We compared the structural characteristics of a silica layer formed on Si(100) by oxidation in hyperthermal atomic oxygen and molecular oxygen at 493K. The laser detonation method was used to create primarily neutral atomic oxygen with kinetic energy of 5.1eV. The silicon oxides were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectrometry (RBS), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). We determined that atomic oxygen forms amorphous silica that is almost twice as thick and nearly double the surface roughness as compared to molecular oxygen - formed silica at the same temperature and time conditions.

Acid-base titration and metal sorption experiments were performed on both mesoporous alumina and alumina particles under various ionic strengths. It has been demonstrated that surface chemistry and ion sorption within nanopores can be significantly modified by a nano-scale space confinement. As the pore size is reduced to a few nanometers, the difference between surface acidity constants (ΔpK = pK2 – pK1) decreases, giving rise to a higher surface charge density on a nanopore surface than that on an unconfined solid-solution interface. The change in surface acidity constants results in a shift of ion sorption edges and enhances ion sorption on that nanopore surfaces.

Thin films of aluminum oxide were deposited on silicon nitride thin films using trimethylaluminum and oxygen at 0.5 Torr and 300 °C. Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopic (XPS) analyses of these films showed no aluminum silicate phase at the film-substrate interface. The O/Al ratio in the deposited film was found to be higher than that in stoichiometric Al2O3 indicating the presence of excess oxygen. FTIR spectroscopy and XPS of the annealed samples did not show any formation of silicon oxide, oxynitride or silicate at the aluminum oxide/silicon nitride interface. In contrast to aluminum oxide on clean silicon substrates, using ultrathin silicon nitride as a barrier layer could prevent excess oxygen migration towards the Si substrate and formation of any interfacial layers.

Application of porous silicon oxide thin films to nanotechnology is under intensive investigation. Introducing a large amount of nano pores into a silicon oxide matrix is important to develop low-k dielectrics for future ultra-large-scale integrated circuits (ULSI). In this work, we applied variable-energy positron annihilation to the characterization of porous silicon oxide thin films fabricated on silicon wafers by sputtering and spincoating. It was found that the sputtered film has higher open pore connectivity than that of the spincoated low-k film.

The segregation of Nasr impurities to a Σ = 5 [001] twist boundary in SrTiO3 is studied using DFT-based plane-wave pseudopotential techniques. The formation energies of the impurities are calculated as a function of oxygen chemical potential and electron chemical potential. The results indicate a strong driving force for segregation to the boundary and that the Na impurities exhibit acceptor-like behaviour. The atomic displacements caused by the impurities are small both in the bulk and at the grain boundary. Based on the results a model is suggested in which Nasr segregation is driven by soft relaxation of the electronic structure.

The modifications in atomistic structure, chemical bonding, and energetics induced by sub-stitutional cation impurities isolated in bulk and segregated at grain boundaries of α-Al2O3 were investigated by first-principles electronic-structure calculations. The dependency of these modifications on the boundary type, species and concentration of defects, was studied by selecting the following variety of systems: two different twin boundaries (the prismatic Σ3 (1010) and the pyramidal Σ13 (1014) twins), five cation impurities X (X=Ti, Sc, Y, Ca, and La), and two concentration regimes for the segregant (≈ 3 and ≈ 6 atoms/nm2). A partial covalent character is found to be a distinctive feature of the X-O bond in both bulk and interfacial atomic environments, and to drive the structural distortions of the octahedral XO6 clusters. The energetics of segregation reveals a linear relationship between segregation energy and impurity size.

Molecular dynamics computer simulations using a robust multibody potential were used to study the structure of the intergranular films (IGFs) formed between two different crystallographic orientations of α-Al2O3 crystals. The simulations show a localized ordering of the IGF at the interface of both the basal and prism planes caused by preferential adsorption of specific ions from the IGF onto the crystal planes. However, the results of the adsorption have significantly different effects on crystal growth of the specific orientations. The preferential adsorption of Ca ions from the IGF onto the (0001) surface inhibit growth in the <0001> direction. However, Ca does not affect adsorption of O and Al from the IGF onto the (1120) surface and potential growth of this orientation in the <1120> direction. The results are consistent with experimental data regarding anisotropic grain growth in this system and provide an atomistic view of this behavior.

Atomistic simulation has been used to predict the segregation of defect clusters containing two substitutional Y3+ ions and one charge compensating oxygen vacancy to the (100) and (101) surfaces of t-ZrO2. The most stable orientation of the defect cluster depends on its distance from the surface. Significantly, segregation energies vary greatly between surfaces. For example, the defect cluster is equally stable up to a depth of 9Å from the (100) surface but only to a depth of 4Å below the (101) surface. In both cases, segregation energies are negligible 12Å beneath the surface.

