Papers by Author: Miguel José-Yacamán

Abstract: Pt-Pd bimetallic nanoparticles were characterized using aberration (Cs) corrected scanning transmission electron microscopy (STEM) along with molecular dynamics simulations. The nanoparticles were synthesized through a microwave-assisted process. This technique has been applied to synthesize metallic nanoparticles at relatively short times, allowing a good control of size distribution. The structure of the bimetallic nanoparticles is fcc-like with an average size of 5 nm. To understand the properties of the bimetallic nanoparticles, it is necessary to know the positions of all the atoms in the nanostructure. We have used a recent quantitative method to analyze HAADF STEM images which allowed us to measure the total intensity of the scattered electrons for each atomic column. Beside with the characterization of the nanoparticles, we have performed classical molecular dynamics simulation for the structural and dynamical analysis of the cuboctahedral Pt-Pd bimetallic nanoparticles.

Abstract: Single crystalline zinc oxide (ZnO) nanorods have been grown on Si (100) substrates by a hydrothermal method at 65 °C. In order to show the habit of crystalline growth and applied these ZnO 1D to the electron radiation. The ZnO nanorods grown on Si (100) have been characterized in detail using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The XRD studies revealed that the ZnO nanowires showed the wurtzite structure (hexagonal). The Secondary Electron SEM image showed different morphology of the ZnO nanorods as a function of the reagents concentration. These nanorods have uneven tops and showed an apparent screw growth pattern with a typical hexagonal facets structure on the (0001) surface. The spiral growth step morphology strongly suggests that screw dislocations can play a significant role in promoting the ZnO nanorods growth and that the screw dislocation is growing in the polar axis of the ZnO nanorods. The ZnO nanorods were irradiated with electron beam (30 kV) for 100 minutes. We observed that the one-dimensional (1-D) ZnO nanorods were resistant to the electron radiation. This finding is interesting because, we can use these 1-D ZnO nanorods to development materials which can be resistant to radiation.

Abstract: The selected area electron diffraction patterns and structure of pentagonal cross-section nanowires reported for silver are commented and interpreted in is work. We show that they are closely related to a decahedron-base structure.

Abstract: In this work we present the synthesis of branched gold nanoparticles based on the seed mediated growth technique. The materials have been characterized by advanced electron microscopy techniques in order to elucidate morphology, size and internal structure.

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.