Degenerate electrical conductive and excitonic photoluminescence properties of epitaxial films of wide gap p-type layered oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=S or Se)

Electrical and photoluminescence properties were investigated for epitaxial films of layered oxychalcogenides, LnCuOCh (Ln=La, Pr, and Nd, Ch=S or Se). Epitaxial films of Mg 10 at.% doped LaCuOS_1-xSe_x are the first demonstration of degenerate conduction with high hole concentration >10²⁰ cm^-3 in wide gap p-type semiconductors. Ion substitution varied the excitonic emission energy from 3.21 eV to 2.89 eV while lanthanide and chalcogenide ion substitutions displayed the opposite tendency against cell volume. These unique properties are discussed with respect to the electronic structure originating from the layered crystal structure. PACS 72.20.-i; 73.50.-h; 78.55.Hx; 78.66.-w     

Heteroepitaxial growth of wide gap p-type semiconductors: LnCuOCh (Lr=La, Pr and Nd; Ch=S or Se) by reactive solid-phase epitaxy

Heteroepitaxial thin films of Cu-based oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=mixture of S and Se), were fabricated and their resulting film structures were characterized. A reactive solid-phase epitaxy method successfully yielded heteroepitaxial films on MgO(001) substrates. A high-resolution electron microscopic examination of a LaCuOS film revealed a sharp film-substrate interface. Four-axes high-resolution X-ray diffraction measurements revealed that crystalline lattices in the films are fully relaxed and that the crystallographic orientation is (001)[110] LnCuOCh || (001)[110] MgO. Furthermore, systematic variations in the lattice constant by lanthanide or chalcogen ion substitutions were observed. PACS 81.10.Jt; 81.15.-z; 81.15.Np; 68.55.-a; 81.20.-n     

Suppression of Gamow-Teller and M1 transitions in deformed mirror nuclei 25Mg and 25Al

The mirror nuclei ²⁵Mg and ²⁵Al are expected to have very similar structures. The Gamow-Teller (GT) transitions from the ground state of ²⁵Mg to the excited states in ²⁵Al were studied by high-resolution measurements of the ²⁵Mg( ) charge-exchange reaction at and at 140 MeV/nucleon. Assuming the usual selection rule for the spin-isospin-type GT transitions, the states with , and 7/2 ⁺ should be excited. However, of the more than ten states with these values below 6 MeV excitation energy, only the 5/2 ⁺ ground state and the 7/2 ⁺ , 1.613 MeV state in ²⁵Al were strongly populated, while all other states were strongly suppressed. The analysis of M1 transitions in ²⁵Mg also suggested a very similar feature for the analogous M1 transitions. Both ²⁵Mg and ²⁵Al are known to be largely deformed, and most low-lying states can be interpreted in terms of one-particle quantum numbers in the deformed potential and the associated rotational spectra. The observed suppression can be explained in terms of the K quantum number selection rules that are inherent to axially deformed nuclei.-1Received: 18 July 2003, Published online: 18 December 2003PACS: 21.10.Re Collective levels - 21.60.Ev Collective models - 25.55.Kr Charge-exchange reactions - 27.30. + t H. Fujita: Present address: Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan.J. Kamiya: Present address: Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan.T. Wakasa: Present address: Department of Physics, Kyushu University, Higashi, Fukuoka 812-8581, Japan.     

Simulation study of angle-resolved photoemission spectra and intramolecular energy-band dispersion of a poly(tetrafluoroethylene) oligomer film

