Low-energy spin fluctuations are studied for the electron-doped Fe-based superconductor LaFeAs-O 1Àx F x by inelastic neutron scattering up to an energy transfer of ! ¼ 15 meV using polycrystalline samples. Superconducting samples (x ¼ 0:057, T c ¼ 25 K and x ¼ 0:082, T c ¼ 29 K) show a dynamical spin susceptibility 00 ð!Þ comparable to that of the parent samples. However, 00 ð!Þ almost vanishes in the x ¼ 0:158 sample, in which the superconductivity is highly suppressed. These results are compatible with the theoretical suggestions that spin fluctuation plays an important role in superconductivity.

The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.

Amorphous SiNx:H films were prepared by rf glow discharge of SiH4-NH3 mixtures at 300 °C, and the optical properties and the density Ns of Si dangling bonds obtained from electron spin resonance were investigated as a function of the N content x. The slope E0 in the Urbach form of the absorption coefficient and Ns, respectively, have a maximum at x=1.2 and 0.7. The dependence of E0 on x was examined on the basis of the random-bonding model including H atoms, and the dependence of Ns was connected with the optical gap and E0, according to the weak-bond dangling-bond conversion model.

Amorphous SiNx:H films were prepared by rf glow discharge of SiH4-NH3 mixtures at 300 °C, and the SiH, NH, and SiN vibrational absorptions were investigated as a function of x. The stretching absorption profiles due to SiH and SiN bonds are reproduced by a superposition of two components at around 2000 and 2100 cm−1, and of three components at around 750, 840, and 960 cm−1, respectively. The dependence of these intensities on x was examined by means of a generation probability analysis on the basis of the random bonding model including SiH and NH bonds which play an important role in the film growth mechanism.

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