Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O3 films obtained by pulsed laser deposition

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance.     

Total electron yield XANES of zinc-blende MnTe

The electronic structure and chemical bond of zinc-blende (zb) MnTe have been studied by using total-electron-yield (TEY) X-ray absorption near-edge structure (XANES) spectroscopy. Close resemblances of the shape of Mn K-edge XANES in zb-MnTe and in Zn_1−xMn_xTe [A. Titov, X. Biquard, D. Halley, S. Kuroda, E. Bellet-Amalric, H. Mariette, J. Cibert, A.E. Merad, G. Merad, M.B. Kanoun, E. Kulatov, Yu.A. Uspenskii, Phys. Rev. B 72 (2005) 115209] indicated predominant influence of the 1st coordination shell. In particular, identical single-peak pre-edge structure for both cases was mainly ascribed to the Mn 1s-3d/4p weakly allowed dipole transitions. The quantitative analysis of XANES in zb-MnTe concerned the observed chemical shift of Mn K-edge threshold energy and a magnitude of the relevant cation-anion charge transfer (or effective cation charge), q(Mn-Te) [calculated after M. Kitamura, H. Chen, J. Phys. Chem. Solids 52 (1991) 731]. It also provided a comparison with our earlier X-ray absorption studies of Zn_1−xMn_xB alloys (B = S, Se). The estimated charge transfer within the chemical bond of zb-MnTe enabled us to complete the q(Mn-B) versus chalcogen ligand (B = S, Se, Te) dependence and to interpret it in terms of p-d hybridization and a contribution of Mn 3d electrons to the overall charge transfer.     

Time resolved spectroscopy with femtosecond soft-x-ray pulses

The most challenging application of time resolved spectroscopy is to directly observe the structural and electronic dynamics. Here we present the combination of x-ray absorption spectroscopy with laser driven x-ray sources, offering atomic spatial and temporal resolution. Our new approaches for optimization of laser driven x-ray sources resulted in the demonstration of spatially coherent sub-20 fs x-ray pulses in a range up to several keV. We excited polycrystalline silicon with an ultrashort laser pulse and characterized the collective motion of atoms with time resolved x-ray absorption spectroscopy at a temporal resolution of less than 20 fs. Finally, we have shown the feasibility of probing the dynamics of the electronic structure of silicon and carbon with near edge x-ray absorption spectroscopy.     

Application of a conproportionation reaction to a synthesis of shape-controlled gold nanoparticles

Synthesis of gold nanoparticles with multiple shapes by a modified seeding growth method is reported. The optical extinction spectra of a mixture of the seed and growth solutions indicate that the seed particle size decreases during stirring the mixture by a conproportionation reaction of Au metal with Au(III) ions. This conproportionation reaction is used to investigate the effects of variation in seed particle size on the resultant gold nanoparticle shape. When single crystalline and multiply twinned particles are used as the seed particles, they grow into gold nanorods and nanobipyramids, respectively. By letting the seed particles experience the conproportionation reaction before the particle growth to decrease the size, the surface of resultant nanoparticles roughens. Increasing the conproportionation reaction time up to 5 min, multi-branched gold nanoparticles with many lattice defects grow from both of the seed particles. This indicates that the conproportionation reaction is useful to generate lattice defects during the particle growth, which lead to the formation of gold nanoparticles with complex shapes.     

The structure of SiO2-GeO2 glasses: A spectroscopic study

Four glasses of the SiO₂-GeO₂ binary system have been synthesized via a sol-gel route followed by a heat treatment and a quench. Glass structure has been determined by Ge K-edge X-ray absorption spectroscopy (XAS) at low temperature and Raman spectroscopy. These mixed glasses present a continuous random network of interconnected GeO₄ and SiO₄ tetrahedra, with GeO₄ tetrahedra similar to the GeO₄ units in GeO₂ glass and continuous compositional variations from GeO₂-rich regions to SiO₂-rich regions. Such a random mixture is consistent with physical properties of these binary glasses as well as with the chemical dependence of their polyamorphism at high pressure. This EXAFS-derived mean Ge-O-Si angles are close to the Ge-O-Ge mean angle in GeO₂ glass, 134° and 130°, respectively. This misfit with the Si-O-Si angles might explain the ease of formation of isolated and pair defects centers, which are suspected to be at the origin of photo-induced modifications of optical properties in Ge-bearing SiO₂ glasses.     

