The interaction of radiation produced point defects with a dislocation microstructure at high temperature is of considerable interest and careful high voltage microscopy experiments can provide valuable insight into the mechanisms. Veyssière and Westmacott carried out in-situ experiments monitoring the partial dislocation climbs in Ni3Al induced by thermal vacancies as well as by Frenkel pairs produced during irradiation.1 We report here the results of some preliminary experiments we performed on alumina (A12O3) single crystals with high dislocation densities to study the modification of the microstructure by electron irradiation at high temperature.

The dislocation microstructures were produced by shock wave deformation using a high-velocity impact technique. The technique is capable of producing a very high density of defects consisting primarily of basal twins, and slips on the basal, pyramidal and rhombohedral planes in alumina. The dislocations are all of glide type, mostly forming shear bands. A typical microstructure prior to irradiation is shown in figure la.

Metal oxide films are are an emerging sensing technology for the identification of gas phase species. Metalorganic chemical vapor deposition (MOCVD) on microhotplate structures provides a method of fabricating gas sensing layers in self-patterned structures. Investigation of the morphological characteristics of film growth is normally not possible inside a MOCVD reactor, especially the nucleation phase and subsequent deposition of a continuous film. The environmental scanning electron microscope (ESEM) operates at a pressure range of 133-666 Pa (1-5 Torr) which is similar to the growth condition normally used for oxide film MOCVD on microhotplates. Our results show that microhotplate MOCVD can be monitored in situby secondary electron and backscattered electron imaging in the ESEM.

The microhotplate chemical sensor devices employed in this work are mounted in conventional 40 pin packages which provide separate electrical connections to each of the four micromachined heater and contact structures.

Gelatin and dextran are two water soluble biopolymers of considerable importance in the food industry, both separately and in combination. A solution of gelatin and dextran (∼ 10% total polymer concentration) forms a single phase at high temperatures, and on cooling undergoes phase separation, which may occur simultaneously with the gelation of the gelatin. The exact phase distribution in the final microstructure is dependent on the initial polymer concentrations, and the relative rates of gelation and phase separation. Much work has been done on such systems in the past, using a variety of techniques. Most recently, optical microscopy and small angle light scattering (SALS) have been used to characterise the structure of this particular system, especially for systems at the critical concentration. However due to the constraints imposed by sample preparation, very little Scanning Electron Microscopy (SEM) has been carried out on such systems - freeze drying and the problems of obtaining contrast between the phases without staining make such experiments difficult and sometimes inconclusive.

High temperature, thin ceramic insulation coatings are necessary for the application of High Temperature Superconductors (HTS) in high field magnet technology. Especially in the so called “wind and react” technology, insulation coatings have to withstand the final heat treatment at about 900°C, otherwise turn to turn insulation will be broken. We have developed a sol-gel coating method for HTS tape conductors at NHMFL. Excellent adhesion at the interface due to the significant interfacial reactions, indicates that this sol-gel route is a feasible method for applying zirconia coatings. Sol-gel technology is a low temperature chemical route of preparing inorganic material. The stability and the coating characteristics of a organozirconium compound have been investigated to coat ZrO2 films on silver sheathed HTS tape conductors. This method was used to coat stainless steel with ZrO2.

The ZrO2 coatings were obtained by dipping the silver sheathed HTS tape in a solution of zirconiumtetrabutoxide, isopropanol and acetylacetone.

We have performed a theoretical investigation of the effects of space charges in the Environmental SEM (ESEM). The ElectroScan ESEM uses an electrostatic field to cause gas cascade amplification of secondary electron signals. Previous theoretical descriptions of the gas cascade process in the ESEM have assumed that distortion of the electric field due to space charges can be neglected. This assumption has now been tested and shown to be valid.

In the ElectroScan ESEM, a positively biased detector is located above the sample, creating an electric field on the order of 105 V/m between the detector and sample surface. Secondary electrons leaving the sample are cascaded though the gas, amplifying the signal and creating positive ions. Because the electrons move very quickly through the gas, they do not accumulate in the specimen-to-detector gap. However, the velocity of the positive ions is limited by diffusion.

Nitride films play an increasing role in modern electronics, for example silicon nitride as insulating layer in Si-based devices or GaN in blue light emitting diodes and lasers. For this reason they have been the subject of many ex situ electron microscopic studies. A much deeper understanding of the growth of these important materials can be obtained by in situ studies. Although these could be done by SEM, LEEM combined with LEED is much better suited because of its excellent surface sensitivity and diffraction contrast. We have in the past studied the high temperture nitridation of Si(l11) by ammonia (NH3)and the growth of GaN and A1N films on Si(l11) and 6H-SiC(0001) by depositing Ga and Al in the presence of NH3 and will report some of the results of this work for comparison with more recent work using atomic nitrogen instead of NH3.

