An experimental high-resolution image of a solid–liquid interface of solid Si and liquid Al–Si alloy has been compared with theoretical images obtained by computer simulation. It has been concluded that the solid–liquid interface has a transition layer, the structure of which is compatible with the 1 × 1 Si-{111} surface.

Direct methanol fuel cells (DMFCs) offer a simpler, safer technology for point-of-use power sources compared to other hydrogen fuel cells, by avoiding the need to store hydrogen fuel or to carry out the reformation of hydrocarbons. The direct methanol oxidation electrocatalyst of choice is a nanoscale black consisting of a 50:50 atom % mixture of Pt and Ru. It has recently become known that these presumed bimetallic alloys in fact contain an array of metal, oxide and hydrous phases, which are easily misidentified in routine x-ray diffraction measurements due to particle size-broadening and poor crystallinity. By combining transmission electron microscopy, electrochemistry and thermogravimetric studies, we demonstrate here that the route to improved catalytic activity is not by phase purification of the bimetallic alloys, but instead phase engineering of hydrous ruthenium oxide and Pt mixtures.

The ability to align single wall carbon nanotubes (SWNTs) is paramount for harnessing their remarkable anisotropic electronic and mechanical properties. D.A. Walters et al. (Rice Univ.) have succeeded in aligning milligram quantities of SWNTs using a strong magnetic field. The nanotubes were aligned in suspension and simultaneously filtered to produce a thin membrane. However, small angle X-ray scattering (SAXS) — the traditional technique for obtaining fiber patterns — has proven ineffective in determining the degree of alignment due in part to carbon's weak atomic scattering factor for X-rays.

In the present work we succeed in quantitatively characterizing this membrane using transmission electron microscopy (TEM). A self-supporting sample was prepared by peeling ∼ 0.5 mm long strips from the material. TEM images reveal that the membrane itself is not a single, large bundle (i.e. rope) of SWNTs. Instead, it has a prominent texture, corresponding to many ropes aligned parallel to the direction of the applied magnetic field.

Annihilation behaviors of athermal ω-phase crystals formed by cooling at 131 K for 10.8 ks under four different electron irradiation conditions of acceleration voltages of 200 kV and 160 kV, and beam currents of approximately 20 pA/cm2 and 5 pA/cm2 were investigated using in situ dark field and HREM observation methods at 131 K. The effect of acceleration voltages on the lifetimes is recognized, i.e., in the case of approximately equal electron beam current, lifetimes at 200 kV become shorter than those at 160 kV. Also, lifetimes depend on the electron beam current at 200 kV, i.e., the higher the beam currents, the shorter the lifetimes become. However, no distinct dependence can be seen at 160 kV. Since annihilations of athermal ω-phase crystals begin after the electron irradiation for a certain period in each condition, which depends on acceleration voltages and beam currents, it is suggested that the annihilation behaviors have incubation periods.

Nanoparticles continue to attract interests because they fall into intermediate stage between molecular and macroscopic materials. Due to their large surface-to-volume ratio, nanoparticles exhibit physical and chemical properties that differ markedly from those characterizing the bulk solid state. One example is the phase diagram of a nanomaterial. Because nanocrystals display clear changes in both the thermodynamics and the kinetics of phase transitions, we expect different solubility limits in the nanometer regime. This means that phases unstable or unobserved in extended solids may be prepared as nanocrystals. We synthesized Au and Pt nanoparticles and performed chemical analysis on the sintered agglomerates.

The colloidal Au and Pt particles were synthesized according to Turkevich's method. An aqueous AuCl3 solution (50mg Au/L) was heated to 70°C. A determined amount of lwt% aqueous sodium citrate dihydrate (Na3C6H5O7.2H2O) solution was added such that the citrate-to-Au mass ratio was 10.

