Mendonça BHS, de Moraes EE, Kirch A, Batista RJC, de Oliveira AB, Barbosa MC, Chacham H. Flow through Deformed Carbon Nanotubes Predicted by Rigid and Flexible Water Models. The Journal of Physical Chemistry B [Internet]. 2023. Publisher's Version
Pinto AA, de Moraes EE, Chacham H, Batista RJC. Modulation of spin and charge currents through functionalized 2D diamond devices. Nanotechnology [Internet]. 2023;35:075704. Publisher's VersionAbstract
In this study, we explore the potential of functionalized two-dimensional (2D) diamond for spin-dependent electronic devices using first-principles calculations. Specifically, we investigate functionalizations with either hydroxyl (−OH) or fluorine (−F) groups. In the case of an isolated layer, we observe that the quantity and distribution of (−OH) or (−F) on the 2D diamond surface significantly influence the sp 2/sp 3 ratio of the carbon atoms in the layer. As the coverage is reduced, both the band gap and magnetic moment decrease. When the 2D diamond is placed between gold contacts and functionalized with (−OH), it results in a device with lower resistance compared to the (−F) functionalization. We predict that the maximum current achieved in the device increases with decreasing (−OH) surface coverage, while the opposite behavior occurs for (−F). Additionally, the surface coverage alone can alter the direction of current rectification in (−F) functionalized 2D diamonds. For all studied systems, a single spin component contributes to the total current for certain values of applied bias, indicating a spin filter behavior.
Mendonça BHS, de Moraes EE, Batista, Ronaldo J. C. AU - de Oliveira AB, de Oliveira AB, Barbosa MC, Chacham H. Water Diffusion in Carbon Nanotubes for Rigid and Flexible Models. The Journal of Physical Chemistry C [Internet]. 2023. Publisher's Version
Marinho JPN, Neme NP, de Matos MJS, Campos Batista RJ, de Macedo WAA, Gastelois PL, Gomes DA, Rodrigues MA, Cipreste MF, de Sousa EMB. Nanostructured system based on hydroxyapatite and curcumin: A promising candidate for osteosarcoma therapy. Ceramics International [Internet]. 2023. Publisher's VersionAbstract
Osteosarcoma is the most common type of bone cancer. Despite therapeutic progress, survival rates for metastatic cases or that do not respond well to chemotherapy remain in the 30% range. In this sense, the use of nanotechnology to develop targeted and more effective therapies is a promising tool in the fight against cancer. Nanostructured hydroxyapatite, due to its biocompatibility and the wide possibility of functionalization, is an interesting material to design nanoplatforms for targeted drug delivery. These platforms have the potential to enable the use of natural substances in the fight against cancer, such as curcumin. Curcumin is a polyphenol with promising properties in treating various types of cancer, including osteosarcoma. In this work, hydroxyapatite (n-HA) nanorods synthesized by the hydrothermal method were investigated as a carrier for curcumin. For this, first-principle calculations based on the Density Functional Theory (DFT) were performed, in which the modification of curcumin (CM) with the coupling agent (3-aminopropyl) triethoxysilane (APTES) was theoretically evaluated. Curcumin was incorporated in n-HA and the drug loading stability was evaluated by leaching test. Samples were characterized by a multi-techniques approach, including Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), X-ray diffraction (XRD), X-ray fluorescence spectrometry (FRX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), zeta potential analysis (ζ), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that n-HAs with a 90 nm average size were obtained and successful incorporation of curcumin in the nanostructure was achieved. Cell viability and the number of osteosarcoma cells were decreased by CMAP-HA treatment. Furthermore, the stability test suggests that hydroxyapatite nanoparticles present great potential for the transportation of curcumin in the bloodstream, crediting this system for biological performance evaluations aiming at the treatment of osteosarcomas. Keywords: nanostructures, curcumin, hydroxyapatite, osteosarcoma.
de Moraes EE, Pinto AA, Batista RJC, de Oliveira AB, Chacham H. Charge and Spin Current Rectification through Functionalized Boron Nitride Bilayers. The Journal of Physical Chemistry C [Internet]. 2022;126:18383-18392. Publisher's Version
Batista AB, Stanley M, de Brito ACF, Vasconcellos R, Munk M, José-Bueno M, Godoy C, de Alvarenga ÉC, de Vasconcelos CKB, Righi A, et al. Improved bioceramic coatings reinforced by nanostructured talc. Surface and Coatings Technology [Internet]. 2022;441:128589. Publisher's VersionAbstract
Nano-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.
Ferrari GA, Chacham H, de Oliveira AB, Matos MJS, Batista RJC, Meireles LM, Barboza APM, Silvestre I, Neves BRA, Lacerda RG. Graphene nanoencapsulation action at an air/lipid interface. Journal of Materials Science [Internet]. 2022;57:6223–6232. Publisher's VersionAbstract
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 µm into graphene. In contrast, such encapsulation effect is negligible in the absence of oleic acid in the channel, with probe penetration of less than 0.02 µm. 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.
