Yttria stabilized zirconia (YSZ) is an important oxygen ion conducting solid electrolyte. YSZ is used in oxygen sensors, oxygen pumps, and fuel cells. Perovskite-type oxides of general formula ABO3 are also of fundamental significance due to their electrical and electro-optical properties. SrZrO3 is a promising material- for application as protonic conductor. in this paper, we present electron microscopy analysis of the formation of SrZrO3 nano-particles in the top surface of YSZ single crystal after ion implantation. These results demonstrate a unique process for obtaining mixed-conducting oxides in the surface layer of YSZ. in addition, it is important to study the behavior of strontium in YSZ because of the potential application of YSZ as an inert fuel matrix for “burning“ excess plutonium in nuclear reactors.

400 keV strontium ions have been implanted into YSZ at room temperature to a fluence of lxl021 ions/m2.

The ion irradiation-induced crystalline-to-amorphous transformation has been studied in many complex ceramics. Direct impact amorphization has been considered to be one of the fundamental amorphization mechanisms for complex ceramics under heavy ion irradiation . Based on the directimpact model, a highly energetic incident ion transfers its kinetic energy to the target as a thermal spike within 10“13 sec creating a “molten-like” displacement cascade, typically nanometer-scaled in diameter (as indicated by the result of a computer simulation in Fig. 1). This “molten” zone quickly quenches to a small amorphous domain within a few pico-seconds. Epitaxial recrystallization occurs around the amorphous/crystalline interface, so that the size of amorphous domains decrease with time. The accumulation and overlap of small amorphous domains eventually leads to complete amorphization of the irradiated material. Although the in-situTEM technique with the setup shown in Fig. 2 has been extensively applied to the study of the amorphization process in complex ceramics, most of the previous studies relied on in-situobservation of the electron diffraction pattern, and there has been a lack of solid evidence of direct impact amorphization due to the small nature of the cascades and the rapid kinetics of its evolution.

In colossal magnetoresistive (CMR) materials, large changes in physical properties stem from the interplay between charge ordering (CO) coupled with orbital and magnetic orderings. Thus detailed microstructural studies are important in understanding these changes in physical properties. In-situTEM observation is a very useful approach to study CO transitions in these CMR compounds. We have recently studied the CO behavior of the three-dimensional perovskite Nd1/2Sr1+2xMnO3. in this work, we report the CO of two-dimensional naturally layered compounds La2-2xSr1+2xMn2O7 (327 phase), where x is the hole doping level and varies from 0.5 to 0.6 in this work.

Thin foil TEM specimens were prepared from polycrystalline bulk samples by conventional thinning and ion milling method at liquid N2 temperature. The in-situ TEM work was carried out in the Electron Microscopy Center at Argonne National Laboratory using a Philips CM30 with a liquid N2 cold stage, and a Hitachi H-9000 with liquid He cold stage.

The traditional application of titanium dioxide was as a white pigment; later, it was discovered their photocatalytic properties as an anode for the photo-oxidation of water. Furthermore, titanium dioxide films are now widely used in catalysis and photocatalysis because of low cost and other advantageous properties. For example, they have been used for decomposition of organic contaminants in air and water. Moreover, recent studies have reported bactericidal and detoxification effects of TiO2 thin films . It has been shown that TiO2- coated materials possess deodorizing, antibacterial, and self-cleaning functions under weak ultraviolet light. Titanium dioxide films can be prepared by many deposition techniques. One of them is the spray pyrolysis (SP) technique which is a low cost, simple to manipulate, and applicable to large-scale areas (final). Photocatalytic TiO2-covered tubing can be used to decompose organic contaminants and/or to sterilize microbial cells in air or water flows , using solar panel reactors or indoor panels irradiated with UV radiation.

In conventional sintering, high heating rates are often used to enhance densification and reduce grain growth. The essence of this concept is to use fast heating rates to favor densification instead of grain growth, if the activation energy for densification is greater than that for grain growth. At low temperatures, surface diffusion is the most effective sintering mechanism but is associated with grain coarsening. Therefore, a high heating rate may take the system for densification at high temperatures before surface diffusion causes grain growth and decreases the sintering driving force. Field activated sintering technique (FAST) is a newly developed sintering method, which applies an external electrical field to enhance densification. The method applies pulsed and continuous current to powders subject to a modest pressure (< 100 MPa). Electrical current application enables fast heating rates. The sintering cycles are very short, typically less than 10 minutes for full densification.

