Alan Barros Oliveira

R. J. C. Batista, et al., “Nanomechanics of few-layer materials: do individual layers slide upon folding?,” Beilstein J. Nanotechnol., vol. 11, pp. 1801–1808, 2020.
L. G. P. Martins, et al., “Hard, transparent, sp3-containing 2D phase formed from few-layer graphene under compression,” Carbon, 2020. Publisher's VersionAbstract
Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental efforts to obtain such structures are in initial stage. Recent high-pressure experiments provided significant advancements in the field, however, expected properties of a 2D-like diamond such as sp3 content, transparency and hardness, have not been observed together in a compressed graphene system. Here, we compress few-layer graphene samples on SiO2/Si substrate in water and provide experimental evidence for the formation of a quenchable hard, transparent, sp3-containing 2D phase. Our Raman spectroscopy data indicates phase transition and a surprisingly similar critical pressure for two-, five-layer graphene and graphite in the 4-6 GPa range, as evidenced by changes in several Raman features, combined with a lack of evidence of significant pressure gradients or local non-hydrostatic stress components of the pressure medium up to ≈ 8 GPa. The new phase is transparent and hard, as evidenced from indentation marks on the SiO2 substrate, a material considerably harder than graphene systems. Furthermore, we report the lowest critical pressure (≈ 4 GPa) in graphite, which we attribute to the role of water in facilitating the phase transition. Theoretical calculations and experimental data indicate a novel, surface-to-bulk phase transition mechanism that gives hint of diamondene formation.
B. H. S. Mendonça, D. N. de Freitas, M. H. Köhler, R. J. C. Batista, M. C. Barbosa, and A. B. de Oliveira, “Diffusion behaviour of water confined in deformed carbon nanotubes,” Physica A: Statistical Mechanics and its Applications, vol. 517, pp. 491 - 498, 2019. Publisher's VersionAbstract
We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of eccentricity at 300 K. We found a water structural transition between tubular-like to single-file for (7,7) nanotubes associated with change from a high to low mobility regimes. Water is frozen when confined in a perfect (9,9) nanotube and it becomes liquid if such a nanotube is deformed above a certain threshold. Water diffusion enhancement (suppression) is related to a reduction (increase) in the number of hydrogen bonds. This suggests that the shape of the nanotube is an important ingredient when considering the dynamical and structural properties of confined water.
R. F. Dias, et al., “Ab initio molecular dynamics simulation of methanol and acetonitrile: The effect of van der Waals interactions,” Chemical Physics Letters, vol. 714, pp. 172 - 177, 2019. Publisher's VersionAbstract
We employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.
G. A. Ferrari, et al., “Apparent Softening of Wet Graphene Membranes on a Microfluidic Platform,” ACS Nano, vol. 12, no. 5, pp. 4312-4320, 2018. Publisher's Version
A. P. M. Barboza, et al., “Compression-Induced Modification of Boron Nitride Layers: A Conductive Two-Dimensional BN Compound,” ACS Nano, pp. null, 2018. Publisher's Version
H. Chacham, A. P. M. Barboza, A. B. de Oliveira, C. K. de Oliveira, R. J. C. Batista, and B. R. A. Neves, “Universal deformation pathways and flexural hardening of nanoscale 2D-material standing folds,” Nanotechnology, vol. 29, no. 9, pp. 095704, 2018. Publisher's VersionAbstract
In 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.
R. F. Dias, J. da Rocha Martins, H. Chacham, A. B. de Oliveira, T. M. Manhabosco, and R. J. C. Batista, “Nanoporous Graphene and H-BN from BCN Precursors: First-Principles Calculations,” The Journal of Physical Chemistry C, vol. 122, no. 7, pp. 3856-3864, 2018. Publisher's Version
L. G. P. Martins, et al., “Raman evidence for pressure-induced formation of diamondene,” Nature Communications, vol. 8, no. 1, pp. 96, 2017. Publisher's VersionAbstract
Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.
J. Nichele, A. B. de Oliveira, L. S. B. de Alves, and I. B. Jr, “Accurate calculation of near-critical heat capacities \CP\ and \CV\ of argon using molecular dynamics,” Journal of Molecular Liquids, vol. 237, pp. 65 - 70, 2017. Publisher's VersionAbstract
Abstract Molecular dynamics (MD) employing the Lennard-Jones (LJ) interaction potential was used to compute the heat capacities of argon at constant volume \CV\ and constant pressure \CP\ near the critical point very close to the asymptotic region. The accurate \MD\ calculation of critical divergences was shown to be related to a careful choice of the cutoff radius rc and the inclusion of long-range corrections in the \LJ\ potential. The computed \CP\ and \CV\ values have very good agreement as compared to available \NIST\ data. Furthermore, values of \CV\ in a range of temperatures for which \NIST\ data is not available could be computed. In the investigated range of temperatures, both \CP\ and \CV\ \MD\ results were fitted to a simple mathematical expression based on an empirical model that describes the critical effects when the asymptotic models are not appropriate. The present approach is of general applicability and robust to compute thermophysical properties of fluids in the near-critical region.
J. A. Gonçalves, R. Nascimento, M. J. S. Matos, A. B. de Oliveira, H. Chacham, and R. J. C. Batista, “Edge-Reconstructed, Few-Layered Graphene Nanoribbons: Stability and Electronic Properties,” The Journal of Physical Chemistry C, vol. 121, no. 10, pp. 5836-5840, 2017. Publisher's VersionAbstract