Júnior JAC, Barboza APM, Machado G, Neves BRA, de Oliveira AB, Batista RJC, Araújo FGS, Soares JS, Manhabosco TM. Physical-Chemical Effects of Nanoparticles on Electropolymerized Polyaniline. Biointerface research in applied chemistry [Internet]. 2022;12(5):5996-6009. Publisher's VersionAbstract
Abstract: The incorporation of nanoparticles on polymer films is possible to obtain materials with desired properties. In the present work, we address the physical-chemical influence of nanoparticles in polymer films by producing and characterizing polyaniline hybrids with SiO2 and Au nanoparticles and comparing them with films with TiO2 nanoparticles. The hybrid films were characterized by SEM, EDS, UV-Vis, AFM, Raman, and cyclic voltammetry. Unlike TiO2 nanoparticles, SiO2 and Au nanoparticles do not promote any noticeable change in polyaniline oxidation state in less acid environments (pH 5.9 and 6.15). However, in those environments, the presence of nanoparticles significantly increases the film's conductivity. At a pH of 1.5 and 3.9, all three kinds of nanoparticles are screened by ions from the solution diminishing their physical-chemical effects on polyaniline. Thus, our results suggest that, in general, nanoparticles don't have any physical-chemical effects on polyaniline films when deposited in acid enough environments but can change their physical and chemical properties when deposited in less acid environments.
Gonçalves JA, dos Santos OFP, Batista RJC, Azevedo S. Optical properties of boron nitride nanoribbons with reconstructed edges. Solid State Communications [Internet]. 2022;344:114627. Publisher's VersionAbstract
In this work, we employ first-principles calculations to investigate the optical properties of boron nitride nanoribbons with reconstructed edges. We found that because of the presence of homopolar B-B and N-N bonds in the edges, such nanoribbons, unlike boron nitride nanotubes, absorb light and have non-null optical conductivity in the low energy range. The stoichiometry and distribution of the homopolar bonds in the edges change the absorption, reflectance, refractive index, and optical conductivity of nanoribbons, which may allow the tuning of those properties. Regarding the absorption in the low energy range, the nanoribbons with B excess are almost unaffected by the direction of light incidence. On the other hand, the direction of light incidence strongly affects the intensity of the absorption peaks of nanoribbons with N excess in the region. At ultraviolet and above non-cylindrical geometry of the ribbons with the homopolar bonds at the edges also lead to a dependence of the optical properties with the direction of light incidence.
Gonçalves JA, dos Santos OFP, Batista RJC, Azevedo S. First-principle investigation of silicon carbide nanosheets fluorination: Stability trends, electronic, optical and magnetic properties. Chemical Physics Letters [Internet]. 2022;787:139266. Publisher's VersionAbstract
We employed first-principles calculations to investigate the fluorination of silicon carbide nanosheets. We found that the Si atoms are the energetically favorable adsorption sites for F atoms in silicon carbide nanosheets in all studied cases. The strain caused by the fourfold coordinated Si atoms in the flat SiC nanosheet determines the relative position of the adsorbed F atoms: occupying nearest-neighbor Si sites if they bound sheet’s opposing sides or away from each other if they are on the same side of the sheet. The fluorinated nanosheets’ electronic and magnetic properties are weakly dependent on which side of the sheet the F atoms bind; however, they are strongly dependent on the relative distance between them. For F atoms adsorbed on nearest-neighbor Si sites, the system is a small gap p-type semiconductor with 1 μB per adsorbed atom. On the other hand, if F atoms do not occupy nearest-neighbor Si sites, the system is a metal with 1/2 μB per adsorbed atom. The adsorption of F atoms strongly affects the optical properties of SiC sheets inducing optical anisotropy regarding the direction of the incidence of light.
Nicomedes DNN, Mota LM, Vasconcellos R, Medrado NV, de Oliveira M, de Alvarenga ÉC, Juste KRC, Righi A, Manhabosco SM, Silva GJB, et al. Comparison between hydroxyapatite/soapstone and hydroxyapatite/reduced graphene oxide composite coatings: Synthesis and property improvement. Journal of the Mechanical Behavior of Biomedical Materials [Internet]. 2021;121:104618. Publisher's VersionAbstract
Economic viability and eco-friendliness are important characteristics that make implants available to the population in a sustainable way. In this work, we evaluate the performance of a low-cost, widely available, and eco-friendly material (talc from soapstone) relative to reduced graphene oxide as reinforcement to brittle hydroxyapatite coatings. We employ a low-cost and straightforward technique, electrodeposition, to deposit the composite coatings on the titanium substrate. Corrosion, wear, and biocompatibility tests indicate that the reduced graphene oxide can be effectively replaced by talc without reducing the mechanical, anticorrosion, and biocompatible composite coatings properties. Our results indicate that talc from soapstone is a promising material for biomedical applications.
Sales JNB, da Silva RT, Lara LRS, Ramos SLLM, Soares JS, Soares TAS, Machado G, Manhabosco SM, de Oliveira AB, de Carvalho HB, et al. Structural, optical, and magnetic evaluation of Co-, Ni-, and Mn-modified multiferroic BiFeO3 ceramics. Ceramics International [Internet]. 2021. Publisher's VersionAbstract
Co-, Ni-, and Mn-doped BiFeO3 (BFO) ceramics were synthesized herein through a solid-state reaction. All doped BFO samples exhibit visible-light response, and the Co- and Ni-doped BFO samples present enhanced ferromagnetic order at room temperature. All doped samples show secondary phases in minor quantities. Optical spectra reveal two absorptions bands, indicating multiple electron transitions for BFO and its secondary phases. M − H hysteresis loops suggest enhanced ferromagnetism in the Co- and Ni-doped BFO samples because of magnetic spinel CFP and NFO phases, respectively, whereas changes in oxygen vacancies and Fe–O–Fe bond angle play minor roles in the ferromagnetic behavior.
