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We have grown ferromagnetic MnAs thin films on Si(001) substrates by molecular beam epitaxy. Epitaxial monocrystalline MnAs films with the growth plane of (1̄101) were obtained when the Si surface was first exposed to an As4 flux and then Mn and As4 fluxes were codeposited. It was found that the very first monolayer of As on Si(001) plays an essential role to obtain epitaxial MnAs thin films. Magnetization measurements indicate that the easy axis of the MnAs thin films is in-plane, along the [1̄1̄20] of MnAs and the [110] of Si, normal to the substrate misorientation. The M-H curve of a 300-nm-thick film shows a hysteresis with a saturation magnetization Ms of 694 emu/cm3 and a coercive field Hc of 94 Oe, when the magnetic field is applied along the easy axis.

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The growth of the AlGaSb∕InAs high-electron-mobility transistor (HEMT) epitaxial structure on the Si substrate is investigated. Buffer layers consisted of UHV/chemical vapor deposited grown Ge∕GeSi and molecular beam epitaxy-grown AlGaSb∕AlSb∕GaAs were used to accommodate the strain induced by the large lattice mismatch between the AlGaSb∕InAs HEMT structure and the Si substrate. The crystalline quality of the structure grown was examined by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Finally, very high room-temperature electron mobility of 27300cm2∕Vs was achieved. It is demonstrated that a very-high-mobility AlGaSb∕InAs HEMT structure on the Si substrate can be achieved with the properly designed buffer layers.

This work reports hygroscopic, thermal, and mechanical properties of biomass composites comprising sisal fiber reinforcing castor oil PU resin. The effects of reinforcement geometry and alkaline treatment of fibers were evaluated. In general, alkaline treatment improved quasi-static tensile properties of composites with short randomly oriented and long aligned sisal fibers, respectively. On the other hand, an adverse effect of alkaline treatment was observed in the mechanical behavior of the composite with bidirectional fabric architecture. The outstanding influence of moisture on thermo-mechanical properties of biomass composites was confirmed through thermogravimetric and differential scanning calorimetry techniques. Dynamical-mechanical thermal analysis showed increased storage modulus (i.e., stiffness) and decreased damping properties of biomass composites as compared to neat PU matrix. Dynamical-mechanical testing also detected unexpected decrease on glass transition temperature of composites in regard to the neat polymer resin; resin plasticization due to moisturized fibers and/or alkaline treatment residues was identified as probably the culprit.

The dielectric strength of films made from poly(ethylene terephthalate) (PET) coated with a thin layer of polyaniline (PANI) was studied. The PANI layer was deposited on the PET films by the `in situ' chemical polymerization method. The PANI layer of the PANI/PET films was undoped in NH4OH 0.1 M solution and re-doped with aqueous HCl solution under different pH values varying from 1 to 10. Electric breakdown measurements were performed by applying a voltage ramp and the results showed a dependence of the dielectric strength on the pH of the doping solution due to the changes in the electrical conductivity of the PANI layer. The dielectric strength of PET/PANI films treated under higher pH conditions showed an electric strength about 30% larger than the PET films, since it leads to a non-conductive PANI layer.

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