Copper overlayers deposited on nearly stoichiometric SrTiO3(001) have been investigated with scanning tunneling microscopy (STM). Vapor deposition of Cu on a SrTiO3(001) surface at ambient temperature leads to the formation of three dimensional islands (clusters). The distribution of Cu islands appears to be inhomogeneous with two characteristic morphologies. In regions with a low density of Cu islands the Cu was always associated with step edges or defect sites. In regions with a high density of Cu islands the islands exhibit a random but nearly close packed morphology. The variation of Cu island density is indicative of diffusion of Cu clusters on the SrTiO3(001) surface. Diffusion was further confirmed by annealing the Cu/SrTiO3 at elevated temperatures yielding agglomeration of Cu clusters.

This paper is devoted to a discussion of how the information derived from the application of in-situ transmission electron microscopy can be used to gain a unique insight into the manner by which various factors dictate the morphological characteristics of metal particles on a variety of ceramic substrates. In this context, we have used the technique to examine the influence of the strength of the metal-support interaction on the mode of sintering of small particles, and how the chemical nature of the gas environment can induce significant changes in the shapes of the metal particles in a given system. Attention is also focussed on the wetting behavior of metal particles dispersed on graphite when reacted in oxygen and how this aspect impacts on their subsequent mode of catalytic attack.

The growth, structure, and electronic properties of Pt films supported on the (0001) and (0001) surfaces of ZnO were investigated using high-resolution electron energy-loss spectroscopy (HREELS) and low-energy electron diffraction (LEED). Vapor-deposited Pt films were found to grow in a layer-by-layer fashion on both surfaces and exhibited hexagonal LEED patterns. HREELS results indicate that there are only weak electronic interactions at the Pt/ZnO(0001) interface, while charge transfer and Schottky barrier formation occurs at the Pt/ZnO(0001) interface.

Glancing-angle x-ray absorption fine structure (XAFS) spectroscopy has been used to characterize the structure of Co(II) complexes adsorbed from aqueous solution on single crystal ∝-Al2O3 surfaces. The spectra reveal considerable differences in the local structure, as a function of both the crystallographic face and the orientation of the sample with respect to the beam polarization. Data analysis indicates that the predominant mode of Co chemisorption is as a tridentate CoO6 octahedral complex edge-shared with surface Al octahedra. For systems where this method is feasible, it is the technique of choice for characterizing metal ion adsorption complexes.

The interaction of cesium at the (0001) and (1102) surfaces of sapphire has been investigated using a variety of surface analytical techniques. Reflection mass spectrometric measurements yield initial Cs adsorption probabilities of 0.9 and 0.85 for the unreconstructed (0001) and (1102) surfaces, respectively. The adsorption probability decreases dramatically for these surfaces at critical Cs coverages of 2.0×10 14 and 3.4×1014 atoms/cm2, respectively. Thermally induced reconstruction of the (0001) surface to form an oxygen deficient surface results in a decrease in the initial probability and capacity for Cs adsorption. Low energy electron diffraction (LEED) demonstrates that an intermediate, mixed domain surface yields an initial adsorption probability of 0.5 while a reconstructed surface yields a value of 0.27. Thermal desorption mass spectrometry (TDMS) shows that surface reconstruction eliminates the high binding energy states of Cs (2.7 eV/atom), consistent with the observed changes in adsorption probability. In contrast, reconstruction of the (1102) surface produces only minor changes in Cs adsorption. Xray photoelectron spectroscopy (XPS) indicates that no formal reductive/oxidative chemistry takes place at the interface. We interpret the facile adsorption and strong binding of Cs on sapphire to result from Cs interacting with coordinatively unsaturated oxygen.

The photoelectron spectra for titanium deposition on a AIN ceramic substrate at room temperature have been measured. Before deposition, the binding energies of Ols and Al 2p show that the substrate contained oxygen as a major impurity and a top layer of degeneration was formed. After deposition of a small amount of titanium, it was found that the Nls separated into two peaks(396.5 eV and 402 eV) and Ti 2p corresponded to the oxide state. With an increase of titanium coverage, the Ti 2p peak shifted toward a lower energy. The peak at 402 eV dominated at a titanium coverage of 0.9 nm, showing the nitrogen-oxygen binding character. For a titanium coverage of 3.0 nm, a new peak at 406 eV was formed. These results suggest that during deposition of Ti onto the AIN substrate which has a top hydrated alumina layer, some of nitrogen atoms tend to be bound with oxygen and to form an interfacial oxynitride layer between the metallic titanium and substrate.