Martins LPG, Silva DL, Smith JS, Lu A-Y, Su C, Hempel M, Occhialini C, Ji X, Pablo R, Alencar RS, et al. Hard, transparent, sp3-containing 2D phase formed from few-layer graphene under compression. Carbon [Internet]. 2021;173:744 - 757. 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.
Batista RJC, Dias RF, Barboza APM, de Oliveira AB, Manhabosco TM, Gomes-Silva TR, Matos MJS, Gadelha AC, Rabelo C, Cançado LGL, et al. Nanomechanics of few-layer materials: do individual layers slide upon folding?. Beilstein Journal of Nanotechnology. 2020;11:1801-1808.
Cipreste MF, Mussel] W [da N, da Silva] J [B, de Marques] M [BF, Batista] RJ [C, Gastelois PL, de Macedo] W [AA, de Sousa] EM [B. A new theranostic system for bone disorders: Functionalized folate-MDP hydroxyapatite nanoparticles with radiolabeled copper-64. Materials Chemistry and Physics [Internet]. 2020:123265. Publisher's VersionAbstract
Hydroxyapatite nanoparticles have been investigated as biological agents for the treatment and diagnosis of bone diseases due to their properties, providing high affinity to bone tissues and also due to the possibility to chemically modify the surfaces of these nanoparticles to provide active targeting to bone tumors or other bone disorders. In this work, synthetic hydroxyapatite nanoparticles and their surface modifications with folic and medronic acid were studied. Copper-64 was produced by neutron irradiation in a TRIGA MARK I nuclear reactor, and the functionalized nanoparticles radiolabeled with this radioisotope. The multi-technique characterization includes FTIR, PXRD, TGA, DSC, CHN, Zeta potential, XPS, SEM, TEM, and Gamma spectroscopy. Furthermore, the evaluation of the chemical interaction stability was through leaching tested for efficiency. The results indicate that folic and medronic acids can be covalently bonded to HA surface, producing a new material not yet described in the literature, been stably attached to hydroxyapatite nanoparticle surfaces, able to provide active targeting for bone disorders. The complexation of copper-64 provides high radiochemistry purity, although the specific activity must be improved.
Mota] L [M, Nicomedes] D [NN, Barboza] AP [M, de Ramos] SL [LM, Vasconcellos R, Medrado] N [V, de Alvarenga] É [C, Machado G, Juste] K[RC, Vasconcelos] CK [de, et al. Soapstone reinforced hydroxyapatite coatings for biomedical applications. Surface and Coatings Technology [Internet]. 2020;397:126005. Publisher's VersionAbstract
Mechanical resistant bioactive materials are of high interest for biomedical applications. In this work, we address the improvement in mechanical properties of HA coatings by the addition of a cheap and widely available secondary phase material, the talc from soapstone. The composites hydroxyapatite/talc (HA/talc) were successfully obtained by pulsed electrodeposition and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, corrosion and wear resistance and biocompatibility tests. We found that the addition of talc greatly improves the mechanical properties of coatings (i. e., wear track and friction coefficient in wear tests were significantly diminished) without diminishing corrosion resistance and biocompatibility. Alamar Blue® tests, alkaline phosphatase activity, and collagen production indicate that the biocomposites are biocompatible and talc itself induce bone maturation.
Freitas] D [deN, Mendonça BHS, Köhler MH, Barbosa MC, Matos MJS, Batista RJC, Oliveira] A [deB. Water diffusion in carbon nanotubes under directional electric frields: Coupling between mobility and hydrogen bonding. Chemical Physics [Internet]. 2020;537:110849. Publisher's VersionAbstract
Molecular Dynamics simulations of water confined in carbon nanotubes subjected to external electric fields show that water mobility strongly depends on the confining geometry, the intensity and directionality of the electric field. While fields forming angles of 0° and 45° slow down the water dynamics by increasing organization, perpendicular fields can enhance water diffusion by decreasing hydrogen bond formation. For 1.2 diameter long nanotubes, the parallel field destroys the ice-like water structure increasing mobility. These results indicate that the structure and dynamics of confined water are extremely sensitive to external fields and can be used to facilitate filtration processes.
Freitas AE, Manhabosco TM, Batista RJC, Segundo ARK, Araújo HX, Araújo FGS, Costa AR. Development and Characterization of Titanium Dioxide Ceramic Substrates with High Dielectric Permittivities. Materials [Internet]. 2020;13. Publisher's VersionAbstract
Titanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 °C up to 1350 °C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.
Batista RJC, Manhabosco TM, Aloni S, Kuykendall TR, Manhabosco SM, Batista AB, Soares JS, Barboza APM, de Oliveira AB, Urban JJ. Electrochemical atomic layer epitaxy deposition of SnTe ultrathin films. Recent Progress in Materials [Internet]. 2019;1(4). Publisher's VersionAbstract
Tin telluride (SnTe) ultrathin films were deposited electrochemically on polycrystalline and monocrystalline gold substrates using the electrochemical atomic layer epitaxy (ECALE) method. The electrochemical behaviors of Sn and Te were studied systematically by means of cyclic voltammetry. Cyclic voltammetry curves for Sn displayed a broad peak in the region between -0.15 V and -0.35 V, which was related to the under-potential deposition (UPD), while the curves for Te displayed a peak at 0.3 V for Te UPD. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) were employed for the characterization of the ultrathin SnTe films. XRD and Raman spectroscopy confirmed the deposition of a single SnTe phase, while SEM revealed that the deposits were composed of nanocrystallites.