The utility of a surface to serve as a substrate depends upon its surface structure. The presence of steps on the surface affects the quality of the deposited material. The basal surface of alumina is one of the most widely used substrate materials and hence considerable effort has been directed towards the study of this surface. The mechanism of formation of a stepped structure on the basal surface of alumina has been investigated using atomic force microscopy. The evolution of steps on the basal surface as a function of temperature has been reported. Flux growth is an attractive route for producing alumina because of the low temperatures required for processing and the extremely low dislocation densities that can be obtained. in the present study, the structure of steps on flux-grown alumina has been investigated. Formation of low-index macrofacets as a result of crystal growth has been observed.

Nanowires have potential applications in future generations of nanoscale electronics. Our motivation of studying Bi nanowires is based on the unique properties of bulk Bi. These include very small effective masses, a long mean-free path and the low melting point (271°C). Calculations of the transport properties predict that the Bi nanowires have a very high thermoelectric efficiency. The effects of quantum confinement are pronounced in Bi because of its small effective masses. The resulting change in the band structure of bulk Bi is shown in Fig. 1. The broken curves depict the band structure in which the T-point valence band overlaps with the L-point conduction band by 38mev making bulk Bi a semimetal. Due to quantum effects, the band edges split into subbands shown by solid curves. As the wire diameter decreases, eventually the lowest conduction subband and the highest valence subband no longer overlap and the material becomes an indirect-gap semiconductor (at ∼50nm diameter).

Many attempts have been made to improve the fracture toughness of brittle materials such as ceramics. Most of the methods developed so far make use of metallurgical processes, for example, phase transformation, refining of grains, formation of composite materials. However, these methods can not be applied universally to brittle materials which do not have such a useful metallurgical processes.

Moon and Saka (1) recently showed that the fracture toughness Klc of a YAG single crystal the sub-surface of which is damaged by micro-Vickers indentation at room temperature, followed by annealing at high temperatures is improved by a factor 2 from 1.13 to 2.26MPam1/2. The fracture toughness Klc was evaluated by measuring the length of cracks which initiate at the corner of Vickers indentation(2). Transmission electron microscopy of the subsurface reveals the healing of cracks introduced by room-temperature indentation and formation of dislocation cells. The thin foil specimens were prepared using a focused ion beam (FIB) technique(3).

SiC, as one of the most promising candidate ceramics for high temperature structural applications, offers many intrinsic advantages, including high melting temperatures, low density, and high elastic modulus. However, the use of SiC to date has been severely limited by its poor fracture toughness (∽ 2-3 MPa√m for commercially available materials) and crack-growth resistance. Our study focuses on the development of silicon carbide as a potentially tough, high-temperature, and damage-tolerant material. The approaches include identifying roles of sintering additives in modifying grain morphology, effects of post-annealing on grain boundary phases, and possibility in introducing nanoscale precipitates in SiC grains. Central in these efforts is structural characterization using state-of-the-art electron microscopy.

The first success was in situtoughening the SiC, by hot pressing in the presence of A1, B and C additions. Elongated and interlocked grains were developed surrounded by an Al-containing amorphous grain boundary film.

Recently, considerable efforts have been made in growing bi-axially aligned thick Yba2cu3O7 (YBCO) films on a flexible, textured metallic substrate for electrical power applications. The BaF2 post-deposition annealing process is one of the most promising methods. to understand the nucleation and growth mechanism of YBCO in this process, extended transmission electron microscopy analysis has been made. Here, we report on the evolution of Ba-Y oxy-fluoride which is pertinent to the epitaxial YBCO nucleation process on SrTiO3 (STO) substrate.

The stoichiometric ratio of Y, Cu and BaF2 was evaporated on (00l)-cut STO substrate Subsequently, these films were annealed at 735°C in an O2-H2O-N2 gas atmosphere and quenched after 10, 20, or 40 minutes. The morphology and phase composition of the precursor changed drastically with the annealing times, e.g. after 10 minutes heat treatment, the precursor consisted of fine grained CU2O and Ba-Y(Cu) oxy-fluoride (cubic, a=0.618nm) as shown in fig.la.

