface. Such structural organization leads to the high optical emission efficiency of the RA SAM, even at room temperature. Additionally, photo-assisted electrical force microscopy, photo-assisted scanning Kelvin probe microscopy and Raman spectroscopy indicate a RA-induced graphene doping and photo-charge generation. Finally, the optical excitation of the RA monolayer generates surface potential changes on the hybrid system. In summary, interface-induced organized structures atop 2D materials may have an important impact on both design and operation of π-conjugated nanomaterialbased hybrid systems.Item Electromechanical modulations in transition metal dichalcogenide nanosheets : implications for environmental sensors.(2021) Bessa, Maurício Vasconcelos; Freitas, Wellington Damaceno de; Neme, Natália Paz; Martins, Luiz Gustavo Pimenta; Barboza, Ana Paula Moreira; Matos, Matheus Josué de Souza; Mazzoni, Mário Sérgio de Carvalho; Neves, Bernardo Ruegger AlmeidaTransition metal dichalcogenides (TMDs) are key players in the two-dimensional materials nanoarena due to their exquisite optoelectronic properties under a standard environment (room temperature and atmospheric pressure). Nevertheless, as reported in the literature, they may also portray interesting physical properties under different environments. Here, we show two distinct and significant electromechanical modulations in TMD nanosheets which are tuned by the environmental conditions (applied pressure and adsorbents). Using scanning probe microscopy techniques, we modify the environmental conditions and observe steplike rises in the electrical response of all studied TMDs (MoS2, WS2, MoSe2, and WSe2monolayers and few layers). Ab initio calculations enable full understanding of specific mechanisms behind these electromechanical modulations, which may find important applications in the design of TMD-based environmental sensors.Item Evaluation of anti-candida albicans activity and release of ketoconazole in PMMA-G-PEG 4000 films.(2022) Reynaldo, Juliana Ribeiro; Novack, Kátia Monteiro; Sousa, Lucas Resende Dutra; Vieira, Paula Melo de Abreu; Amparo, Tatiane Roquete; Souza, Gustavo Henrique Bianco de; Teixeira, Luiz Fernando de Medeiros; Barboza, Ana Paula Moreira; Neves, Bernardo Ruegger Almeida; Alvarenga, Meiry Edivirges; Martins, Felipe Terra; Santos, Viviane Martins Rebello dosModified release systems depend on the selection of an appropriate agent capable of controlling the release of the drug, sustaining the therapeutic action over time, and/or releasing the drug at the level of a particular tissue or target organ. Polyethylene glycol 4000 (PEG 4000) is commonly employed in drug release formulations while polymethyl methacrylate (PMMA) is non-toxic and has a good solubility in organic solvents. This study aimed at the incorporation of ketoconazole in PMMA-g-PEG 4000 and its derivatives, thus evaluating its release profile and anti-Candida albicans and cytotoxic activities. Ketoconazole was characterized and incorporated into the copolymers. The ketoconazole incorporated in the copolymer and its derivatives showed an immediate release profile. All copolymers with ketoconazole showed activity against Candida albicans and were non-toxic to human cells in the entire concentration tested.Item Exfoliation and characterization of a two-dimensional serpentine-based material.(2019) Santos, Joyce Cristina da Cruz; Barboza, Ana Paula Moreira; Matos, Matheus Josué de Souza; Barcelos, Ingrid David; Fernandes, Thales Fernando Damasceno; Soares, Edmar Avellar; Moreira, Roberto Luiz; Neves, Bernardo Ruegger AlmeidaWe report on an experimental investigation of serpentine, an abundant phyllosilicate, as an alternative source of two-dimensional (2D) nanomaterials. We show, through scanning probe microscopy (SPM) measurements, that natural serpentine mineral can be mechanically exfoliated down to few-layer flakes, where monolayers can be easily resolved. The parent serpentine bulk material was initially characterized via conventional techniques like XRD, XPS, FTIR and Raman spectroscopies and the results show that it is predominantly constituted by the antigorite mineral. From ab initio calculations using density functional theory, we also determine the geometry and electronic structure of antigorite, the observed structural form of serpentine. Additionally, we further characterized electrical and mechanical properties of the obtained 2D material flakes using SPM and broadband synchrotron infrared nanospectroscopy. Wavelength tuning of the serpentine vibrational resonances, assigned to in- and out-of-plane molecular vibrations, are observed and compared with the FTIR characterization of the parent bulk material. They show that there is no degradation of serpentine's structural properties during its mechanical exfoliation down to nanometer-thin sheets. Therefore, our results introduce the serpentine mineral as an attractive low-cost candidate in 2D materials applications.Item Glass-ionomer-propolis composites for caries inhibition: flavonoids release, physical-chemical, antibacterial and mechanical properties.