When a noble gas element such as Xe is implanted in an fee metal matrix such as Al at room temperature, a fine dispersion of precipitates forms. The precipitates are elementary fee crystals up to diameters of several nanometers (for Xe in Al, 8-10 nm), above which they are non-crystalline. The precipitates exhibit a cube-on-cube orientation relation with the matrices and have lattice parameters which are much larger than those of the matrices (axe ≃ 1-5aAl). Thus the interphase interfaces are incommemsurate though the lattices are isotactic. The precipitates assume the shape of matrix cavities; for an Al matrix, at equilibrium this is a cuboctahedron, a {111} octahedron truncated at the corners on {100}. Fig. 1 is a sketch of a dispersion of such cuboctahedra, viewed approximately along a <110>.

For this study specimens were prepared in the HVEM-Tandem Facility at Argonne National Laboratory by implanting 35 keV Xe to a dose of 4x1019 m−2 into well-annealed 5N Al discs which had been thinned by jet electropolishing.

The Optical Solar Reflector (OSR) of Earth Observing System-PM (EOS-PM) is made of a flexible function layer of silvered Teflon/Inconel/Kapton laminate bonded to a honeycomb panel. After having been thermal cycled in vacuum, the laminate/panel was irradiated in air with UV at 2.2 equivalent suns intensity for 500 hours. Severe darkening was observed in areas exposed to UV but little or no darkening occurred in adjacent but shaded areas. Drastic increase of absorptance was observed-due to the darkening.

In order to investigate the cause of the degradation, test samples were irradiated at different configurations for 1000 equivalent sun hours (ESH). These samples were freestanding laminates and irradiated in vacuum and air, respectively. No darkening was observed on the sample that was irradiated in vacuum. Severe darkening was observed on the sample that was irradiated in the air. A laminate sample was irradiated in dry nitrogen for 1000 ESR and found no darkening either.

We report x-ray absorption near edge structure (XANES) and extended x-ray fine structure analysis (EXAFS) spectra from the plutonium Llll and cerium Lm edges in prototype titanate ceramic hosts for disposal of surplus fissile materials. These spectra were obtained using the MRCAT beamline at the Advanced Photon Source (APS). The XANES and EXAFS results are compared with electron loss spectra (EELS) determination of oxidation state from the plutonium MlV,V and cerium MlV,V edges [1,2]. The titanate ceramics studied are based upon the hafniumpyrochlore and zirconolite mineral structures and will serve as an immobilization host, containing as much as 10 weight % fissile plutonium, and 20 weight % (natural or depleted) uranium. Similar formulations were composed using cerium as a “surrogate” element, replacing both plutonium and uranium in the ceramic matrix. We find the plutonium to be present almost entirely as Pu (IV), while the cerium is clearly in a mixed III-IV oxidation state in the surrogate ceramic.

As the size of Si integrated circuit structures is continually reduced, interest in semiconductor-oninsulator (SOI) structures has heightened. SOI structures have already been developed for Si using oxygen ion implantation. However, the application of Si devices is limited due to the physical properties of Si. As an alternative to Si, SiC is a potentially important semiconductor for high-power, high-speed, and high-temperature electronic devices. Therefore, this material is a candidate for expanding the capabilities of Si-based technology. In this study, we performed oxygen ion implantation into bulk SiC to produce SiC-on-insulator structures. We examined the microstructures and compositional distributions in implanted specimens using transmission electron microscopy and a scanning transmission electron microscope equipped with an energy-dispersive X-ray spectrometer (STEM-EDX).

Figures 1(a) and 2(a) show bright-field images of 6H-SiC implanted with 180 keV oxygen ions at 650 °C to fluences of 7xl017 and 1.4xl018 cm−2, respectively. Three regions with distinct image contrast are apparent in Figs. 1(a) and 2(a), as indicated by A, B, and C.

The Al alloy composites reinforced with Si3N4 or SiC have been reported to exhibit superplasticity at high strain rate of faster than 1x10−2 s−1. It has been shown in many aluminum alloy composites that the optimum superplastic temperature coincides with an incipient melting temperature. The coincidence suggests a contribution of the liquid phase to the superplasticity mechanism. This paper shows a direct evidence of partial melting along matrix grain boundaries and matrix-reinforcement interfaces. Based on the obtained results, the role of the liquid phase in the high-strain-rate superplasticity is discussed.

