Investigation of the structure and properties of modified Armenian minerals for polymer-based composites

The results of investigation of the modification of the Armenian minerals with fluorine-containing oligomers show that a modified product appears when the mineral fillers are treated with fluoroalkanes. The product preserves the structure of the fillers with a “grafted” fluoroalkane layer in which chlorine atoms locate mainly over their periphery. The composite materials based on heterochained polymers and the modified fillers possess a stronger wear resistance and a low friction coefficient.     

Influence of small additives of rare-earth elements on the structure of fluorophosphate glasses

The physicochemical properties and Raman spectra of glasses of the composition 40Ba(PO₃)₂ · 60MgCaSrBaAl₂F₁₄ doped with europium and terbium have been investigated. The results of the performed investigations have been compared with the data of the analysis of the recorded EPR spectra of irradiated glasses of the same compositions in terms of the model of the effective capture volume and with the luminescence data available in the literature. The concentration ranges of terbium and europium ions (0.05–0.10) mol % or (0.7–1.3) × 10¹⁹ ions/cm³, in which these ions retain the oxygen environment according to the analysis of the studies carried out by different methods, are in satisfactory agreement. The dependence of the local environment of rare-earth ions in fluorophosphate glasses on their concentration has been established.     

Fabrication of new elements and devices on the glass surface under a combined action of short-wavelength radiation and ion-exchange diffusion

The possibilities for using the photocrystallization diffusion method in combination with low temperature ion exchange and etching in acid solutions to fabricate devices of integrated optics and optoelectronics on the surface of alkali aluminosilicate glasses are demonstrated. A two-stage low temperature ion-exchange technique is developed for producing surface crystallized layers with a controlled thickness and configuration. These layers can serve as a photomask on the glass surface in the course of high-temperature ion exchange. Etching of the glasses and crystals on their base in solutions of mineral acids is investigated. A procedure is proposed for preparing the relief structures on the glass surface.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Bocharova, Karapetyan.     

Optical Properties of Gamma-Irradiated Ba(PO3)2-Containing Fluoroaluminate Glasses

Optical absorption and electron paramagnetic resonance measurements were used to assess the nature of the paramagnetic and color centers in gamma-irradiated LiF-containing BaSrCaMgAl₂F₁₄glasses with Ba(PO₃)₂additions. The radiation-induced processes in the glasses containing 1.5 mol % Ba(PO₃)₂are dominated by PO₄ ^2–and PO₃ ^2–centers, which have large capture cross sections. Substitution of 0.8–1.8 mol % oxides has a significant effect on the formation of radiation-induced color centers in the glasses studied.     

Investigation of the Effect of Barium Metaphosphate Additives on the Structure of Fluoroaluminate Glasses by Optical and EPR Spectroscopy

Optical fluoroaluminate glasses containing 0.3–5 mol % Ba(PO₃)₂ have been investigated by IR and EPR spectroscopy. It is found that the PO₄ ^2– and PO₃ ^2– centers play the main role in the radiation processes over the entire Ba(PO₃)₂ concentration range under consideration. The assumption is made that the structure of fluoroaluminate glasses with small additives of Ba(PO₃)₂ is built up of a set of fragments that involve the [AlF₆] octahedra and are linked by the P–O–P bonds.     

Dependence of the Spectroscopic Properties of Europium on the Spatial Distribution of Rare-Earth Ions in Fluorophosphate Glasses

Doped fluorophosphate glasses containing 4–13 mol % Ba(PO₃)₂ have been studied. Analysis of the Raman spectra has revealed that the structure of glasses containing up to 1 mol % Ba(PO₃)₂ involves isolated [PO₄] tetrahedra. An increase in the Ba(PO₃)₂ content brings about the formation of pyrophosphate groups, which are dominant in the glass containing 11 mol % Ba(PO₃)₂. The introduction of up to 2 mol % EuF₃ into the glasses containing 5 and 7 mol % Ba(PO₃)₂ leads to a decrease in the Landau-Placzek ratio. This is interpreted within the model of segregation of dopant ions. From analyzing the induced absorption spectra, the content of Eu³⁺ ions with a predominantly phosphate environment is estimated at ∼0.005 mol %. It is shown that, for the glasses containing 4 mol % Ba(PO₃)₂, the intensity ratio of the Eu³⁺ luminescence bands attributed to the ⁵ D ₀-⁷ F ₁ and ⁵ D ₀-⁷ F ₂ transitions changes with an increase in the EuF₃ content from 0.01 to 2.0 mol %. This dependence of the intensity ratio on the EuF₃ content exhibits a maximum at 0.5 mol % EuF₃, which is explained by the change in the local environment of the rare-earth ion.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Bocharova, Karapetyan, Mironov, Tagil’tseva, Yanush.     

Large‐Scale Synthesis of Bi‐layer Graphene in Strongly Coupled Stacking Order

Large‐scale synthesis of single‐layer graphene (SLG) by chemical vapor deposition (CVD) has received a lot of attention recently. However, CVD synthesis of AB stacked bi‐layer graphene (BLG) is still challenging. Here, we report synthesis of BLG homogeneously at large scale by thermal CVD. The 2D Raman band of CVD BLG splits into four components, suggesting splitting of electronic bands due to strong interlayer coupling. The splitting of electronic bands in CVD BLG is further evidenced by the study of near infrared absorption and carrier dynamics are probed by transient absorption spectroscopy. UV photoelectron spectroscopy invesigation also indiates CVD BLG possesses different electronic structures to those of CVD SLG. The growth mechanism of BLG is found to be related to catalytic activity of the copper (Cu) surface, which is determined by the purity of Cu foils employed in the CVD process. Our work shows that strongly coupled or even AB stacked BLG can be grown on Cu foils at large scale, which is of particular importance for device applications based on their split electronic bands.     

Specific features of the charge carrier mobility in nanowires in transverse electric and magnetic fields

The effect of an electric field E orthogonal to the quantum-wire axis and a magnetic field H (H ⊥ E, H ‖ E) on conductivity is studied within the context of the parabolic potential model. It is shown that, if the interaction of charge carriers with the rough surface of the nanostructure is taken into account, the charge-carrier mobility μ as a function of increasing E is described by an unsteady oscillating curve. A physical interpretation of such behavior of μ with E is proposed. The specific features of mobility in a transverse magnetic field are discussed.