Transmission electron diffraction patterns from ultra-thin aromatic and aliphatic organic films at beam energies of 200 eV–1 keV have been recorded in a custom low energy electron transmission (LEET) chamber. A significant reduction of the molecular damage cross-section, measured by fading of diffraction spots, was found for thin films of the aromatic perylene when the beam energy was reduced from 400 to 200 eV. The corresponding measurements for the aliphatic tetracontane showed a smaller “threshold energy” and the differences are discussed. Electron beam damage from other aromatic materials has also been studied at low energy. Comparison of the carbon K shell ionization cross-section and the measured damage cross-sections show that carbon K-shell ionization is strongly correlated with the damage observed in aromatics at beam energies higher than 284 eV. Calculation of the minimum number of unit cells needed for imaging a single molecule, and comparison of calculated elastic with measured damage cross-sections both indicate new possibilities for imaging biomolecules with low energy electrons.

An overview and new results are presented of the investigations carried out in the last 5 years on nano-sized tips by means of electron microscopy, an electron optical bench, and computation. Tungsten and, in particular, carbon nano-tips prepared by carbon contamination in a scanning electron microscope, were studied for applications as field-emission electron sources. Several features of their use are described and the results concerning the determination of some of their basic properties are reported.

High spatial resolution chemical microanalysis of heterogeneous catalysts is traditionally done in transmission electron microscopy or scanning transmission electron microscopy (TEM/STEM) instruments. A major limitation of TEM/STEM techniques is, however, the stringent requirement of samples that can be examined: useful information can be extracted from only very thin areas of a sample. The preparation of suitable TEM samples may also pose a major problem for observing certain types of commercial catalysts, for example, beads, powders, or cylinders that are frequently used in catalytic reactions. These limitations preclude the application of TEM/STEM techniques to extracting information about the surface properties of thick or bulk catalyst samples.

With the recent development of high-resolution, field-emission scanning electron microscopes (FESEM), bulk samples can now be examined at a nanometer or sub-nanometer spatial resolution. At low incident beam energies, not only the emitted SE signal is more surface-sensitive but also charging of non-conducting materials is significantly reduced.

Platinum nanoparticles finely dispersed in activated carbon powders have been observed with high contrast in secondary electron (SE) and backscattered electron (BE) images. The factors that contribute to the visibility of small metal particles in high-resolution BE and SE images are discussed. Monte Carlo simulations provided insight into the scattering of electrons by small, heavy-element particles located on, or embedded in, light-element supports. The visibility of Pt nanoparticles in BE images depends on many factors including the size and the location of the Pt particles, the energy of the incident electrons, and the size of the electron probe. The SE signals generated by backscattered electrons may not significantly contribute to the visibility of small Pt particles in high-resolution SE images of carbon supported Pt catalysts. Only those small Pt particles that are located on or very close to the surface of the carbon support can be revealed in high-resolution SE images.

The large-scale commercial production of polyolefins by catalytic Ziegler-Natta polymerization have stimulated the development of the third, fourth and fifth generation heterogeneous catalysts comprising high surface area defective MgCl2 with TiCl4, electron donors, and AlR3-co-catalysts. In spite of intensive research over the years, the present level of understanding of the catalysts is still incomplete because of their complex composition leading to a multitude of local active site environments. The aim of this work is to provide a new insight into the process via in situ video microscopy of gas phase propylene polymerization over MgCl2-supported Ziegler-Natta catalysts combined with ex situ characterization by light and electron microscopy techniques (SEM, TEM, HRTEM, STEM, PEELS and windowless EDX). Procedures for catalyst synthesis are described elsewhere. The catalysts were stored in a dry box under a He atmosphere (<lppm H2O/O2). Samples were transferred to specimen holders in the dry box and then transferred into the microscopes under high purge N2 conditions to prevent poisoning of the catalysts by air and moisture.

A previously unknown form of charge ordering has been observed in dislocation free thin films of magnetite, Fe3O4. This charge ordering exists on tetrahedral sites and is unrelated to the well known low temperature ordering on octahedral sites that occurs below 120K. From modeling of electron diffraction patterns we deduce that the best fit to the observed diffraction patterns was obtained by reducing the scattering power on one tetrahedral site per unit cell by about 80%.