The sample was Al-Mg (5052) alloy reinforced with 20vol% Si3,N4 particles, fabricated by a powder metallurgy process. The sample showed an excellent superplasticity under the conditions given in Table 1. Partial melting was confirmed to occur at 821 K by differentail scanning calorimetry. The microstructural changes during heating were observed in situ by TEM using a heating stage. The structure of interfaces and grain boundaries was observed by HREM. Chemical analysis was performed with EDS attached to VG-STEM.

Characteristics of the interfacial region between a polymer and substrate are critical to the durability of adhesive-adherend system performance. The High Speed Civil Transport (HSCT) requires structural laminates to be light weight, non-corrosive, environmentally safe, and able to withstand extreme service conditions (Mach 2.4 with in-service temperatures at 177°C, projected life to 120,000 hours). The present work characterizes multi-layer laminates comprised of a Titanium substrate (6A1-4V and 15V-3Cr-3Al-3Sn alloy), a silicate/zirconate sol-gel coating with aminopropyl functionality (nominally 1000 Angstroms), a NASA developed PETI-5 psuedothermoplastic polyimide primer (nominally 1000 Angstroms), and a high toughness, thermo-oxide stable PETI-5 adhesive. Previous studies report the physical effect of aging; therefore, this work aims to measure the nano-mechanical properties of the interface utilizing nano-indentation and AFM, focusing on the accelerated time-dependent changes due to extreme environmental exposure.

Samples were prepared by sectioning each laminate (No Environmental Exposure, 1000 and 2000 Hours at 200°C) in two locations, one section externally exposed to environmental test conditions and the other from the middle of the laminate.

Nanoindentation allows the hardness of thin coatings and synthetic multilayer structures to be measured, since indentation depths can be as little as a few 10s of nm. In combination with the cross-sectional transmission electron microscopy (TEM) analysis described here it is possible to observe the deformation structure under an indent, and potentially to understand deformation mechanisms on a nm scale in a wide variety of materials. Synthetic multilayers are a particularly interesting system to investigate. Variations in hardness with the multilayer compositional repeat distance (A) have been reported for several systems. The highest hardnesses, which are in excess of what a simple “rule of mixtures” would predict, occur in nitride multilayers at A ∼5nm. Here we present some preliminary results showing the deformation structure in both a monolithic NbN film and a TiN/NbN multilayer in which both components have the rQck salt structure with lattice parameters 0.424nm (TiN) and 0.439nm (NbN).

Lath-like silicon oxynitride crystals have often been observed in the microstructure of silicon nitride based ceramics after processing. They are usually located in glassy regions which are siliceous solidified sintering aid liquid, and usually contain a small (∼100nm) a-Si3N4 crystal. These nitride crystals are considered to be seeds, incompletely dissolved in the melt, that are heterogeneous nucleation sites for the oxynitride crystals. We present here the first observations of morphological and crystallographic habits between the seed nanocrystals and the host oxynitride laths.

Fig. 1 shows a typical oxynitride lath containing a nitride seed crystal. The lath is surrounded by glass and ß-Si3N4 particles, and a small cristobalite particle (a minor constituent). This microstructure is from an Si02-Si3N4 ceramic processed with Al2O3 sintering aid. The same oxynitride lath/seed structures were observed when other sintering aids (eg. Y2O3, MgO, ZrO2) were used, so they are independent of sintering aid.

Ferroelectrics are used in many applications such as non-volatile memory, infrared detectors, phased array radar and optical switches. While substantial progress has been made in the development of commercial ferroelectric devices, we still do not possess a good understanding of the fundamental processes in ferroelectrics. Trapped charge and oxygen vacancies are believed to strongly influence domain motion. In order to study these issues, we have designed an in situ TEM holder that can subject ferroelectric crystals to voltage, heat and UV irradiation.

Bulk BaTi03 crystals, grown by the Remeika method, were mechanically polished and thinned in hot ophosphoric acid. The resulting thin flakes were attached to copper rings with conductive carbon paint and electrical wires were glued to the copper rings, which act as electrodes. The sample was placed in the cradle of the in situ TEM holder and examined in a Hitachi H9000NAR TEM.

