We present the results of detailed chemical and structural characterization of the VO2/Al/Si(100) thin film heterostructures fabricated by chemical vapor deposition and physical vapor deposition methods. The presence of the thermochromic behavior in the VO2 layer around 68°C and its correlation with the layer composition and structure are discussed. The study compares the structural and chemical properties of the two types of thin VO2 layers: one which exhibits a metal-insulator phase transition around 68°C, and another which fails to undergo the temperature-induced transition. The study of interfaces was carried out by transmission electron microscopy, and showed the existence of an aluminum oxide interfacial layer between VO2 and Al for the samples with the metal-insulator phase transition. The smooth VO2/Al interface and the presence of more than one VO2 monoclinic polytypes were observed for the CVD films exhibiting no phase transition.

The electronic structure of the bulk TiO2 in the rutile structure, geometric and electronic structure of two dimensional titanium oxide and lithium titanium oxide layers have been investigated. Not only density functional approach within the local density approximation (LDA) but also GW approach has been tried and the LDA electronic band structures have been compared with the quasiparticle energy structures. The unit cells which include a few atomic layers and open space of more than several angstroms have been used as geometric model of the surface. The surface geometric relaxation has been investigated by the Car-Parrrinello quantum molecular dynamics method based on the plane wave basis with pseudo potential within Becke-Lee-Yang-Parr (BLYP) generalized gradient approximation (GGA) and the quasiparticle energy structure has been obtained by the GW method based on the linearized muffin tin orbital (LMTO) basis with the atomic sphere approximation (ASA). Good applicability of this hybridized first principles approach has been confirmed.

The microstructure of TiO2/SiO2 multilayer optical filters has been investigated in detail by cross-sectional transmission electron microscopy and related to their optical properties and stability. The amorphous TiO2 layers in the as-deposited multilayers are found to consist of nanocolumns and intercolumnar regions with non-stoichiometric or lower density material. In humid ambients this microstructure absorbs moisture which causes a shift in the absorption edge of the filters. Upon annealing the TiO2layers are found to recrystallize into the low-temperature anatase modification which leads to significantly improved stability of the optical properties of the filters.

The cathodic kinetic processes on a highly oriented LSCO thin film electrode supported on YSZ(100) surface were studied with a 3-probe ac impedance method under varying bias potential and annealing temperatures. Three distinctive features observed in the impedance spectra were assigned to contributions from the ionic conduction of the YSZ electrolyte, the ionic transfer at the LSCO/YSZ interface, and the oxygen exchange on the LSCO electrode surface. The changes of the three features with respect to the annealing history and bias potential were measured. The impedance data were analyzed using an equivalent circuit model: (RelCel)(RinterfaceQinterface)(RsurfCsurf).

Tetragonal zirconia, (t′–ZrO2) a ferroelastic material, readily forms domains with domain boundaries on {011}. For example, by compressing a single crystal along [100] the formation and movement of such domain walls has been demonstrated experimentally. We have made atomistic simulations of a domain wall with a self-consistent tight-binding model which cor- rectly reproduces both the high temperature tetragonal to cubic phase transition exhibited by zirconia, and its low temperature monoclinic phase. We analyse the results of our simulation, in particular the width of the domain wall, in terms of a Landau–Ginzburg theory in which the order parameter measures the degree of tetragonality of the lattice

Bulk crystals of Si0.4Ge0.6, grown using the vertical Bridgman method, were oxidized at 800 °C for 1 h using oxygen in dry oxidation and a stream of de-ionized water in wet oxidation. Single-like and polycrystalline Si0.4Ge0.6samples were used. The oxidized samples were analyzed using x-ray photoelectron spectroscopy to determine the chemical states of the Si and Ge in the oxide. In the sample oxidized using a dry ambient, the oxide layer consisted mainly of SiO2, and GeO2 formed the subsurface area only. This can be accounted for by the differences in the formation of the free energies of the SiO2 and GeO2. In wet oxidation, the oxide layer had a mixed structure consisting of SiO2 and GeO2. To understand the oxide formation mechanisms in the wet oxidation process, an introduction of a chemical bond manipulation explained the formation of the mixed structure.

The structural integrity of oxide/metal interfaces is important in many applications. While most attention has focused on the debonding of oxide/metal interfaces by conducting strength and fracture toughness tests, very few investigations have looked at time dependant failure of interfaces under cyclic or static loading. Tests have been conducted on sandwich specimens consisting of 5 - 100 micron thick aluminum layers bonded between either polycrystalline or single crystal Al2O3 to determine cyclic fatigue-crack growth, as well as static loaded moisture- assisted crack-growth, properties of Al/Al2O3 interfaces. Under cyclic loading, crack growth was observed to occur predominantly by interfacial debonding, but was also observed to make excursions into the Al2O3. Static loading in a moist environment also caused interfacial cracks to deviate into the Al2O3 or alternatively to arrest. Due to the poor crack growth resistance of the Al2O3, cracks leaving the interface grew at faster rates than those at the interface. Trends in crack trajectories and crack growth rates are explained in terms of the degree of plastic constraint in the aluminum layer, the modulus mismatch, and the effects of environmental mechanisms.