Nuclear magnetic resonance and transferred hyperfine interaction study of the crystallographically inequivalent Cs(I) and Cs(II) in a Cs2CuCl4 single crystal

¹³³Cs (I=7/2) nuclear magnetic resonance in a Cs₂CuCl₄ single crystal grown by using the slow evaporation method was measured in its three mutually perpendicular crystal planes. The ¹³³Cs resonances of two different groups with two crystallographically inequivalent cesium nuclei, Cs(I) and Cs(II), in the unit cell were recorded. The transferred hyperfine fields for Cs(I) and Cs(II) calculated from the paramagnetic shift and the molecular susceptibility measurements could be expressed by the linear equation H_hf=AT+B. The angular dependence of the ¹³³Cs nuclear magnetic resonance spectra showed that the Cs(I) and the Cs(II) nuclei had different values for the quadrupole coupling constant. The electric field gradient tensors of Cs(I) and Cs(II) were symmetric, and the orientations of their principal axes did not coincide. The Cs(I) ion surrounded by 11 chlorine ions had a small quadrupole parameter, a smaller charge distribution, and a small value for the transferred hyperfine field. However, the Cs(II) ion surrounded by nine chlorine ions had a larger quadrupole parameter, a larger charge distribution, and a larger value for the transferred hyperfine field.     

Lawvere Completeness in Topology

It is known since 1973 that Lawvere’s notion of Cauchy-complete enriched category is meaningful for metric spaces: it captures exactly Cauchy-complete metric spaces. In this paper, we introduce the corresponding notion of Lawvere completeness for (\mathbbT,V)(\mathbb{T},\mathsf{V})-categories and show that it has an interesting meaning for topological spaces and quasi-uniform spaces: for the former ones it means weak sobriety while for the latter it means Cauchy completeness. Further, we show that V\mathsf{V} has a canonical (\mathbbT,V)(\mathbb{T},\mathsf{V})-category structure which plays a key role: it is Lawvere-complete under reasonable conditions on the setting; this structure permits us to define a Yoneda embedding in the realm of (\mathbbT,V)(\mathbb{T},\mathsf{V})-categories.     

Magnetic properties of disordered ferrite and ilmenite-hematite thin films

We have synthesized thin films of disordered zinc ferrite (ZnFe₂O₄) and ilmenite-hematite (FeTiO₃-Fe₂O₃) solid solution, the former and the latter of which are interesting from the viewpoints of magnetooptics and spintronics, respectively, by utilizing sputtering and pulsed laser deposition methods, and have explored their magnetic, magnetooptical, and electrical properties. Although ZnFe₂O₄ possesses a normal spinel structure as its stable phase, some of the Fe³⁺ ions occupy the tetrahedral as well as the octahedral sites in ZnFe₂O₄ of which the sputtered thin film is composed. Consequently, the as-deposited thin film manifests large magnetization even at room temperature although the magnetic phase transition temperature of the stable phase of ZnFe₂O₄ is as low as 10 K. Also, the thin film exhibits a cluster spin glass transition at a temperature as high as 325 K. Furthermore, the ZnFe₂O₄ thin films exhibit large Faraday effects at a wavelength of 400 nm or so. The ilmenite-hematite solid solution is one of the ferrimagnetic semiconductors. Most of the compositions possess Curie temperatures higher than room temperature, and the type of carrier can be tuned only by changing the composition. We have succeeded in synthesizing solid-solution thin films of various compositions grown epitaxially on sapphire substrates with a (0 0 0 1) plane, and have shown that the thin films are ferrimagnetic semiconductors.     

Early stages of decomposition in Al alloys investigated by X‐ray absorption

We demonstrate the sensitivity of X‐ray absorption fine‐structure (XAFS) measurements to the earliest stages of decomposition in Al alloys, i.e. just a few minutes after quenching. XAFS is one of the few applicable experimental approaches to this regime. Three different AlCu(Mg) samples were investigated by XAFS at the Cu K edge. Significant changes of the XAFS can be detected in the course of the decomposition in these alloys during the first 15 minutes. Actually, these changes correspond to relaxations of the nearest neighbours towards the absorbing Cu atoms. The Fourier transformation of the XAFS spectra thus leads to a pseudo radial distribution function which reflects this relaxation. In addition, XAFS measurements of the S‐phase of AlCuMg are used to decide in favour of the Perlitz and Westgren model for the S‐phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

五元联系数在高职院校学生综合素质评价中的应用

学生综合素质评价是高校素质教育测量的重要侧面,其综合素质的概念、评价指标内容的确定、权重的分配及评价方法选定直接影响着学生评价的客观性和公正性,采用"三选"法概括评价指标,用矩阵法确定各指标的权重,利用五元联系数建立数学模型试行评价,最后算例表明了它的有效性和实用性.