Narrow Results

La_0.5Ca_0.5MnO₃ (LCMO) thin films grown on SrTiO₃ substrate with different thickness were investigated using high resolution X-ray diffraction, small angle reflectivity, and atomic force microscope (AFM). All the films are demonstrated to be c-axis oriented. The surface and interface structure of the films were obtained. It was found that the surface morphology of the films strongly depends on the thickness, and the film will crack when the thickness of the film reach a critical thickness. The surface roughness of the films increases with the thickness. The interface between the films and the substrates are very clear. There exists a non-designed cap layer on the surface of the LCMO layer.

Ramp junctions have been successfully synthesized utilizing an Y_1-xPr_xBa₂Cu₃O_y barrier with a continually graded concentration of Pr. The properties of these junctions are dominated by the barrier material rather than the boundary. Also, the damaged ramp surface is excluded from the weak link region so its influence is minimized. The Josephson coupling occurs at the naturally formed S/N interfaces within the Y_1-xPr_xBa₂Cu₃O_y layer. Thus it leads to a highly transparent S/N boundary and greatly enhances the performance of the junctions. The effective thickness of the barrier can be varied even post fabrication, depending on the measuring temperature and the concentration gradient. The temperature dependence of the barrier thickness and Josephson properties were investigated and compared with those junctions with a conventional single barrier. These unique features should motivate further studies on the nature of these junctions.

A molecular dynamics simulation (MDS) was performed to investigate the characteristics of the interfacial feature between coexisting phases in equilibrium. It is considered that the interface is a fractal surface. The fractal configuration and the dimension of it were presented in the paper.

Top and bottom NiO-pinning spin valves, e.g. Ta/NiO/Co/Cu/Co/Ta and Ta/Co/Cu/Co/NiO/Ta multilayers, were investigated extensively. At the same thickness of the Cu layer, the GMR ratio for the bottom one is about 30% larger than that for the top one, which is unambiguously due to the roughness effect at the NiO/Co interface. The roughness of NiO/Co interface of the top NiO-pinning spin valve is much larger than that of the bottom one, which may be due to the deposition sequence. On the other hand, although the preferred orientation of the top NiO-pinning spin valve is more prominent than that of the bottom one, it seems not favorable to the specular reflection effect.

The mechanical properties of materials such as elastic modulus, hardness, and fracture toughness, can be measured by nanoindentation. For a thin film coated on an elastic substrate, the cross-sectional nanoindentation technique can decrease the influence of plastic deformation around the nanoindenter apex on fracture toughness for interface delamination. Considering the effect of the elastic substrate, the theory of an elastic beam bonded to an elastic foundation is further developed to obtain the energy release rate of interfacial debonding. Explicit closed-form solutions are determined, and the influence of the substrate on the energy release rate is shown graphically.

Influence of substrate-temperature on the interfacial structure of Fe₃Si/FeSi₂ layered films deposited on a Si(111) substrate were studied. Fe₃Si/FeSi₂ films with sharp interfaces were grown at room substrate-temperature. At a substrate-temperature of 300 °C, interfaces between the Fe₃Si and FeSi₂ layers were obviously unsharpened, while the crystallinity of Fe₃Si was enhanced. The compositional periodic structure was barely unsharpened and it was nearly the same as that of the films deposited at room substrate-temperature. Epitaxial growth of Fe₃Si layers across FeSi₂ layers was carried out. This substrate-temperature is the upper limit at which the heterostructure formation takes place. At 400 °C, ε-FeSi was formed due to activated interdiffusion, and the structure of Fe₃Si changed partially from B2-type to DO₃-type.

A recently proposed third order + second order perturbation density functional theory (DFT) approach is made self-contained by using a virial pressure from the Ornstein–Zernike integral equation theory as input to determine the numerical value of an associated physical parameter. An exacting examination is formulated by applying the self-contained perturbation DFT approach to a short-range square well fluid of low temperatures subject to various external fields and comparing the theoretical results for density profiles to the corresponding grand canonical ensemble Monte Carlo simulation results. The comparison seems favorable for the third order + second order perturbation DFT approach as a self-contained and accurate predictive approach. It is surprisingly found that this self-contained third order + second order perturbation DFT approach is displayed outstandingly even if a deep SW perturbation term is being accounted for by a second order perturbation expansion. A discussion is presented about potential opportunity for this perturbation scheme.

