RESUMO
The interaction between sodium salicylate (NaSal) and the two macrocycles 5,11,17,23-tetrakissulfonatomethylene-2,8,14,20-tetra(ethyl)resorcinarene (Na4EtRA) and ß-cyclodextrin (ß-CD) has been studied by the determination of ternary mutual diffusion coefficients, and spectroscopic and computational techniques. The results obtained by the Job method suggest that the complex formation is given in a 1:1 ratio for all systems. The mutual diffusion coefficients and the computational experiments have shown that the ß-CD-NaSal system presents an inclusion process, whereas the Na4EtRA-NaSal system forms an outer-side complex. This fact is also in line with the results obtained from the computational experiments, where the calculated solvation free energy has been found to be more negative for the Na4EtRA-NaSal complex because of the partial entry of the drug inside the Na4EtRA cavity.
Assuntos
Salicilato de Sódio , beta-Ciclodextrinas , beta-Ciclodextrinas/química , ResorcinóisRESUMO
Experimental realizations of two-dimensional materials are hardly free of structural defects such as e.g. vacancies, which, in turn, modify drastically its pristine physical defect-free properties. In this work, we explore effects due to point defect clustering on the electronic and transport properties of bilayer graphene nanoribbons, for AA and AB stacking and zigzag and armchair boundaries, by means of the tight-binding approach and scattering matrix formalism. Evident vacancy concentration signatures exhibiting a maximum amplitude and an universality regardless of the system size, stacking and boundary types, in the density of states around the zero-energy level are observed. Our results are explained via the coalescence analysis of the strong sizeable vacancy clustering effect in the system and the breaking of the inversion symmetry at high vacancy densities, demonstrating a similar density of states for two equivalent degrees of concentration disorder, below and above the maximum value.
RESUMO
The increasing interest in developing safe and sustainable energy storage systems has led to the rapid rise in attention to superconcentrated electrolytes, commonly called water-in-salt (WiS). Several works indicate that the transport properties of these liquid electrolytes are related to the presence of nanodomains, but a detailed characterization of such structure is missing. Here, the structural nano-heterogeneity of lithium WiS electrolytes, comprising lithium trifluoromethanesulfonate (LiTf) and bis(trifluoromethanesulfonyl)imide (LiTFSI) solutions as a function of concentration and temperature, was assessed by resorting to the analysis of small-angle neutron scattering (SANS) patterns. Variations with the concentration of a correlation peak, rather temperature-independent, in a Q range around 3.5-5 nm-1 indicate that these electrolytes are composed of nanometric water-rich channels percolating a 3D dispersing anion-rich network, with differences between Tf and TFSI anions related to their distinct volumes and interactions. Furthermore, a common trend was found for both systems' morphology above a salt volume fraction of â¼0.5. These results imply that the determining factor in the formation of the nanostructure is the salt volume fraction (related to the anion size), rather than its molality. These findings may represent a paradigm shift for designing WiS electrolytes.
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The cloaking effect of electronic states was only reported in bilayer graphene. Here in this work we show that this effect can also be induced in armchair graphene nanoribbons (AGNRs), by potential barriers that modulate the chirality property of the system (correlation between pseudospins). These barriers manipulate the chirality and generates pseudospin polarizations on the sides of the barrier, which leaves spatial regions in evidence, in which states behave differently. In AGNRs the extended states (ES), associated with the tunneling of Klein, use only some sites in the nanoribbon lattice (sublattice of ES). On the other hand, the barrier applied in the nanoribbon, induces states totally localized within the region of the barrier, these states use only the sites not used by the sublattice of ES. The localized states remain invisible for electronic transport for all the energies and characteristics of the barrier in the region of the first effective transport band, the same as the states are changing. This electronic cloaking effect can be suppressed by the application of a magnetic field, detecting in the conductance the previously invisible states in the form of Fano resonances. We discuss here the possibility of using this cloaking effect to generate mechanisms that can hide information or to activate hidden system effects.
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In this work we investigate the ballistic transport of electrons through three-terminal graphene-based devices. The system consists of a Y-shaped junction formed by three armchair-edged graphene nanoribbons with a rectangular gate potential applied to one of the output branches, whereby current control can be established by the controlling of the refractive index in graphene p-n junctions. Transport properties are obtained by using the Landauer-Büttiker formalism and the tight-binding model within the nearest-neighbor approximation, which allows the calculation of the conductance as function of the Fermi energy, the applied potential, and the system size, as well as the current density. The results demonstrate that the applied electric field can tune the current transmission between the input and two output leads and, consequently, the proposed system acts as a current switch.
