Interfaces play an important role in determining the effect of electric fields on the mechanism of the formation of spinel by solid-state reaction. The reaction occurs by the movement of phase boundaries but the rate of this movement can be affected by grain boundaries in the reactants or in the reaction product. Only by understanding these relationships will it be possible to engineer their behavior. As a particular example of such a study, Mgln2O4 can be formed by the reaction between single-crystal MgO substrate and a thin film of In2O3with or without an applied electric field. High-resolution backscattered electron (BSE) imaging and electron backscattered diffraction (EBSD) in a scanning electron microscope (SEM) has been used to obtain complementary chemical and crystallographic information.

The adhesion properties were evaluated for untreated and modified cellulose (cellophane) films. Several functional groups were introduced on the film surfaces by plasma based treatments. All the films were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM was employed to study the adhesion properties using both standard silicon nitride tips as well as self-assembled monolayer (SAM) modified gold coated tips containing a variety of specific functional groups. The acetone extracted cellulose films, which are rich in –OH groups, were used as substrates. The adhesion force detected with –COOH terminated AFM tips (∼ 34.8 nN) was much larger than that with –CH3 terminated AFM tips (∼16.7 nN), which was attributed to the hydrogen bonding between –COOH and –OH functional groups. The adhesion force of –NH2 terminated AFM tips on the acetone extracted cellulose film was higher at 42.92 nN. However, after surface modification of the cellulose films with argon and oxygen based plasma treatments, the adhesion force were decreased to 17.4 and 19.4 nN respectively as a result of greatly enhanced surface roughness. Hydrazine plasma treatment also was used to introduce –NH2 groups on the film surfaces, and the strongest adhesion behavior was observed with AFM tips terminated with -COOH groups on the aminated film due to acid-base interaction. The argon and oxygen plasma treatment greatly increased the surface roughness, resulting in poor adhesion properties. Both surface roughness and chemical modification of the cellophane films affected the adhesion properties as measured by AFM force curves.

Grain boundaries in polycrystalline silicon are most likely to generate localized states in band gap. The localized states play a dominant role in determining the performance of solar cells by acting as traps or recombination center of carriers. In the present investigation, the scanning electron microscope - electron channeling pattern(SEM/ECP) method and SEM - electron back scattered diffraction pattern(SEM/EBSD) technique were applied to characterize the grain boundaries in p-type polycrystalline silicon with 99.999%(5N) in purity. Thereafter, temperature dependence of electrical activity of individual grain boundaries was measured by an electron beam induced current(EBIC) technique.

It has been found that temperature dependence of EBIC contrast at grain boundaries can change, depending on the misorientation angle the orientation of the boundary plane. The results can be explained by the difference in the position of the localized state within the band gap on the basis of the Shockley-Read-Hall statistics. The {111} ∑3 symmetrical tilt boundary has shallow states, while high ∑ boundaries have deep states. Low angle boundaries reveal high electrical activities. The EBIC contrast at low angle boundaries was found to increase with increasing misorientation angle up to 2° followed by an almost constant value. High electrical activity at low angle boundaries is probably attributed to a stress field of primary dislocations forming low angle boundaries.

Magnetic domain structures in Fe-3wt%Si alloy have been observed by a Kerr microscopy to understand the interaction between the magnetic domain wall and grain boundaries. It was found that the domain structures in the vicinity of the grain boundary depend on the misorientation angle; the high angle random boundary disturbs the magnetic domain structure more than the low angle boundary. In addition to the misorientation angle, magnetic domain structures were affected by the inclination of the grain boundary plane. Moreover, dynamic observations of rearrangement of the magnetic domain structure during magnetization revealed that grain boundaries could act as the sink and/or the source for magnetic domains.

Phase equilibria and transformations in near-equiatomic titanium aluminides lead to the formation of a lamellar structure comprising of the intermetallic phases α2(Ti3Al) and γ(TiAl). Due to the differences in lattice parameters and crystal structure, coherency stresses and mismatch structures occur at various types of semicoherent interfaces present in the material. The present paper reports an electron microscope study of the atomic structure of the interfaces. The residual coherency stresses present at the interfaces were determined by analysing the curvature of dislocation loops which were emitted from the network of interfacial dislocations. The implication of these stresses on creep will be discussed.