Nascimento R, Moraes EE, Matos MJS, Prendergast D, Manhabosco TM, de Oliveira AB, Chacham H, Batista RJC. Graphene/h-BN In-Plane Heterostructures: Stability and Electronic and Transport Properties. The Journal of Physical Chemistry C [Internet]. 2019:null. Publisher's Version
Gonçalves JA, Batista RJC, Tromer R, Azevedo S. Study of the stability and electronic properties of h-BN nanoribbons with reconstructed edges. Chemical Physics Letters [Internet]. 2019;727:126 - 132. Publisher's VersionAbstract
Energetics and electronic properties of three-layered hBN nanoribbons, with reconstructed edges, were investigated, using density functional theory. Such edges present lines of pentagonal and heptagonal rings, where homopolar B-B and N-N bonds exist. The homopolar bonds and their distribution, determine the energetic stability of hBN nanoribbons. The structures with the lowest amount of homopolar bonds presents a value of formation energy smaller than the single hBN layer, which suggests that such kind of reconstruction may indeed occur in real three-layered hBN systems. In addition, our results suggest that reconstructed edges on hBN nanoribbons are more stable than their carbon counterparts.
Dias RF, da Costa CC, Manhabosco TM, de Oliveira AB, Matos MJS, Soares JS, Batista RJC. Ab initio molecular dynamics simulation of methanol and acetonitrile: The effect of van der Waals interactions. Chemical Physics Letters [Internet]. 2019;714:172 - 177. 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.
Mendonça BHS, de Freitas DN, Köhler MH, Batista RJC, Barbosa MC, de Oliveira AB. Diffusion behaviour of water confined in deformed carbon nanotubes. Physica A: Statistical Mechanics and its Applications [Internet]. 2019;517:491 - 498. 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.
Ferrari GA, de Oliveira AB, Silvestre I, Matos MJS, Batista RJC, Fernandes TFD, Meireles LM, Eliel GSN, Chacham H, Neves BRA, et al. Apparent Softening of Wet Graphene Membranes on a Microfluidic Platform. ACS Nano [Internet]. 2018;12:4312–4320. Publisher's Version
Barboza APM, Matos MJS, Chacham H, Batista RJC, de Oliveira AB, Mazzoni MSC, Neves BRA. Compression-Induced Modification of Boron Nitride Layers: A Conductive Two-Dimensional BN Compound. ACS Nano [Internet]. 2018. Publisher's Version
Nhavene EPF, da Silva WM, Junior RRT, Gastelois PL, Venâncio T, Nascimento R, Baptista RJC, Machado CR, de Macedo WAA, de Sousa EMB. Chitosan grafted into mesoporous silica nanoparticles as benznidazol carrier for Chagas diseases treatment. Microporous and Mesoporous Materials [Internet]. 2018:-. Publisher's VersionAbstract
Abstract The use of chitosan functionalized silica for benznidazole delivery in the treatment of neglected disease such as Chagas disease is one of the forms not yet explored, but with great potential for this therapy, as little is known about nanoformulations for the treatment of Chagas disease. In this work, we used chitosan-succinate covalently attached to the surface pore of \MSNs\ to act as anchor for benznidazole as a delivery system. The samples were characterized structurally and chemically with multiple techniques. The applicability of functionalized \MSNs\ as platforms for benznidazole delivery into T. cruzi parasites was assessed. The results demonstrate that the proposed system is a potential promising nanoplatform for drug and gene delivery targeting neglected diseases such as Chagas disease.
Dias RF, da Martins JR, Chacham H, de Oliveira AB, Manhabosco TM, Batista RJC. Nanoporous Graphene and H-BN from BCN Precursors: First-Principles Calculations. The Journal of Physical Chemistry C [Internet]. 2018;122(7):3856-3864. Publisher's VersionAbstract
We 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.
Campos Batista RJ, Chacham H, Barboza APM, de Oliveira AB, Neves BAR, de Oliveira CK. Universal deformation pathways and flexural hardening of nanoscale 2D-material standing folds. NANOTECHNOLOGY. 2018;29:095704.Abstract
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 κas a function of its characteristic height h 0. We observe a more than tenfold increase of κ as h 0increases 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.
Campos Batista RJ, Torres EAS, de Oliveira AB, Barbosa MC. A coarse-grained model based on core-softened potentials for anomalous polymers. Journal of Chemical Sciences, Accepted (2017). 2017.
Gonçalves JA, Nascimento R, Matos MJS, de Oliveira AB, Chacham H, Campos Batista RJ. Edge-Reconstructed, Few-Layered Graphene Nanoribbons: Stability and Electronic Properties. The Journal of Physical Chemistry C. 2017;121(10):5836-5840.Abstract
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 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.
de Moraes EE, Coutinho-Filho MD, Campos Batista RJ. Transport Properties of Hydrogenated Cubic Boron Nitride Nanofilms with Gold Electrodes from Density Functional Theory. ACS Omega. 2017;2(4):1696-1701.Abstract
The electrical transport properties of a four-layered hydrogen-terminated cubic boron nitride sub-nanometer film in contact with gold electrodes are investigated via density functional calculations. The sample exhibits asymmetric metallic surfaces, a fundamental feature that triggers the system to behave like a typical p–n junction diode for voltage bias in the interval −0.2 ≤ V ≤ 0.2, where a rectification ratio up to 62 is verified. Further, in the wider region −0.3 ≤ V ≤ 0.3, negative differential resistance with a peak-to-valley ratio of 10 is observed. The qualitative behavior of the I–V characteristics is described in terms of the hydrogenated cBN film equilibrium electronic structure. Such a film shows metallic surfaces due to surface electronic states at a fraction of eV above and below the Fermi level of the N–H terminated and B–H terminated surfaces, respectively, with a wide bulk-band gap characteristic of BN materials. Such a mechanism is supported by transmission coefficient calculations, with the Landauer–Büttiker formula governing the I–V characteristics.
