In 1992, researchers at Mobil Research and Development created a new class of porous silicates, most notably mesoporous MCM-41.2-3 This material features a hexagonal arrangement of linear pores and surface areas in excess of 1000 m2 g-1. MCM-41 exhibits narrow pore size distributions in the nanometer range. The walls of MCM-41 are essentially amorphous silica, but its porous nature makes it about 3 kJ mol-1 less stable than the collapsed form. Particles of MCM-41 are beam sensitive and it appears that they cannot withstand the large current densities required to obtain reliable analytical data at the nanometer scale in the transmission electron microscope (TEM). For example, low beam currents were used to preserve the pore structure but resulted in energy-filtered TEM elemental maps of oxygen K and Ti L2,3 edge intensities that were too noisy to reveal structure at 5 nm resolution.

Amorphous chalcogenides films coated with certain metals are known to possess a remarkable sensitivity to radiation. Based on these effects they have found several important applications in the production of microcircuits, e.g. as resists in photo- and electron beam lithography. A variety of chalcogenides in combination with a range of metals has been extensively investigated with regard to potential applications in the fabrication of semiconductor devices.

The objectives of the present project are to extend knowledge of the behaviour of amorphous chalcogenides in contact with metals. This includes studying the metal diffusion process, understanding the film-electron beam interaction process and evaluating the potential of the metal lines formed by the electron beam in fabrication of photomasks for the production of higher densities of silicon microcircuits.

A recent development in the study of nanocrystalline materials has been the self-assembly of passivated nanometer scale building blocks into larger, well ordered structures reaching the micron scale. Nanocrystal supercrystals (NCS) have been observed in metallic, semiconductor, and magnetic materials. In most cases the nanocrystals (NXs) are encapsulated in some inert medium that effectively protects the nanocrystal core and its unique electronic and optical properties. Here we describe the self-assembly of gold nanocrystals (∼4.5 nm core diameter), passivated with hexanethiol self-assembled-monolayers into ordered regions exhibiting a body-centered-cubic (bcc) superstructure. Transmission Electron Microscopy (TEM) imaging and Electron Diffraction (ED) experiments were used to characterize the NCSs and their resulting superstructures.

A large agglomeration of NCSs can be seen in figure 1. One can clearly see regions of periodicity within the nanocrystal aggregation.

ZnS particles consisting of nanocrystallites have potential applications as light emitters for displays. The possibility of encapsulating chemicals into porous particles and the temperature-controlled release of them could also be of interest in chemical engineering. The objective of this study is to determine the size distribution, shape and morphology of ZnS particles synthesized under different conditions, since they strongly influence the optical and electric properties.

The ZnS powders were prepared by precipitation from homogeneous aqueous solutions, following a procedure described elsewhere1-3 The initial solution consists of a zincsalt precursor dissolved in ultrapure water under acidic pH conditions. Adding Thioacetamide (TAA: CH3C(S)NH2) to this acidic solution at elevated temperature leads to the precipitation of ZnS nanocrystals. Four different types of zincsalt precursors were used to study their influence on the precipitation process and the final powder morphology: acetate (CH3COO), chloride (Cl-), trifluoromethanesulfonate (tFMS: CF3SO3-) and dimethyldithiocarbamate (dMdTC: S4N2C6H12-). The dried powder were subjected to 350°C and 700°C heat treatments, respectively.

NiAl is an important high temperature structural material, with a high melting point (1640°C), low density and excellent high temperature oxidation resistance. The room temperature ductility of NiAl may potentially be improved with the use of nanocrystalline grain size. However, a key question concerning the application of nanostructured NiAl is about its structural stability at high temperature. The current study is thus focused on the investigation of the structural stability of nanocrystalline NiAl using in-situ transmission electron microscopy (TEM) and differential thermal analysis (DTA).

Nanocrystalline B2-NiAl was prepared by ball milling (24 hrs) from elemental Ni and Al powders. Subsequent consolidation into bulk form was performed using dynamic consolidation employing a 3-capsule plate-impact fixture at approximately 400 m/s [1-3]. Powder nanocrystalline NiAl was dispersed on a holey carbon film for TEM observation. TEM specimens of shock compacted bulk NiAl nanocrystals were prepared by cutting, polishing, dimpling and ion milling.

