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.
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.
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.
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.
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.
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.
Polyaniline (PAni) films obtained by means of pulsed potentiostatic electropolymerization were used as hole-transporting layer in organic photovoltaic devices. PAni films were deposited onto Indium Tin Oxide (ITO) from an acid solution containing 0.1 M aniline monomer at pulsed potentials of 1 V and 1.5V. The PAni films were characterized by Atomic Force Microscopy (AFM), Cyclic voltammetry and UV-Vis absorption spectroscopy. The active layer of poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and phenyl-C61-butyric acid methyl ester (PCBM) was spin coated onto PAni films to obtain the ITO/PAni/MDMO-PPV\_PCBM/Al photovoltaic device structures. The power conversion efficiency (.) of multilayered devices was evaluated by current density-voltage (J-V) curves. The results indicate that devices obtained with PAni films exhibit a 4-fold increase in conversion efficiency compared to devices without PAni films.
Surface characteristics such as roughness and contact angle of flat and nanostructured titanium samples and diamond-like carbon films (DLC) electrodeposited on the nanostructured samples were evaluated. Also, the mechanical properties and the corrosion resistance of the samples were evaluated in phosphate buffered saline (PBS). Biocompatibility was assessed by analyzing an in vitro cell culture. Nanostructured samples presented better cell biocompatibility. DLC deposited onto nanostructured samples remained with nanostructured morphology, presented high hardness and improved corrosion resistance compared to bare titanium. The DLC films electrodeposited from acetonitrile presented higher corrosion resistance in PBS solution when compared to DLC films deposited from N,N-dimethylformamide. (c) 2012 Elsevier Ltd. All rights reserved.
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.
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.
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.
Tribological, electrochemical and tribo-electrochemical behaviour of bare and nitrided Ti6Al4V alloy was studied. Scanning Electron Microscopy (SEM), X-ray diffraction and microhardness profile were used to characterize the nitrided Ti6Al4V. The anticorrosive properties of nitrided Ti6Al4V in phosphate buffer saline solution (PBS), simulating the body environment, were evaluated by Electrochemical Impedance Spectroscopy (EIS). Nitriding increased the alloy resistance to corrosion and to dry wear. Resistance to tribocorrosion in PBS at the open circuit potential (OCP) for the nitrided alloy was also significantly increased compared to the bare alloy; nevertheless at an anodic potential this influence became less important. (c) 2011 Elsevier Ltd. All rights reserved.
Tribological and corrosion properties of Ti6Al4V alloy both bare and coated by diamond-like carbon (DLC) were investigated in PBS solution. The films obtained by a PACVD technique present high hardness, good corrosion and wear resistance and lower friction coefficient compared to bare alloy. Tribocorrosion tests on bare alloy showed that when wear stops, the alloy rapidly passivates. DLC films present superior wear resistance under dry conditions. However, film life is greatly reduced during tribocorrosion tests.
In this study, thin cobalt films were electrodeposited directly onto n-Si (100) using two different electrodeposition techniques: galvanostatic and potentiostatic. The morphological difference between galvanostatic and potentiostatic deposits was observed by atomic force microscopy (AFM) and X-ray diffraction (XRD). Analysis of the deposits by an alternating gradient field magnetometer (AGFM) showed the influence of the electrodeposition process on the magnetic properties of the film.
Diamond-like carbon films (DLC) were deposited on titanium substrates in acetonitrile and N, N-dimethyl formamide (DMF) liquids by the liquid-phase electrodeposition technique at ambient pressure and temperature. The applied voltage between the electrodes was high ( 1200 V) due to the use of resistive organic liquids. The surface morphology was examined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Corrosion performance of the coatings was investigated by potentiodynamic polararization tests in phosphate buffer saline solution. Raman spectroscopy analysis of the films revealed two broad bands at approximately 1360 cm(1) and 1580 cm(1), related to D and G-band of DLC, respectively. The coated Ti was tested in a ball-on-plate type wear test machine with Al(2)O(3) balls. The films presented a low friction coefficient ( about 0.1), and the films deposited from DMF presented the best wear resistance. (C) 2008 Elsevier B. V. All rights reserved.
TRIBOCORROSION OF Ti6Al4V ALLOY IN PHOSPHATE BUFFERED SALINE SOLUTION. The tribocorrosion behavior of Ti6Al4V alloy was investigated in a Phosphate Buffered Saline (PBS) solution by a reciprocating wear, using alumina ball as the counterface material, at different normal forces and sliding velocities. Dry wear experiments were performed in order to compare with the tribocorrosion experiments at open circuit potential and under anodic polarization. Dry wear induced a superior damage oil the counterface, forming larger and shallower wear tracks compared with those experiments performed in PBS solution. The anodic current was increased by wear; however the volume of oxidized metal in tribocorrosion experiments correspond to a relative low percentage of the wear track volume.
The use of additives to improve the quality of electrodeposited magnetic films is of current interest since magnetic films are widely used in data storage devices and sensors. This is a study of the influence of adding sodium saccharin in the electrodeposition of cobalt thin films on silicon, the most widely used material in magnetic recording media. Saccharin was added to the cobalt solution at three different concentrations: 10 g/l, 20 g/l and 50 g/l. The additive caused a morphological, microstructural and magnetic behaviour change in cobalt films. The levelling and brightening effect of saccharin was verified visually and by atomic force microscope. The films became single-phase structured by adding 50 g/l saccharin, on the contrary of the dual-phase structure found in the basic Co solution. The remanent magnetization (M-r) and the coercive field (H-e) of the films were improved and the metallic nuclei size decreased as the saccharin concentration increased. (c) 2008 Elsevier B.V. All rights reserved.
Electrodeposition appears as an option to obtain thin films of technological interest. In the present study, galvanostatic and potentiostatic deposition of cobalt films onto n-type Si(100) with two different resistivities, < 0.005 ohm cm and 50- 100 ohm cm, was performed. The influence of silicon resistivity on electrochemical parameters and on nucleation features was investigated by chronogalvanometric and chronopotentiometric curves. Atomic force microscopy characterization of the deposits indicated that electrochemical parameters and the deposition method (galvanostatic or potentiostatic) influence the morphology of the deposits. For potentiostatic deposition an instantaneous nucleation was found and the cobalt nuclei deposited onto low silicon resistivity were smaller in size and greater in quantity than those onto high silicon resistivity. For galvanostatic deposition a progressive or two-step nucleation was observed without significant influence of the substrate resistivity on deposit morphology. (c) 2005 Elsevier B.V. All rights reserved.