Valence fluctuations in the 3D + 3 modulated Yb3Co4Ge13 Remeika phase.

Yb3Co4Ge13 is the first example of a Remeika phase with a 3D + 3 [space group P4̄3n(α,0,0)000(0,α,0)000(0,0,α)000; a = 8.72328(1) Å, α = 0.4974(2)] modulated crystal structure. A slight shift of the composition towards higher Yb-content (i.e. Yb3.2Co4Ge12.8) leads to the disappearance of the satellite reflections and stabilization of the disordered primitive cubic [space group Pm3̄n, a = 8.74072(2) Å] Remeika prototype structure. The stoichiometric structurally modulated germanide is a metal with hole-like charge carriers, where Yb-ions are in a temperature-dependent intermediate valence state varying from +2.60 to +2.66 for the temperature range 85-293 K. The valence fluctuations have been investigated by means of temperature dependent X-ray absorption spectroscopy, magnetic susceptibility and thermopower measurements.

Extreme Biomimetics: Designing of the First Nanostructured 3D Spongin-Atacamite Composite and its Application.

The design of new composite materials using extreme biomimetics is of crucial importance for bioinspired materials science. Further progress in research and application of these new materials is impossible without understanding the mechanisms of formation, as well as structural features at the molecular and nano-level. It presents a challenge to obtain a holistic understanding of the mechanisms underlying the interaction of organic and inorganic phases under conditions of harsh chemical reactions for biopolymers. Yet, an understanding of these mechanisms can lead to the development of unusual-but functional-hybrid materials. In this work, a key way of designing centimeter-scale macroporous 3D composites, using renewable marine biopolymer spongin and a model industrial solution that simulates the highly toxic copper-containing waste generated in the production of printed circuit boards worldwide, is proposed. A new spongin-atacamite composite material is developed and its structure is confirmed using neutron diffraction, X-ray diffraction, high-resolution transmission electron microscopy/selected-area electron diffraction, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and electron paramagnetic resonance spectroscopy. The formation mechanism for this material is also proposed. This study provides experimental evidence suggesting multifunctional applicability of the designed composite in the development of 3D constructed sensors, catalysts, and antibacterial filter systems.

Quantum plasmon excitations in gold-fullerene mixture films.

Controllable access to the hybrid plasmonic nanostructures built of small metal nanoparticles and organic spacer offers a tempting set of electronic excitations, which proper handling promises valuable applications and bright fundamental prospect. Here, we report on remarkable plasmonic properties of the Au x C60 hybrid nanostructures formed through self-assembling the depositing mixture of metal and fullerene. Using optical absorption spectra, we demonstrate establishing of quantum plasmon (QP) excitations upon the controllable increase of spatial density and size of the Au clusters formed in the films. Detection of two plasmonic modes evidences the QP hybridization enabling by nm-scaled proximity of the neighboured Au clusters. Variation of the QP mode parameters with gradual decrease of the inter-cluster spacing ΔL to the sub-nanometre scale driven by the Au concentration in the film x allowed us to evidence the quantum tunnelling regime in the QP hybridization launching at ΔL ≈ 0.9 nm. The later result designates an important role of the C60 molecules, separating the Au clusters, in design of plasmonic and transport properties of the hybrid films. The obtained results represent the self-assembled Au x C60 nanocomposites as the promising plasmonic materials with potential for application in nanoplasmonics, nanoelectronics, and nanomedicine.

Structure model of γ-Al2O3 based on planar defects.