A description of the microstructure of heterogeneous catalysts is important in understanding the mechanisms for catalysis and may result in improvements in catalyst performance. Many commercial catalysts consist of small metal particles and/or metal oxide particles dispersed on a porous support. For bimetallic catalysts, the metals may be in the form of alloys, metal mixtures or completely phase separated. HREM has been demonstrated to be a powerful technique for determining the lattice spacing from small particles[l]. In many studies of catalysts it is necessary to prepare TEM samples by microtomy so that the particle location relative to the porous support is preserved. However, such samples show a reduction in particle visibility and signal-to-noise ratio of lattice fringes. In spite of these difficulties, we have been able to routinely use HREM to rapidly determine the relative distributions of metal and metal oxides in many systems because of the large difference in spacing between strong reflections from the metal and metal oxide (typically 20 %).

High-temperature catalysts containing Pd supported on high-surface area ceria-zirconia are optimum materials for fuel economy when automotive engines operate under high speed or load conditions. A prerequisite for developing such thermally stable catalysts is to gain a good understanding of the thermal deactivation modes contributing to the aging and degradation of catalysts in harsh thermal environments. It was discovered by X-ray diffraction that upon hightemperature aging, Pd may sinter into large (about 10 nm diameter) particles and become encapsulated in the ceria-zirconia. To confirm this conclusion, a prototype high-temperature catalyst containing Pd supported on high-surface area ceria-zirconia, aged at temperature above 1100 °C is studied by transmission electron microscopy (TEM).

The ceria-zirconia supported Pd (0.25 wt%) catalyst was aged at 1105 °C and calcined at 700 °C for 2 h. For TEM sample preparations, first of all, a large-size aggregate with diameter about 1 mm was selected and sandwiched between by two pieces of silicon crystal.

Processing can be controlled to produce a family of mesoporous silica films with either disordered, lamellar, hexagonal, or cubic pore distributions[l]. These films, formed by surfactant-templated synthesis and exhibiting a unimodal pore size, promise potential use as inorganic membranes, catalysts, and optically-based sensors[l,2]. The mesoporous films can be formed from initially homogeneous silica sols by a continuous, surfactant-templated process, which relies upon solvent evaporation during the sol-gel dip-coating process. Films of 100-500 nm thick are formed within seconds in a continuous coating operation. The microstructure of the films is dependent upon the cationic surfactant concentration CTAB (CH3(CH2)15N+(CH3)3Br-) and the dip-coating rate. Several films, processed under differing conditions, were investigated by TEM to characterize pore size, structure, and orientation.

Figures 1 a & b show the plan view and cross-sectional microstructure of a 2-d hexagonal mesoporous silica film deposited on silicon; the sample was calcined at 400 °C for 3 hours in air. The images were obtained on a Philips CM30 TEM, operated at 300 kV.

Nanoparticles and the physical and chemical functional specificity and selectivity they possess, suggest them as ideal building blocks for two- and three-dimensional cluster self-assembled superlattice structures, in which the particles behave as well-defined molecular matter and they are arranged with long-range translation and even orientation order [1]. Self-assembled arrays involve self-organization into monolayers, thin films, and superlattices of size-selected nanoclusters encapsulated in protective compact organic coating. The macroscopic properties of the nanocrystal superlattice (NCS) are determined not only by the properties of each individual particle but by the coupling/interaction between nanocrystals interconnected and isolated by a monolayer of thin organic molecules.

Periodic packing of nanocrystals is different from the 3-D packing of atoms. First, to an excellent approximation atoms are spherical, while nanoparticles can be faceted polyhedra, thus, the 3-D packing of particles can be critically affected by their shapes and sizes.

Recently we have reported that the silica mesoscopic thin films can be formed at water/solid interface at room temperature. These self-assembled thin films are comprised of hexagonally packed nanotubules ((∼ 5 nm in diameter), with a percolating one-dimensional channel network that extends from one side of the film to the other. The solid substrate can affect strongly the overall alignment of assembly of surfactant micelle array. These films hold much promise for applications such as their use as orientated nanowires, sensor/actuator arrays and optoelectronic devices. Here, we report further electron microscopy studies of free standing thin film formed at air/water interface and patterned silica mesoscopic thin film formed with the guidance of micro-molding and electric field.