Iterative algorithms, which use diffracted intensities and some a-priori knowledge of an image to solve the phase problem, have been under development for many years. The promised super-resolution images, reconstructed from diffraction information alone, would be of the greatest value for molecular imaging and for the image of nonperiodic structures in materials. Using simulated data it is possible, for example, to reconstruct a complex object from a knowledge of its diffracted intensities with certain known support functions. Some success has recently been achieved reconstructing micrometer-sized non-periodic objects using coherent X-rays by the Feinup method. One favorable support function consists of two holes spanned by the coherence width of the beam, with one or both holes containing an unknown object. Our simulations, which iterate between diffracted intensities and the image, applying the known support (either completely opaque or completely transparent) and intensities in each domain, confirm that image reconstruction is possible for loose supports and noiseless data.

Soot particles are generated from a number of sources, including auto emissions, aircraft emissions and various domestic and industrial combustor sources. Particle size and composition has been the focus of recent Environmental Protection Agency directives, especially due to the impact of small particulates on the inner urban environments. Single particle microanalysis is advantageous in these studies since, morphology and composition can be examined simultaneously. When a small sample size is available, single particle microanalysis is the only possible micro analytical approach. Chemical fingerprinting using the energy dispersive x-ray spectroscopy (EDS) signature of trace elements contained in the particles has shown remarkable source based uniqueness. Previous studies involving diesel soot particulates have indicated that most samples analyzed on a discrete basis are reasonably homogeneous, but questions still remain as to the ultimate statistical limit of this technique.

Nearly all metals form a passivation film due to oxidation in air at ambient temperatures, that acts as a diffusion barrier to protect the materials from further corrosion. Aluminum demonstrates excellent passivation behavior due to the formation of a protective amorphous alumina film during exposure to air at ambient temperatures. However, H. Ebinger and J. Yates discovered that the passivation of aluminum can be significantly improved by artificial oxidation. Both electron-beam induced oxidation in water vapor and oxidation in ozone atmospheres3 showed higher impedance in electrochemical impedance spectroscopy measurements to anion diffusion than the thermally grown oxides. To understand the nature of this beneficial passivation, we probed the microstructure of these amorphous oxide films by transmission electron microscopy (TEM).

The oxide films were grown on a polycrystalline Al substrate. The Al substrate was cleaned with a sputter cleaner inside a UHV (ultra-high vacuum) system.

Carbon nanotubes (NTs) have novel electronic properties and exceptionally high Young's moduli on the order of TPa. so NTs have potential applications in advanced composite materials such as conductive polymers, electromagnetic-radio frequency interference (EMI/RFI) shielding material and opto-electronic materials. The utility of the nanotubes in composite applications depends strongly on the ability to disperse the NTs homogeneously throughout the matrix without destroying the integrity of the NTs. Furthermore, interfacial bonding between the NT and matrix is necessary to achieve load transfer across the interface, which is desirable for improving the mechanical properties of polymer composites.

In this work, aligned multiwalled carbon nanotubes (MWNTs) produced by continuous chemical vapor deposition (CVD) (see Fig.l), were homogeneously dispersed in polystyrene (PS) matrices by a simple solution-evaporation method. Using this procedure, we made uniform MWNT-PS composite films ∼0.4mm thick for ex-situ mechanical tensile test and very thin films, ∼100nm, for in-situ TEM tests, as shown in Fig.2.

It is of fundamental and practical interest to understand the oxidation process since a desirable property for metals is resistance to corrosion. But there is a wide gap between information provided by surface science methods and that provided by bulk oxidation studies. The former have mainly examined the adsorption of ∼ 1 ML of oxygen on the metal surface, where as both low and high temperature bulk oxidation studies have mainly focused on the growth of an oxide layer at the later stages of oxidation.