The A1/MgO system has been used as a model system to study growth processes and structure at metal/ceramic interfaces. Aluminum films were grown on air-cleaved MgO (100) substrates in ultra high vacuum (UHV) by molecular beam epitaxy (MBE). The substrates and films were characterized by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), conventional transmission electron microscopy (CTEM), and high resolution transmission electron microscopy (HREM). XRD measurements exhibited a pronounced {100} texture. Employing electron diffraction in the TEM on cross sectional samples, we observed the following orientation relationship between Al and MgO: (100)A1 II (100)MgO; [010]A1 II [010]MgO. The atomistic structure of the interface was investigated by HREM. Regions of structural defects can be identified clearly at the interface.

Ultra-thin films of Mg and MgO were grown on ∝-Al2O3 (1012) surfaces (r-cut sapphire) and studied using reflection high energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). When Mg is deposited at 30°C in ultra-high vacuum (UHV), the first monolayer of Mg atoms chemically bonds to the oxygen anions of the sapphire surface. At Mg coverages above a monolayer, a polycrystalline metallic Mg overlayer is formed. Annealing above 250°C in UHV causes the metallic Mg to desorb from the surface. However, annealing above 250°C in 10−6 torr O2 produces a polycrystalline MgO film. This MgO film recrystallizes after annealing in O2 at 900°C for 60 minutes and exhibits a crystallographic orientation of MgO (100) // ∝-Al2O3 (1012). RHEED indicates that the recrystallized MgO layer dewets the sapphire surface and forms islands. When Mg is deposited at 30°C in 10−6 torr O2, a polycrystalline MgO layer is created. This layer also becomes recrystallized and dewets the sapphire surface after extended annealing in O2 at 900°C. No evidence for a MgAl2O4 spinel phase was observed.

A near-surface thin layer is melted when single crystal alumina (sapphire) is pulsed laserirradiated in an Ar-4%H2 atmosphere. γ-alumina grows epitaxially from the (0001) face of axalumina (sapphire) during the rapid solidification of this layer that occurs once the laser pulse is over. Cross sectional high resolution transmission electron microscopy (HRTEM) reveals that the interface between unmelted sapphire and γ-alumina is atomistically flat with steps of one to a few close-packed oxygen layers; however, pronounced lattice distortions exist in the resolidified γ-alumina. HRTEM also is used to study the metal-ceramic interface of a copper film deposited on a laser-irradiated alumina substrate. The observed changes of the interfacial structure relative to that of unexposed substrates are correlated with the strong enhancement of film-substrate bonding promoted by laser irradiation. HRTEM shows that a thin amorphous film is produced after irradiation of 99.6% polycrystalline alumina. Formation of a diffuse interface and atomic rearrangements that can take place in metastable phases contribute to enhance the bonding strength of copper to laser-irradiated alumina.

Auger Electron Spectroscopy (AES) was employed to study metal/ceramic interfaces. Adhesion pull testing showed that a strong bonding between metallic films and alumina substrates is obtained when alumina is laser-irradiated in an oxygen atmosphere before deposition and, after deposition, the couple is annealed at 300°C for 1 h. On the other hand the gold/alumina bonding is extremely weak when laser-irradiation of the substrate is performed in argon-4% H2. Fresh surfaces were exposed for AES at several distances from the metal/ceramic interface by sputtering the specimens in situ after each analysis. In the region of the interface the sputtering rate was slower than in the film in order to minimize any spurious effect due to ion beam bombardment. AES of a gold/alumina couple prepared in this way reveals that the Auger peaks of gold from the film and oxygen and aluminum from the alumina substrate, when the substrate was irradiated in oxygen atmosphere, shift by ∼ 1.5 eV, 1.6eV, and 1.4eV respectively when the analysis area encompasses the metal/ceramic interface. On the other hand, no shift of the Auger peaks are observed at the interface when the laser-irradiation was performed in argon-4%H2. In the case of copper deposited on alumina laser-irradiated in an oxygen atmosphere, an interfacial compound is formed. This compound is a double oxide of aluminum/copper or two separated oxides, and promotes strong copper/alumina bonding.