Filho VFL, Machado G, Batista RJC, Soares JS, de Oliveira AB, de Vasconcelos C, Lino AA, Manhabosco TM. Effect of TiO2 Nanoparticles on Polyaniline Films Electropolymerized at Different pH. JOURNAL OF PHYSICAL CHEMISTRY C. 2016;120:14977-14983.Abstract
In this work hybrids of titanium manopartides and polyaniline are obtained by pulsed electrodeposition at different pH (1.5, 3.9 and 5.9) and characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, cyclic voltammetry, ultraviolet-visible, and Raman spectroscopies. We found that films deposited at pH 5.9 with nanoparticles incorporation are composed of emeraldine meanwhile films without nanoparticles are composed of pernigraniline. As a result, films deposited with nanoparticles incorporation present conductivity 6 times higher than that of films deposited. without nanoparticles. Films deposited at pH 3.9 with or without nanoparticles incorporation are both made of pernigraniline. Even though films with nanoparticles incorporation still present higher conductivity. To explain such a result, we performed first-principles calculations on polyaniline/TiO2 interface. The calculations predict a metallic polyaniline/TiO2 interface in spite of polyaniline and TiO2 being semiconductors. At pH 1.5, the presence of nanoparticles has negligible effect on films characteristics. We believe that at low pH (pH 1.5) H atoms tend to bind TiO2 surface resulting in positively charged nanoparticles, which are further screened by SO4-2 anions. Such a screening layer prevents the physical contact between nanoparticles and polyaniline monomers diminishing the effects of nanopartide presence.
de Vasconcelos CKB, Batista RJC, da Regis MGR, Manhabosco TM, de Oliveira AB. A simple model for solute-solvent separation through nanopores based on core-softened potentials. PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS. 2016;453:184-193.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. (C) 2016 Elsevier B.V. All rights reserved.
de Oliveira AB, Chacham H, Soares JS, Manhabosco TM, de Resende HFV, Batista RJC. Vibrational G peak splitting in laterally functionalized single wall carbon nanotubes: Theory and molecular dynamics simulations. CARBON. 2016;96:616-621.Abstract
We present a theoretical study of the vibrational spectrum, in the G band region, of laterally hydrogenated single wall carbon nanotubes through molecular dynamics simulations. We find that bilateral hydrogenation which can be induced by hydrogenation under lateral strain causes permanent oval deformations on the nanotubes and induces the splitting of vibrational states in the G-band region. We propose that such splitting can be used as a Raman fingerprint for detecting nanotubes that have been permanently modified due to bilateral hydrogenation. In particular, our results may help to clarify the recent findings of Araujo and collaborators [Nano Lett. 12, 4110 (2012)1 which have found permanent modifications in the Raman G peaks of locally compressed carbon nanotubes. We have also developed an analytical model for the proposed phenomenon that reproduces the splitting observed in the simulations. (C) 2015 Elsevier Ltd. All rights reserved.
Oliveira CK, Gomes EFA, Prado MC, Alencar TV, Nascimento R, Malard LM, Batista RJC, de Oliveira AB, Chacham H, de Paula AM, et al. Crystal-oriented wrinkles with origami-type junctions in few-layer hexagonal boron nitride. NANO RESEARCH. 2015;8:1680-1688.Abstract
Understanding 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.
Nascimento R, da Martins JR, Batista RJC, Chacham H. Band Gaps of BN-Doped Graphene: Fluctuations, Trends, and Bounds. JOURNAL OF PHYSICAL CHEMISTRY C. 2015;119:5055-5061.Abstract
A Monte-Carlo-based simulated annealing process combined with ab initio calculations is employed to investigate electronic and structural properties of boron nitride (BN)-doped graphene, in a wide doping range. We find that, for a given BN doping concentration, the doping-induced band gap can vary over an order of magnitude depending on the placement of the B and N atoms. We propose an analytical tight-binding model that reproduces the dependence of the band gap on both the concentration and the morphology obtained in the ab initio calculations and provides an upper bound for the band gap at a given BN concentration. We also predict that the dependence of the band gap with applied tensile stress should be strong, nonmonotonic, and anisotropic, within the range of strain values attainable experimentally.
A new experimental procedure was used to analyse the corrosion behaviour of hot-dip Zn coated steel based on the association of the scanning vibrating electrode technique (SVET) and uniaxial tensile strain applied up to 3.1% in 0.01 M NaCl solutions without release of the elastic strain during the test. The nucleation of localized corrosion sites on the coating occurs at very low strain values around the yield point and the maximum current densities increase continuously with the increase of the applied strain. The nucleation of localized corrosion on the Zn surface was favoured by the rupture of the passive film in contact with the solution by the action of slip steps and fine intergranular cracks, rather than by the exposure of the steel substrate. Straining of the Zn coating immersed in the solution was comparatively a much more aggressive condition than straining the sample in air before the corrosion tests. (C) 2015 Elsevier Ltd. All rights reserved.