Observation of stone deterioration using in situ,time-lapse microscopy techniques has revealed previously undescribed material behaviors that help to explain the destructive effects of several important processes in wall paintings, historic structures and monuments. It has long been acknowledged that cyclic stresses imparted by humidity changes, wet-dry cycling, and the crystallization and hydration of soluble salts, are important agents in the deterioration of these porous structures. The crystallization of salts is a particularly serious conservation problem (Arnold, 1975). Over time, cyclic salt crystallization results in the physical breakdown of the material (Goudie, 1993). Objects affected by such processes are often difficult to conserve since they are weak to begin with and the presence of salt inhibits the curing of some common conservation materials (Price and Kumar, 1994).

Sodium sulfate is one of the most damaging of salts, apparently because it expands during the transition from the anhydrous phase (Na2SO4; thenardite) to the decahydrate form (Na2SO4•l0H2O; mirabilite).

The passing of current through thin metal lines results in the formation of voids which will eventually cause the line to fail electrically. Gathering of experimental data on electromigration has been limited by two facts: The dimensions of the metal lines on modern integrated circuits are on the order of the resolution limit of light microscopy; and voids in these lines behave quite differently when they are surrounded by a protective film of SiO2 or other dielectric. This dielectric protects the metal surface and constrains the line, pushing back on the metal displaced by void formation. Several additional factors further complicate experimental analysis: the sample test current must be precisely controlled during observation; the sample must be accurately heated to several hundred degrees; the metal lines must be long and narrow (typically 0.2-3.0 (am wide by 300 μm long); testing is often lengthy, sometimes extending over several days even under conditions selected to minimize the time to failure; and electromigration failures are characterized by long incubation periods during which no changes are observed followed by rapid and complex behavior.

Dynamic interactions between gas molecule and solid surfaces are central to heterogeneous catalytic processes. Recently, we have developed a novel in-situ environmental high resolution electron microscopy (EHREM) method, capable of probing live gas-catalyst reactions at elevated temperatures directly (in-situ) on the atomic scale1. A Philips CM30 (S)TEM has been modified with an integrated environmental cell maintaining atomic resolution in controlled gas environments, upto ∼ 1000 °C. Using this method, we have studied important real-life catalysts, vanadyl pyrophosphates ((VO)2P2O7, hereafter referred to as VPO), used in n-butane oxidation to maleic anhydride (MA with end uses in furans.

The catalyst samples were prepared using V2O5, anhydrous phosphoric acid in isobutyl alcohol and benzyl alcohol followed by calcination and activation. VPO is orthorhombic with a ∼ 16.59Å, b ∼ 7.76Å and c ∼ 9.58 Å . An EHREM lattice image of the fresh catalyst with electron diffraction (ED) and ‘rose’ morphology, is shown in Fig 1(a).

Comprehensive studies by HREM, SAED, and EDXS have been recently devoted to the real structure of the ternary reduced molybdenum oxides in the series Mn±δMo4n+2O6n+4 with M = Sn,In. These compounds contain condensed clusters Mo4n+2O8n+10 with a core of n transedge-sharing molybdenum octahedra. The individual clusters are interconnected via common oxygen atoms. of course, the appropriate choice of counter-cations M is essential for the stability of the clusters, whose core of condensed molybdenum octahedra is a more or less extended metal-metal bonded structure. In tin oxomolybdates condensed clusters with n = 2,3 have been observed, in indium oxomolybdates with n = 3,4,5,6. In Sn2Mo10O16 and Sn2.8Mo14O22 each Sn atom provides 2 electrons to the cluster, in In5Mo18O28, e.g., with n = 4 an In57+ polycation, a metal-metal bonded unit itself, provides 7 electrons.

It became obvitalicous that both tin and indium oxomolybdates undergo a structure transformatitalicon when irradiated a 300kV electron mitaliccroscope (Philips CM30/ST, Cs = 1.15mm).

Reactions at solid-solid interfaces are important both scientifically and technologically. Firstly, there is quite a wide variety of possibilities. Materials can react with one another, forming equilibrium, meta-stable or even amorphous phases. The interface can provide a means to promote phase reactions kinetically, in an analogous manner to catalysis. Even when the materials are mutually compatible chemically, the interface topography and atomic structure can evolve over the course of time. From the practical point-of-view, changes in the interface chemistry and structure can profoundly alter the physical properties. This is especially notable in thin film technology, whereby the interfaces constitute a signigicant proportion of the whole device. In this article, contributions to understanding this field are illustrated through application of in situ and high-resolution electron microscopy (HREM).

