We synthesized ACu 3 Ru 4 O 12 (A = Na, Na 0.5 Ca 0.5 , Ca, Ca 0.5 La 0.5 , La) and measured their DC magnetization, AC susceptibility, specific heat, and resistivity, in order to investigate the effects of the hetero-valent substitution. A broad peak in the DC magnetization around 200 K was observed only in CaCu 3 Ru 4 O 12 , suggesting the Kondo effect due to localized Cu 2+ ions. However, the electronic specific heat coefficients γ exhibit large values not only for CaCu 3 Ru 4 O 12 but also for all the other samples. Moreover, the Wilson ratio and the Kadowaki-Woods ratio of our samples are all similar to the values of other heavy-fermion compounds. These results question the Kondo effect as the dominant origin of the mass enhancement, and rather indicate the importance of correlations among itinerant Ru electrons.

Fe/Cr multilayers with monatomic Sn layers embedded in the Cr layers were grown epitaxially on MgO(001) substrates, and the magnetic hyperfine field at the 119Sn nuclear sites was examined using Mössbauer spectroscopy. It was found that nonzero hyperfine field is induced at the Sn sites at room temperature and that the value reduces drastically from 10 to 2 T when the Cr layer thickness decreases from 80 to 10 A. The result indicates that the Cr layers are magnetically ordered even when the thickness is very small and that the magnetic moments of Cr become smaller as the Cr layer thickness decreases.

We have studied the d-electron heavy-fermion states in ACu 3 Ru 4 O 12 ͑A = Ca, Na, and La͒ using x-ray photoemission spectroscopy and high-resolution photoemission spectroscopy at bulk-sensitive photon energy ͑7 eV͒. The bulk-sensitive photoemission measurements for A = Ca, Na, and La show that a resonancelike structure within a pseudogap commonly evolves in the low-temperature range where the Kadowaki-Woods relation holds. The origin of the resonancelike peak and the heavy-fermion behavior is basically attributed to the hybridization between the Cu 3d and Ru 4d orbitals. The A-site substitution controls the filling of the Cu 3d and Ru 4d hybridized bands. Interestingly, while the resonancelike peak position roughly follows the rigidband shift for A = Na and La, the resonancelike peak deviating from the rigid-band behavior is located just at the Fermi level as expected in a Kondo system. The difference in the resonancelike peak near the Fermi level is correlated with that in the Cu 2p core-level spectra.

High-resolution electron energy loss spectroscopy (EELS) has been applied to the study of the Si(111)(7×7)–H2O(D2O) system. At 300 K, H2O(D2O) is partially dissociated on the Si(111) surface to form the SiOH(SiOD) and SiH(SiD) species. Angle and primary-electron-energy dependences of the vibrational loss intensities were measured. Relative contributions to the vibrational excitations of the dipole, impact, and resonance mechanisms were estimated. The O–H(O–D) stretching and Si–O–H (Si–O–D) bending vibrations are partly excited by the resonance mechanism in the primary energy region of Ep ≂2–7 eV. EELS spectra of the Si(111) surface exposed to H2O(D2O) at 300 K and of the same surface heated to ∼700–900 K are presented, and surface reaction mechanisms are discussed.

We have investigated heavy-fermion behavior of the transition-metal oxides ACu 3 Ru 4 O 12 ͑A = Na, Ca, La, and their mixtures͒. It has been known that CaCu 3 Ru 4 O 12 exhibits Kondo-like behavior attributable to Cu 2+ 3d electrons, similar to that of some Ce-based heavy-fermion systems. However, we find striking suppression of the mass enhancement in CaCu 3 Ru 4 O 12 , in which the Kondo-type effect is most pronounced. Such decrease in the density of states is reminiscent of the coherent-gap formation in Kondo lattice systems. Nevertheless, the behavior can not be interpreted within the conventional Kondo picture with localized moments because the Cu electrons are apparently itinerant. The present results indicate the importance of the duality of localized and itinerant nature, found also in some other d-electron systems which exhibit the Kondo-like behavior.