Transition metal-oxide interfaces suffer within their thermodynamic stability range Gibbs' adsorption and show important changes in chemical composition with oxygen activity. As a consequence, specific free interfacial energy and adhesion energy also vary with oxygen activity. Adhesion at a given non-reactive transition metal-oxide interface can then be optimised by establishing the proper oxygen activity during processing or by a post-treatment at the interface.

In the present work, the approach of Gibbs' adsorption is extended to crystalline, anisotropic (special) transition metal-oxide interfaces. It is demonstrated that interfacial energy varies with oxygen activity. The variation in energy is studied for different adsorption energies, temperatures and interfacial planes.

In this study, stressed overlayers and nanoindentation were used to study the effect of elevated temperature on the resistance to interfacial fracture of gold-chromium films in hybrid microcircuits. The samples were prepared by sputter deposition of gold films and chromium adhesive layers onto sapphire substrates. Some films were left in the as-deposited condition for testing. Others were annealed until either most or all the chromium adhesive layer had diffused from the substrate interface. Stressed overlayers and nanoindentation were then used to drive interfacial delamination and blister formation. From these blisters, interfacial fracture energies were determined using mechanics-based models modified for multilayer film effects. The results clearly showed that the chromium interlayers increased interfacial fracture energy. However, they showed an even greater increase in fracture energy after diffusion had reduced the continuous chromium adhesion layer to a solid solution of gold and chromium, suggesting two different mechanisms act to control resistance to interfacial fracture in these films.

For high-temperature performance of ceramic composites, interfaces are designed to provide toughness through debonding while resisting thermal oxidation in aggressive environments. Thus, the evaluation of interfacial properties at high temperatures is of critical importance. In recent work at USC, interfacial properties were measured at high temperatures by single fiber pushout tests. Six advanced ceramic composites were selected to perform pushout testing at 20–1000°C. Variation in interface designs and effects of thermal history were evaluated with respect to interface failure strength. At higher temperatures, the average interfacial bond strength was often higher. SEM observations were correlated with pushout measurements to evaluate the interfacial behavior.

Copper-based leadframe sheets were oxidized in a black-oxide forming solution, molded with epoxy molding compound (EMC), and the interfacial fracture toughness was measured using sandwiched double cantilever beam (SDCB) and sandwiched Brazil-nut (SBN) specimens.

Results showed that pebble-like Cu2O precipitates on the leadframe had almost no adhesion to EMC while the opposite was true of the acicular CuO precipitates. Thus, the fracture toughness of the leadframe/EMC interface was close to zero in the beginning but rapidly increased to ˜100 J/m2 as acicular CuO nucleated on the smooth-faceted Cu2O layer. Under the mixed Mode loading the fracture toughness increased parabolically with the phase angle (ψ) with minimum at ψ = 0°. For ψ < -340, interface crack kinked into EMC. Fractography analyses based on XRD, SEM and AES studies showed that the failure path along the leadframe/EMC interface varied significantly with the loading condition and the crack speed.

Intergranular fracture is a common failure mechanism for which many issues remain to be resolved. In this study we investigate intergranular fracture behavior of specially oriented symmetric tilt bicrystals of aluminum as well as the fracture behavior of a crack along the interface of a copper-sapphire bicrystal. We begin by describing briefly the structure of a symmetric tilt grain boundary which leads to a discussion of the types of issues related to intergranular fracture that can be addressed with symmetric tilt grain boundaries. We then discuss in detail one of these issues, that of the directional dependence of fracture, and present results of finite element simulations of a copper-sapphire bicrystal specimen that exhibits the directional dependence of fracture. The simulations account for the single crystal nature of the constituents and use a cohesive-zone model, for which the grain boundary energy can be varied, to simulate the fracture process along the interface. The directional dependence of fracture emerges from the simulations for a broad range of parameters in the constitutive models of both the single crystal constituents as well as the interfacial cohesive-zone.

This paper presents a study of creep in polycrystalline aluminum. The sample was deformed in a scanning electron microscope and local strain was measured by analyzing micrographs taken during the test. EBSP was used to examine grain curvature and recrystallization The results showed that tensile strain developed during the test. The strain was not constant but varied both spatially and with time. Significant grain boundary migration occurred during the test, and near a triple point a grain with a completely new orientation was formed.