The defect structure of γ-Al2O3 derived from boehmite was investigated using a combination of selected-area electron diffraction (SAED) and powder X-ray diffraction (XRD). Both methods confirmed a strong dependence of the diffraction line broadening on the diffraction indices known from literature. The analysis of the SAED patterns revealed that the dominant structure defects in the spinel-type γ-Al2O3 are antiphase boundaries located on the lattice planes , which produce the sublattice shifts . Quantitative information about the defect structure of γ-Al2O3 was obtained from the powder XRD patterns. This includes mainly the size of γ-Al2O3 crystallites and the density of planar defects. The correlation between the density of the planar defects and the presence of structural vacancies, which maintain the stoichiometry of the spinel-type γ-Al2O3, is discussed. A computer routine running on a fast graphical processing unit was written for simulation of the XRD patterns. This routine calculates the atomic positions for a given kind and density of planar defect, and simulates the diffracted intensities with the aid of the Debye scattering equation.

Quantum plasmon and Rashba-like spin splitting in self-assembled Co x C60 composites with enhanced Co content (x > 15).

Driving by interplay between plasmonic and magnetic effects in organic composite semiconductors is a challenging task with a huge potential for practical applications. Here, we present evidence of a quantum plasmon excited in the self-assembled Co x C60 nanocomposite films with x > 15 (interval of the Co cluster coalescence) and analyse it using the optical absorption (OA) spectra. In the case of Co x C60 film with x = 16 (LF sample), the quantum plasmon generated by the Co/CoO clusters is found as the 1.5 eV-centred OA peak. This finding is supported by the establishment of four specific C60-related OA lines detected at the photon energies E p  > 2.5 eV. Increase of the Co content up to x = 29 (HF sample) leads to pronounced enhancement of OA intensity in the energy range of E p  > 2.5 eV and to plasmonic peak downshift of 0.2 eV with respect to the peak position in the LF spectrum. Four pairs of the OA peaks evaluated in the HF spectrum at E p  > 2.5 eV reflect splitting of the C60-related lines, suggesting great change in the microscopic conditions with increasing x. Analysis of the film nanostructure and the plasmon-induced conditions allows us to propose a Rashba-like spin splitting effect that suggests valuable sources for spin polarization.

Effect of screw threading dislocations and inverse domain boundaries in GaN on the shape of reciprocal-space maps.

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features.

Crystallization dynamics and interface stability of strontium titanate thin films on silicon.

Different physical vapor deposition methods have been used to fabricate strontium titanate thin films. Within the binary phase diagram of SrO and TiO2 the stoichiometry ranges from Ti rich to Sr rich, respectively. The crystallization of these amorphous SrTiO3 layers is investigated by in situ grazing-incidence X-ray diffraction using synchrotron radiation. The crystallization dynamics and evolution of the lattice constants as well as crystallite sizes of the SrTiO3 layers were determined for temperatures up to 1223 K under atmospheric conditions applying different heating rates. At approximately 473 K, crystallization of perovskite-type SrTiO3 is initiated for Sr-rich electron beam evaporated layers, whereas Sr-depleted sputter-deposited thin films crystallize at 739 K. During annealing, a significant diffusion of Si from the substrate into the SrTiO3 layers occurs in the case of Sr-rich composition. This leads to the formation of secondary silicate phases which are observed by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy.

Capability of X-ray diffraction for the study of microstructure of metastable thin films.

Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species.

Extreme Biomimetics: formation of zirconium dioxide nanophase using chitinous scaffolds under hydrothermal conditions.

Chitinous scaffolds isolated from the skeleton of marine sponge Aplysina cauliformis were used as a template for the in vitro formation of zirconium dioxide nanophase from ammonium zirconium(iv) carbonate (AZC) under extreme conditions (150 °C). These novel zirconia-chitin based composites were prepared for the first time using hydrothermal synthesis, and were thoroughly characterized using a plethora of analytical methods. The thermostability of the chitinous 3D matrix makes it ideal for use in the hydrothermal synthesis of monoclinic nanostructured zirconium dioxide from precursors like AZC. These zirconium-chitin composites have a high potential for use in a broad range of applications ranging from synthetic catalysis to biocompatible materials for bone and dental repair. The synthetic methods presented in this work show an attractive route for producing monoclinic zirconium dioxide on a 3D biocompatible scaffold with ease.