We employ tetraethoxy silane (TEOS), dissolved in acidic solution, as a silicate source and cetyltrimethyl ammonium chloride (CTAC) as the templating surfactant. Typical molar ratios are 1 TEOS : 1.2 CTAC : 9.2 HC1 : 1000 H2O.

Of recent interest in the science of nano-scale materials is the production and characterization of substances composed of ordered lattices of up to millions of identical nanometer scale particles. Silver nanocrystals of ∼ 4.5 nm diameter passivated with dodecanthiol surfactant were produced in the aerosol phase. Characterization of the individual particles and the subsequent supercrystals (SXs) resulting from their periodic packing was brought about using Mass Spectrometry, Transmission Electron Microscopy (TEM)/Electron Diffraction (ED), Scanning Electron Microscopy and Atomic Force Microscopy (AFM). It was determined that the micrometer and greater sized faceted SXs exhibited an hexagonal-close-packed (HCP) superstructure (fig.l) resulting in triangular shapes bounded by ﹛1100﹜ facets (fig. la); their platlet-like nature (∼20 nanocrystal layers thick) owing to their particular growth pattern. Knowledge of the growth mechanism is important to production of these materials on a macroscopic scale. Here we report a proposed growth model for these supercrystals.

We have recently synthesized superlattices of Pt and Au nanoclusters grown by inverse micelle techniques. The monodisperse nanosize metal clusters used in this study were synthesized as surfactant aggregates surrounded by an oil-like environment (inverse micelle), a technique developed and patented at Sandia. Reaction byproducts, such as excess surfactant and inorganic ion salts, are often separated from the metal clusters using liquid chromatography size exclusion techniques; however, the Pt and Au nanoclusters in this study have been fractionated using a liquid-liquid technique. The nanoclusters are capped with a ligand.

Two-dimensional hexagonal arrays formed readily on surfaces, and large twinned three-dimensional crystals form from solution. Both the cluster size and the size of the capping ligand can be controlled to form superlattices having a range of lattice parameters. We have found that the capping agent exerts a marked influence on the tendency of these clusters to order.

Nanocrystal materials are an emerging research field of chemistry, physics and materials science. The size and shape specificity of nanocrystals suggests them as building blocks for constructing selfassembly passivated nanocrystals superlattices (NCS's) or nanocrystals arrays (NCA) [1-6]. In this paper, NCAs of CoO with controlled tetrahedral shape are reported and their structural stability is examined by in-situ TEM.

Cobalt oxide nanocrystals were synthesized by chemical decomposition of Co2(CO)8 in toluene under oxygen atmosphere, as given in detail elsewhere [1].Sodium bis(2-ethylhexyl) sulfosuccinate (Na(AOT)) was added as a surface active agent, forming an ordered monolayer passivation (called the thiolate) over the nanocrystal surface. The particle size was controlled by adjusting the wt.% ratio between the precursor and Na(AOT). The as-prepared solution contained Co, CoO and possibly C03O4 nanoparticles, and pure CoO nanoparticles were separated by applying a small magnetic field, which is generated by a horseshoe permanent magnet in vertical direction.

Formation of metallic nanoparticles produces an increased surface area per unit volume of material, which provides potential applications in enhancing surface catalyzed reactions. Recently, attention has been focused on moving from the solution based syntheses to solid phase materials by arranging such particles into well ordered 2- and 3- dimensional structures, or forming cluster engineered materials that posses well defined structures. Such studies have shown the importance of size, size distribution, and shape of particles upon self assembled monolayers. We have recently prepared shape-controlled Pt nanoparticles with ﹛111﹜ (tetrahedral), ﹛100﹜ (cubic), and mixed ﹛111﹜ - ﹛100﹜ (truncated octahedral) faces. To study how these faces may orient to form particle point superlattice structures we have prepared monolayer distributions of Pt particles in humidity chambers for analysis by TEM.

Our shape controlled Pt particle synthesis yields between 60 and 80 % cubes, tetrahedra, or truncated octahedra with average diameters ≥ 7 nm.

Catalyst characterization plays a vital role in new catalyst development and in troubleshooting of commercially catalyzed processes. The ultimate goal of catalyst characterization is to understand the structure-property relationships associated with the active components and supports. Among many characterization techniques, only electron microscopy and associated analytical techniques can provide local information about the structure, chemistry, morphology, and electronic properties of industrial heterogeneous catalysts. Three types of electron microscopes are usually used for characterizing industrial supported catalysts: 1) scanning electron microscope (SEM), 2) scanning transmission electron microscope (STEM), and 3) transmission electron microscope (TEM). Each type of microscope has its unique capabilities. However, the integration of all electron microscopic techniques has proved invaluable for extracting useful information about the structure and the performance of industrial catalysts.

