Thin films of TiO2 and boron-nitrogen (B/N) co-doped TiO 2 on glass substrates have been prepared by a simple sol-gel dip coating route. Titanium (IV) isopropoxide, boric acid and urea have been used as titanium, boron and nitrogen sources, respectively. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, Raman spectroscopy and UV-vis spectroscopy. The TiO 2 thin films with co-doping of different B/N atomic ratios (0.27-20.89) showed better photo-catalytic degradation ability of methylene blue compared to that of bare-TiO2 under visible light. The TiO 2 film doped with the highest atomic concentration of N showed repeatedly the best photo-catalytic performance. The high activity of co-doped TiO2 thin films toward organic degradation can be related to the stronger absorption observed in the UV-vis region, red shift in adsorption edges and surface acidity induced by B/N doping. Furthermore, several atomic models for B/N doping have been used to investigate the effect of doping on electronic structure and density of states of TiO2 through ab-initio density functional theory calculations. The computational study suggested a significant narrowing of the band gap due to the formation of midgap states and the shift of Fermi-level for the interstitial N model supporting the experimental results. © 2013 Elsevier B.V

Cataloged from PDF version of article.Multi-walled carbon nanotubes (MWCNTs) were synthesized through pyrolysis of the sulfuric acid-carbonized byproduct of sucrose. While the presence of sulfur in the reaction media has a key role in the formation and population density of MWCNTs, we have not observed the formation of Y-junctions or encountered other novel carbon nanotube formations. Results indicate the presence of sulfur in catalyst particles trapped inside nanotubes, but failed to find sulfur in the side-walls of the CNTs. In order to verify and explain these findings, we analyzed the behavior of sulfur and its possible effects on the side-wall structure of CNTs by using density functional theory-based calculations on various atomic models depicting sulfur inclusion in the side-walls. The results of the computational study were in line with the experimental results and also provided a new perspective by suggesting that the defects such as pentagons may act as nucleation sites for the Y-branches. The results indicated that sulfur prefers to adsorb on these defective regions, but it is not responsible for the formation of these structures or defects. (C) 2010 Elsevier Ltd. All rights reserved

In this study, we have synthesized boron, carbon, and nitrogen containing films using RF sputter deposition. We investigated the effects of deposition parameters on the chemical environment of boron, carbon, and nitrogen atoms inside the films. Techniques used for this purpose were grazing incidence reflectance-Fouriertransform infrared spectroscopy (GIR-FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). GIR-FTIR experiments on the B-C-N films deposited indicated presence of multiple features in the 600 to 1700 cm − 1 range for the infrared (IR) spectra.Analysis of the IR spectra, XPS and the corresponding EELS data from the films has been done in a collective manner. The results from this study suggested even under nitrogen rich synthesis conditions carbon atoms in the B-C-N films prefer to be surrounded by other carbon atoms rather than boron and/or nitrogen. Furthermore, we have observed a similar behavior in the chemistry of B-C-N films deposited with increasing substrate bias conditions. In order to better understand these results, we have compared and evaluated the relative stability of various nearest-neighbor and structural configurations of carbon atoms in a single BN sheet using DFT calculations. These calculations also indicated that structures and configurations that increase the relative amount of C-C bonding with respect to B-C and/or C-N were energetically favorable than otherwise. As a conclusion, carbon tends to phase-segregate in to carbon clusters rather than displaying a homogeneous distribution for the films deposited in this study under the deposition conditions studied.

We investigate the optical response of a graphene spherical shell which has a semi-conducting material core through their absorption spectrum. The semi-conducting material is described by a Lorenztian expression, which approximates the optical responce of a quantum emitter. We present the tunability of the localized plasmon resonance of the graphene sphere by changing the value of its chemical potential and radius. The semi-conducting sphere supports a localized exciton mode, appearing as a maximum in its absorption spectrum. When the localized exciton mode energy, of the semi-conducting sphere, matches the localized plasmon resonance of the graphene, a splitting is observed in the absorption spectrum. This splitting is due to the interaction of the localized exciton mode with the plasmon mode of the graphene sphere, where a splitting of 80 meV is observed close to the telecommunication wavelength of 1550 nm. Using a theoretical model, we explain the modulations in the intensity of the hybrid exciton-plasmon mode, which can be controlled by the radius and the chemical potential of the graphene sphere and the localized exciton mode of the semi-conducting sphere. The results presented here can be used for designing broadband tunable photonic devices. *

Cubic boron nitride (c-BN) nucleation takes place on hexagonal boron nitride (h-BN) layers growing perpendicular to the substrate surface during thin film synthesis. Studies focused on the nucleation of the cubic phase suggest the possibility that transient phases and/or defects on these h-BN structures have a role in sp3-bonded cubic phase nucleation. In this study, we have investigated the nature, energetics, and structure of several possible defects on BN basal planes, including point defects, 4-, and 5-fold BN rings, that may possibly match the experimentally observed transient phase fine structure. TEM image observations are used to build approximate atomic models for the proposed structures, and DFT calculations are used to relax these structures while minimizing their respective total energies. These optimized atomic geometries are then used to simulate TEM images, which are compared to the experimentally observed structures. Data from DFT calculations and analysis of simulated images from the proposed atomic structures suggest that 4-fold BN rings are more likely to exist on the transient phase possibly leading to c-BN nucleation.