Basic studies of metal-semicoductor interfacial reactions have been successfully carried out for a number of years. of increasing importance in microelectronics is the stability of layers which prevent chemical interaction, namely the diffusion barriers.

It is well known that diffusion in ionic materials occurs primarily by the movement of charged species. Therefore, an electric field should provide a very powerful driving force for mass transport. In the present study, solid-state reactions, in the presence of an electric field, have been carried out between thin films of In2O3 and bulk monocrystalline MgO ﹛001﹜. In solid-state reactions of this type, reaction rates and interfacial stability are affected by the transport properties of the reacting ions. by applying an electric field across the sample, at elevated temperatures, the reaction rates and interfaces are affected as a result of ionic conductivity. Through the use of electron microscopy techniques the reaction kinetics and interface morphology have been investigated, in this spinel forming system, to gain a better understanding of the influence of an electric field on interface morphology and solid-state reactions.

The reaction couples used in this study were produced by means of pulsed-laser deposition (PLD).

TiAl alloys are being developed for future use as lightweight, high strength structural materials for the aerospace and automotive industries. The growth of titanium borides in-situ in a TiAl melt can lead to a variety of structures, such as TiB (Bf and B27 structures) and TiB2, depending on the Ti/Al ratio in the melt, and on the presence of further alloying additions [1,2]. The morphologies of the boride particles can be significantly altered if they grow coupled with other boride or intermetallic phases [2-4]. Since the morphology and distribution of the borides with the intermetallic matrix can significantly affect their effectiveness as creep reinforcements, the structures and growth mechanisms of these composites need to be quantified at the atomic scale.

In a Ti-45.5at.%Al-1.6at.%Fe-l.lat.%V-0.7at.%B alloy know to contain TiB2 precipitates [2,3], the morphology of the boride particles have been investigated using HREM. The Stuttgart JEOL-ARM, operated at 1250kV using the side-entry pole-piece with 0.12nm point resolution, enables the distinction between individual boron and titanium columns in the titanium borides to be achieved for the first time.

Precipitate interfaces are ideal for studying the relationship between atomic bonding, structure and composition at internal interfaces and the mechanisms and kinetics of their motion as a function of temperature or driving force for reaction. The crystallography between coherent and semicoherent precipitates and the matrix is well-defined and the precipitate interfaces are often planar and grow by a terrace-ledge-kink mechanism, making them well-suited for study by conventional and high-resolution transmission electron microscopy (HRTEM).

Motion of precipitate interfaces, or more generally, interphase boundaries, involves a change in lattice, composition or both. In order to understand the mechansims of interfacial motion, it is necessary to determine the structural and compositional changes that occur at the highest possible resolution, i.e., as close to the atomic level as possible, and also, to determine the corresponding kinetics of interface motion. HRTEM is an excellent technique for determining the atomic structure of transformation interfaces and in situhot-stage HRTEM is deal for determining interface dynamics at the atomic level, provided the transformation mechanisms are not altered by the thinness of the TEM foil.

Small Pb inclusions in Al have been studied by a number of investigators because the alloy system offers the possibility of observing the processes of melting and solidification directly. Both solids are fee, and the mutual solubility of solid Pb and Al is negligible. Despite a large difference in lattice parameter, it has been found that inclusions follow a parallel-cube orientation relationship and their equilibrium shape is a cuboctahedron, bounded by ﹛111﹜ and ﹛100﹜ facets [1]. Following Herring, the relative extent of the two types of facet directly indicates a ratio of interfacial energies γl00/γ111- However, recent investigations have shown that for inclusions in the range of a few to a few tens of nanometers the equilibrium shape becomes a function of size [2].

In the present work, this size dependence of the equilibrium shape has been investigated further. Al alloys with about lat.% Pb were prepared by rapid solidification or by ion implantation, and equilibrated by annealing at about 300°C.

The crystallization of glass ceramics provides processing advantages for difficult shapes. Machining and sintering are limited to produce complex parts; similarly (superplastic) forming is limited to special ceramics. In theory, however, a liquid (or glass) may be simply poured into any shape, and then crystallized (or partially crystallized) to provide a strong, tough ceramic. In this work, a thin layer of glass ceramic, cordierite (2MgO.2Al2O3.5SiO2), joins SiC [1]. Tailoring secondary phases and percent crystallization provide flexible control of the coefficient of thermal expansion to minimize strain mismatches between the joint components.

