Search results for "boron"
showing 10 items of 352 documents
First-principles calculations of point defects in inorganic nanotubes
2013
The first-principles calculations have been performed to investigate the ground-state properties of monoperiodic boron nitride (BN), TiO2, and SrTiO3 single-walled nanotubes (SW NTs) containing extrinsic point defects. The hybrid exchange–correlation functionals PBE, B3LYP, and B3PW within the framework of density functional theory (DFT) have been applied for large-scale ab initio calculations on NTs with the following substitutional impurities: AlB, PN, GaB, AsN, InB, and SbN in the BN NT, as well as CO, NO, SO, and FeTi in the TiO2 and SrTiO3 NTs, respectively. The variations in formation energies obtained for equilibrium defective nanostructures allow us to predict the most stable compos…
The boron effect on low temperature luminescence of SrAl2O4:Eu, Dy
2020
V.V. acknowledges the financial support of ERDF PostDoc project No. 1.1.1.2/VIAA/3/19/440 (University of Latvia Institute of Solid State Physics, Latvia) and K.S., I.B., A.Z., D.M. and K.L. acknowledge the financial support of ERDF, European-Union Project No. 1.1.1.1/16/A/182 (University of Latvia Institute of Solid State Physics, Latvia).
High-pressure synthesis of boron-rich chalcogenides B12S and B12Se
2022
The authors thank Drs. I. Dovgaliuk and T. Chauveau for assistance with Rietveld analysis; and Drs. V. Bushlya and A. Jamali for help with EDX/SEM measurements. This work was financially supported by the European Union's Horizon 2020 Research and Innovation Program under Flintstone2020 project (grant agreement No 689279).
Optical Contrast and Raman Spectroscopy Techniques Applied to Few-Layer 2D Hexagonal Boron Nitride
2019
The successful integration of few-layer thick hexagonal boron nitride (hBN) into devices based on two-dimensional materials requires fast and non-destructive techniques to quantify their thickness. Optical contrast methods and Raman spectroscopy have been widely used to estimate the thickness of two-dimensional semiconductors and semi-metals. However, they have so far not been applied to two-dimensional insulators. In this work, we demonstrate the ability of optical contrast techniques to estimate the thickness of few-layer hBN on SiO2/Si substrates, which was also measured by atomic force microscopy. Optical contrast of hBN on SiO2/Si substrates exhibits a linear trend with the number of h…
High-Pressure Softening of the Out-of-Plane A2u(Transverse-Optic) Mode of Hexagonal Boron Nitride Induced by Dynamical Buckling
2019
We investigate the highly anisotropic behavior of the in-plane and out-of-plane infrared-active phonons of hexagonal boron nitride by means of infrared reflectivity and absorption measurements under high pressure. Infrared reflectivity spectra at normal incidence on high-quality single crystals show strict fulfillment of selection rules and an unusually long E1u[transverse-optic (TO)] phonon lifetime. Accurate values of the dielectric constants at ambient pressure ϵ0= 6.96, ϵ∞= 4.95, ϵ 0= 3.37, and ϵ∞ = 2.84 have been determined from fits to the reflectivity spectra. The out-of-plane A2u phonon reflectivity band is revealed in measurements on an inclined facet, and absorption measurements a…
Heteropolyacids supported on boron nitride and carbon nitride for catalytic and catalytic photo-assisted alcohol dehydration
2021
Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O60 (P2W18) heteropolyacids (HPAs) are photo(catalysts) for various acid-promoted and redox catalytic reactions. Their activity increases if they are deposited on certain supports as metal oxides or carbon materials. Although the surface area and acid-base interactions of the HPAs with supports are considered as key factors for the performance of the binary material, the role of the local structure changes in the HPAs upon their immobilization on solids must be also of primary importance, directly affecting both acidity and photoredox properties. Here, the (photo)catalytic performance of Keggin and Wells-Dawson heteropolytungstates supported o…
Luminescence of Ce‐doped borate‐oxyfluoride glass ceramics
2007
In the present work we studied the possibility to obtain oxyfluoride glass ceramics based on a lithium and potassium borate glasses with addition of fluorides. Lithium-borate glasses without lanthanum fluoride are transparent up to 275 nm. In samples with LaF3 doped with Ce-activator, an additional absorption at about 300 nm and intense photoluminescence could be observed. Ce-doped potassium-borate glass with addition of fluorides LaF3, LiF and GdF3 was milky and not transparent, an intense photoluminescence has been observed, X-ray diffraction measurements showed a presence of well-pronounced crystalline phases of LiF as well as of GdBO3. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
A nondestructive analysis of the B diffusion in Ta–CoFeB–MgO–CoFeB–Ta magnetic tunnel junctions by hard x-ray photoemission
2010
This work reports on hard x-ray photoelectron spectroscopy (HAXPES) of CoFeB based tunnel junctions. Aim is to explain the role of the boron diffusion for the observed improvement of the tunneling magnetoresistance ratio with increasing annealing temperature. The high bulk sensitivity of HAXPES was used as a nondestructive technique to analyze CoFeB–MgO–CoFeB magnetic tunnel junctions. The investigated samples were processed at different annealing temperatures from 523 to 923 K. Hard x-ray core level spectroscopy reveals an enforced diffusion of boron from the CoFeB into the adjacent Ta layer with increasing annealing temperature. The dependence of the tunneling magnetoresistance on the ann…
A stable path to ferromagnetic hydrogenated graphene growth
2014
In this paper, we propose a practical way to stabilize half-hydrogenated graphene (graphone). We show that the dipole moments induced by an hexagonal-boron nitride (h-BN) substrate on graphene stabilize the hydrogen atoms on one sublattice of the graphene layer and suppress the migration of the absorbed hydrogen atoms. Based upon first principle spin polarized density of states (DOS) calculations, we show that the half hydrogenated graphene (graphone) obtained in different graphene-h-BN heterostructures exhibits a half metallic state. We propose to use this new exotic material for spin valve and other spintronics devices and applications.
Electrochemical treatment of real wastewater. Part 1: Effluents with low conductivity
2018
Abstract The treatment of a real wastewater characterized by low conductivity was performed by anodic oxidation at boron doped diamond (BDD) in both conventional and microfluidic cells. The electrolyses carried out in conventional cells without supporting electrolyte were characterized by very high TOC removals but excessively high energetic consumptions and operating costs. The addition of sodium sulphate, as supporting electrolyte, allowed to strongly reduce the cell potentials and consequently the energetic consumptions and the operating costs. However, under various operating conditions, the addition of Na2SO4 caused a lower removal of the TOC. The best results in terms of both TOC remo…