CVD growth of InGaN nanowires

In this paper, the chemical vapor deposition (CVD) growth of InGaN nanowires was systematically studied. The catalyst was Au and the starting materials were Ga, In and NH₃. The samples were characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron spectroscopy (TEM), and X-ray diffraction (XRD), etc. The influence of the growth temperatures, Au thicknesses, gas flowrates and Ga and In amount on the morphology and properties of InGaN nanowires was investigated. It is found that 600 °C is a suitable growth temperature. On the substrate with Au thickness of 150 Å, helical InGaN nanowires are obtained. The change of NH₃ partial pressure and Au thickness will result in the morphology change of the samples. An increase of Ga results in shorter InGaN nanowires while an increase of In amount will lead to longer InGaN nanowires. The morphology will also change when both the amount of In and Ga were increased or reduced without changing the ratio of Ga to In.     

Slurry deposition by airbrush for selective laser sintering of ceramic components

To obtain ceramic components of high density by means of laser sintering, a high density of the green-compact is necessary. This is a problematic aspect when using ceramic granulates. We present a new procedure based on an airbrush spraying technique using slurries of high solid content. Alumina as well as zirconia slurries were developed and optimized for the process. After the layer-wise airbrush deposition of slurry, the microstructure of green, sintered and laser sintered samples were analyzed using SEM. On the basis of the high density of the green-compact achieved the described technique could be used for individual production of laser sintered structural ceramic components.     

Electrolytes for solid oxide fuel cells

The high operating temperature of solid oxide fuel cells (SOFCs), as compared to polymer electrolyte membrane fuel cells (PEMFCs), improves tolerance to impurities in the fuel, but also creates challenges in the development of suitable materials for the various fuel cell components. In response to these challenges, intermediate temperature solid oxide fuel cells (IT-SOFCs) are being developed to reduce high-temperature material requirements, which will extend useful lifetime, improve durability and reduce cost, while maintaining good fuel flexibility. A major challenge in reducing the operating temperature of SOFCs is the development of solid electrolyte materials with sufficient conductivity to maintain acceptably low ohmic losses during operation. In this paper, solid electrolytes being developed for solid oxide fuel cells, including zirconia-, ceria- and lanthanum gallate-based materials, are reviewed and compared. The focus is on the conductivity, but other issues, such as compatibility with electrode materials, are also discussed.     

Photoluminescence of 2,4,6-tris[4-(phenylethynyl)phenyl]-1,3,5-triazines dispersed in polymer films

Photoluminescence of three types of 1,3,5-triazine derivatives with three kinds of diphenylacetylene side chains was investigated. They showed quantum yields higher than 46% in chloroform, and the Stokes shift (66–114 nm) in chloroform depended on the kind of the diphenylacetylene side chain. In cast films, the three compounds gave a larger Stokes shift of 132–211 nm, suggesting formation of an excimer in the solid. The 1,3,5-triazine derivatives were dispersed in films of polymers such as polystyrene and poly(vinyl acetate), and photoluminescence of the films containing the 1,3,5-triazine derivatives was investigated. Dispersion of the compound in a poly(vinyl acetate) film still gave a rather larger Stokes shift of 128–203 nm. In contrast, dispersion in polystyrene reduced the Stokes shift to about 60 nm, revealing an excellent dispersing effect of polystyrene for the compounds.     

Gas and humidity sensors based on iron oxide–polypyrrole nanocomposites

Nanocomposites of iron oxide and polypyrrole were prepared by simultaneous gelation and polymerization process. This resulted in the formation of mixed iron oxide phase for lower polypyrrole concentration, stabilizing to a single cubic iron oxide phase at higher polypyrrole concentration. The composites in the pellet form were used for humidity and gas sensing investigations. Their sensitivity to humidity was found to increase with increasing concentration of polypyrrole. Gas sensing was performed for CO₂, N₂ and CH₄ gases at varying pressures. The sensors showed a linear relationship between sensitivity and pressures for all the gases studied. The sensors showed highest sensitivity to CO₂ gas.     

Improved mechanical behavior of Cu–Ti-based bulk metallic glass by in situ formation of nanoscale precipitates

The mechanical properties of Cu₄₇Ti₃₄Zr₁₁Ni₈, Cu₄₇Ti₃₃Zr₁₁Ni₈Fe₁, and Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ bulk metallic glasses prepared by copper mold casting are investigated. Room temperature compression tests reveal fracture strengths above 2000 MPa, Young’s moduli around 100 GPa and elastic strains slightly exceeding 2.0%. Only Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ exhibits distinct plastic strain due to a unique composite microstructure with in situ formed nanoscale precipitates in the glassy matrix.     

Preparation and characterization of NiO nanofibres via an electrospinning technique

Thin PVA/nickel acetate composite fibres were prepared by using sol–gel processing and electrospinning technique. After calcinations of the above precursor fibres, NiO nanofibres with a diameter of 50–150 nm could be successfully obtained. The fibres were characterized by SEM, FT-IR, WAXD, respectively. The results showed that the crystalline phase and morphology of NiO fibres were largely influenced by the calcination temperature.     

Saturation magnetostriction in Co–Ag films

Magnetostriction can be described as the fractional change in length of a sample depending on the state of magnetization and describes the contribution to the magnetic anisotropy energy resulting from the interaction between film strain and magnetization direction. In this paper, both longitudinal (λ_) and transverse (λ_⊥) saturation magnetostrictions of a Co–Ag granular system, prepared by molecular beam epitaxy, are studied as a function of Co concentration and temperature.     

Electrical effects generated by mechanical loading of hardened Portland cement paste

This work presents results on the effect of applied load on the electrical properties (resistivity and capacitance) of hardened cement paste. Impedance spectroscopy measurements in the high frequency region (100 kHz–15 MHz) show two time constants, one associated to the solid phase, and the other to the liquid filling the pores. The time constant associated with the liquid phase is sensitive to external loads acting on the specimen. The observed variations are explained in terms of electrolyte drag from interlaminar spaces and structure pores and vice versa. The importance of those electrolyte movements concerning structure fatigue and rebars corrosion is also discussed.