The intergranular brittleness in polycrystalline materials is a source of serious problem in material processing and practical applications. To obtain a fundamental knowledge of improvement in the brittleness, we have examined the relationship between fracture behaviour and grain boundary (GB) microstructures in polycrystalline molybdenum. Quantitative analyses of GB microstructures were performed by orientation microscopy (OIM), and followed by 4-points bending tests at 77K. Thereafter, crack propagation was analyzed in connection with GB microstructures. We found the fracture stress depends on the grain size in similar manner to the Hall-Petch relation. In addition, the Hall-Petch relation also depends on the grain boundary character distribution (GBCD). The fracture stress increases with increasing the frequency of low σ GBs at constant grain size. Conversely, random GBs seem to act as weak intrinsic defects and the interconnection among them may give rise to premature failure. Therefore, the connectivity of random GBs probably becomes important as well as the GBCD to suppress the intergranular fracture.

Sintered coatings of cordierite-base glass-ceramic do not adhere readily on bare molybdenum substrates. This is due to the absence of a stable metal oxide film on the substrate that serves as a suitable transition layer between the glass-ceramic and the substrate. To address this problem, dual layers of either chromium/nickel or chromium/copper were deposited by electroplating on the molybdenum substrates. Glass powder in slurry form was then cast on the substrates using a doctor blade and sintered in a helium-hydrogen atmosphere at 950°C. The metallic interlayer structure was found to produce an excellent bond between the coating and the substrate. The adhesion of the coatings was observed to be sensitive to the thickness of the deposited metal layers. Quantitative chemical analysis of the interface region was performed to explain the difference in adhesion quality. In all instances, the fracture surface was found to occur at the chromium oxide/chromium boundary providing a clear indication that the chromium oxide layer plays an important role in enhancing the adhesion. The superior adhesion in samples with the Cr-Cu interface was attributed to Cu acting as an effective diffusion barrier to Mo. Cr however, was able to diffuse through the Cu layer enhancing the bond between Mo and Cu by alloying with the Mo. Ni was not as effective as Cu in preventing the diffusion of Mo towards the glass-ceramic coating but a thicker Cr layer still produced a strong bond. In samples where the distinct Cr layer was either too thin or non-existent, adhesion was poor possibly because the Cr oxide does not bond well to the Ni-Cr alloy layer that formed after firing.

Biaxial zero creep experiments were performed on Ni/Ag multilayer films on sapphire substrates. The equilibrium curvature was measured using a scanning laser and position sensitive photodetector. The experiments were designed to measure the free energy of Ni/Ag interfaces and to investigate their effect on the structural stability of multilayered materials. For the Ni/Ag multilayers studied, significant plastic straining occurs at temperatures above 400°C, enabling the growth stresses and thermal stresses in the multilayers to decay to zero. After a long time at elevated temperatures, the equilibrium curvature is reached for the film/substrate couple. This curvature is determined by the number and the energy of the Ni/Ag interfaces. Using this equilibrium technique, a free energy of 0.44 ± 0.03 N/m was measured for Ni/Ag interfaces at an equilibrium temperature of 550°C.

Thin film adhesion can be measured by means of the nanoindentation technique [1]. In the case of a ductile film (Cu, Al, Au, etc.) well adhered to a brittle substrate, plastic deformation in the film acts as an energy dissipation mechanism, preventing film debonding. Depositing a brittle layer of W (about 1 micron thick) on top of the film of interest increases the driving force for delamination, thus solving the problem [2]. Indentation produces circular delaminations (blisters), sometimes two orders of magnitude bigger than the indenter contact radius. Thin film adhesion was shown to scale with the film thickness, approaching the true work of adhesion of 0.8 J/m2 for Cu films less than 100 nm thick [3].

