Journal of Nano Research Vol. 5

Abstract: We report the findings concerning the preparation and characterization of Au nanoparticles deposited on sol-gel derived TiO2, TiO2-Al2O3 and TiO2-In2O3 semiconductors. The gold nanoparticles were obtained by the deposition-precipitation method using urea. The mean particle size was determined by HAADF-STEM. The gold nanoparticles ranged form 2.4 to 4.4 nm, and the smallest corresponding to the TiO2-Al2O3 support was 2.4 nm. The effect of support on the growth of the gold nanoparticles was analyzed by HRTEM. The gold nanoparticles showed different shapes depending on the semiconductor supports. Truncated cuboctahedral gold nanoparticles were identified and analyzed.

Abstract: Au/TiO2 and Au/TiO2-CeO2 catalysts were prepared by the sol-gel method and carbon monoxide, hydrogen chemisorption and TEM spectroscopy have been exploited to determine the size of gold particles. The gold nanoparticles (8.1 to 2.1 nm) were deposited by using the deposition-precipitation method. The XRD characterization shows the presence of anatase as the TiO2 crystalline phase; while by XPS spectroscopy, the presence of Au°, Au2O3, Ce3+ and Ce4+ species co-existing in the Au/TiO2-CeO2 catalysts is shown. The characterizations by TPD-CO as well as by TPD-H2 (temperature programmed desorption) showed that on catalysts containing cerium, the gold particle size can be determined with great accuracy by using these chemisorption methods. The gold particle size calculated from either the CO or H2 thermodesorption values is in good agreement with that obtained by High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy (STEM) analyses. It was proposed that the TPD-CO and/or TPD-H2 techniques could be helpful for the characterization of the gold particles by TEM; especially when the high contrast in the pictures of the supports containing CeO2 prevents the particle size from being determined.

Abstract: We have performed first principles total energy calculations to investigate the structural properties of copper iodide (CuI) in its sodium chloride, cesium chloride, zincblende and wurtzite structures. Calculations are done using the density functional theory. We employ the full potential linearized augmented plane wave method as implemented in the wien2k code. The exchange and correlation potential energies are treated in the generalized gradient approximation (GGA), and the local density approximation (LDA). Optical absorption experiments and x-ray diffraction measurements have shown that zincblende is the ground state of CuI. Our calculations find that in the GGA formalism wurtzite and zincblende have similar total energies, while in the LDA formalism the lowest minimum corresponds to zincblende. Results show that the energy difference between the wurtzite and the zincblende structures, as calculated within the GGA formalism is 2 meV, and within the LDA formalism, is 31 meV. These results may suggest a coexistence of both wurtzite and zincblende structures in the ground state of CuI. Structural parameters are correctly reproduced by the GGA calculations. We obtain that under the application of external pressure the atomic configuration may transform into the NaCl structure. At higher pressures it is possible to have a phase transition to the CsCl geometry.

Abstract: The Nafion perfluorinated membranes are one of the best electrolytes used in the Proton Exchange Membrane Fuel Cell (PEMFC). Some methods have been used to study the electrical properties of Nafion; nevertheless, there are some aspects of the conduction process that are not well understood, such as the contribution of the bulk and the interfacial phenomena to the total proton conduction process. In this work the Electrochemical Impedance Spectroscopy (EIS) was employed in a four electrode system to study the protonic charge transport under conditions that simulate the operation of the PEMFC. Two Nafion membranes were evaluated to determine the relation of the activation procedure with the resistance to the protonic charge transference. The results are not only consistent with other measurements but also allow to separate the protonic charge transference process in two stages. Each stage was studied and their electrical parameters were calculated using Electrical Equivalent Circuits.

Abstract: Bromobenzenethiol passivated gold nanoparticles were mixed with a poly(phenylene ethynylene) bearing thioester flexible sequences in order to obtain a fluorescent composite for optical biosensors. The particles and the composite were characterized by 1H, 13C NMR, UV-Vis and fluorescence spectroscopy, TEM and STEM. The particles are homogeneously dispersed in the polymer matrix as observed by electron microscopy. The NMR spectra suggest that the gold particles and the poly(phenylene ethynylene) are probably interacting through the sulfur atoms of the –C(O)S- and –CH2-S-CH2- moieties of the flexible sequences of the polymer as well as through  interactions between the aromatic ring of 4-bromobenzenthiol and the conjugated backbone of pPET3OC12-sqS. The quantum yield of the composite both in solution and in solid state films is slightly lower than that of pPET3OC12-sqS because of the quenching effect of gold. Nonetheless, a change of the fluorescence intensity of the composite films can be detected as a consequence of the contact with microorganisms. Preliminary microbiological assays indicate an antimicrobial effect of the composite film with the E. coli bacteria.

