Ab Initio Calculation of the Lattice Distortions induced by Substitutional Ag- and Cu- Impurities in Alkali Halide Crystals

An ab initio study of the doping of alkali halide crystals (AX: A = Li, Na, K, Rb; X = F, Cl, Br, I) by ns2 anions (Ag- and Cu-) is presented. Large active clusters with 179 ions embedded in the surrounding crystalline lattice are considered in order to describe properly the lattice relaxation induced by the introduction of substitutional impurities. In all the cases considered, the lattice distortions imply the concerted movement of several shells of neighbors. The shell displacements are smaller for the smaller anion Cu-, as expected. The study of the family of rock-salt alkali halides (excepting CsF) allows us to extract trends that might be useful at a predictive level in the study of other impurity systems. Those trends are presented and discussed in terms of simple geometric arguments.Comment: LaTeX file. 8 pages, 3 EPS pictures. New version contains calculations of the energy of formation of the defects with model clusters of different size

Electronic, electrical and magnetic behaviours of reduced graphene-oxide functionalized with silica coated gold nanoparticles

[[abstract]]We have synthesized graphene-oxide (GO) by the modified hummer's process and subsequently reduced it with gold-nanoparticles (Au-NPs) using silica coated colloidal Au-NPs and hydrazine monohydrate solutions to form r-GO:Au-NPs nanocomposites. We have studied the microstructure, electronic, electrical and magnetic properties of r-GO and r-GO:Au-NPs nanocomposites. We have observed from the Raman spectroscopy that the intensity of D-peak (disorder) gets reduced with respect to G (graphite-cluster) in r-GO:Au-NPs composites. The reduction of ID/IG ratio obtained from Raman spectra [r-GO: 1.22 → r-GO:(Au-NPs)4.88: 0.98] clearly indicates that the sp2-cluster is reduced in r-GO:Au-NPs nanocomposites. The reduction of sp2-cluster and/or enhancement of sp3-cluster is due to replacement of sp2-cluster by the Au-NPs. This observation also observed from the X-ray absorption near edge structure (XANES) spectroscopy, X-ray photoelectron spectroscopy (XPS) measurements that are consistence with reduction of conductivity as we observe from the current (I) - voltage (V) characteristics of the nanocomposites. Magnetic M-H hysteresis loops show the magnetization is enhanced in r-GO:Au-NPs nanocomposites. We believe that the reduction of conductivity and enhancement of magnetization of r-GO:Au nanocomposites would be most suitable for ferro-electro-magnetic materials for the memory storage device applications.[[notice]]補正完

Tuning of electronic and magnetic properties of multifunctional r-GO-ATA-Fe2O3-composites for magnetic resonance imaging (MRI) contrast agent

[[abstract]]We have synthesized r-GO-ATA-Fe2O3 nanocomposites and studied their microstructural and electromagnetic properties for future possible magnetic resonance imaging for biomedical application. X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption near edge spectroscopy were used to study the structural and electronic properties, while a superconducting quantum interface device magnetometer was used for investigating the magnetic behavior of the nanocomposites. The nanocomposites have been found to reduce the graphitic structure of GO due to the substitution of carbon/oxygen and/or iron nanoparticles. Conversely, the electrical conductivity of nanocomposites is found to be high due to the formation of Fe—C/Fe—O bonds in the structure of the nanocomposites. The composites also exhibit superparamagnetic features as observed from the M-H hysteresis loop with saturation magnetization of ≈0.1 emu/g at 1.8 K temperature. The results, in general, suggest possible applicability of r-GO/Fe2O3 nanocomposites as an effective multifunctional platform for magnetic resonance imaging in biomedical applications.[[notice]]補正完

Correlation Between Electrochromism and Electronic Structures of Tungsten Oxide Films

