Optical properties of nanostructures in layered metal tri-iodide crystals

The optical response of excitons confined in characteristic nanostructures in layered metal tri-iodide crystals introduced by some irregular stackings from the bulk structures is reviewed. In BiI₃ a specific stacking fault takes place during crystal growth constructing macroscopic planar defects. In this space conspicuous localized exciton transitions occur below the intrinsic absorption edge. Another stacking disorder introduced by applying external stress in this crystal brings about a new nanostructure domain of symmetry D_3d different from that of bulk symmetry C²_3i. The optical transitions due to new structures appear in the lower energy region as an absorption and luminescence line series. The similar nanostructures are induced in SbI₃ crystals under the hydrostatic pressure. In these nanostructures, the electronic structure is analyzed by a model based on the confined excitons in a nanoscale disk-like shape space. The magnetic field effect confirms the structure in the wave function-size scale. The nanoscale disk-like structure of BiI₃ in CdI₂ matrices is also obtained by a hot wall technique and mixed crystal annealing, which is realized by observing the size distribution with an electron microscope. In a BiI₃ disk in CdI₂ Stokes shifted photoluminescence bands appear. The Stokes shifts of the luminescence bands are understood by considering the size-dependent exciton-phonon interaction. In these nanostructures large optical nonlinearity under the intense laser field was obtained.     

Low temperature synthesis of TiO2−xNy powders and films with visible light responsive photocatalytic activity

Nitrogen-doped titania powders and films with excellent visible light photocatalytic activity were successfully prepared by an unadulterated ‘low-temperature process’ below 60 °C using mechanochemical doping and oxygen plasma treatment.     

Morphology of the stabilized natural faces of a CdS1−x Sex solid solution

The morphology of the stabilized surfaces of CdS_1?x Se_x crystals exposed to air at room temperature is studied by atomic force microscopy. The characteristic features of the relief of the natural faces of these crystals are described, and the causes of the appearance of these features are discussed. The morphological results are related to the results of the microcathodoluminescence study of surface micro-and nanostructures. This study revealed objects that contribute to exciton emission and, hence, are CdS_1?x Se_x solid solutions.     

Wave-packet dynamics of Bloch electrons—Role of Berry phase

Motivated by a recent proposal on the possibility of observing a monopole in the band structure, and by an increasing interest in the role of Berry phase in spintronics, we reconsidered the problem of adiabatic motion of a wave packet of Bloch functions, under a perturbation varying slowly and incommensurately to the lattice structure. We showed, using only the fundamental principles of quantum mechanics, that the effective wave-packet dynamics of Bloch electrons is conveniently described by a set of equations of motion (EOM) in which a non-Abelian Berry phase associated with the internal degree of freedom appears.     

Correlation of57Fe hyperfine interactions with Fe-Fe distance in Laves phase compounds RFe2 (R=rare earth)

The⁵⁷Fe Mössbauer isomer shifts and magnetic hyperfine fields in Laves phase compounds RFe₂ (R=Pr, Nd and Sm) are studied with particular reference to the effect of the Fe–Fe interatomic distance on the hyperfine interactions. It is shown that the charge density at the Fe nuclei scales linearly with fractional volume change up to 20%. The⁵⁷Fe hyperfine field corrected for the influence of rare-earth moment shows a systematic variation with the distance, which can be understood in terms of the Bethe-Slater curve arguments. The similarity of the atomic volume dependence of the⁵⁷Fe hyperfine interactions in Lves phase compounds to those in iron with close-packed structure is emphasized.This paper is based on a paper presented at the 5th Int. Conf. on hyperfine interactions, Berlin, July 21–25, 1980.     

Solution behavior of styrene–ethylene oxide block copolymers

Hydrophobic–hydrophilic water-soluble block copolymers were prepared by “living” anionic polymerization. They consist of a polystyrene block and a polyethylene oxide block. From data on solution viscosity and high-resolution NMR in water, the molecular dimensions of the two-blocks copolymers are found similar to that of polyethylene glycols of the same molecular weight in the same solvent. These block copolymers exhibit microphase separation.     

Synthesis and electrochemical properties of novel dimeric fullerenes incorporated in a 2,3-diazabicyclo[2.2.2]oct-2-ene framework

Novel dimeric fullerenes incorporated in a 2,3-diazabicyclo[2.2.2]oct-2-ene framework, with and without direct inter-fullerene-cage bonds, were synthesized and fully characterized spectroscopically; the electronic communication between the two fullerene cages was clarified by differential pulse voltammetry.