The fundamental interactions involved in the bonding of atoms and molecules to metal oxides are discussed. Surface defects play a major role in many of those interactions. Both acid/base and oxidation/reduction reactions occur at metal-oxide surfaces, with the latter dominating at point defect sites. The reaction of metals with oxide surfaces is governed largely by the relative heats of formation of the respective oxides, although surface point defects also play an important role. Preliminary studies of ceramic/ceramic interfaces indicate that interfacial interactions are much weaker than for metal/ceramic interfaces.

Scanning tunneling microscopy (STM) was used to determine the structure of cleaved, single crystal surfaces of V205, V6013, Mo18052, and Mo8023. Constant current images were recorded in ultrahigh vacuum and in air. By imaging well-defined surfaces that exhibit structural and chemical similarities, and comparing the observations to the known bulk structures, it is possible to establish a reliable interpretation for the contrast in the STM images. A comparison of images from the V6013(001) and the V205(001) surfaces clearly shows that the surface V coordination polyhedra that are capped by vanadyl 0 can be distinguished from those that are not. This allows vacancies in the vanadyl 0 position to be identified on cleaved V205(001) surfaces. Mo18052(100) and Mo8023(010) provide models for two different characteristic types of surface/crystallographic shear (CS) plane intersections. The shear in Mo8023 lies in the (010) surface plane and creates dark contrast along the [001]. The CS planes in Mo18052, on the other hand, have components of shear both in and normal to the (100) surface plane and create white contrast parallel to [010]. These standards for contrast identification can be used to identify defects on inhomogeneous surfaces.

The influence of surface structure on the interaction of water with TiO2(100) (rutile) was investigated. Two unique surface structures of the (100) crystal face can be prepared by oxidation (the bulk-terminated surface) and by vacuum reduction (the {110}-microfaceted surface). Thermal desorption profiles, which measure of the strength of the adsorbate-surface interaction, indicate that submonolayer coverages of water are more stable on the bulk-terminated surface than on the {110}- microfaceted surface. Also, subtle differences exist in the way water interacts with 2-coordinate 02 sites on these two surfaces. The implications of these results are considered for the acid/base properties of microcrystalline particles.

The adsorption of liquid and vapor water on defective and nearly defect-free TiO2 (110) surfaces has been examined using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). The study has focused on examining electronic defects as created in vacuum and after exposure to both liquid and vapor water. The defective surfaces were prepared by electron-beam exposure and Ar+ bombardment. With exposure up to 104 L low vapor pressure (<10−5 Torr) water to defective surfaces, little or no changes on Ti 3d defect intensities were observed, in agreement with the previous studies. However, defect intensities were greatly reduced after exposing defective surfaces to ∼ 108 L higher vapor pressure (0.2 - 0.6 Torr) water for 5 min. More significantly, XPS and UPS spectra showed that electron-beam induced defects were completely removed upon liquid water exposure, while defects created by Ar+ bombardment were only partially removed. It was found that surface defects created by Ar+ bombardment were removed more readily than sub-surface defects. For a nearly defect-free surface, water coverages were ∼ 0.02 ML at 104 L exposure to low vapor pressure water, ∼ 0.07 ML at 108 L exposure to higher vapor pressure water, and ∼ 0.125 ML with liquid water exposure, respectively.

Direct bonding by forming interface hydrogen bridges has been investigated for both combinations of AI.Si and Al.PZT{Pb(Zr,Ti)03). Hydrogen bridges are formed between OH-groups and oxygen atoms on each bonding surface. Therefore, the surface adsorbing of OH-groups (hydrophilic treatment) is required to the pre-treatment of bonding surface. In this study, two ways of conventional hydrophilic treatment by wet-process and novel treatment by the surface bombardment of hydro-ions(H2O+, OH+, O+, and others) in vacuum (dry-process) have been examined.

