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The optical, electronic and structural properties of n-type and p-type doped amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon films prepared by hot-wire chemical vapor deposition are studied. Intrinsic a-Si:H films deposited at filament temperatures Tfil∼1900 °C and 2500 °C using equal silane and hydrogen flow rates, and intrinsic μc-Si:H films deposited either by increasing the hydrogen dilution (FH2/FSiH4⩾10) or decreasing the filament temperature (Tfil∼1500 °C), were doped using phosphine (PH3, n-type doping) or trimethylboron (B(CH3)3, p-type doping). The dependence of the properties of the doped films on Tfil, dopant-to-silane gas flow ratio, and hydrogen dilution is studied. Both p-type and n-type μc-Si:H films were prepared and showed dark conductivities σd∼1  Ω−1 cm−1 and activation energies of σd, Ea,σd∼0.05 eV. N-type a-Si:H films were prepared and showed σd∼10−2  Ω−1 cm−1, Ea,σd∼0.25 eV, whereas p-type doping was less efficient, showing σd∼2×10−6  Ω−1 cm−1, Ea,σd∼0.45 eV. High growth rates (rd⩾15 Å/s) were obtained for all the a-Si:H doped samples. Tungsten (W) contamination of the amorphous samples was kept below the detection limit of the secondary ion mass spectroscopy analysis (∼5×1017 atoms/cm3) for all Tfil. The μc-Si:H samples showed W incorporation close to the detection limit (5–7×1017 atoms/cm3) for Tfil⩾1900 °C. The deep defect density dependence on the dopant-to-silane flow rate ratio was found to be consistent with the defect equilibrium doping model.

Several authors have reported the workability, mechanical properties, and durability of concrete produced with construction waste replacing the natural aggregate. However, a systematic microstructural characterization of recycled aggregate concrete has not been reported. This work studies the use of fine recycled aggregate to replace fine natural aggregate in the production of concrete and reports the resulting microstructures. The used raw materials were natural aggregate, recycled aggregate obtained from a standard concrete, and Portland cement. The substitution extent was 0, 10, 50, and 100 vol%; hydration was stopped at 9, 24, and 96 h and 28 days. Microscopy was focused on the cement/aggregate interfacial transition zone, enlightening the effect of incorporating recycled aggregate on the formation and morphology of the different concrete hydration products. The results show that concretes with recycled aggregates exhibit typical microstructural features of the transition zone in normal strength concrete. Although overall porosity increases with increasing replacement, the interfacial bond is apparently stronger when recycled aggregates are used. An addition of 10 vol% results in a decrease in porosity at the interface with a corresponding increase of the material hardness. This provides an opportunity for development of increased strength Portland cement concretes using controlled amounts of concrete waste.