Substrate-Induced Changes on the Optical Properties of Single-Layer WS2.

Among the most studied semiconducting transition metal dichalcogenides (TMDCs), WS2 showed several advantages in comparison to their counterparts, such as a higher quantum yield, which is an important feature for quantum emission and lasing purposes. We studied transferred monolayers of WS2 on a drilled Si3N4 substrate in order to have insights about on how such heterostructure behaves from the Raman and photoluminescence (PL) measurements point of view. Our experimental findings showed that the Si3N4 substrate influences the optical properties of single-layer WS2. Beyond that, seeking to shed light on the causes of the PL quenching observed experimentally, we developed density functional theory (DFT) based calculations to study the thermodynamic stability of the heterojunction through quantum molecular dynamics (QMD) simulations as well as the electronic alignment of the energy levels in both materials. Our analysis showed that along with strain, a charge transfer mechanism plays an important role for the PL decrease.

Acute toxicity of titanium dioxide microparticles in Artemia sp. nauplii instar I and II.

In this study, the toxicity effects of titanium dioxide (MTiO2 ) microparticles on Artemia sp. nauplii instar I and II between 24 and 48 h was evaluated. The MTiO2 were characterized using different microscopy techniques. MTiO2 rutile was used in toxicity tests at concentration of 12.5, 25, 50, and 100 ppm. No toxicity was observed in Artemia sp. nauplii instar I at the time of 24 and 48 h. However, Artemia sp. nauplii instar II toxicity was observed within 48 h of exposure. MTiO2 at concentrations of 25, 50 and 100 ppm was lethal for Artemia sp. with a significant difference (p ≤ .05) in relation to the control artificial sea water with LC50 value at 50 ppm. Analysis of optical and scanning electron microscopy revealed tissue damage and morphological changes in Artemia sp. nauplii instar II. By using confocal laser scanning microscopy, cell damage was observed due to the toxicity of MTiO2 at a concentration of 20, 50, and 100 ppm. The high mortality rate is related to the filtration of MTiO2 by Artemia sp. nauplii instar II due to the complete development of the digestive tract.

Silver nanoparticles (AgNPs) internalization and passage through the Lactuca sativa (Asteraceae) outer cell wall.

Silver nanoparticle (AgNPs) toxicity is related to nanoparticle interaction with the cell wall of microorganisms and plants. This interaction alters cell wall conformation with increased reactive oxygen species (ROS) in the cell. With the increase of ROS in the cell, the dissolution of zero silver (Ag0) to ionic silver (Ag+) occurs, which is a strong oxidant agent to the cellular wall. AgNP interaction was evaluated by transmission electron microscopy (TEM) on Lactuca sativa roots, and the mechanism of passage through the outer cell wall (OCW) was also proposed. The results suggest that Ag+ binds to the hydroxyls (OH) present in the cellulose structure, thus causing the breakdown of the hydrogen bonds. Changes in cell wall structure facilitate the passage of AgNPs, reaching the plasma membrane. According to the literature, silver nanoparticles with an average diameter of 15nm are transported across the membrane into the cells by caveolines. This work describes the interaction between AgNPs and the cell wall and proposes a transport model through the outer cell wall.

Tripentaphenes: two-dimensional acepentalene-based nanocarbon allotropes.

Tripentaphenes are 2D nanocarbon lattices conceptually obtained from the assembly of acepentalene units. In this work, density functional theory is used to investigate their structural, electronic, and vibrational properties. Their bonding configuration is rationalized with a resonance mechanism, which is unique to each of the 2D assemblies. Their formation energies are found to lie within the range of other previously synthesized carbon nanostructures and phonon calculations indicate their dynamical stability. In addition, all studied tripentaphenes are metallic and display different features (e.g., Dirac cone) depending on the details of the atomic structure. The resonance structure also plays an important role in determining the electronic properties as it leads to delocalized electronic states, further highlighting the potential of the structures in nanoelectronics.

International collaboration in Brazilian science: financing and impact.