An experimental study was conducted to examine the effect of cyclic hygrothermal environment on the interfacial property of CCF300/BMI composites. The moisture weight and interlaminar shear strength of CCF300/BMI composites specimen of each stage during three absorption-desorption cyclical stages was investigated. The results showed the ILSS of composites after water absorption dramatically decreased, but it could make a comeback on the whole after removal of water.

The wetting behavior of Ti-78Cu and Ti-50Cu alloys on graphite has been investigated by the sessile drop method in high vacuum. The contact angle of Ti-Cu alloys on graphite is influenced by the wetting temperature. The wetting of Ti-78Cu and Ti-50Cu alloys on graphite is chemical wetting. The microstructure and composition of the interfacial zone of the wetting samples were analyzed by SEM, EDX and XRD. Microstructure and phase analysis reveals that inter-diffusions and interfacial reactions take place in the wetting process. The reaction products include TiC and the intermetallic compounds composed of Ti and Cu. The inter-diffusions and interfacial reactions contribute to the interfacial bonding.

The structural, electronic, optical properties and band offsets of Co₂VGa/GaAs(001) interfaces are discussed within the framework of density functional theory (DFT) using the FP-LAPW method, and the exchange-correlation potential is approximated by GGA. All interface structures are stable in the energy point of view, however the V–Ga/As case is found to be more stable than the others. A remarkable potential difference ($\mathrm{\Delta }$V) appeared in all the interfaces, so the Co₂VGa/GaAs(001) interfaces are good candidates for electron injection. In all the cases, there is no full spin polarization at the Fermi level, but high CBO and ${\mathrm{\Phi }}_p$ coefficients make them promising candidates for spin injection in the transport devices. Optical studies confirm the high metallic treatment of these interfaces as the main electron transitions had occurred in the infrared and visible regions. The real parts of the dielectric function in the x-direction indicate the different behaviors of “Co–Co/As and V–Ga/Ga” and “Co–Co/Ga and V–Ga/As” in the infrared area. In addition, the plasmon frequencies had occurred at high UV energies.

Granular materials as typical soft matter, their transport properties play significant roles in durability and service life in relevant practical engineering structures. Physico-mechanical properties of materials are generally dependent of their microstructures including interfacial and porous characteristics. The formation of such microstructures is directly related to particle components in granular materials. Understanding the interactive mechanism of particle components, microstructures, and transport properties is a problem of great interest in materials research community. The resulting rigorous component-structure-property relations are also valuable for material design and microstructure optimization. This review article describes state-of-the-art progresses on modeling particle components, interfacial and porous configurations and incorporating these internal structural characteristics into modeling transport properties of granular materials. We mainly focus on three issues involving the simulation for geometrical components, the quantitative characterization for interfacial and porous microstructures, and the modeling strategies for diffusive behaviors of granular materials. In the first aspect, in-depth reviews are presented to realize complex morphologies of geometrical particles, to detect the overlap between adjacent nonspherical particles, and to simulate the random packings of nonspherical particles. In the second aspect, we emphasize the development progresses on the interfacial thickness and porosity distribution, the interfacial volume fraction, and the continuum percolation of soft particles representing compliant interfaces and discrete pores. In the final aspect, a literature review is also provided on modeling of transport properties on the forefront of the effective diffusion and anomalous diffusion in multiphase granular materials. Finally, some conclusions and perspectives for future studies are provided.

In this study, Pb-free solders were bonded to soda-lime glass and fused quartz plates using the ultrasonic assisted soldering (UAS) method. The solder–glass interfaces were observed and analyzed to clarify the effect of the elements in the solder and glass bonding behavior. As a result, the Sn–Zn solder was bonded to glass without the intermetallic compound (IMC) layer. However, the Sn–Ag–Cu solder was not able to bond to glass even though ultrasonication was performed during the soldering process. Chemical shifts for Zn 2p and O 1s spectra were observed at the interface by X-ray photoelectron spectroscopy (XPS) analysis, which is attributed to the chemical bonding between the substrates and elements in solder alloy. In conclusion, O in the substrate and Zn in the solder were important to form the bond between the glass and solder.