Interfaces can be considered at a variety of length scales. All interfaces except grain boundaries are dielectric interfaces. In many cases, the geometric constraints of matching two lattices must be considered, together with the misfit strains that are often present. Continuum mechanics is useful for tackling such problems. In many cases, however, the local ordering of ions must also be considered. Atomistic simulation is therefore necessary, together with the problems associated with large length scales and long time scales. We discuss a number of examples to illustrate the issues involved and the compromises between different approaches that must be made.

The Re oxide films were deposited on quartz glasses by RF reactive sputtering from a Re metal target. The lowest resistivity was observed in the film in-situ annealed at 200?C in Ar atmosphere and showed the order of 10-4 Ωcm of which the value was still about 10 times as large as that of a single crystal ReO3. The temperature dependence of the resistivity revealed a metallic behavior. A superconductivity did not take place in the bilayered film of ReO3 / NdBa2Cu3O6. In the interface region the resistivity minimum probably caused by the Kondo effect was observed in the neighborhood of 120K.

The microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are investigated to find their effect on the macroscopic fracture properties. It is found that by heat treating a model Si3N4-2wt% Y2O3 ceramic for ∼200 hr at 1400°C in air, the fracture toughness can be increased by ∼100%, coincident with a change in fracture mechanism from transgranular to intergranular. Structural phase transformations occur in the thin grain boundaries during oxidation that are revealed by XRD, EDX, Raman and EELS analyses. They affect the local bonding of atoms. It is concluded that only specific crystal “building blocks”, i.e., tetrahedra, are transformed along the grain boundary and the resulting difference in the atomic structure of the oxide interface is seen directly to alter the macroscopic fracture behavior.

For fabricating Yb3+ doped La2O3-Al2O3-SiO2 glasses for high-powered fiber lasers, it is critical to choose the right core glass composition to obtain a high numerical aperture and to avoid phase separation. TEM techniques were used to study the relationship between the core composition and phase separation. In the study, inter-diffusion between the core and cladding glasses was found. The inter-diffusion caused large density fluctuation in the region of the core/cladding interface in fibers containing relatively high concentrations of La2O3. The TEM results were used to optimize the chemical composition of the core glass for high-power fiber lasers.

Thin film strain gages based on indium-tin-oxide (ITO) are being developed to measure to static and dynamic strain at temperatures approaching 1500°C. These ceramic strain gages exhibit excellent oxidation resistance and high temperature stability, surviving more than 25 hours of testing in air at 1470°C. Electron spectroscopy for chemical analysis (ESCA) studies indicated that interfacial reactions between ITO and alumina can increase the stability of ITO at elevated temperature. Solid state diffusion of aluminum into the ITO at these temperatures can produce a very stable ITO/Al2O3 solid solution [1, 2]. To determine the nature of the interfacial reaction product, ITO films were deposited onto both Al2O3 and AlN surfaces and thermally cycled to 1500°C. AlN films were used to reduce/eliminate oxygen transport to the interface, so that aluminum-indium interactions alone could be studied. ITO films were deposited onto Al2O3 and AlN films, which were rf sputtered on platinum-coated alumina substrates. The resulting ESCA depth files showed that an interfacial reaction had occurred between the ITO and the Al2O3 and AlN. The presence of two new indium-indium peaks at 448.85 and 456.40eV, corresponding to the indium 3d5 and 3d3 binding energies were observed in both cases; i.e. the AlN and the Al2O3. These binding energies are significantly higher than those associated with stoichiometric indium oxide. In addition, aluminum doped ITO films were formed by co-sputtering from multiple targets and electrical stability of these films was compared to undoped ITO films over the same temperature range (25–1500°C) [1–4].

The adsorption process of water molecules on the surface of InVO4 has been investigated via first principles molecular dynamics simulations and compared with that of the well-known rutile TiO2. We have found that the surface of InVO4 shows a remarked chemical reactivity whenever comes in contact with water and H2O molecules are often adsorbed dissociatively on its surface. The reaction proceeds spontaneously in a way similar to the case of TiO2 and does not require the overcoming of an activation energy barrier. The peculiar atomic connectivity of the InVO4 bulk crystal structure and the changes at the catalyst surface induced by the water adsorption are discussed and compared with the TiO2 system.

We have studied the properties of epitaxial La(1-x)SrxMnO3 (x=0.3, 0.5) epitaxial thin films grown on BaTiO3 and SrTiO3. Significant modifications of properties are observed in magnetization and resistivity versus temperature experiments. These modifications occur at temperatures corresponding to structural phase transitions in the substrate. The x=0.5 composition is particularly sensitive to changes in the epitaxial strain state, exhibiting a direct correlation between changes in strain, magnetization and resistivity. Strain can also be induced in BaTiO3 by the inverse piezoelectric effect, which results in as much as a 13% decrease in the resistivity of the film.