The study of international collaborations can help in understanding the benefits of such relationships and aid in developing national financing policies. In this paper, the international collaboration of Brazilian scientists was studied using SciVal® and Incites® database, looking at its effect on the universities, financing agencies and different areas of knowledge and research topic clusters. Cluster and principal component analyses of scientometric data were carried out. While the results confirmed known knowledge that international collaboration increases impact, this study shows that Brazilian researchers are contributing to prominent research topics worldwide, in all areas of knowledge. This finding is contrary to several points of view that identify Brazil as a regional and not an international partner in science. Important also to note the impact of Brazilian authors in international collaboration that is well above the world mean. The collaboration of Brazil with foreign partners brings benefits for both sides, creating the opportunity of Brazilian research access to financing from international agencies. Increases in measures of impact are also seen for both sides. Foreign partners likewise benefit from higher impact factors in the same topic cluster, when collaborating with Brazilian partners. Publishing open access in high impact journals is fundamental for maintaining Brazilian science at the forefront.

Vibrational Spectroscopy and Morphological Studies on Protein-Capped Biosynthesized Silver Nanoparticles.

Silver nanoparticles (AgNPs) have a large number of applications in technology and physical and biological sciences. These nanomaterials can be synthesized by chemical and biological methods. The biological synthesis using fungi represents a green approach for nanomaterial production that has the advantage of biocompatibility. This work studies silver nanoparticles (AgNPs) produced by fungi Rhodotorula glutinis and Rhodotorula mucilaginosa found in ordinary soil of the Universidade Federal do Ceará campus (Brazil). The biosynthesized AgNPs have a protein-capping layer involving a metallic Ag core. The focus of this paper is to investigate the size and structure of the capping layer, how it interacts with the Ag core, and how sensitive the system (core + protein) is to visible light illumination. For this, we employed SEM, AFM, photoluminescence spectroscopy, SERS, and dark-field spectroscopy. The AgNPs were isolated, and SEM measurements showed the average size diameter between 58 nm for R. glutinis and 30 nm for R. mucilaginosa. These values are in agreement with the AFM measurements, which also provided the average size diameter of 85 nm for R. glutinis and 56 nm for R. mucilaginosa as well as additional information about the average size of the protein-capping layers, whose found values were 24 and 21 nm for R. mucilaginosa and R. glutinis nanoparticles, respectively. The protein-capping layer structure seemed to be easily disturbed, and the SERS spectra were unstable. It was possible to identify Raman peaks that might be related to α-helix, ß-sheet, and protein mixed structures. Finally, dark-field microscopy showed that the silver cores are very stable, but some are affected by the laser energy due to heating or melting.

Molecular spintronics: destructive quantum interference controlled by a gate.

The ability to control the spin-transport properties of a molecule bridging conducting electrodes is of paramount importance to molecular spintronics. Quantum interference can play an important role in allowing or forbidding electrons from passing through a system. In this work, the spin-transport properties of a polyacetylene chain bridging zigzag graphene nanoribbons (ZGNRs) are studied with nonequilibrium Green's function calculations performed within the density functional theory framework (NEGF-DFT). ZGNR electrodes have inherent spin polarization along their edges, which causes a splitting between the properties of spin-up and spin-down electrons in these systems. Upon adding an imidazole donor group and a pyridine acceptor group to the polyacetylene chain, this causes destructive interference features in the electron transmission spectrum. Particularly, the donor group causes a large antiresonance dip in transmission at the Fermi energy EF of the electrodes. The application of a gate is investigated and found to provide control over the energy position of this feature making it possible to turn this phenomenon on and off. The current-voltage (I-V) characteristics of this system are also calculated, showing near ohmic scaling for spin-up but negative differential resistance (NDR) for spin-down.

Influence of concentration and position of carboxyl groups on the electronic properties of single-walled carbon nanotubes.

The effects of attaching COOH groups at different sites and in various concentrations on electronic and structural properties of (8,0) single-walled carbon nanotubes (SWNT) were investigated using ab initio calculations. The binding energies and the charge transfers between the COOH functional groups and the tube were calculated for several configurations and a novel feature in the electronic structure of these groups was observed. The electronic character of these systems can be modulated by playing with the concentration and the position of the carboxyl groups bonded on the tube wall. The carboxyl groups bound to different carbon atom sub-lattices are more hybridized than those bound in the same one. These results suggested that SWNT-COOH systems are a playground for engineering electronic properties through a proper chemical functionalization which exploit both the attachment site and concentration of functional groups.