A series of homologous compounds InMO3(ZnO)m (M=In, Fe, Ga and Al, m=integer) has been synthesized successfully by the present authors. From x-ray diffraction, the strutcure is considered to be a layered structure, consisting of InO2−1-(In-O layer) interleaved with M/ZnmOm−l1+ (M/Zn-O layer). The space group is assigned to be R3m when m is an odd number, while it is P63/mmc when m is an even number. The distribution of M atoms within the M/Zn-O layers is considered to be random. However, from electron microscopy study, the existence of the modulated structures showing non-integral periodicities has been observed. The high spatial resolution EDS analysis using 0.5 nm electron probe diameter under a 300kV FE-TEM showed that the sinusoidal modulated structure is caused by the ordering of M atoms within the M/Zn-O layers. In the present study, modulated structures of InMO3(ZnO)13, where M atoms consists of two metals such as In and Fe, Ga, Al and Fe are studied by combined use of HRTEM and high spatial resolution EDS analysis using a 300kV FE-TEM.

The fiber/matrix interfaces play a critical role in the mechanical performance of fiber-reinforced ceramic-matrix composites (CMCs). In this vein, the placement of an interphase material between the fiber and matrix phases has received considerable attention. The main purpose of the interphase coating is to enhance toughness of the composite by influencing crack trajectories at the mechanically critical (weak) fiber/coating interface.

This interest in coated-fiber composites has been accompanied by the need for accurate microanalysis of the CMC systems, owing to issues of both morphological and chemical incompatibilities between the dissimilar fiber and coating materials. Consequently, microanalysis has been driven below the micrometer scale, into the length scale of nanometers. Thus, the examination of the fiber/coating interfaces in CMCs falls squarely into the realm of transmission electron microscope (TEM) and scanning transmission electron microscopy (STEM) analyses.

However, the success of TEM/STEM-based microanalysis of CMCs hinges critically on the quality of TEM specimen.

The establishment of ALCHEMI (atom location by channeling-enhanced microanalysis) as a viable microanalytical technique owes much to its early success in determining cation distributions in crystals having the structure of the mineral spinel, MgAl2O4. The first application of ALCHEMI was to a synthetic chromite spinel, and geological applications to natural mineral spinels containing multiple 3d transition elements provided many of the early applications of the technique. Spinel has three distinct regular lattice sites, two cation sites and one anion site, occupying the 8a, 16d and 32e Wyckoff positions of the Fd3m space group. In projection along (800), tetrahedrally coordinated (8a) cations occupy one set of alternate planes, whereas octahedrally coordinated (16d) cations and, to a good approximation, the anions occupy the other set. In principle, therefore, ALCHEMI performed at an 800 planar channeling condition could be used to analyze site distributions in spinel, using oxygen as a marker for the planes containing the octahedral cations, as was early noted.

The most widely spread application of energy filtering transmission electron microscopy (EFTEM) is the determination of elemental distributions in analytical investigations. The new EFTEM techniques are based on data acquisition by electron spectroscopic imaging (ESI), which offers the advantage of fast two-dimensional recording of the inner-shell loss intensities. In a more general framework, the new ESI methods and the standard PEELS technique both aim at exploring the same three dimensional data space. This data space is represented by the spatial coordinates x, y and the energy loss ΔE and the resulting intensity distribution I(x,y,ΔE) is the quantity which is evaluated. It is intuitively clear, that acquiring more than just three consecutive ESI images gives us the possibility to get quantitative information about the spectra and the shape of the ionization edge. The information on the EEL spectrum can be extracted from a series of ESI images for each individual pixel or, by integrating over corresponding pixels, for a given image area and can be quantified by applying standard EELS quantification techniques.

It is known that radiation produces microscopic and macroscopic changes in silicas and other silicate glasses that result in densifications of several percent [1], This change in density is matched by a corresponding linear change in refractive index via the Lorentz-Lorenz relation such that where R is the molar polarizablilty, V the molar volume and n the refractive index.- Measurements of neutron irradiated bulk a-Si02 yield an exact correlation between the refractive index and density as shown by Fig. 1 such that dn/dp =185 m3/kg [ 1 ].

Utilizing a VG HB603 STEM fitted with a parallel EELS, measurement of irradiation-induced density changes in silicas were attempted using the 0-100 eV low-loss region of the electron energy-loss spectrum. The dielectric function and refractive index changes were extracted from these data using a modified Kramers-Kronig analysis (Fig. 2).

Grain boundaries have long been known to have a dominant effect on the electronic properties of polycrystalline materials. In the case of electroceramic oxides, the thermodynamics of defect formation (vacancies or interstitials, cations or anions) are usually invoked to predict the presence of a space charge potential at the grain boundaries. The relative energetics for the formation of each type of defect determines the size and sign of this potential barrier and thus, the effect that boundaries have on the overall electronic properties of the materials. However, a limitation to this continuum thermodynamics approach is that it does not consider the effect of the grain boundary structure.