de Lima AL, Muessnich LAM, Manhabosco TM, Chacham H, Batista RJC, de Oliveira AB. Soliton instability and fold formation in laterally compressed graphene. NANOTECHNOLOGY. 2015;26.Abstract
We investigate-through simulations and analytical calculations-the consequences of uniaxial lateral compression applied to the upper layer of multilayer graphene. The simulations of compressed graphene show that strains larger than 2.8% induce soliton-like deformations that further develop into large, mobile folds. Such folds were indeed experimentally observed in graphene and other solid lubricants two-dimensional (2D) materials. Interestingly, in the soliton-fold regime, the shear stress decreases with the strain s, initially as s(-2/3) and rapidly going to zero. Such instability is consistent with the recently observed negative dynamic compressibility of 2D materials. We also predict that the curvatures of the soliton-folds are given by r(c) = delta root beta/2 alpha, where 1 <= delta <= 2, and beta and alpha are respectively related to the layer bending modulus and to the interlayer binding energy of the material. This finding might allow experimental estimates of the beta/alpha a ratio of 2D materials from fold morphology.
Batista RJC, de Oliveira AB, Carara SS, Chacham H. Controlling the Electrical Response of Carbon Nanotubes Deposited on Diamond through the Application of Electric Fields. JOURNAL OF PHYSICAL CHEMISTRY C. 2014;118:21599-21603.Abstract
We apply first-principles methods to investigate the electronic properties of semiconductor carbon nanotubes deposited on hydrogen-terminated diamond surfaces. We found that the band gap of the diamond-nanotube system can be continuously varied (from 0 to 0.8 eV) through the application of an external electric field. The metal semiconductor transition occurs for values of field between 0.03 and 0.035 V/angstrom, which could make viable the production of stable field-effect devices at nanometric scale. We also found that at zero value of electric field the nanotube electrical behavior can be modified by changing the diamond surface termination, which may be useful for producing ohmic metal semiconductor contacts. On the other hand, at zero values of field, tubes deposited on nitrogen-doped diamond are metallic regardless of the surface termination. Thus, nitrogen doping could be useful in situations in which the atomistic details of the diamond surface are difficult to control.
Marques dos Santos AM, Campos Batista RJ, Meira Martins LA, Ilha M, Vieira MQ, Miquita DR, Rodrigues Guma FC, Mueller IL, Manhabosco TM. Corrosion and cell viability studies of graphite-like hydrogenated amorphous carbon films deposited on bare and nitrided titanium alloy. CORROSION SCIENCE. 2014;82:297-303.Abstract
This work presents a study of corrosion resistance and cell viability of carbon films on bare and nitrided Ti-6Al-4V. Films deposited on bare alloy significantly improve the corrosion resistance. Unexpectedly, films deposited on nitrided alloy present delamination and cracking after 16 days. We associate, film failure with the presence of pores combined with a weak film/substrate interaction that allows diffusion of ions at the interface. We found that films tend to diminish the osteoblastic cell viability and the observed variations on film roughness do not improve cell viability. (C) 2014 Elsevier Ltd. All rights reserved.
Batista RJC, Carara SS, Manhabosco TM, Chacham H. A Ferromagnetic Pure Carbon Structure Composed of Graphene and Nanotubes: First-Principles Calculations. JOURNAL OF PHYSICAL CHEMISTRY C. 2014;118:8143-8147.Abstract
A hybrid structure that presents phases of three extended allotropes of carbon, nanotube, graphene, and diamond, is proposed in this work. According to our first-principles calculations, such structure can be made energetically stable through the application of pressures of the order of 100 kbar to alternate graphene nanotube layers, which were recently synthesized in large-area films. The existence of sp(3) dangling bonds in the hybrid structure gives rise to an exceptionally large density of states near the Fermi level, leading to a ferromagnetic ground state.
Manhabosco TM, Barboza APM, Batista RJC, Neves BRA, Mueller IL. Corrosion, wear and wear-corrosion behavior of graphite-like a-C:H films deposited on bare and nitrided titanium alloy. DIAMOND AND RELATED MATERIALS. 2013;31:58-64.Abstract
This 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 low with appreciable wear resistance at room conditions. 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/nitrided alloy interaction facilitates fluid penetration between the film and the substrate which 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. (C) 2012 Elsevier B.V. All rights reserved.
Moraes EE, Manhabosco TM, de Oliveira AB, Batista RJC. Tunable band gap of boron nitride interfaces under uniaxial pressure. JOURNAL OF PHYSICS-CONDENSED MATTER. 2012;24.Abstract
In this work we show, by means of a density functional theory formalism, that the interaction between hydrogen terminated boron nitride surfaces gives rise to a metallic interface with free carriers of opposite sign at each surface. A band gap can be induced by decreasing the surface separation. The size of the band gap changes continuously from zero up to 4.4 eV with decreasing separation, which is understood in terms of the interaction between surface states. Due to the high thermal conductivity of cubic boron nitride and the coupling between band gap and applied pressure, such tunable band gap interfaces may be used in highly stable electronic and electromechanical devices. In addition, the spatial separation of charge carriers at the interface may lead to photovoltaic applications.
Barboza APM, Chacham H, Oliveira CK, Fernandes TFD, Ferreira EMH, Archanjo BS, Batista RJC, de Oliveira AB, Neves BRA. Dynamic Negative Compressibility of Few-Layer Graphene, h-BN, and MoS2. NANO LETTERS. 2012;12:2313-2317.Abstract
We report a novel mechanical response of few-layer graphene, h-BN, and MoS2 to the simultaneous compression and shear by an atomic force microscope (AFM) tip. The response is characterized by the vertical expansion of these two-dimensional (2D) layered materials upon compression. Such effect is proportional to the applied load, leading to vertical strain values (opposite to the applied force) of up to 150%. The effect is null in the absence of shear, increases with tip velocity, and is anisotropic. It also has similar magnitudes in these solid lubricant materials (few-layer graphene, h-BN, and MoS2), but it is absent in single-layer graphene and in few-layer mica and Bi2Se3. We propose a physical mechanism for the effect where the combined compressive and shear stresses from the tip induce dynamical wrinkling on the upper material layers, leading to the observed flake thickening. The new effect (and, therefore, the proposed wrinkling) is reversible in the three materials where it is observed.