Mullite (3Al2O3•2SiO2) exists in a solid solution field (∼57-63 mol% Al2O3) as the only stable compound in the Al2O3•SiO2 phase diagram at ambient pressures. Equilibrium 3:2 mullite has an orthorhombic structure with b>a (o-mullite). However, when initially crystallized from molecularly mixed, 3:2 precursors at temperatures < 1200°C, the first phase that forms has lattice parameters with a ≈b. This structure is often termed pseudotetragonal mullite (pt-mullite), since even when the ‘a’ and ‘b’ lattice parameters are identical, they are symmetrically independent. Pseudotetragonal mullite has been shown to contain approx. 70 mol% Al2O3. with increasing time and temperature, the structure gradually assimilates the residual SiO2, and the lattice parameters change, such that by 1400°C, the material has attained its equilibrium structure and composition.

TEM was used to determine the spatial relationship between the crystalline phase and the residual, amorphous, SiO2-rich phase in pt-mullite. The starting materials were quenched, 3:2 mullite beads and fibers (made by containerless processing).

Carbon nanotubes have previously been grown on Ni coated glass, aligned vertical to the substrate over a multi-centimeter square area1. Under vacuum, the aligned nanotubes were grown below 666° C (strain point of the best display glass) by plasma-enhanced hot filament, chemical vapor deposition. It was found, the size and alignment of the nanotubes could be varied by changing the dwell time and the thickness of the catalytic Ni layer by plasma etching. in more recent, ongoing studies, the size of carbon nanotubes is varied by changing the growth temperature and dwell time under acetylene/nitrogen atmosphere using chemical vapor deposition onto W and Ni coated Si.

Multiwall carbon nanotube films are grown using a thermally-activated chemical vapor deposition process. Thin Ni catalyst layers are sputtered onto W-coated Si(100) and reduced in a 600°C CO anneal. Nanotubes then grow at temperatures ranging from 630 - 790°C in an acetylene/nitrogen mixture.

The problem of phase retrieval from intensity measurements plays an important role in many fields of physical research, e.g. optics, electron and x-ray microscopy, crystallography, diffraction tomography and others. in practice the recorded images contain information only on the intensity distribution I(x,y) = ψ*ψ*= |A|2 of the imaging wave function ψ = A*exp(-iϕ) and the phase information (ϕ(x,y) is usually lost. in general, the phase problem can be solved either by special holographic/interferometric methods, or by noninterferometric approaches based on intensity measurements in far Fraunhofer zone or in the Fresnel zone at two adjacent planes orthogonal to the optical axis. The latter approach uses the transport-of-intensity equation (TIE) formalism, introduced originally by Teague [1] and developed later in [2]. Applications of TIE to nonmagnetic materials and magnetic inductance mapping were successfully made in [3,4]. However, this approach still needs further improvement both in mathematics and in practical solutions, since the result is very sensitive to many experimental parameters.

Due to their ability to undergo a refractive index change (Δn) induced by appropriate UV irradiation and thermal development, Photo-Thermo-Refractive (PTR) glasses are candidate materials for use in optical applications such as hologram recording, optical data storage, or spectral filters. Although this induced index modulation (Δn) has been characterized in terms of its optical ramifications, glass scientists are working to understand more clearly, the underlying mechanisms associated with the photo-induced crystallization process. For example, the phase, concentration and size of crystals responsible for the induced index change, the diffusion and growth process leading to the resultant optical behavior, and the precise role of the active components of PTR glasses, has yet to be completely elucidated. Numerous techniques have been employed to address these questions and this paper reports results of sample preparation and analysis of PTR glasses using Transmission Electron Microscopy (TEM).

Electronic phase separation is known to occur in complex oxides ranging from high-Tc superconductors to colossal magnetoresisitive (CMR) manganites. Accumulating experimental evidences show regions of temperature dependent conducting and insulating regions, whose exact origin is unknown. Theoretically, it is has been shown that these systems are unstable from the strong interplay between the lattice, charge and spin degrees of freedom.

The key to understand the electronic phase separation in complex oxides is the structure. Electron diffraction is the only probe that covers the length scales from angstroms to microns. Characterization at these length scales is critical (electronic phase separations are typically about nanometers in sizes). Traditionally, electron diffraction has been played important roles in discovering the new types of phase separations, but has contributed little to the quantitative understanding. The reason is the strong interaction of electrons with matter, which gives both strong inelastic background and multiple scattering.