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To achieve superior photovoltaic performance on Sb2S3 solid state solar cells (ssSCs), the concomitant development of efficient hole transport materials (HTMs) is required. Herein, a novel solution processed HTM obtained by mixing NiOx nanoparticles (NiOx-NP) and poly(3-hexylthiophene) (P3HT) is reported. These P3HT:NiOx-NP nanocomposite HTMs were obtained with different controlled concentrations of NiOx-NP using a common solvent. Incorporation of NiOx-NP significantly impacts on the structural and hole-transport layer properties of the nanocomposite films, which in turn contributes to improve the photovoltaic performance of the corresponding devices. Thus, Sb2S3 ssSCs based on HTM with an optimum concentration of NiOx-NP in P3HT, i.e. P3HT:2% NiOx-NP, yield a 50% improvement in the power conversion efficiency relative to control devices fabricated with pristine P3HT. The improved hole separation and injection at the Sb2S3/HTM interface, determined by steady-state photoluminescence quenching and electrochemical impedance spectroscopy studies, correlate well with the higher hole mobility of the nanocomposite and the current density and fill factor enhancements.
RESUMO
Se presentan propiedades eléctricas y de transporte en películas nanocristalinas del compuesto cuaternario Cu2ZnSnSe4 (CZTSe) por método de co-evaporación física. Las muestras fueron crecidas sobre sustratos de vidrio soda-lime y variando en rango los parámetros de síntesis: masa de Cu y temperatura de sustrato. A partir de termopotencia a temperatura ambiente y de transmitancia espectral, se encontró que el material está caracterizado por conductividad tipo n y ancho de banda de energía prohibida de 1.7 eV, respectivamente. Las medias de conductividad eléctrica (región de bajas temperaturas; 90-200 K) mostraron que los procesos de conducción se realizan vía hopping de rango de variable entre estados extendidos. Los parámetros que caracterizaron éste mecanismo, energía de activación (Whopp) y rango hopping (Rhopp), fueron obtenidos mediante teoría de percolación y modelo difusional. Se obtuvo, que para las muestras CZTSe la densidad de estados de defecto cerca del nivel de Fermi del material, N(Ef), está alrededor de 3,403x10(18) cm-3 eV-1. Se presentó correlación entre parámetros de depósito y propiedades eléctricas. Se observó influencia de parámetros sobre formación de fases adicionales en el compuesto.
Here, we present electronic and transport properties of quaternary Cu2ZnSnSe4 (CZTSe) nanocrystalline films fabricated by physical co-evaporation. The samples were grown on soda-lime glass substrates and synthesis parameter ranges, Cu mass and substrate temperature were varied. Using thermopower at room temperature and spectral transmittance we found that the material is characterized by n-type conductivity and forbidden energy bandwidth of 1.7 eV, respectively. Electrical conductivity means (low temperature region; 90-200 K) showed that conductivity processes occur via variable range hopping between extended states. We obtained the parameters characterizing this mechanism, activation energy (Whopp), and range hopping (Rhopp), by employing the percolation theory and diffusion model. The density of defect states near the Fermi level of the material, N (Ef) of the CZTSe samples is about 3,403x10(18) cm-3 eV-1. We found a correlation between deposition parameters and electrical properties and observed a parameter influence on the formation of additional phases in the compound.
Apresentam-se propriedades elétricas e de transporte em películas nano-cristalinas do composto quaternário Cu2ZnSnSe4 (CZTSe) pelo método de co-evaporação física. As amostras foram crescidas sobre substratos de vidro soda-lime e variando a amplitude dos parâmetros de síntese: massa de Cu e temperatura do substrato. A partir de termo-potência a temperatura ambiente e de transmissão espectral, encontrou-se que o material está caracterizado pela condutividade tipo n e largura de banda de energia proibida de 1.7 eV, respetivamente. As medidas de condutividade elétrica (regiões de baixas temperaturas; 90-200 K) mostraram que os processos de condução se realizam via hopping de amplitude variável entre estados estendidos. Os parâmetros que caracterizaram este mecanismo, energia de ativação (Whopp) e amplitude hopping (Rhopp), foram obtidos mediante a teoria de percolação e o modelo de difusão. Obteve-se que, para as amostras CZTSe, a densidade de estados de defeito próximos do nível de Fermi do material, N(EF), está ao redor de, 3,403x10(18) cm-3 eV-1. Apresentou-se correlação entre parâmetros de depósito e propriedades elétricas. Observou-se influencia de parâmetros sobre a formação de fases no composto.