Browsing by Author "Santos, Joyce Cristina da Cruz"

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    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 Almeida
    We 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.
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    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 Almeida
    Gypsum 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.
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    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 Castro
    Industrial 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.