Novel Ni-Doped Bismuth-Magnesium Tantalate Pyrochlores: Structural and Electrical Properties, Thermal Expansion, X-ray Photoelectron Spectroscopy, and Near-Edge X-ray Absorption Fine Structure Spectra.

The samples of Ni-doped bismuth magnesium tantalate pyrochlores with the general formula Bi1.4(Mg1-x Ni x )0.7Ta1.4O6.3 (x = 0.3, 0.5, 0.7) were obtained by solid-phase synthesis. The crystal structure of the pyrochlore type (sp. gr. Fd3̅m:2) was clarified by the Rietveld method on the basis of X-ray powder diffraction data. The unit cell parameters increase with the decreasing nickel content in the range from 10.5319(1) to 10.5391(1) Å. The electronic state of atoms is established by the XPS method. According to XPS analysis, bismuth atoms have an effective charge of +3, nickel atoms +(2 + δ), and tantalum ions +(5 - δ). The coefficient of thermal expansion of the lattice of the samples was calculated from high-temperature X-ray structural measurements in the range of -180 to 1050 °C. The average values of linear TECs α in the temperature ranges of 30-570 and 600-1050 °C are 5.1 × 10-6 and 8.1 × 10-6 °C-1, respectively. The monotonicity of the change in the thermal expansion coefficient in the temperature range from -100 to 1050 °C indicates the absence of phase transformations. All samples are dielectric and exhibit high activation energies ∼2.0 eV, moderately high dielectric constants ∼24-28, and tangent dielectric losses ∼0.002 at 1 MHz and 21 °C. The electrical properties of the samples are described by a simple parallel equivalent scheme. The chemical composition of the materials has little effect on the polarizability of the medium or on the value of the activation energy of the conductivity. Ionic processes in investigated materials at frequencies 200-106 Hz and at temperatures 100-450 °C were not detected.

Speciation of organosulfur compounds in carbonaceous chondrites.

Despite broad application of different analytical techniques for studies on organic matter of chondrite meteorites, information about composition and structure of individual compounds is still very limited due to extreme molecular diversity of extraterrestrial organic matter. Here we present the first application of isotopic exchange assisted Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for analysis of alkali extractable fraction of insoluble organic matter (IOM) of the Murchison and Allende meteorites. This allowed us to determine the individual S-containing ions with different types of sulfur atoms in IOM. Thiols, thiophenes, sulfoxides, sulfonyls and sulfonates were identified in both samples but with different proportions, which contribution corroborated with the hydrothermal and thermal history of the meteorites. The results were supported by XPS and thermogravimetric analysis coupled to FTICR MS. The latter was applied for the first time for analysis of chondritic IOM. To emphasize the peculiar extraterrestrial origin of IOM we have compared it with coal kerogen, which is characterized by the comparable complexity of molecular composition but its aromatic nature and low oxygen content can be ascribed almost exclusively to degradation of biomacromolecules.

Inhibition of chemical interaction of molybdenum and silicon in a Mo/Si multilayer structure by the formation of intermediate compounds.

In the present study, the formation of intermediate compounds in the Mo/Si multilayer was realized by the introduction of barrier layers at the interfaces. Their impact on the interdiffusion of Mo and Si was analyzed via X-ray photoelectron spectroscopy. It was established that the insertion of a thin Be barrier layer led to the formation of beryllide MoBe12 at the interface Si-on-Mo, which prevented the formation of molybdenum disilicide and improved the interface. The insertion of the B4C barrier layer led to its complete decomposition with the formation of borides and carbides of molybdenum and silicon (MoBx, SiBx, MoxC and SiCx) at the Si-on-Mo interface. The formation of only MoBx and SiCx was detected at the Mo-on-Si interface. It was important that the insertion of a thin B4C barrier layer did not fully prevent the formation of MoSi2 at both (Si-on-Mo and Mo-on-Si) the interfaces. These facts allowed us to assume that the diffusion barrier function of the B4C interlayer could be caused by the stability of the formed compounds, rather than the stability of the B4C layer itself.

From graphene oxide towards aminated graphene: facile synthesis, its structure and electronic properties.

In this paper we present a facile method for the synthesis of aminated graphene derivative through simultaneous reduction and amination of graphene oxide via two-step liquid phase treatment with hydrobromic acid and ammonia solution in mild conditions. The amination degree of the obtained aminated reduced graphene oxide is of about 4 at.%, whereas C/O ratio is up to 8.8 as determined by means of X-ray photoelectron spectroscopy. The chemical reactivity of the introduced amine groups is further verified by successful test covalent bonding of the obtained aminated graphene with 3-Chlorobenzoyl chloride. The morphological features and electronic properties, namely conductivity, valence band structure and work function are studied as well, illustrating the influence of amine groups on graphene structure and physical properties. Particularly, the increase of the electrical conductivity, reduction of the work function value and tendency to form wrinkled and corrugated graphene layers are observed in the aminated graphene derivative compared to the pristine reduced graphene oxide. As obtained aminated graphene could be used for photovoltaic, biosensing and catalysis application as well as a starting material for further chemical modifications.

Gold Decoration and Photoresistive Response to Nitrogen Dioxide of WS2 Nanotubes.

Composites of WS2 nanotubes (NT-WS2 ) and gold nanoparticles (AuNPs) were prepared using aqueous HAuCl4 solutions and subjected to surface analysis. The obtained materials were jointly characterized by X-ray photoelectron (XPS), Raman scattering (RSS), and ultraviolet photoelectron (UPS) spectroscopies. Optical extinction spectroscopy and electron energy loss spectroscopy in the scanning transmission electron microscopy regime (STEM-EELS) were also employed to study plasmon features of the nanocomposite. It was found that AuNPs deposition is accompanied by a partial oxidative dissolution of WS2 , whereas Au-S interfacial species could be responsible for the tight contact of metal nanoparticles and the disulfide. A remarkable sensitivity of n-type resistance of NT-WS2 and Au-NT-WS2 to the adsorption of NO2 gas was also demonstrated at room temperature using periodical illumination by a 530 nm light-emitting diode. Au-NT-WS2 nanocomposites are found to possess a higher photoresponse and enhanced sensitivity in the 0.25-2.0 ppm range of NO2 concentration, as compared to the pristine NT-WS2 . This behaviour is discussed within the physisorption-charge transfer model to explore sensing properties of the nanocomposites.