We have investigated the correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 thin films. The films were epitaxially grown by pulsed laser deposition on (001) SrTiO3 substrates in a temperature range of 690–810°C. According to x-ray measurements, the structure of all films is a mixture of highly oriented domains of strained orthorhombic phases (ortho-I and ortho-II) with different lattice parameters. Films deposited at 780°C show a minimum resistivity (270 μΩcm at 300 K) and a maximum magnetoresistance (8% at 5 K). These films consist mainly of ortho-I phase (a=0.393 nm). Films deposited at 690°C (predominantly ortho-II) have the highest resistivity (up to 1700 μΩcm at 300 K) and lowest magnetoresistance (3% at 5K).

PZT films between 1 and 3 μm thick were grown using solution deposition techniques to study the effects of crystal structure, orientation, chemistry and PZT/PZT crystallization interfaces on the piezoelectric output of these films. By varying the chemistry of the film from Zr-rich to Ti-rich the film orientation increased towards {h00}. PZT with 60 wt% Ti exhibited tetragonality and produced greater electrical output at a given strain than the rhombohedral films with concentrations less than 50 wt% Ti. Multiple steps of solution deposition left identifiable PZT/PZT interfaces within the film. TEM, FESEM, and Auger spectroscopy were used to characterize these interfaces, which form upon crystallization of the amorphous PZT film. Internal PZT interfaces are associated with both structural defects (voids) as well as chemical variations such as Pb deficiencies.

We have studied the electronic properties of single crystal rutile TiO2(110) with surface electrical techniques; impedance spectroscopy and high sensitivity DC measurements. In the impedance spectroscopy we observed a spectrum involved in the dissociation of pure water on the TiO2 surface under UV irradiation. In the high sensitivity DC measurements we observed oscillations of the surface photo-current with three different long periodicities, which might have originated from the oxidation and reduction processes of water on TiO2 via photo-catalytic reactions induced by UV irradiation.

(Pb, La)TiO3 (PLT) ferroelectric thin films are one of the promising candidates for applications in dynamic random memory and pyroelectric detectors, etc. However, the chemical composition in the surface layer of thin films is usually different from that in the “bulk” region of the thin films. For instance, it has been reported that there is Pb, Ti, or La enrichment in the surface layer of the (Pb, La)TiO3 thin films. According to a numerical modeling using effective-medium theory, which was developed in our group, we discussed the effect of the surface layer on the dielectric constant of (Pb, La)TiO3 thin films. The effect of Pb, Ti, or La enrichment in the surface layer on the dielectric constant of PLT thin films was discussed. And a case of the “upgraded” and the “down-graded” thin films was expatiated and discussed.

Electrochemistry of oxides is an expanding area of oxide characterization. Although, interfacial characterization techniques including surface science methods have contributes substantially to our current understanding of the processes involved in the oxidation of metals and alloys. The characterization of subsurface zones and buried interfaces still remain a major challenge. Copper reactions with oxygen have been studied by high vacuum based techniques of AES, ELS, ISS, XPS. SIMS, LEED. STM, SEXAFS, HEIS and PFDMS and with optical methods, like UV-Vis-NIR, diffuse reflectance spectroscopy, FTIR and photoluminescence spectroscopes. However it has become evident that the processes that produce thermally and plasma grown oxide films on metals and alloys are electrochemical in nature and can be modeled by electrochemical concepts. Therefore, it is important that the oxide over layers, thin films and thick films be characterized by electrochemical means -with electrochemical methods, such as linear potential sweep voltammetry, cyclis voltammetry, galvanostatic reduction and coulometry which allow the identification of copper (I), copper (II) and copper (III) oxides. Interest in copper as a technologically important material needs to be met with greater understanding of the fundamental nature of copper oxide structures. In this study, the authors demonstrate the use of Linear Sweep Voltammetry (LSV) to study buried structures in the thermally grown oxide layers on copper. In particular, LSV can be used to detact reactions at buried interfaces. It also recognizes Cu3O2 and the decomposition of copper oxides at the metal-oxide layers on copper. In particular, LSV can be used to detect reactions at buried interface. The two key parameters that drive oxide growth and decomposition are demonstrated to be oxygen activity and the free energies of formation of the oxides. The complex nature of the oxidation of copper, as well as other metals and alloys, will be described qualitatively using the Modified Cabrera-Mott (C-M) Model. Surface studies of oxidation of metals and alloys need to be supported and complemented by other techniques such as electrochemical methods.