Three processing steps are involved in crystallization of glass ceramics: first a fast quench produces the initial glass; the second step is a lower temperature “nucleation” anneal, where phase separation and/or precursors and/or the final structure is nucleated and ideally as a fine dispersion; the third step is the higher temperature “crystallization” anneal, where renucleation and/or growth develops a homogeneous (ideally fine grained) final crystalline product [2, 3].

Electroluminescence (EL)-based displays are an emerging technology for next generation flat panel displays. ZnS is an important component material for light emitting devices and EL-displays. To make this material useful for high efficiency and low voltage EL applications, the density of dislocations is required to be low. High quality single crystalline ZnS thin films have recently been grown by chemical beam epitaxy [1]. This paper focuses on studying the formation mechanism of stacking faults in the film and its relation with the interface structure between the substrate and the film [2].

Stacking faults are the main defects present in the film (Fig. 1). All four stacking faults (sf) are intrinsic and sf1, growing towards the left-hand side from the interface, is only of short range since after crossing sf2 the defect is terminated by a Shockley partial dislocation and the normal stacking sequence is restored. This is the mechanism that annihilates most of the stacking faults generated from the interface within the first 70 nm thickness range.

An ultra high vacuum (UHV) planar interface unit has been constructed to study the effect of interface/boundary structure and chemistry on properties. We report here initial observations of substrate morphology and chemistry prior to bonding and resulting interface morphology obtained using austenitic stainless steel.

To synthesize chemically clean planar interfaces by diffusion bonding, the substrate must be macroscopically and microscopically flat and chemically clean. Macro-flatness, necessary for bonding to occur over large areas, was ensured by conventional mechanical polishing and lapping. Substrate surfaces were cleaned by a broad (3cm) 500 eV ion beam (Ar or Xe) at 15° incidence. The resulting changes in substrate near-atomic-scale roughness and chemistry were analyzed using Auger spectroscopy (AES) and Atomic Force Microscopy (AFM). Before ion beam cleaning, the sub-strates exhibited high oxygen and carbon contamination (Fig la). Both Xe and Ar ion cleaning reduced these values; the result for 5 minutes Ar cleaning is shown in Fig lb.

We are investigating the structure of the Al (11l)/Al2O3 (0001) interface. Interfaces for this study were produced by epitaxial thin film deposition of aluminum metal onto (0001) oriented single crystal α-Al2O3. The majority of grains within the films are oriented with:

(0001)Al2O3 || (lll)Al [10Î0]Al2O3 || [ī10]Al

This relationship results in a matching of the close-packed planes and directions of the aluminum metal with those of the oxygen ion sub-lattice in the Al2O3and allows for two variants related by 180° rotations about the aluminum [111] axis. A diffraction pattern showing these two variants is given in Figure 1. Figure 2 shows a HRTEM image of the heteroepitaxial aluminum/Al2O3 interface. The Al2O3 substrate and aluminum overlayer are imaged along the [10Ï0]Al2O3 and [ī10]A1 zones. Over the width of the image, the interface is sharp to within a few atomic layers.

The calculated lattice misfit for the Al/Al2O3 system, taken as the difference between the translation vectors of a/3[10ī0]Al2O3 (2.7447 Å) and a/2[ī10]AI (2.8634 Å), is 4.3%. A fundamental issue is the manner in which this misfit is accommodated.

K0.19Ba3.18Mo22O34is a representative of the quaternary reduced molybdenum oxides in the series Mn±δMo4n+2O6n+4. These compounds contain condensed clusters Mo4n+2O8n+10 with a core of n trans edge-sharing molybdenum octahedra. The general concept of cluster condensation is discussed elsewhere. In the case of n being finite the clusters are designated as ‘oligomeric’. The individual clusters are interconnected via common oxygen atoms and arranged in layers. For the title compound with n = 5, the clusters consist of 5 molybdenum octahedra and are accompanied by 4 counter-cations (potassium and barium).

The real structure of K0.19Ba3.81Mo22O34 has been recently studied with a Philips CM30/ST (Cs = 1.15 mm) by HREM, SAED, and EDXS. Besides chemical intergrowth of oligomeric clusters with n = 2—18 in the matrix consisting of pentameric clusters, polytypism was observed. Three ordered polytypes (modifications) were found, whereas only one of them, lM (Ramsdell notation), was detected and analyzed with x-ray methods.