Barboza APM, Carara SS, Batista RJC, Chacham H, Neves BRA. Controlling the Electrical Behavior of Semiconducting Carbon Nanotubes via Tube Contact. SMALL. 2012;8:220-224.
Araujo PT, Barbosa Neto NM, Chacham H, Carara SS, Soares JS, Souza AD, Cancado LG, de Oliveira AB, Batista RJC, Joselevich E, et al. In Situ Atomic Force Microscopy Tip-Induced Deformations and Raman Spectroscopy Characterization of Single-Wall Carbon Nanotubes. NANO LETTERS. 2012;12:4110-4116.Abstract
In this work, an atomic force microscope (AFM) is combined with a confocal Raman spectroscopy setup to follow in situ the evolution of the G-band feature of isolated single-wall carbon nanotubes (SWNTs) under transverse deformation. The SWNTs are pressed by a gold AFM tip against the substrate where they are sitting. From eight deformed SWNTs, five exhibit an overall decrease in the Raman signal intensity, while three exhibit vibrational changes related to the circumferential symmetry breaking. Our results reveal chirality dependent effects, which are averaged out in SWNT bundle measurements, including a previously elusive mode symmetry breaking that is here explored using molecular dynamics calculations.
Batista RJC, de Oliveira AB, Pereira NR, Paolini RS, Manhabosco TM. Boron nitride nanotubes as templates for half-metal nanowires. JOURNAL OF PHYSICS-CONDENSED MATTER. 2012;24.Abstract
We investigate by means of a GGA + U implementation of density functional theory the electronic and structural properties of magnetic nanotubes composed of an iron oxide monolayer and (n, 0) boron nitride (BN) nanotubes, with n ranging from 6 to 14. The formation energy per FeO molecule of FeO covered tubes is smaller than the formation energy of small FeO nanoparticles, which suggests that the FeO molecules may cover the BN nanotubes rather than aggregating locally. Both GGA (PBE) and Van der Waals functionals predict an optimal FeO-BN interlayer distance of 2.94 angstrom. Depending on the diameter of the tube, novel electronic properties for the FeO covered BN nanotubes were found. They can be semiconductors, intrinsic half-metals or semi-half-metals that can become half-metals if charged with either electrons or holes. Such results are important in the spintronics context.
Batista RJC, de Oliveira AB, Rocco DL. Iron oxide doped boron nitride nanotubes: structural and magnetic properties. JOURNAL OF PHYSICS-CONDENSED MATTER. 2010;22.Abstract
A first-principles formalism is employed to investigate the interaction of iron oxide (FeO) with a boron nitride (BN) nanotube. The stable structure of the FeO-nanotube has Fe atoms binding N atoms, with bond length of roughly similar to 2.1 angstrom, and binding between O and B atoms, with bond length of 1.55 angstrom. In case of small FeO concentrations, the total magnetic moment is (4 mu(Bohr)) times the number of Fe atoms in the unit cell, and it is energetically favorable to FeO units to aggregate rather than randomly bind to the tube. As a larger FeO concentration case, we study a BN nanotube fully covered by a single layer of FeO. We found that such a structure has a square FeO lattice with Fe-O bond length of 2.11 angstrom, similar to that of FeO bulk, and total magnetic moment of 3.94 mu(Bohr)/Fe atom. Consistent with experimental results, the FeO covered nanotube is a semi-half-metal which can become a half-metal if a small change in the Fermi level is induced. Such a structure may be important in the spintronics context.
da Martins JR, Batista RJC, Chacham H. Doped Assemblies of Gold Nanoparticles: Structural and Electronic Properties. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. 2010;132:11929-11933.Abstract
We performed an ab initio study of molecular-doped periodic assemblies of ligand-stabilized Au nanoparticles. We found that the most stable dopant positions are near the nanoparticle surfaces, away from the center of interstitial positions. The dopants provide an effective screening mechanism, strongly reducing the nanoparticles charging energies. We also found a linear dependence of the Fermi level with dopant concentration, consistent with recent experiments, up to a critical concentration. For larger concentrations, a new regime is predicted. These features are well reproduced by a simple, analytical model for the material.
Batista RJC. Stoichiometric boron nitride fullerenes with homopolar B-B and N-N bonds. CHEMICAL PHYSICS LETTERS. 2010;488:209-212.Abstract
A new class of boron nitride fullerenes, which are stoichiometric and presents homopolar bonds, is proposed in this work. A combined first-principles/elastic-model approach predicts that stoichiometric fullerenes with more than 1000 atoms which present homopolar bonds are energetically more stable than those without homopolar bonds. The HOMO-LUMO gap of stoichiometric fullerenes with homopolar bonds is 1.7 eV smaller than that of fullerenes without homopolar bonds, which may lead to distinct optical and electrochemical properties. The distribution of B-B and N-N in those new fullerenes gives rise to an electric dipole moment which could make possible to separate them from apolar fullerenes. (C) 2010 Elsevier B.V. All rights reserved.