Abstract: A theoretical study of the electronic and structural properties of single wall SnO one dimensional (1D) nanotubes and nanorods is presented in models with arm chair (n,0) and zig-zag (n,n) chirality. The nanonotube and nanorod models were built setting periodic boundary conditions along the axis of the 1D structures. In both cases, nanotubes and nanorods, the geometry was optimized keeping the periodic cell dimensions constant and relaxing the atomic positions through DFT calculations carried out for various k points, and using the GGA-PW91 functional. The surface charge characteristics of the systems were mapped with the Hirshfeld charge, showing a small tendency towards to increase the outer tin atomic charges, and to reduce the inner oxygen atomic charges of the nanotube with regard to the flat bulk structure charges. The nanotubes shows stable configurations in both chiralities, whereas the nanorod geometry shows a stable configuration only in the (n,0) chirality. The conduction properties were studied as function of the curvature of the 1D tin monoxide structures through the total density of states and the band gap observing a tendency to the larger the nanotube radius the larger band gap.

Abstract: Spherical submicrometer-sized silica particles were prepared from a reaction mixture containing tetraethoxysilane, ammonia and ethanol, and deposited onto silicon wafers. The properties of these SiO2 particles depend on their size, size distribution and shape. Even if some of these characteristics can be perfectly controlled by appropriate synthesis conditions, several alternative approaches must be explored in order to modify the shape of silica particles. The samples were then irradiated at room temperature with Si ions at different energies (4, 6 and 8 MeV) and fluences up to 5×1015 Si/cm2, at an angle of 45° with respect to the sample surface. After the Si irradiation the spherical silica particles turned into ellipsoidal particles, as a result of the increase of the particle dimension perpendicular to the ion beam and a decrease in the parallel direction. This effect increases with the ion fluence and depends on the electronic energy loss of the impinging ions. We observed that the particle deformation decreases with the beam energy, mainly because our samples were irradiated at room temperature. Thermal effects must be studied in detail in order to elucidate the complete deformation mechanism, as the existence of additional mechanisms related to the electronic energy loss effects can not be excluded.

Abstract: To investigate the optical properties in non-periodic dielectric systems, we study here the reflection of light from nanostructured porous-silicon-based period doubling heterostructures. The multilayered systems are fabricated in such a way that the optical thickness of each layer is one quarter of 650nm. The results for the optical reflectance are presented and compared with that of Fibonacci, Thue-Morse, and random structures fabricated under the same conditions. Numerical simulation for the reflectance along the lines of the transfer matrix approach is performed. In addition, optical reflection from Gaussian porous silicon multilayers is also briefly discussed. We find that porous silicon Period Doubling dielectric multilayers could demonstrate the optical properties similar to the classical periodic Febry-Perot interference filters with one or multiple resonant peaks, but with an advantage of having total optical thickness much lesser than that of the periodic structures.

Abstract: Conducting Polyaniline (Pani)-crooked Gold nanocomposites were synthesized by in situ chemo-oxidative polymerization of aniline with previously made crooked gold nanoparticles by using ammonium per oxidisulphate as oxidizing agent and p-toluene sulphonic acid (p-TSA) as dopant. The formation of nano gold was established by UV-visible spectroscopy with a SPR peak at 512 nm and crooked morphology was confirmed by TEM. Spectroscopic analysis confirmed the formation of the conducting emeraldine salt phase of the polymer. Due to clustering of composite nanoparticles, the polymer composite formed one-dimensional rod-like morphologies. Thermogravimetric analysis revealed a typical three-step decomposition pattern pertaining to polyaniline emeraldine salt. The conductivity of the nanocomposite was found to be lower (2.47 S/cm) than the virgin p-TSA doped polyaniline (5.55 S/cm).