Applying the glass fluxing method, a peritectic Fe–Ni alloy with a composition of Fe–4.35 at.% Ni was undercooled. It was found that when the initial melt undercooling (ΔT) is smaller than 130 K, the overall thickness of the peritectic phase formed in peritectic reaction (PR) and peritectic transformation (PT) decreases as ΔT increases. The nonequilibrium effects of the primary solidification on PR and PT in the undercooled peritectic Fe–Ni alloys were illuminated. With increasing ΔT, since the driving forces for PR and PT change slightly, the decrease of the overall thickness of the peritectic phase formed in PR and PT can be mainly ascribed to the reduced transformation time for PT.

The initial stage of oxidation of Ti45Al7Nb0.4Y alloy (at.%) oxidized at 900 °C in air was investigated by using x-ray photoelectron spectroscopy and Auger electron spectroscopy. Experimental results revealed that YAl2 segregated along the grain boundaries preferentially oxidized to Y2O3 and Al2O3 due to strong affinity of Y to oxygen. Oxides grew faster at the grain boundaries than in lamellar colonies. As a result, Y and Al oxides pegs protruded into the substrate, which can increase the contact areas of oxide scale and substrate. Moreover, inward diffusion of oxygen more easily occurred along the grain boundaries. As a result, it promoted the external oxidation of Al within the grains due to lower inward diffusion flux of oxygen. And coarse-grained Y2O3 blocked the cationic intergranular diffusion. Therefore, Y addition can effectively enhance the Al2O3 layer and suppress the TiO2 outermost layer.

Van der Waals (vdW) interactions play a prominent role in the structure and function of organic/organic and organic/inorganic interfaces. Their accurate determination from first principles, however, is a notoriously difficult task. Recently, a surge of interest in modeling vdW interactions has led to promising theoretical developments. This article reviews the state-of-the-art of describing vdW interactions by density-functional theory with respect to accuracy and practicability. The performance of the different methods is demonstrated for simple systems, such as rare-gas dimers and small organic molecules. The nature of binding at organic/inorganic interfaces is then exemplified for the perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) molecule at surfaces of coinage metals. This fundamental system is the best-characterized organic molecule/metal interface in experiment and theory. We emphasize the crucial importance of a balanced description of both geometry and electronic structure in order to understand and model the properties of such systems. Finally, the relevance of vdW interactions to the function of actual devices based on interfaces is discussed.

Oxidation-induced stress evolutions in Ta thin films were investigated using ex situ microstructure analyses and in situ wafer curvature measurements. It was revealed that Ta thin films are oxidized to a crystalline TaO2 layer, which is subsequently oxidized to an amorphous tantalum pentoxide (a-Ta2O5) layer. Initial layered oxidation from Ta to TaO2 phases abruptly induces high compressive stress up to about 3.5 GPa with fast diffusion of oxygen through the Ta layer. Subsequently, it is followed by stress relaxation with the oxidation time, which is related to the slow oxidation from TaO2 to Ta2O5 phases. The initial compressive stress originates from the molar volume expansion during the layered formation of TaO2 from the Ta layer, while the relaxation of the compressive stresses is ascribed to the amorphous character of the a-Ta2O5 layer. According to Kissinger's analysis of the stress evolution during an isochronic heating process, the oxygen diffusion process through the a-Ta2O5 layer is the rate-controlling stage in the layered oxidation process of forming a a-Ta2O5/TaO2/Ta multilayer and has an activation energy of about 190.8 kJ/mol.

BaCo1/3Nb2/3O3 ceramics, with a high density and a similar, high degree of 1:2 B-site cation ordering, exhibit very different quality factors, Q. The ceramics exhibit p-type behavior with higher conductivity and lower Q for samples processed in O2 as compared with those processed in air. It is proposed that unavoidable Co loss during high-temperature ceramic processing leads to p-type doping that must be compensated by oxygen vacancies to impede hole formation. The composition exhibiting only intrinsic conduction and optimized Q is not achieved with processing in atmospheric oxygen due to filling of oxygen vacancies and hole formation during cooling.