Commercial catalysts usually have a high surface area with complex geometric structures to enable reacting gases or fluids to access as much of the active surface of the catalyst as possible.

The role of cation promoters on the microstructure and stability of complex vanadyl pyrophosphate ((VO)2P2O7 or VPO) catalysts in the selective oxidation of n-butane to maleic anhydride (MA) is of major technological importance. Although several studies have been cited in the literature on the specific activity and MA selectivity of promoted VPO, no direct evidence for the formation of solid solutions with VPO has been reported. A better fundamental understanding of the location and the complex role of promoters in the catalyst-adsorbate interactions is therefore required. We have synthesized novel promoted catalyst powders with several cations including iron and antimony, as well as with ceria. We have probed their nanostructures in n-butane directly (in-situ) at the atomic level using environmental-HREM (EHREM) and their composition by high spatial resolution depth profiling using EDX (and STEM probe size) on the nanometer (nm) scale.

The ability to vary the plane spacing in different clays is becoming increasingly important in catalysis and other technological applications [Baker and Murrell, 1990]. Considerable effort is now being devoted to understanding the mechanisms involved in pillaring such materials with a view to being able to fine-tune parameters such as the plane spacing and active sites for the application of interest. We have been able to use analytical electron microscopy to directly image the pillars in zirconia pillared montmorillonite. By using a combination of TEM techniques, we are able to correlate morphological information with elemental composition and conclusively identify the location of the zirconia pillars.

A sample of natural montmorillonite clay, trade name HPM-20, was obtained from American Colloid and used as received. Zirconia pillared clays were prepared following published procedures [Bartley, 1988]. The Z1O2 pillars were prepared by using hydroxyzirconium cations produced by the solvation of zironyl chloride.

Many studies on colloidal nanoparticles have focused on the control of nanoparticle size and correlated this to the catalytic activity. Recently, our group has reported for the first time a technique that controlled the shape distribution of Pt nanoparticles. This was done by varying the concentration of the capping polymer and the platinum ion ratio used in the reductive synthesis of colloidal nanoparticles at room temperature. Cubic, tetrahedral and truncated octahedral (TO) particles have been prepared, making it possible to study the catalytic activities of nanoparticles with different shapes and facets.

Using transmission electron microscopy (TEM), we imaged the shapes and determined the shape distribution of platinum nanoparticles at different stages of their growth as a function of time. The small nanoparticles formed during the early stages of growth or at high polymer concentration displayed distributions with a dominance of tetrahedral shapes (see Figure la).

Palladium based catalyst have technological applications in catalytic converters in automobile industry for the combustion of NOx and CO gasses. Pd can also adsorb up to 900 times its volume H2 and is useful for purifying H2. Electron holography studies with model Pd on silica catalysts [1] show that under some circumstances, the Pd particles may form voids. The reason for the formation of these voids and the conditions under which they are formed are not well understood. We have done in situ and ex situ studies on oxidation and reduction of similar model Pd/SiO2 to develop a better understanding of the conditions under which voids are formed.

The catalyst samples were prepared by impregnating silica with acetyl acetoneate (acac) and oxidizing in air and then reducing in H2 at 300°C [1]. High resolution images (Fig. 1) of Pd particles show a central feature with low contrast attributed to the presence of voids.

Many nanostructured materials are formed from powder precursors having ultra-fine particle sizes. Techniques of electron microscopy have proven invaluable for characterizing the structure of the precursor materials in order to better understand the fundamental processes that govern consolidation of the materials into the final nanophase structures. In recent years, the rapidly developing technique of electron holography has increasingly been applied for characterizing particle morphologies. The advent of the modern field emission microscope, which offers beam coherency sufficient to produce high contrast interference fringes for optimum hologram formation, and especially the availability of digital camera systems for hologram acquisition and rapid processing have both combined to bring electron holography to the forefront of techniques for characterization of nanostructured materials.

Electron holograms typically yield phase images that can give quantitative information on crystal morphologies, but much additional information can result from digital processing of holograms.