The Si/SiO2 interface is attracting new interest as gate dielectrics in MOS devices become ultra thin. In this paper, the impact of pre-gate cleaning on the morphology of the Si/SiO2 interface and the electrical performance of CMOS gate oxides has been systematically investigated. Using the High-Resolution Transmission Electron Microscopy (HRTEM) technique, we observed the Si/SiO2 interface at an atomic level. We have found a direct experimental relationship between the pre-gate cleaning scheme, Si/SiO2 interface morphology, and the electrical properties of CMOS gate oxides. When the ratio of H2O2:NH4OH ≥ 1.45, the roughness of the Si/SiO2 interface was dramatically improved, which, in turn, increased the Charge-to-Breakdown to an ideal value.

It has been shown for the first time how atmospheric oxygen eff ects maj or electrical characteristics of MBE grown CdTe thin f ilms and CVD grown p-/p+ Si junction. I-V and C--V barrier-like characteristics indicate presence of CdO/CdTe quasi-3D microheteroj unctions and complexes at p/p+ interface.

Three-dimensional atom-probe (3DAP) microscopy permits the atom-by-atom reconstruction of a small volume (typically 10 nm × 10 nm × 100 nm) of a material with respect to both the positions and chemical identities of individual atoms. It is, therefore, ideally suited for the study of solute segregation at internal heterophase interfaces. We present recent results of a 3DAP microscopy study of solute segregation at ceramic/metal (C/M) heterophase interfaces prepared by internal oxidation. In particular, results on the CdO/Ag(Au) (where Au is the segregating species) system are presented. In the 3DAP atomicreconstructions, the interfaces of nanometer-size CdO ceramic particles are delineated as Cd isoconcentration surfaces. The distribution of the segregating species as a function of distance to the isoconcentration surfaces is determined with the proximity histogram (or proxigram) method. Two interfaces are investigated in detail. The first shows no appreciable Au segregation, while the second exhibits segregation with a Gibbsianinterfacial excess of 1.65 nm-2 at 650°°C.

The atomic-scale structure of grain boundaries (GBs) in yttria-stabilized cubic zirconia (YSZ) was investigated by high-resolution electron microscopy (HREM). Non-stoichiometric oxides have found a wide range of applications and therefore it is of importance to explore the role of GBs and their atomic-scale relaxation modes. [001] and [110] tilt GBs were examined by HREM in highly textured thin films of YSZ grown by metal-organic chemical vapor deposition (MOCVD). In addition, a special technique was developed to also allow the HREM study of twist and general GBs. GBs and triple junctions show quite dense arrangements of cation atomic columns. The GB core structures in YSZ can be contrasted to the more open structures in stoichiometric cubic oxides, such NiO, which are characterized by a relatively large GB excess volume. This appears to be due to several factors, including the necessary rearrangement of the oxygen sublattice near GBs in a CsCl2 type structure, the redeployment of oxygen vacancies near GBs, and the segregation of Y to the GB. Relative to stoichiometric oxides, such mechanisms provide additional degrees of freedom for atomic relaxations at GBs and the development of low-energy GBs. These additional relaxation modes, which result in GB cation arrangements more akin to metallic systems, are also reflected by Burgers vector dissociations observed in low-angle YSZ GBs.

The atomic arrangement and electronic structure in the vicinity of Ni(111)- ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) interfaces have been studied by atomistic simulation and by first-principles Density Functional theory. “Depth Profiling” is carred out in both methodologies, to determine modifications of cohesive energy and electron distribution of atomic layers from the interface plane. The energy profiling results show the interface consists of only a few atomic layers. Simulation results and electron density analyses are in good agreement with High Resolution Spatially Resolved Electron Microscopy data.

Quantitative X-ray analysis allows the investigation of yttrium-doped grain boundaries. In the present study well-defined bicrystal interfaces were characterized. The quantitative comparison of segregation at different bicrystals requires a correction of artifacts in the X-ray spectra due to mass absorption, fluorescence, and beam spread. Mean grain boundary excess values of 3 Y/nm2 and around 5 Y/nm2 were found at a ∑17 and ∑37 symmetrical grain boundary, respectively. Additionally, with the ∑17 bicrystal YAG precipitation and presence of silicon was found.