Uncoated ceramics are difficult to analyze because specimen charging can reduce the energy of the electron beam at the specimen. This effect may decrease the measured k-ratio to a fraction of its expected value. Thin carbon coatings are the usual solution to this problem. However, the coating procedure takes time, and the same coating thickness also must be applied to the standard. in the environmental SEM (ESEM). surface charge can be mitigated at the higher accelerating voltages normally used for x-ray microanalysis. in the ESEM, electrons are accelerated toward an electrically biased electron detector producing a cascade of electrons and ions from the imaging gas (water vapor) as part of the secondary electron imaging process. Positive ions drift toward the specimen and neutralize negative surface charge; however, the degree of neutralization is a function of a number of operating variables.

Recently, a promising new route to prepare nano phase composites with fine transition metal particles (2 - 50nm) has been proposed via dehydroxylation and dehydration process. Thermal and mechanical dehydroxylation process has also been used to form ultra fine powders of NiO-Ni(OH). We have found a substantially increased carbonation rate at room temperature (RT) for partially dehydroxylated brucite (Mg(OH)2) single crystal fragments. BET measurements confirm the increase in the surface area of partially dehydroxylated (90%) single-crystal Mg(OH)2 fragments, which directly contributes to the increase in carbonation reactivity. As dehydroxylation proceeds rapidly in a TEM column, due to high vacuum and electron beam effects, the atomic level nature of the process has not been understood until recently.6 We have observed the development of nanocrystals during in situdehydroxylation of Mg(OH)2.

Experiments were performed using a PHILIPS-430 electron microscope operated at 300KV, fitted with a differentially pumped environmental-cell (E-cell) and a Gatan Imaging Filter (GIF).

The application of modern transmission electron microscopes (TEM) in catalytic research has accelerated the progress in understanding the mechanism of catalytic reactions. For instance, using environmental TEM, the novel glide shear defect process was revealed as an efficient mechanism for the release of the structural oxygen of vanadyl pyrophosphate in the n-butane oxidation [1]. On the other hand, electron energy-loss spectroscopy (EELS), which is nowadays commercially available on modern TEM, appears unknown in the catalytic community. in fact, core-loss EELS is a powerful tool to identify the chemical state of elements and to study the modification of this sate in various compounds.

Fig.l shows EELS-spectra of various vanadium oxides in which the oxidation state of vanadium varies from 2+ (VO) to 5+ (V2O5). The first two features, marked as V L3 and V L2 edges, are attributed to the excitations from V 2p3/2and V 2p1/2core levels to the unoccupied V 3dstates, respectively.

Carbon nanotube (NT) growth by chemical vapor deposition (CVD) requires a catalyst -typically a transition metal- to nucleate NT growth because of the low synthesis temperatures as compared to arc-discharge or laser ablation methods. The catalyst can be introduced to the CVD system by preprepared nano-scale catalyst particles sitting on fine support powders, thin catalyst films deposited on substrates by sputter deposition, or floating catalysts. The floating-catalyst CVD method is an in-situprocess in which the organo-metallic precursors (e.g. metallocenes) decomposed to form nanoscale catalyst particles. Floating catalyst methods can produce both multi-wall carbon nanotubes (MWNTs), single-wall nanotubes, and even C-N nanotubes and facilitate continuous growth processes. in this study we employ a variety of electron imaging, diffraction and spectroscopy techniques to investigate the growth mechanisms and kinetics of multi-walled NTs (MWNTs) produced by the floating-catalyst CVD method.

The vasculature of two recessive dwarf mutants, nana-1 (nal) (FIG 1) and nana-2 (na2) (FIG 2) of maize (Zea mays)were studied. All the plants used in this study were grown at the field station of University of Western Ontario, London, Ontario, Canada, in the summer of 2000. The specimens were fixed in methanol, serially sectioned with a razor blade using a specially made jig. The image was obtained by using a modified Acer 620T flat-bed scanner in liquid (Cheng et al., 2001). The optical sections were obtained by twophoton florescence microscopy using an Olympus Fluorview FL300 confocal microscope equipped with a Spectra-Physics Mai-Tai tunable ultra-fast Ti-sapphire laser. Excitation wavelengths was set at 780nm NIR with a pulse width of l00fs, <550nm autofluorescence was detected. Extended focus views were generated by using AutoQuant's AutoVisualize-3D™ software.

Different from the parallel arranged longitudinal vascular bundles commonly found in the internodes of wild type, nal/nalhas a complex stem vasculature (FIG 3)(Cheng et al., 2000a; 2000b).