Antiferromagnetic excitations in single crystals of Pr2 Ce Cu04~, Nd, "Ce"Cu04~, and Sm2 Ce Cu04~were investigated as a function of Ce concentration using Raman scattering at room temperature.The introduction of electrons by Ce doping significantly broadens the twomagnon peak in the B&g mode, indicating that zone-boundary magnons become damped with increasing Ce concentration. The existence of broad spin-pair-excitation spectra in the B,~and B2g modes at x =0.15 suggests that the short-range spin fluctuations persist in these electron-doped superconductors. The energy of the spin-pair-excitation peak in Pr~"Ce Cu04~is not affected by doping up to x=0.2. This is similar in behavior to the Sm& "Ce Cu04~system up to x=0.17.The absence of softening of the short-wavelength magnons in these systems is in marked contrast to the magnon softening behavior in La2 "Sr"Cu04~. The Raman spectra in Pr2 Ce Cu04 make no distinction between the superconducting and the metallic regions. The highly damped magnetic-excitation spectra support the picture that the spin-spin correlation length in the present systems decreases gradually with increasing Ce concentration.

We have investigated chemical states and band offsets in SiN∕Si by photoemission spectroscopy and x-ray absorption spectroscopy. N1s photoemission spectra in SiN for three kinds of layer-thickness films are fitted by a single component, suggesting that a nitrogen atom is surrounded by three silicon and nine nitrogen atoms for the first and the second nearest neighbor, respectively. Valence-band offsets between SiN and the Si substrates are determined to be 1.6 eV using valence-band spectra by subtracting the contribution from Si substrates. Band gap of SiN is estimated to be 5.6–5.7 eV from valence-band, N1s core level, and NK-edge-absorption spectra. Furthermore, time-dependent measurements of N1s photoemission spectra reveal that the x-ray irradiation time is a significant factor to determine the precise valence-band offsets excluding the differential charging effects.

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We have investigated chemical-state-resolved in-depth profiles of SiO 2 /SiN stack films using angular-dependent photoemission spectroscopy and maximum-entropy method (MEM). MEM enables to reproduce the gate-stack structure from angulardependence of core-level spectra, and it is utilized to determine atomic concentration of the interfacial layer. In-depth profile of the SiO 2 /SiN stack film reveals that the SiO 2 layer is distributed in the surface region and that the SiN layer is partly oxidized, which is well related to nitrogen bonding states analyzed by angular-dependence of N 1s core-level spectra.

We have investigated the mechanism for silicidation by chemical reactions at polycrystalline-Si (poly-Si)∕HfO2∕Si gate stacks by annealing in ultrahigh vacuum using photoemission spectroscopy and x-ray absorption spectroscopy. Si 2p, Hf 4f, and O 1s high-resolution photoemission spectra have revealed that a Hf-silicide formation starts at as low temperature as 700°C and that a Hf silicate is also formed at the interface between poly-Si electrodes and HfO2. The metallic Hf silicide is formed at the interface between HfO2 and Si substrates, which changes the band offsets on Si substrates. We have found that poly-Si electrodes promote the interfacial reaction between HfO2 and Si substrates, while the crystallization in a HfO2 layer is independent of the silicide formation. The silicidation mechanism based on photoemission spectra is also confirmed from the thermodynamical analysis considering the Gibbs’ free energy.