Surface defects are important in oxide surface chemistry, because they change not only the surface geometric structure, but also affect the local electronic structure. Scanning Tunneling Microscopy (STM) images with atomic-scale resolution, in combination with area-averaging surface spectroscopies, is an ideal tool to study local surface defects and their relationship to surface reactivity. We report STM results onTiO2(110) surfaces which show the surprising influence of bulk defects on surface properties. Thereduced crystals used in this and other surface science studies contain Ti interstitials and oxygen vacancies. Re-oxidation at elevated temperatures results in the growth of additional TiO2 layers with Ti coming from the bulk of the crystal and O from the gas phase. This often result in partially incomplete surface structures with many undercoordinated atoms. The esorption behavior of elemental S, dosed at room temperature, depends on the reduction state of the sample. This is explained by a mechanism where desorption froma weaklybound precursor state competes with the availability of new adsorption sites in the form of oxygen vacancies which migrate from the bulk to the surface.

In the last few years, the combination of atomic-resolution Z-contrast microscopy, electron energy loss spectroscopy and first-principles theory has proved to be a powerful means for structure property correlations in complex materials1. Here we demonstrate the effectiveness of this combined approach by demonstrating the origins of electrical activity at grain boundaries in the prototypical perovskite SrTiO3 and the high-temperature superconductor YBa2Cu3O7-x, materials that are closely related in structure. We show, both experimentally and theoretically, that grain boundaries in SrTiO3 are intrinsically non-stoichiometric. Electron energy-loss spectroscopy (EELS) provides direct evidence of non-stoichiometry, in agreement with total- energy calculations that predict non-stoichiometric grain boundaries to be energetically favorable. The predicted structures are consistent with atomic-resolution Z-contrast micrographs. These results provide a consistent explanation of the grain boundary charge that was previously inferred from electrical measurements, and provides a microscopic explanation of the resulting “double-Schottky barriers”. We also present experimental evidence for non-stoichiometry at grain boundaries in the high-temperature superconductor YBa2Cu3O7-x, where the same phenomenon explains the observed exponential reduction of critical currents with grain boundary misorientation.

A modified-embedded-atom-method (MEAM) potential is derived for the ternary system Al-O-Nb in order to simulate the model oxide-metal interface sapphire-niobium. In the present work, MEAM parameters for Al and O given by Baskes were adopted, and the parameters for Nb are adjusted to match experimental data for pure Nb and calculated properties for Nb oxides and aluminides. The properties for niobium oxides and aluminides were obtained from local- density-functional-theory (LDFT) calculations. The resultant potential was tested in simulations for the Nb(111)/α -alumina(0001) interface. MEAM predictions of the work of separation and the interlayer relaxations for two interface terminations are in excellent agreement with LDFT calculations. The MEAM potential therefore appears suitable for large-scale computer simulation of oxide-metal interface properties.

On the basis of new experimental results a previous proposed correlation between the optical band gap of oxides and the difference of electronegativity of their constituents is extended to mixed crystalline and amorphous TiO2-Fe2O3 (d,d-metal oxides) as well as to amorphous passive films grown on Al-Ta, Al-Ti, Al-Nb and Al-W alloys (sp,d-metal oxides). Moreover in analogy with previous results on anhydrous oxides, a correlation is proposed between the optical band gap of hydroxides and the electronegativities of their constituents after substituting the electronegativity of hydroxilic group to that of the oxygen. Like in the case of anhydrous oxides, two different interpolation lines have been found for sp-metal and d-metal hydroxides, respectively.

Rutherford backscattering spectrometry and channeling techniques have been used to investigate the crystalline quality and interfacial properties of epitaxially grown CeO2 and Ce0.7Zr0.3O2 films on yttria-stabilized ZrO2(111) substrates. Both films appear to have high crystalline quality with minimum yield of Ce in the CeO2and Ce0.7Zr0.3O2 films determined to be 4.7% and 12.1% respectively. Visibility of more Ce atoms to the ion beam at the interface compared to the bulk of the film indicates that both films show significant disorder at the interface. The normalized angular yield curves obtained from Ce and Zr indicate that the Ce atomic rows in the CeO2 film are parallel to the Zr atomic rows in the substrates. Approximately 88% of the Zr atoms substitutionally occupy the Ce cation lattice sites in the Ce0.7Zr0.3O2 film.

We present secondary ion mass spectrometry (SIMS) study results on interfaces of LiNbO3 based optoelectronic devices, which have been performed in order to examine the cause of device failures. The devices are widely used in current high-speed optical fiber communication systems, and such investigation from a materials-viewpoint is important to improve the device quality. Especially, the device long-term stability is strongly affected by alkali-contaminants diffused into the SiO2 buffer layer of device, and here we confirmed that an adoption of common Si3N4 passivation is effective in preventing the process-induced contamination without any influence to device performance.

Atomic Force Microscopy (AFM) is used to characterize fracture surfaces in silicon oxide / silane adhesion promoter / BCB polymer systems. Fatigue striations were found on some samples, and these were correlated with the crack growth rate per fatigue cycle. X-ray Photoelectron Spectroscopy (XPS) was used to identify the species present on each surface, and it was found that striations only form when the fracture path is through the polymer.