Theoretical simulations of the angle-resolved ultraviolet photoemission spectra (ARUPS) for the oligomer of poly(tetrafluoroethylene) [(CF(2))(n); PTFE] were performed using the independent-atomic-center approximation combined with ab initio molecular orbital calculations. Previously observed normal-emission spectra for the end-on oriented sample (with long-chain axis perpendicular to the surface) showed the incident photon-energy (hnu) dependence due to the intramolecular energy-band dispersion along the one-dimensional chain, and the present simulations successfully reproduced this hnu dependence of the observed spectra. We employed the experimentally observed helical structure for PTFE oligomers for the simulations. We also calculated the density of states (DOS) for the planar zigzag structure, and examined the changes in the electronic structure due to the difference in the molecular structure by comparing the DOS for the helical and planar zigzag structures. Only a small change in the DOS was found between these structures, showing little change of the electronic structure between these conformations. We also evaluated the inner potential V(0), which is the parameter defining the energy origin of the free-electron-like final state, and checked the validity of the value of -10 eV estimated in our previous study using the experimentally observed hnu dependence of the peak intensity. The estimation of V(0) was performed by pursuing the best agreement between the energy-band dispersion [E=E(k)] relation along the chain direction obtained from the simulated spectra and the experimentally deduced one. An excellent agreement in the topmost band was achieved when the assumed inner potential V(0) was set at about zero. This value of V(0) is much different from the value of V(0)=-10 eV in the previous study, suggesting the invalidity of the previous assumption at the estimation of V(0) from the peak intensity variation with hnu. Using the presently obtained V(0), we could derive more reliable E=E(k) dispersion relation from the observed ARUPS spectra. The comparison of this newly derived relation gave good agreement with theoretically calculated E=E(k) relations, in contrast to the poor agreement for the previous results with V(0)=-10 eV.     

Submitochondrial distribution of basic drugs in the isolated perfused lung

To clarify the mechanism by which basic drugs accumulate in the lung mitochondria, the binding selectivity of drugs to different submitochondrial components of the perfused rat lung was examined. The accumulation of basic drugs was the highest in the mitochondrial outer membrane fraction. The drug accumulation in this fraction increased with lipid solubility and was dose-dependent. It appears then that selective binding sites for basic drugs are present in the mitochondrial outer membrane.     

Gas transport in poly [bis(trifluoroethoxy) phosphazene] above the T(1) transition

Gas permeation measurements were performed by the time-lag method for 13 gases in poly [bis(trifluoroethoxy) phosphazene] above the mesophase transition, T (1) transition, of the crystals. Hysteresis was found in the temperature dependence of the permeability coefficients for CO₂, O₂, and N₂ in the transition region as observed by dilatometry and differential scanning calorimetry. Independently the solubility of CO₂ was determined gravimetrically above and below T(1). Noticeable change and hysteresis were also observed in the temperature dependence of the solubility coefficients. Diffusion of CO₂ in the measophase is suggested from the permeation and sorption measurements. Gas transport parameters of CO₂ in the mesophase are estimated, and the contributions of the mesophase and the crystalline phase to gas transport are considered.     

Blue Light-induced Acidification of the Medium and the Uptake of Nitrate in a Nitrate-starved Chlorella

When cells of nitrate-starved Chlorella kessleri (Fott et Novakova, no. 211-11h) were suspended in phosphate buffer containing nitrate, they could barely take up nitrate in the dark. The addition of glucose resulted in the initiation of nitrate uptake by Chlorella. Irradiation with blue light stimulated the uptake of nitrate about two-fold as compared with those of glucose-treated cells and the acidification of the suspension medium, which, after 60-90 min of blue irradiation, turned to alkalinization. These effects of blue light on the uptake of nitrate and pH changes were also observed in nitrate-starved colorless (Fott et Novakova, no. 9.80) and yellow (Fott et Novakova, no. 211-11h/20) mutants of C. kessleri. Staurosporine and K252a, potent inhibitors of protein kinase C, inhibited the blue light-induced acidification of the medium and nitrate uptake. The data are discussed with regard to transduction of the signal for blue light-induced acidification and nitrate uptake.     

Molecular orbital quantities of conjugated ketenes and influence of structural variations on their electronic features

MO quantities by CNDO/2 method on several valence isomeric ketenes and structurally corresponding allene molecules were calculated to evaluate the influence of structural feature on magnitude of back-donation of oxygen n-electrons in ketene, and to rationalize an unusual cycloaddition involved in diphenyl ketene.