(2019) Andrade, Ângela Leão; Lima, Adriana M.; Santos, Vagner Rodrigues; Silva, Rosangela Maria Ferreira da Costa e; Barboza, Ana Paula Moreira; Neves, Bernardo Ruegger Almeida; Vasconcellos, Walison Arthuso; Domingues, Rosana ZacariasThe addition of propolis extract (PE) to the glass ionomer results in an adhesive material for restorative treatment, with interesting properties mainly due to the flavonoids contained in the propolis extract. However, no study of the flavonoid release profile in these materials was reported. This work studies the flavonoid release profile in such materials aiming to contribute to the future synthesis of optimized devices adept to prolong the efficacy of the drug. The study involved the synthesis and study of the physicochemical, antibacterial and mechanical properties of glass ionomer cement (GIC) and glassionomer- propolis composites (GIC-PE). The samples were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analyses. The released concentration of flavonoids, the antimicrobial activity and the compressive strength were also evaluated. Antimicrobial activity was assessed against Streptococcus mutans, Streptococcus salivarius, and Candida albicans, common pathogens in the mouth. The results indicate that the antibacterial activity of GIC-PE samples is closely correlated with the release of flavonoids. The method used to prepare the composite GIC-PE leads to an initial drug delivery burst effect able to diminish partially the population of bacteria tested. The mechanical properties and thermal stability of GIC-PE are higher than those of the GIC and are clearly related to its microstructure. This study is clinically significant because the addition of propolis extract (PE) to the GIC resulted in a novel differentiated product with enhanced mechanical and antimicrobial properties compared to the GIC.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 Gypsum : an environment-friendly, inexpensive and robust height calibration standard at nanometer-scale for atomic force microscopy.(2019) Barboza, Ana Paula Moreira; Santos, Joyce Cristina da Cruz; Pinto, Elisângela Silva; Neves, Bernardo Ruegger AlmeidaGypsum is an Earth-abundant mineral with enormous applications in agriculture and civil engineering. Here, we show it is also an excellent height calibration standard alternative for atomic force microscopy (AFM). Using plain water as etchant, gypsum flakes readily review 0.75 nm tall terraces which are easy to image (lateral dimensions from tens to hundreds of nanometers) and robust against time in ambient conditions. Therefore, the present work demonstrates a new height standard alternative which is easily-available for all AFM microscopists around the world.Item High-pressure studies of atomically thin van der Waals materials.(2023) Martins, Luiz Gustavo Pimenta; Comin, Riccardo; Matos, Matheus Josué de Souza; Mazzoni, Mário Sérgio de Carvalho; Neves, Bernardo Ruegger Almeida; Yankowitz, MatthewTwo-dimensional (2D) materials and their moire superlattices represent a new frontier for quantum matter research due to the emergent properties associated with their reduced dimensionality and extreme tunability. The properties of these atomically thin van der Waals (vdW) materials have been extensively studied by tuning a number of external parameters such as temperature, electrostatic doping, magnetic field, and strain. However, so far pressure has been an under-explored tuning parameter in studies of these systems. The relative scarcity of high- pressure studies of atomically thin materials reflects the challenging nature of these experiments, but, concurrently, presents exciting oppor- tunities for discovering a plethora of unexplored new phenomena. Here, we review ongoing efforts to study atomically thin vdW materials and heterostructures using a variety of high-pressure techniques, including diamond anvil cells, piston cylinder cells, and local scanning probes. We further address issues unique to 2D materials such as the influence of the substrate and the pressure medium and overview efforts to theoretically model the application of pressure in atomically thin materials.Item Improved bioceramic coatings reinforced by nanostructured talc.(2022) Batista, Ana Bárbara; Silva, Michael Stanley da; Brito, Ana Carolina Ferreira de; Vasconcellos, Rebecca; Munk, Michele; Bueno, Mário José; Godoy, Geralda Cristina Durães de; Alvarenga, Érika Lorena Fonseca Costa de; Vasconcelos, Cláudia Karina Barbosa de; Righi, Ariete; Sousa, Edésia Martins Barros de; Oliveira, Alan Barros de; Batista, Ronaldo Junio Campos; Soares, Jaqueline dos Santos; Neves, Bernardo Ruegger Almeida; Barboza, Ana Paula Moreira; Manhabosco, Taíse MatteNano-talc was successfully incorporated in the hydroxyapatite matrix via pulsed electrodeposition after being obtained using an eco-friendly liquid-phase exfoliation process. Scanning electron microscopy, atomic force microscopy, X-ray spectroscopy, Raman spectroscopy, corrosion and wear resistance, and cytocompatibility tests were used to characterize the biocomposite ceramics. Talc significantly improves the nanomechanical and wear properties of bioceramics (i.e., higher stiffness, reduced friction coefficient, and lower wear damage) as well as corrosion resistance. Talc does not induce cytotoxic activity in in vitro cells and may induce bone maturation as per biocompatibility tests.