In this paper, selective laser sintering (SLS) was applied to join two materials by printing Ti–6Al–4V powder on a Ti substrate without any support parts. The characteristics of the interface between the as-built Ti–6Al–4V sample and the substrate were investigated. The analysis indicates that a heat-affected zone (HAZ) and the fish-scale type were formed at the joining area. The combination of smaller grains, acicular ${\alpha }^{\prime }$ martensite, and lamellar $(\alpha +\beta )$ structures was observed inside the interface zone. The hardness value at the interface area was measured by about 320 HV which is higher than 280 HV of the substrate and smaller than 369 HV of the as-built sample. The results predict that the SLS process is a promising method for manufacturing of hybrid materials.

Coupling resonance mechanism of interfacial fatigue stratification of adhesive and/or welding butt joint symmetric and/or antisymmetric structures excited by horizontal shear waves are investigated by forced propagation analytical solutions derived by plane wave perturbation methods, integral transformation methods and global matrix methods. The influence of materials on the coupled resonance frequency is analyzed and discussed by the analytical methods. Coupling resonance of interface shear stress is a structure inherent property. Even a very small excitation amplitude at the coupling resonance frequency can result in interface shear delamination. The coupling resonance frequency decreases with the increase of interlayer thickness or shear wave velocity difference between substrate and interlayer. The results could be applied to layered and/or anti-layered structural design.

On the basis of Xu’s interfacial wave theory, the stability of dendritic growth in a convective binary alloy melt with buoyancy effect is studied using the asymptotic method. The resulting asymptotic solution of equations reveals that the stability mechanism of dendritic growth in the binary alloy melt with buoyancy-driven convection is similar to that in a pure melt. Dendritic growth is stable above and unstable below a critical stability number ${𝜀}_{\ast }$, which is determined by the quantization condition. In particular, there is a critical morphological number in the binary alloy melt. When the morphological number is less than the critical morphological number, the tip growth velocity increases, the tip curvature radius and oscillation frequency decrease, and the interface becomes thinner and smooth. When the morphological number is larger than the critical morphological number, the tip growth velocity decreases, the tip curvature radius and oscillation frequency increase, and the interface becomes fatter and rough. The result demonstrates that in a microgravity environment, there is a critical initial concentration such that below it thermal diffusion dominates, the tip growth velocity increases, the tip curvature radius and oscillation frequency decrease, and the interface becomes thinner and smooth; above it, solute diffusion dominates, the tip growth velocity decreases, the tip curvature radius and oscillation frequency increase, and the interface becomes fatter and rough.

The time evolution of the roughness is investigated for one-dimensional systems described by the Kargar–Parisi–Zhang equation. Scaling behavior of the roughness is studied, and the scaling function is obtained.

We develop a simple model of the interface exciton with an electron strongly confined in the interface plane and a hole confined in the quantum well. The main parameters of the theory are: the distance d between the interface plane and center of the quantum well, and the parameters of quantum well (the half-width a and the height V₀). Using the variational method, we obtained the binding energy and effective optical efficiency of this type of interface exciton. This model can be developed to investigate the properties of two-dimensional excitons in coupled quantum well.¹

The generalized two-dimensional Peierls–Nabarro (PN) model⁷ for studying interfaces is developed further, where an exact generalized stacking fault energy γ-surface obtained from ab initio calculations acts as an input function for the generalized PN model. Using the multiscale modeling techniques, which combines elastic theory with ab initio calculations, the structure and energy of the Al/MgO(100) interface are studied, and the effectiveness of this method is demonstrated.

The focus of this study is to experimentally investigate the effect of debonding stress, the interface between the fibers and the polymer matrix, on the damping properties of the short fiberglass reinforced polymer composites. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated and characterized for their tensile properties by varying the fiberglass loading fraction. The debonding stress was evaluated by coupling the acoustic emission technique with the tensile testing. After the determination of the debonding stress was completed, dynamic cyclic testing was performed in order to investigate the effect of debonding on the damping properties of the polymer composites. It was experimentally observed in this study that the debonding can facilitate the stick-slip friction under cyclic loadings, which then gives rise to better damping performance in the fiberglass composites.

Continuous silicon carbide fiber-reinforced silicon carbide (SiC_f/SiC) composites are promising structure candidates for future fusion power systems such as gas coolant fast channels, extreme high temperature reactor and fusion reactors, because of their intrinsic properties such as excellent mechanical properties, high thermal conductivity, good thermal-shock resistance as well as excellent physical and chemical stability in various environments under elevated temperature conditions. In this study, bonding of tungsten and SiC_f/SiC was produced by hot-press method. Microstructure analyses were performed using SEM and TEM.