Batista RJC, Mazzoni MSC, Chacham H. First-principles investigation of electrochemical properties of gold nanoparticles. NANOTECHNOLOGY. 2010;21.Abstract
A first-principles formalism is employed to investigate the effects of size and structure on the electronic and electrochemical properties of Au nanoparticles with diameters between 0.8 and 2.0 nm. We find that the behavior of the ionization potentials (IPs) and the electron affinities (EAs) as a function of cluster size can be separated into many-body and single-electron contributions. The many-body part is only (and continuously) dependent on particle size, and can be very well described in terms of the capacitance of classical spherical conductors for clusters with more the 55 atoms. For smaller clusters, molecule-like features lead the capacitance and fundamental gap to differ systematically from those of a classical conductor with decreasing size. The single-electron part fluctuates with particle structure. Upon calculating the neutral chemical potential mu(0) = (IP + EA)/2, the many-body contributions cancel out, resulting in fluctuations of mu(0) around the bulk Au work function, consistent with experimental results. The values of IP and EA changes upon functionalization with thiolated molecules, and the magnitude of the observed changes does not depend on the length of the alkane chain. The functionalization can also lead to a transition from metallic to non-metallic behavior in small nanoparticles, which is consistent with experimental observations.
Carara SS, Batista RJC, Chacham H. Modifications in graphene electron states due to a deposited lattice of Au nanoparticles: Density functional calculations. PHYSICAL REVIEW B. 2009;80.Abstract
We perform first-principles investigations of two-dimensional, triangular lattices of Au-38 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 (approximate to 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.
Batista RJC, Mazzoni MSC, Chacham H. Boron nitride fullerene B36N36 doped with transition metal atoms: First-principles calculations. PHYSICAL REVIEW B. 2007;75.Abstract
We perform first-principles calculations for the interaction of the transition metal atoms Fe, Co, and W, as well as the FeO molecule, with the boron nitride fullerene B36N36. The stable structure of the atom-fullerene complexes may have the dopant atom either at the center of the cage or making covalent bonds with the fullerene wall, with similar total energies. We also find that the FeO molecule has a binding energy with the fullerene 2.5 eV larger than those of the transition metal atoms, and that it produces larger distortions in the cage. The electronic structure changes upon doping with the presence of several gap states. No magnetic moment is induced on the BN cage and, in general, the hybrid structures have the same magnetic moments as the isolated dopants.
Batista RJC, Ordejon P, Chacham H, Artacho E. Resistive and rectifying effects of pulling gold atoms at thiol-gold nanocontacts. PHYSICAL REVIEW B. 2007;75.Abstract
We investigate, by means of first-principles calculations, structural and transport properties of junctions made of symmetric dithiolated molecules placed between Au electrodes. As the electrodes are pulled apart, we find that it becomes energetically favorable that Au atoms migrate to positions between the electrode surface and thiol terminations, with junction structures alternating between symmetric and asymmetric. As a result, the calculated IV curves alternate between rectifying and nonrectifying behaviors as the electrodes are pulled apart, which is consistent with recent experimental results.
Batista RJC, Mazzoni MSC, Garzon IL, Beltran MR, Chacham H. Electron states in a lattice of Au nanoparticles: The role of strain and functionalization. PHYSICAL REVIEW LETTERS. 2006;96.Abstract
We make use of first-principles calculations to study the effects of functionalization and compression on the electronic properties of 2D lattices of Au nanoparticles. We consider Au-38 particles capped by methylthiol molecules and possibly functionalized by the dithiolated conjugated molecules benzenedimethanethiol and benzenedicarbothialdehyde. We find that the nonfunctionalized lattices are insulating, with negligible band dispersions even for a compression of 20% of the lattice constant. Distinct behaviors of the dispersion of the lowest conduction band as a function of compression are predicted for functionalized lattices: The band dispersion of the benzenedimethanethiol-functionalized lattice increases considerably with compression, while that of the benzenedicarbothialdehyde-functionalized lattice decreases.
Batista RJC, Mazzoni MSC, Chacham H. A theoretical study of the stability trends of boron nitride fullerenes. CHEMICAL PHYSICS LETTERS. 2006;421:246-250.Abstract
We perform first-principles calculations to study the relative stability of boron nitride fullerenes B(n)N(m). We consider fullerenes with octahedral, icosahedral and tubular shapes, in a size range with (n + m) between 20 and 288. A scaling analysis allows the total energy comparisons to extend to larger sizes. We find that tubular-shaped fullerenes are as stable as octahedral-shaped ones for (n + m) <= 80. We also find that, in N-rich conditions, icosahedral fullerenes with line defects composed of N-N bonds may be as stable as octahedral fullerenes. (c) 2006 Elsevier B.V. All rights reserved.
Batista RJC, Mazzoni MSC, Ladeira LO, Chacham H. First-principles investigation of Au-covered carbon fullerenes. PHYSICAL REVIEW B. 2005;72.Abstract
We investigate, by means of first-principles calculations, the possible formation of Au-covered carbon fullerenes. Coverages between 32 and 92 Au atoms over C-60 were considered. Among those, the most stable structure is Au92C60, which retains the I-h symmetry of C-60 after geometry optimization. Au92C60 has a small formation energy per Au atom (0.65 eV), which is in fact smaller than those of the Au-38 and Au-55 gold clusters, which were already observed. Au92C60 can be further stabilized by an overlayer of methylthiol molecules, which reduces the formation energy per gold atom to a value smaller than that of the bulk phase of gold.