Nitrogen-doped titania with a unique two-level hierarchical structure and visible light photocatalytic activity is reported. Thus, nitrogen-doped titanium oxide microrods decorated with N-doped titanium oxide nanosheets were synthesized by a hydrothermal reaction in NH4OH and postcalcination. During the calcination, the in situ incorporation of nitrogen atoms of ammonium ion into titania lattice was accompanied by the structural evolution from titanate to anatase titania. The morphological and structural evolution was monitored by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TGA/DTA), Raman, Fourier transform infrared (FTIR), x-ray absorption near edge structure (XANES), x-ray photoelectron spectroscopy (XPS), and adsorption isotherms. The N-doping brought visible light absorption, and the material exhibited high photocatalytic activity in the decomposition of Orange II under visible light irradiation (λ ≥ 400 nm), especially when it was loaded with 1 wt% Pt as a cocatalyst.

The strain rate dependence of anisotropic compression behavior in porous iron with cylindrical pores oriented in one direction was investigated. Through high strain rate (˜103 s−1) compression tests along the orientation direction of pores using the split Hopkinson pressure bar method, it was shown that the stress–strain curve exhibits a unique plateau-stress region where deformation proceeds with almost no stress increase. The appearance of the plateau-stress region is related to the buckling deformation of the iron matrix and provides superior energy absorption. However, for the middle (˜10−1 s−1) and low strain rates (˜10−4 s−1), compression along the same direction produces no such plateau region. In fact, in contrast to compression in the parallel direction, compression perpendicular to the orientation direction of pores produces no plateau-stress regions in any of the three strain rates.

Heteroepitaxial ZnxMg1−xO thin films were grown on lattice-matched MgO (100) substrates using radiofrequency plasma-assisted molecular-beam epitaxy. High-quality epilayers with zinc concentrations ranging from x = 0 (MgO) to x = 0.65 were grown and characterized optically, structurally, and electrically. The ZnxMg1−xO films were found to maintain the rocksalt cubic (B1) crystal structure for concentrations z < 0.65, with a linear dependence of lattice constant on Zn concentration. X-ray diffraction (XRD) also revealed the emergence of phase segregation into wurtzite (B4) phase for the highest concentration film. The band gap energy of the films was successfully varied from 4.9 to 6.2 eV (253–200 nm), showing a linear relationship with Zn concentration. The strictly cubic films exhibit roughness on the order of 10 Å and resistivities of approximately 106 Ω·cm.

Systematic microstructural and mechanical investigations of the Fe84.3Cr4.3Mo4.6V2.2C4.6 alloy cast under special manufacturing conditions in the as-cast state and after specific heat treatment are presented to point out that the special manufacturing of the alloy led to high compression strength (up to 4680 MPa) combined with large fracture strain (about 20%) already in the as-cast state. One select chemical composition of the alloy, which was mentioned previously [Kühn et al., Appl. Phys. Lett.90, 261901 (2007)] enhanced mechanical properties already in the as-cast state. Furthermore, that composition is comparable to commercial high-speed steel. By the special manufacturing used, a high purity of elements and a high cooling rate, which led to a microstructure similar to a composite-like material, composed of dendritic area (martensite, bainite, and ferrite) and interdendritic area (e.g., complex carbides). The presented article demonstrates an alloy that exhibits already in the as-cast state high fracture strength and large ductility. Furthermore, these outstanding mechanical properties remain unchanged after heating up to 873 K.

The AlGaN-based ultraviolet (UV) light-emitting diode (LED) structures with AlN as buffer were grown on sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE). A series of cathodoluminescence (CL) spectra were measured from the cross section of the UV-LED structure using point-by-point sampling to investigate the origins of the broad parasitic emissions between 300 and 400 nm, and they were found to come from the n-type AlGaN and AlN layers rather than p-type AlGaN. The parasitic emissions were effectively suppressed by adding an n-type AlN as the hole-blocking layer. Electroluminescence (EL) and atomic force microscopy (AFM) measurements have revealed that the interface abruptness and crystalline quality of the UV-LED structure are essential for the achievement of the EL emissions from the multiple quantum wells (MQWs).