Electronic and magnetic structures of coronene-based graphitic nanoribbons.

We study the electronic properties of a series of coronene-derived graphitic nanoribbons recently synthesized in a pre-programmed, nanotube assisted, chemical route [Talyzin et al. Nano Lett., 2011, 11, 4352 and Fujihara et al. J. Phys. Chem. C, 2012, 116, 15141]. We employ a combination of density functional theory and spin-polarized tight-binding methods to show how details of the molecular building blocks and their assembly uniquely determine the electronic structure of the resulting ribbon. We demonstrate the onset of multiple magnetic states for these systems and a non-trivial dependence of the electronic bandgap with both atomic structure and spin configuration, which make these coronene-based ribbons potential candidates for applications in nanoelectronics.

Inflammatory and hyperalgesic effects of oxidized multi-walled carbon nanotubes in rats.

We evaluated local inflammatory activity of oxidized multiwalled carbon nanotubes in rat experimental models of acute inflammation (paw edema and hyperalgesia) by analyzing their toxicity in non-mesoendothelial tissues. Subcutaneous injection of the nanotubes induced paw edema, that was maximal in the first 2 h after administration at 0.1 mg/kg (43.25 +/- 3.8 AUC) and 1 mg/kg (30.1 +/- 1.8 AUC) compared to saline (18.32 +/- 02.05 AUC). The histopathological analysis showed acute inflammation characterized by vasodilatation, edema formation, neutrophil infiltrate and tissue damage. The nanotubes also elicited hyperalgesic response, seen by the increase of animal paw withdrawal that was maximal in the first 3 hours. The data obtained at the 3rd h was: 75 +/- 9.3% (0.01 mg/kg), 58 +/- 8.3% (0.1 mg/kg) and 53 +/- 6.69% (1 mg/kg) in relation with saline (28 +/- 3.5%). In conclusion, the oxidized multiwalled carbon nanotubes elicit inflammatory and hyperalgesic effects associated to severe tissue damage in rats.

Electronic transport properties of carbon nanotoroids.

We investigate the electronic transport properties of carbon nanotori covalently connected to external electrodes made up of carbon nanotubes of various chiralities. The study is based on computing ballistic transport characteristics within the framework of Green's function theory using a simple π-orbital tight-binding model. The calculations focus on the effect of the relative angle made by the electrodes as they are placed at different positions along the nanoring. The conductance behavior is found to depend on the details of the atomic structure of the torus but also on the positions of the electrodes. Our findings are rationalized using an elementary quantum mechanical interference model, which reproduces well the main features of the numerical data.

Conductive carbon-clay nanocomposites from petroleum oily sludge.

Oily sludge samples formed in water-oil separation tanks from a petroleum industry were collected, characterized and heat-treated at different temperatures, in order to yield carbon-clay composites. EDX microanalysis, XRD and FTIR data revealed that before carbonization the oily sludge was formed mainly by a mixture of quartz, montmorillonite, calcite, barite and oil residues. After carbonization, mineral phases present were mainly quartz, anorthite and gehlenite, in addition to graphitic and disordered carbon domains, according to XRD, Raman and TEM measurements. A preliminary evaluation of the electrical conductivity performed by Impedance Spectroscopy revealed that the composites formed are conductive, exhibiting conductivity values typical of semiconductors, in contrast to the precursor material.

A single molecule rectifier with strong push-pull coupling.

We theoretically investigate the electronic charge transport in a molecular system composed of a donor group (dinitrobenzene) coupled to an acceptor group (dihydrophenazine) via a polyenic chain (unsaturated carbon bridge). Ab initio calculations based on the Hartree-Fock approximations are performed to investigate the distribution of electron states over the molecule in the presence of an external electric field. For small bridge lengths (n=0-3) we find a homogeneous distribution of the frontier molecular orbitals, while for n>3 a strong localization of the lowest unoccupied molecular orbital is found. The localized orbitals in between the donor and acceptor groups act as conduction channels when an external electric field is applied. We also calculate the rectification behavior of this system by evaluating the charge accumulated in the donor and acceptor groups as a function of the external electric field. Finally, we propose a phenomenological model based on nonequilibrium Green's function to rationalize the ab initio findings.