Conceptually it is important to know along what interface the fracture occurs during the blister formation. Auger electron spectroscopy (AES) has been used to determine where fracture occurs for different film systems. Cu films on SiO2 failed along the Cu/SiO2 interface. Fracture of Cu films with a 10 nm adhesion-promoting Ti underlayer occurred along the Ti/Cu interface. Significantly, Ti increased the thin Cu film adhesion by a factor of ten. Blisters were removed from the substrate, and the fracture surface was analyzed. In the case of thin Cu films, crack arrest (fiducial) marks were found upon blister removal, and represent the shape of the crack tip [4]. AFM has been used to determine the geometry of the marks. The main component of the arrest marks is carbon, which comes either from the diamond tip or from the hydrocarbons adsorbed on the newly formed surfaces in the indentation process.

In this research we used an original method to study the role of hydrogen bonding in ice adhesion and to minimize the effect of this mechanism on ice adhesion. We coated metals (Au and Pt) with a mono-molecular layer of specific organic molecules that had either strong hydrophobic properties (CH3(CH2)11SH) or strong hydrophilic properties (OH(CH2)11SH). To determine the contribution of hydrogen bonding to ice adhesion, self-assembling monolayers (SAMs) of varying degrees of hydrophobicity/hydrophilicity were created by mixing the hydrophobic and hydrophilic components. All of the SAMs were composed of similar molecules that differed only in their outermost groups, OH- and CH3-. Thus, when the SAMs were grown on the same substrate (almost atomically smooth metal coatings), any differences in their adhesion to ice were due to differences in the hydrogen bonding between the ice and SAMs. The SAMs structure and quality were examined with scanning force microscopy (SFM) and the degree of the SAM's hydrophobicity/hydrophilicity was characterized by the contact angle of water on the monolayers. We then froze water on the SAMs and measured the shear strength of the ice/SAM/metal interfaces. Possible damage to the interfaces was examined with SFM after the ice had melted. We found a good correlation between the contact angle of water and the ice adhesion strength and determined the fraction of ice adhesion caused by hydrogen bonding.

A continuum Peierls model of a screw dislocation being pushed through an interface and an atomistic EAM study of dislocation transmission across a [0 0 1] Al-Ni interface suggest that core spreading into the interface and misfit dislocations in the interface are both potent effects that can significantly increase barrier strength of interfaces.

In order to evaluate the practical strength of a joint and its fracture mode, it is important to find the stress distribution near the edge of the interface by analyses of strength and fracture. The index of stress singularity based on theoretical analysis is a useful tool to indicate the stress distribution.

In this paper, investigations on the evaluation of the practical strength of bonded dissimilar materials based on the stress singularity are carried out. The secant stiffness module, which was used for plastics analysis, was applied to the evaluation of thermal elastoplastic behavior near the interface. Spherical conditions of the interface shape were used for the evaluation of stress behavior and the experiment of bonding strength. The relationship between the index of stress singularity, λ, and the practical strength of the bonded TiB2-Ni system was investigated by comparing theoretical λ, which was determined by substituting the secant stiffness module into Bogy's eigenequation, with the practical strength in the edge angle of the interface between 60° and 90° The correlation factor of the relationship between λ and the practical bonding strength of the TiB2-Ni system was found positive. These results show that the structural design of a geometrical interface which is getting a higher strength joint based on the index of stress singularity is verified experimentally.

The delamination behavior of thermal barrier coatings (TBC) in transition ducts of inservice used combusters has been characterized using a protruded four-point bending testing technique recently developed by the authors. A reinforced protruded TBC specimen allowed the formation of TBC cracks adjacent to the TBC/alumina interface in a similar mode to inservice TBC failure. Finite element stress analysis showed that a peak transverse stress appeared in a protruded TBC part away from the interface and a large principal tensile stress operated on planes inclined to the interface. It was found that the onset of near-interface TBC cracks in the protruded TBC specimen did not occur under the high transverse and principal tensile stresses. The critical local tensile stress for the onset of TBC cracks near the interface, estimated to be 127 MPa, was lower than that of the near-center TBC. The near-interface TBC cracking behavior in the protruded TBC tests is discussed in light of the residual stress distribution and stressed volume effect.

This paper will present details of interfacial design, structure and properties in a variety of different nanocomposites. The materials discussed include co-sputtered nanoscale Ag/SiO2 and Ag/Si thin films which exhibit novel optoelectronic behaviour, and melt spun nanoscale Pb/Al and Sn/Al sheets which exhibit novel mechanical behaviour. The relationships between processing, structure and properties are discussed for these unusual materials systems.