M. José-Yacamán

Catalytic growth of carbon microtubules with fullerene structure

A method to grow carbon microtubules with fullerene structure (buckytubes) has been identified. The method consists of the catalytic decomposition of acetylene over iron particles at 700u2009°C. Carbon microtubules of up to 50 μm in length are synthesized by this method. Electron diffraction and high resolution electron microscopy studies demonstrate that the structure of these microtubules corresponds to the helical structure recently reported by S. Iijima, Nature 354, 56(1991), prepared using an arc‐discharge evaporation method.

Maya Blue Paint: An Ancient Nanostructured Material

Maya blue paint was often used in Mesoamerica. The origin of its color and its resistance to acids and biocorrosion have not been fully understood. High-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray microanalysis studies of authentic samples show that palygorskite crystals in the paint form a superlattice that probably occurs as a result of mixing with indigo molecules. An amorphous silicate substrate contains inclusions of metal nanoparticles encapsulated in the substrate and oxide nanoparticles on the surface. The beautiful tone of the color is obtained only when both the particles and the superlattice are present.

Structure determination of small particles by HREM imaging: theory and experiment

The characterization of the structure of small particles (with a size of a few nanometers) is very important in order to understand their optical, electronic and magnetic properties. High-resolution electron microscopy is a fundamental tool to obtain a full characterization of nanometric particles. In the present work, we report a systematic theoretical study of the HREM images of metallic particles with nanometric sizes. The images of gold clusters with FCC, decahedral, icosahedral and amorphous structures are reported for a number of orientations with respect to the electron beam. Experimental images of a number of particles are reported and compared with the calculated images and Fourier transforms.

Studies of MoS2 structures produced by electron irradiation

In this letter, we report the study of MoS2 crystals after irradiation with a high dose of electrons. A pelletron accelerator was used to irradiate the sample with electrons at an energy of 0.5 MeV. Samples were examined in high resolution electron microscopy. Two main structures were observed: onion layers with fullerene like structure and others with their planes rotated with respect to each other by well‐defined angles. We present a calculation showing that relative rotation of the sulphur layers by 3°, 5°, 8°, and 16° basically have the same average energy as the unrotated structure. Therefore rotations of the layers through those angles will be favored. Instability on the structure produced by irradiation will induce rotations on the structure.

Epitaxially grown model catalyst particles of platinum, rhodium, iridium, palladium and rhenium studied by electron microscopy

In order to obtain oriented thin film model catalysts, small particles of Pt, Rh, Ir, Pd and Re (2–20 nm in size) were grown by high vacuum evaporation on NaCl cleavage faces or on in situ deposited NaCl films at 523–673 K. The particles were covered with a supporting film of Al2O3 or carbon and removed from the substrate. High resolution electron microscopy, selected area electron diffraction and weak-beam dark-field imaging were applied to determine the particular morphology, microstructure and orientation of the observed particles. Special attention was paid to Rh particles which appear in a variety of shapes. Pt, Ir and Pd model catalysts consist mainly of (001) oriented half octahedra which may exhibit truncations at the corners or on the top. This was also the dominant shape of Rh particles but in addition half tetrahedra in (011) epitaxy and multiply-twinned particles like decahedra in (001), (011) and (111) orientation were evident. These habits provide a definite “initial state” for study of the changes in structure and morphology of the particles during activating heat treatments necessary to induce catalytic activity of the Al2O3 supported metal films. Although Re films consisted of irregularly shaped particles, electron diffraction revealed a partial epitaxial alignment of both c.p.h. and f.c.c. Re.

Carbon structures grown from decomposition of a phenylacetylene and thiophene mixture on Ni nanoparticles

Abstract A method based on the decomposition of phenylacetylene and thiophene on a Ni-powder catalyst has been used to produce nanotubes, circular hollow structures, and other interesting graphitic morphologies. The structures obtained are analyzed using HREM. The stability of bent graphite sheets is studied.

Microstructural study of hollandite-type MnO2 nano-fibers

A new morphology of manganese oxide in the form of nano-fibers was synthesized using a novel synthetic route, and structurally characterized using high-resolution transmission electron microscopy. The obtained manganese oxide, doped with potassium, adopts a hollandite-type structure with “few useful defects” which provide an open tunneled structure in three-dimensions. This characteristic is actually believed to improve, to a high extent, the ionic conductivity of the material and exhibits the doped hollandite-type manganese oxide as a highly promising candidate for electrochemical applications such as rechargeable batteries.

Decagonal and hexagonal structures in small gold particles

Abstract In the present work we report the study of gold particles using HREM and image processing. Particles which are not conventional fcc are discussed as well as penta-twinned particles which show twin boundaries that do not join along a common point. It is shown that there are particles with an hcp structure. This structure is probably due to repeated faulting and excess vacancies.

On the high temperature coalescence of metallic nanocrystals

Abstract The high temperature properties of metallic particles with a size of a few nanometers are very important in modern materials science. In the present work we report in situ transmission electron microscope studies of coalescence behavior of nanoparticles at high temperatures. At T > 700 K a new mechanism for coalescence was found. This phenomenon occurs on a time scale 3 to 20 times faster than the classical liquid-like coalescence reported by Pashley [Adv. Phys. 14 (1965) 327]. Before the coalescence the particles undergo shape convulsions of the type described by Iijima and Ichihashi [Phys. Rev. Lett. 56 (1986) 616] which has been termed “quasimelting”, then fast coalescence occurs. The newly formed particles also undergo convulsions until stabilized by the substrate. It is also shown that the electron beam plays a significant role on this process.

Microscopic structure of gold particles in a metal polymer composite film

Gold particles embedded in a polymer are studied using high resolution electron microscopy, nanodiffraction, and image processing. These particles have interesting properties such as nonlinear optical susceptibility. It is found that most of the nanoparticles are single crystals, and twins and planar defects are scarcely observed. On the other hand, it is found that nanoparticles do not show smooth facets but they are instead very rough. The effects of this extended roughness in the optical properties are discussed.