Browsing by Author "Lacerda, Rodrigo Gribel"

Now showing 1 - 6 of 6
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    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 Gribel
    Molybdenum 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.
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    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 Gribel
    Graphene 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.
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    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 Gribel
    In 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.
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    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 Gribel
    A 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.
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    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 Gribel
    In 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.
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    Near-edge X-ray absorption spectroscopy signature of image potential states in multilayer epitaxial graphene.
    (2016) Coelho Neto, Paula Maciel; Reis, Diogo Duarte dos; Matos, Matheus Josué de Souza; Sá, Thiago Grasiano Mendes de; Gonçalves, Além Mar Bernardes; Lacerda, Rodrigo Gribel; Souza, Angelo Malachias de; Paniago, Rogério Magalhães