J. Phys. Chem. C, 2017, 121 (10), pp 5836–5840

We report a first-principles study of edge-reconstructed, 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 three-layer 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 sp2bonds 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.

J. Nichele, I. B. Jr., A. B. Oliveira, and L. S. Alves, “Molecular dynamics simulations of momentum and thermal diffusion properties of near-critical argon along isobars,” The Journal of Supercritical Fluids, vol. 114, pp. 46 - 54, 2016. Publisher's VersionAbstract
Abstract Three basic diffusion properties of argon – shear viscosity, bulk viscosity and thermal conductivity – were studied in the neighborhood of the critical point using molecular dynamics (MD) and the Lennard-Jones potential energy function. \MD\ simulations were performed along the 1.0Pc and 1.2Pc isobars. Green-Kubo relations and a Lennard-Jones pair potential were used. Four different sets of Lennard-Jones parameters were used. A comparison of computed shear viscosity and thermal conductivity values with data available from the National Institute of Standards and Technology (NIST) displayed a good agreement. Results for bulk viscosity indicated that values of this property cannot be neglected in this thermodynamic region, a result that violates the traditional and much-assumed Stokes hypothesis in classical fluid mechanics. Furthermore, it was shown that in the neighborhood of the critical region the bulk viscosity can have larger values than the shear viscosity.
V. F. L. Filho, et al., “Effect of TiO2 Nanoparticles on Polyaniline Films Electropolymerized at Different pH,” The Journal of Physical Chemistry C, vol. 120, no. 27, pp. 14977-14983, 2016. Publisher's Version
C. K. B. de Vasconcelos, R. J. C. Batista, M. G. R. da Régis, T. M. Manhabosco, and A. B. de Oliveira, “A simple model for solute–solvent separation through nanopores based on core-softened potentials,” Physica A: Statistical Mechanics and its Applications, vol. 453, pp. 184 - 193, 2016. Publisher's VersionAbstract
Abstract We propose an effective model for solute separation from fluids through reverse osmosis based on core-softened potentials. Such potentials have been used to investigate anomalous fluids in several situations under a great variety of approaches. Due to their simplicity, computational simulations become faster and mathematical treatments are possible. Our model aims to mimic water desalination through nano-membranes through reverse osmosis, for which we have found reasonable qualitative results when confronted against all-atoms simulations found in the literature. The purpose of this work is not to replace any fully atomistic simulation at this stage, but instead to pave the first steps towards coarse-grained models for water desalination processes. This may help to approach problems in larger scales, in size and time, and perhaps make analytical theories more viable.
A. B. Oliveira, H. Chacham, J. S. Soares, T. M. Manhabosco, H. F. V. de Resende, and R. J. C. Batista, “Vibrational G peak splitting in laterally functionalized single wall carbon nanotubes: Theory and molecular dynamics simulations,” Carbon, vol. 96, pp. 616-621, 2016. Publisher's Version
C. K. Oliveira, et al., “Crystal-oriented wrinkles with origami-type junctions in few-layer hexagonal boron nitride,” Nano Research, vol. 8, no. 5, pp. 1680-1688, 2015. Publisher's Version
A. L. de Lima, L. A. M. Muessnich, T. M. Manhabosco, H. Chacham, R. J. C. Batista, and A. B. Oliveira, “Soliton instability and fold formation in laterally compressed graphene,” Nanotechnology, vol. 26, no. 4, 2015. Publisher's Version
R. J. C. Batista, A. B. Oliveira, S. S. Carara, and H. Chacham, “Controlling the Electrical Response of Carbon Nanotubes Deposited on Diamond through the Application of Electric Fields,” Journal of Physical Chemistry C, vol. 118, no. 37, pp. 21599-21603, 2014. Publisher's Version
J. R. Bordin, A. B. Oliveira, A. Diehl, and M. C. Barbosa, “Diffusion enhancement in core-softened fluid confined in nanotubes,” Journal of Chemical Physics, vol. 137, no. 8, 2012. Publisher's Version
A. P. M. Barboza, et al., “Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS2,” Nano Letters, vol. 12, no. 5, pp. 2313-2317, 2012. Publisher's Version