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The spectral absorption properties of ultrananocrystalline diamond (UNCD)/amorphous carbon composite films grown by pulsed laser deposition with graphite were experimentally investigated. The indirect optical band gaps estimated from the absorption spectrum were 1.0 eV and approximately 5.65 eV, which correspond to those for the amorphous carbon surrounding the UNCDs and for UNCDs themselves, respectively. In addition, the spectrum revealed a direct gap having a value of approximately 2.2 eV. One probable origin can be the presence of grain boundaries between UNCDs and amorphous carbon since they are specific to UNCD/amorphous carbon; further, its appearance is consistent with the theoretical predictions.

For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloy Fe3-xMnxSi epitaxially grown on Ge(111) by tuning the Mn composition x. Interestingly, we obtain L2(1)-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with x approximately 0.6 exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric Fe3-xMnxSi alloys become half-metallic for 0.75 < or = x < or = 1.5. We discuss the possibility of room-temperature ferromagnetic Fe(3-x)Mn(x)Si/Ge epilayers with high spin polarization.

For the two crystal materials, XaI(T1) and CsI(Sa), total, photoelectric and photopeak efficiencies are derived at several y-ray energies and crystal thicknesses. The effects of the stochastic variations in photomultiplier pulse production and of multiple Compton events on resolution are combined so as to give the modulation transfer function of gamma cameras without collimators. The effect of a hypothetical Compton discrimination on sensitivity and resolution is discussed.

The complex permittivity, permeability and electromagnetic (EM) wave absorption properties have been investigated for resin compacts containing 75 wt% composite powders of α-Fe/C(a) and Fe2B/C(a). The real and imaginary parts ( and εr′) of relative permittivity for the resin composites remained almost constant in the 0.05–20.05 GHz range. The imaginary part of the relative permeability (μr′) exhibited a wide peak in the 1–9 GHz range for α-Fe/C(a) and in the 2–18 GHz range for Fe2B/C(a). Both resin composites exhibited good EM wave absorption properties (RL < −20 dB) in the 4.4–8.3 GHz range with an absorber thickness of 1.9–3.4 mm, and in the 7.5–16 GHz range for an absorber thickness of 1.2–2.2 mm, respectively.

Ferromagnetic epitaxial B2-type Fe3Si∕FeSi2 superlattices were prepared on Si(111) at room temperature by facing target direct-current sputtering. The bilinear and biquadratic coupling constants J1 and J2 of the antiferromagnetically coupled superlattice were comparable to those of the similar superlattices using Fe layers although the saturation magnetization of Fe3Si is approximately half as large as that of Fe. The authors believe that this is due to the formation of a well-ordered quantum well in the spacers, which is mainly caused by the regular accumulation of highly oriented Fe3Si layers.

We have investigated the melt growth of Mg2Si crystal and its electrical and optical properties. Progress in Mg source purity and stoichiometric control during the growth enabled the development of a high purity Mg2Si crystal with low carrier density and a high stable Mg2Si with good doping controllability. The Mg2Si crystal grown by the pressure controlled Bridgman method using 5N purity or 6N purity of Mg source and purified PG crucible showed low electron density (∼1015 cm−3) and high electron mobility (485 cm2 V−1 s−1 at 300 K and 21900 cm2 V−1 s−1 at 40 K). Silver doping in the high purity crystals performed the low-hole density of p-type Mg2Si (∼3 × 1016 cm−3). Ionization energy of residual Al donor in the high purity crystal and Ag acceptor in the Ag doped crystals was determined as 8–9 meV and 26 meV, respectively. Indirect band gap energy Eg of approximately 0.61 eV at 300 K and 0.69 eV at 4 K were estimated by the optical transmission measurements on the high purity crystals. It is also found that the Sb-doped melt grown crystal had good power factor around room temperature (26 µW cm−1 K−2 at 270 K).

Ferromagnetic Fe3Si thin films with an extremely smooth surface morphology can be epitaxially grown on Si(111) at room temperature by facing target direct-current sputtering. The epitaxial relationship is Fe3Si(111)‖Si(111) with Fe3Si[11¯0]‖Si[1¯10]. By the application of the extinction rule of x-ray diffraction, the generated Fe3Si was confirmed to possess a B2 structure and not a DO3 one. The film showed a saturation magnetization value of 960emu∕cm3, which was slightly lower than that of bulk DO3-Fe3Si. It was observed that the magnetization easy axis was along the [11¯0] direction in the film plane.