[[abstract]]The in-situ X-ray absorption spectroscopy of three tungsten oxide films was performed to study the electronic and atomic structures following repeated cycles of coloration and bleaching processes. The transparent tungsten oxide films become deep blue upon intercalation of Li+ ions in the WO6 octahedra when an external electrical bias was applied. These films reverted to transparent when a reverse external electrical bias was applied. W L3-edge X-ray absorption near-edge structure (XANES) measurements of the nanocrystalline and crystalline tungsten oxide films revealed that the intensity of the white-line feature decreases after coloration and recoverably increases after bleaching owing to the filling and unfilling of the W 5d–O 2p conduction band states. The second derivative of the W L3-edge XANES spectra indicated an increase in structural disordering following repeated cycles of coloration and bleaching. However, the extended X-ray absorption fine structure analysis showed that the nearest-neighbor W–O bond distances in the samples overall remain unchanged by coloration and bleaching. The nanocrystalline tungsten oxide film exhibited more effective recovery ([similar]97% after first cycle) of the electronic structures than the other two crystalline samples in terms of the filling and unfilling of the W 5d–O 2p conduction band states after repeated coloration and bleaching. These results show that the nanocrystalline tungsten oxide sample has superior electrochromic properties to the crystalline samples.[[journaltype]]國外[[booktype]]電子版[[countrycodes]]GB

Electronic Structure of EuMo6Se8 Studied by X-Ray Absorption Spectroscopy

[[abstract]]The rare-earth based molybdenum chalcogenides, REMo6Se8 (RE = rare-earth metals) have been extensively studied because of their unique crystal structure based on Mo6Se8 clusters and their outstanding properties involving coexistence of superconductivity and magnetism. Among all these compounds, Ce and Eu based chalcogenides are magnetic and non-superconductors and possess many novel properties. Understanding their electronic structure is likely to provide valuable information about these materials. We employ X-ray absorption near-edge structure (XANES) spectroscopy at Mo and Se K-edges of EuMo6Se8 to identify the local environment respectively around Mo and Se ions and XANES spectra at L3-edge of Eu ion to identify their valence state. Results from this study demonstrate that Se ions in EuMo6Se8 are in two inequivalent sites and the valency of Eu is divalent.[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]US

[[alternative]]稀磁性半導體Zn1-xMnxY(Y=S, Se)和Zn1-xCoxS之XAFS

[[abstract]]X-ray absorption near edges structure (XANES) spectra of the Diluted Magnetic Semiconductors (DMS) system Zn1-xMxS (M=Mn, Co) have been measured at the Mn and Co L3,2-edge using sample current mode. Analysis of the M L3,2-edge XANES spectra for Zn1-xMxS revealed the presence of a white line feature in each series, whose intensity increased linearly with concentration x. The white line feature is assigned to M 2p3/2 and 2p1/2 photoelectron excitations to nonbonding 3d(e) states and to the relatively broadened band of M 3d(t2) - S 3p hybridized antibonding states. The rate of increase of L3,2 white line intensity with x is associated with the difference in the degree of p-d hybridization of states between M 3d and S 3p.[[notice]]補正完

Electronic structure of aligned carbon nanotubes studied by scanning photoelectron microscopy

We have investigated the local electronic structures from tip and sidewall regions of aligned multi-walled carbon nanotubes (MWCNTs) by employing scanning photoelectron microscopy (SPEM) and micro-photoemission spectroscopy. Spatially resolved spectra of C 1s, Si 2p and valence band have been measured. In particular, we compared the results from MWCNTs grown on Fe thin film catalyst with those using Ti catalyst, where the quality of alignment is much lower. For Fe catalyst, the SPEM data show that the tips have a larger density of states (DOS) and a higher C 1s binding energy than those of the sidewalls. In the case of Ti catalyst, Si 2p signal is detected within the CNT bundles. Different Si species can be identified. It is suggested that during the plasma-enhanced growth process, Si is transported into the CNT layer

Electronic structures of hexagonal manganites HoMnO3 studied by X-ray absorption near-edge structure

AIP Conf. Proceed., 2007, CP879, 1659-166