We are probing the initial oxidation stage of a model metal system by in situ ultra-high vacuum (UHV) transmission electron microscopy (TEM) in order to gain insights into the initial kinetics of oxidation. We have previously shown that the growth mechanism of the cuprous oxide is initially dominated by oxygen surface diffision.

The mechanical alloying (MA) process is an effective method to develop strategic materials with novel structures. These can be solid solutions (even in immisible systems), amorphous phases, fine particle sized and nano-metric crystals etc. Conventional powders metallurgy routes can process the mechanical alloyed products. However, the novel features conferred into the powders, can be lost during the sintering operations. The spark plasma sintering process (SPS) is an alternative route to dense mechanically alloyed products at a high grade while retaining their novel structures. Co-Ti alloys were produced by mechanical alloying the elemental powders mixtures with nominal composition Co50Ti50 (at. %). Details on the preparation and characterisation of the milled products can be found in related publications. Densification of the powders products was conducted using a Dr. Sinter equipment. Previous studies on Co-Ti alloys processed by MA and SPS have shown that the final products are composed of mixtures of metastable intermetallic compounds.

Mn oxides of pervoskite-related structure containing Mn ions have attracted considerable interest due to the colossal magnetoresistence (CMR) effect. Doping the family of compounds La1-x Cax MnO3 with divalent Ca ion oxidizes Mn+3 to Mn4+, introducing holes in the 3d bond orbital that give rise to a series of interesting physical properties. The parent compound LaMnO3 (Pbnm) with unit cell of a=5.5367Å b=5.7473Å and c=7.6929Å, is an antiferromagnetic insulator in which orbital ordering is established due to the cooperative Jahn-Teller (JT) effect breaking the degeneracy of the electronic configuration of Mn3+ (t2g3eg1). This particular C-type orbital ordering is responsible for the A-type magnetic structure observed by Wollen and Kohler. Theoretical Monte-Carlo simulation has shown that the A-type antiferromagnetic state is stable in a model based on JT phonons, using coupling values physically reasonable for LaMnO3 and considering the small but important effect of octahedral tilting.

Doping carbon nanotubes with either electron donors or acceptors can improve their electrical conductivity [1-2]. In order to fully understand the doping mechanisms and the corresponding changes in the electronic properties, it is essential to reveal the spatial distribution of the dopants within the carbon nanotubes. In this study we have investigated both iodine- and bromine-doped single wall carbon nanotubes(SWNT) by Z-contrast scanning transmission electron microscopy (STEM). The SWNT bundles were made by arc-discharge method and doped with either molten iodine or bromine vapor. Both iodine and bromine were incorporated linearly within the nanotube bundles as shown in Fig. l and Fig.2 respectively. Higher resolution images of iodine doped nanotubes reveals that two iodine atomic chains are inside each individual SWNT as shown in Fig. lc. This unexpected result is contrary to the common belief that dopants can only enter interstitial site of the SWNT bundles.

Discoveries of C multi-walled (MWNTs) and single-walled (SWNTs) nanotubes opened up a wide horizon for applications of these nanostructures as electronic and structural materials. Later on, it has been realized that the nanotubular structures are formed in other layered compounds, e.g. in the B-C-N materials. However, in contrast to the C-based nanotubes whose synthesis parameters are well-established, synthesis of B- and N-doped C and pure BN nanotubes is a challenging issue. The present paper reports on large-scale synthesis and detailed HRTEM and EELS characterization of nanotubes in the B-C-N system.

MWNTs and SWNTs of B-C-N and BN were produced from C nanotube templates via a substitution chemical method through oxidation by B2O3, in a flowing N2 atmosphere at 1573- 1773 K. HRTEM of a product was carried out using a high-resolution field emission transmission electron microscope JEM-3000F (JEOL) equipped with a parallel EELS detector Gatan 666 and an ultra thin window Si(Li) EDS detector.