To investigate whether the grain boundary atomic structure can have an effect on the energetics of defect formation and hence the electronic properties, here we examine the structure of Σ5 boundaries in two systems, SrTiO3 (perovskite) and TiO2(rutile).

The technique of electron backscatter diffraction (EBSD) in the scanning electron microscope is becoming a standard technique for the characterization of materials. EBSD has evolved into a tool that can determine the orientation of a crystalline area of interest or the technique can be used for the identification of unknown phases from their composition and crystallography. The application of the technique to ceramic materials has demonstrated the many advantages of this technique over classical x-ray diffraction techniques or electron diffraction in the TEM.

EBSD patterns are obtained by illuminating a highly tilted sample (>45° from horizontal) with a stationary electron beam. Electrons that are backscattered from the sample may satisfy the condition for channeling (or diffraction) and produce images that contain bands of increased and decreased intensity that are equivalent to channeling patterns. The patterns are imaged by placing a phosphor screen near the sample and imaging the screen with either TV rate or a slow scan CCD camera.

Highly textured (Bi,Pb)2Sr2Ca2Cu3O10(Bi-2223)/Ag composite tapes have received considerable attention as high-Tc superconducting materials for electric power and high-magnetic-field applications because of their relatively high-critical current densities and their flexibility. In order to improve the performance of these tapes for many commercial applications, it is essential that the mechanisms that limit the critical current density are fully understood. Previous microscopical studies of these tapes have revealed that interfaces such as grain boundaries strongly influence the transport of large currents1. From a morphological point of view, several models have been proposed to describe potential current transport mechanisms. However, as these models consider mainly the large-scale configuration of the boundaries, the underlying mechanism controlling the properties is still unclear. In order to elucidate the exact role of grain boundaries, systematical studies on the effect of the atomic structure as well as any chemistry change that occurs at the interface are required.

Silicon carbide is a versatile material possessing properties such as a wide energy bandgap, high thermal conductivity, high elastic modulus and high-temperature creep resistance, which enable it to be used in a variety of electronic, optical and structural applications. Chemical vapor infiltration/deposition (CVI/CVD) coupled with the application of a temperature gradient and forced flow of reagents is particularly suited to the production of SiC structural composites due to the benefits of reduced infiltration time and uniform composite density. In this work, the growth and orientation of polycrystalline SiC on graphite during CVI is investigated using TEM and HRTEM.

The composites studied possess a laminated matrix of alternating layers of carbon and SiC which were deposited by alternating the reagent streams from one layer to the next. Specimens for TEM examination were obtained by cutting ∽1 mm thickness slices from the bulk sample with a low speed diamond saw.

Liquid-Phase Sintering (LPS) is a conventional fabrication route for the densification of alumina and other ceramics. The polycrystalline ceramics processed by LPS contain siliceous phases along the grain boundaries. This wetting of the grain boundaries has a strong dependence on the crystallography of the boundary. The liquid preferentially wets certain orientations while some special boundaries are ‘dry’. The mechanism of dewetting of these boundaries is not well understood. Several approaches have been adopted to study the nature of the liquid-solid interaction at the grain boundaries. In commercial alumina, anorthite is the most commonly found intergranular phase.

Basal twist boundaries in alumina which contain a thin layer of anorthite glass have been investigated in the present study. Pulsed laser deposition has been used to deposit thin films of anorthite glass on optically flat basal sapphire. The substrate-film assembly is then bonded to an optically polished basal sapphire by sintering the assembly at 1650°C for 2h.

The knowledge of interface properties is important in understanding the adhesion of metal films to glasses. To simplify the analysis, silicate glasses are usually regarded as amorphous SiO2. Comparing the measured energy loss functions of Code 7059 (BaO-B2O3-SiO2) and Code 1737 (Al2O3-B2O3-Si2) glasses by EELS with the calculated result of a-Si02 from optical data, this is a fairly good assumption in bulk materials. Depositing metals, which have strong affinity for oxygen on glasses, however, may result in minor elements, such as Ba in both 7059 and 1737 glasses, segregating to interfaces, and breaking down the chemical balance.

Figs. 1 and 2 show the EELS spectra acquired with a 2Å electron probe in Cr film, interface and bulk glass respectively. The Cr film in Fig. 1 was sputtered on 7059 glass at room temperature, and annealed at 450°C in compressed Ar gas for 10 min. The preparation of Cr thin film in Fig. 2 is mentioned elsewhere.