Each bonding surface is contacted in the air after the hydrophilic treatment. In the case of hydrophilic treatment by wet-process, the bonding strength of Al-Si shows about 20 MPa after the heat treatment of above 350°C. As for the dry-process, both combinations of At.Si and AI.PZT are bondable, and their strength shows the similar tendency as wet-process with the time and the temperature of heat treatment. However, the bonding area increases more quickly than the ones of wet process. From the results of SIMS and cross-sectional TEM observation of AlSi bonding interface, it is suggested that these bonding are caused by the hydrogen bond formation without interfacial water molecules.

Stannous fluoride SnF2 and mixed fluorides containing divalent tin are the highest performance fluoride ion conductors known to date. Since the fluoride ion mobility increases with temperature, and that these materials are sensitive to hydrolysis of the Sn-F bonds and oxidation of tin(II) to tin(IV) when heated, there is a significant chance of material degradation on heating. Surface oxidation provides a thin coating of highly refractory Sn02, which passivates against further degradation. The details and limits of this protection in SnF2 have been studied and are presented here.

In the electroceramic SrTiO3 the grain boundary atomic structure governs a variety of electrical properties such as non-linear I-V characteristics. An understanding of this atomic structure-property relationship for individual grain boundaries requires a technique which probes both composition and chemical bonding on an atomic scale. Atomic structure models for [001] tilt boundaries in SrTiO3 bicrystals have been determined directly from experimental data, by combining high-resolution Z-contrast imaging to locate the cation columns at the boundary, with simultaneous electron energy loss spectroscopy to examine light element coordination at atomic resolution. In this paper we compare and contrast the grain boundary structure models of symmetric and asymmetric boundaries in SrTiO3.

The most prominent lattice defects in barium titanate, i.e., twins on two distinct lattice planes { 111 } and { 110 }, were characterized using dynamic transmission electron microscopy techniques in the image and diffraction modes. In-situ heating experiments from room temperature up to 130°C and then cooling down to -168°C reveal a dependence of { 110 } twins on ferroelectric transition. On the other hand, { 111 } twins are found to be completely stable through the ferroelectric transition and exist in all phases. Streaking is observed in the diffraction spots leading to an estimation of { 1111 twin wall thickness to be about 10Å while no such streaking was observed corresponding to { 1101 twins. Based on these observations and the behavior of the twin boundaries under dynamic heating cycles, an estimate of the twin wall energies indicates that { 111 } walls have three orders of magnitude higher energy than that of { 110 } walls which explains their relative thermal and mechanical stability.

The atomic structure of [001] tilt grain boundaries of Σ25 (210), Σ5 (310), Σ213 (320) and Σ217 (410) in TiO2 (rutile) were studied using high resolution electron microscopy and computer simulation. Regularly separated small steps (1/2 [120] high) and big steps (3/2 [120] high) which contain secondary dislocations were found in the (210) boundary as a result of deviation from the exact Σ5 misorientation and (210) symmetric plane. Similar steps were also found in (310) and (320) boundaries. Flat segments between the steps were found to have very accurate misorientation of their, Σ's and a nearly symmetric boundary plane. Their rigid body translation, volume expansion and relaxed structures were determined by comparing HRTEM images with computer calculated structures and simulated images. An irregular core structure was found in the (410) boundary when its misorientation deviated 2° from the exact Σ17 misorientation.

Twins in YBa2Cu3O7-δ may be “correlated” at [001] tilt grain boundaries (i.e. twin boundaries from one grain may meet twin boundaries from the other grain in quadruple junctions) and the twins may also be narrowed or “constricted” at the boundary. These effects are more pronounced in the regime of small angle grain boundaries. Based on TEM observations, a tentative threshold misorientation angle of approximately 15° is identified, below which there is a significant driving force reducing the system energy by correlation. The energies of various grain boundary domain structures associated with the twins were estimated on the basis of the dislocations they contain. Success has been obtained in explaining twin correlation in symmetrical tilt boundaries.