Search results for "Optical properties"
showing 10 items of 102 documents
An approach to the measurement of the nonlinear refractive index of very short lengths of optical fibers
2018
A method for the measurement of the nonlinear-refractive index coefficient in single-mode optical fibers is presented. It takes advantage of the high sensitivity of the acousto-optic interaction effect in optical fibers to the fiber properties. Direct measurement of the nonlinear-refractive index change resulting from cross-phase modulation between a probe and a pump signal is obtained from the fiber's acousto-optic interaction performance. It is a non-interferometric method in which a very short length of fiber (<0.25 m) is required.
Influence of F centres on structural and electronic properties of AlN single-walled nanotubes
2007
We analyse the influence of uncharged N vacancies (neutral F centres), created either under conditions of AlN nanotube growth or by its soft irradiation, on the atomic and electronic structure. Periodic one-dimensional (1D) density functional theory (DFT) calculations on models of defective single-walled nanotubes (SW NTs) allow us to analyse how NT chirality and concentration of F centres change their properties compared to the corresponding defect-free nanotubes. We have simulated reconstruction around periodically repeated F centres on 1 nm AlN SW NTs with armchair- and zigzag-type chiralities. To achieve the limit of an isolated vacancy for both chiralities, we have considered different…
SrTiO3 Nanotubes with Negative Strain Energy Predicted from First Principles
2011
On the basis of hybrid density functional theory calculations, we predict that the most energetically favorable single-walled SrTiO3 nanotubes with negative strain energy can be folded from SrTiO3 (110) nanosheets of rectangular morphology. Further formation of multiwalled tubular nanostructure with interwall distance of ∼0.46 nm yields an additional gain in energy of 0.013 eV per formula unit. (The formation energy of the most stable nanotube is 1.36 eV/SrTiO3.) Because of increase in the Ti–O bond covalency in the outer shells, SrTiO3 nanotubes can demonstrate an enhancement of their adsorption properties. Quantum confinement leads to a widening of the energy band gap of single-walled SrT…
Linear and nonlinear optical properties of some organoxenon derivatives
2007
We employ a series of state-of-the-art computational techniques to study the effect of inserting one or more Xe atoms in HC2H and HC4H, on the linear and nonlinear optical (L&NLO) properties of the resulting compounds. It has been found that the inserted Xe has a great effect on the L&NLO properties of the organoxenon derivatives. We analyze the bonding in HXeC2H, and the change of the electronic structure, which is induced by inserting Xe, in order to rationalize the observed extraordinary L&NLO properties. The derivatives, which are of interest in this work, have been synthesized in a Xe matrix. Thus the effect of the local field (LF), due to the Xe environment, on the properties of HXeC2…
Structural, electronic, and electrical properties of an Undoped n-Type CdO thin film with high electron concentration
2014
Transparent conducting metal oxides (TCOs) combine the properties of optical transparency in the visible region with a high electrical conductivity. They are a critical component as the window electrode in liquid crystal and electroluminescent display devices, as well as in many designs of solar cells now under development. Sn-doped In2O3 is currently the most important TCO, but it suffers from some drawbacks. These include the high cost of indium, weak optical absorption in the blue-green region, as well as chemical instability that leads to corrosion phenomena in organic light-emitting devices. Indium tin oxide (ITO) films are also brittle and of relatively low durability. A number of oth…
Temperature Dependence of Electronic Transitions of Single-Wall Carbon Nanotubes: Observation of an Abrupt Blueshift in Near-Infrared Absorption
2007
Near-infrared (NIR) absorption spectra of single-wall carbon nanotube (SWNT) films are studied between 10 and 293 K. The most prominent effect is the shift of bands with temperature. Some nanotubes show a redshift of transition upon increasing temperature while some show blueshift and others show no shift. The shift is interpreted to originate mainly from the effect of strain induced in the tubes because of interaction with the environment. In particular, at temperatures T = 175−225 K, for some bands, there is an abrupt large blueshift, which is interpreted to originate from interaction of the nanotubes with water. Two models could be considered to explain the effect: (1) strain induced by…
Ab initio simulations on the atomic and electronic structure of single-walled BN nanotubes and nanoarches
2009
To simulate the perfect single-walled boron nitride nanotubes and nanoarches with armchair- and zigzag-type chiralities and uniform diameter of � 5 nm, we have constructed their one-dimensional (1D) periodic models. In this study, we have compared the calculated properties of nanotubes with those for both hexagonal and cubic phases of bulk: bond lengths, binding energies per B–N bond, effective atomic charges as well as parameters of total and projected one-electron densities of states. For both phases of BN bulk, we have additionally verified their lattice constants. In the density functional theory (DFT), calculations performed using formalism of the localized Gaussian-type atomic functio…
The influence of nitrogen incorporation on the optical properties of anodic Ta2O5
2012
Abstract Anodic oxides were grown on sputter-deposited Ta in different aqueous solutions. A photoelectrochemical investigation was performed in order to estimate the band gap of the films as a function of the anodizing bath composition and formation voltage, i.e. thickness. Photoelectrochemical results provided evidence of sub-band gap photocurrent for films formed in a bath containing ammonium ions at pH 9. Elemental depth profiles obtained by glow discharge optical emission spectroscopy revealed the presence of nitrogen species in the outer part of the anodic films, which is bonded to Ta according to XPS analysis. A mechanism of nitrogen incorporation is proposed in order to account for t…
Dependence of Exciton Mobility on Structure in Single-Walled Carbon Nanotubes
2010
Optically generated excitons in semiconducting single-walled carbon nanotubes (SWCNTs) display substantial diffusional mobility. This property allows excitons to encounter ∼104 carbon atoms during their lifetime and accounts for their efficient deactivation by sparse quenching sites. We report here experimental determinations of the mobilities of optically generated excitons in 10 different (n,m) species of semiconducting SWCNTs. Exciton diffusional ranges were deduced from measurements of stepwise photoluminescence quenching in selected individual SWCNTs coated with sodium deoxycholate surfactant and immobilized in agarose gel. A refined data analysis method deduced mean exciton ranges fro…
Gamma irradiation of graphene quantum dots with ethylenediamine: Antioxidant for ion sensing
2020
Due to the low consumption of chemicals, the absence of toxic residual side products, the procedure simplicity and time-saving aspects, gamma irradiation offers advantages over the classical chemical protocols. We successfully employed gamma irradiation in order to introduce N-atoms in Graphene Quantum Dots (GQDs). By irradiating GQDs water dispersions in the presence of isopropyl alcohol and ethylenediamine, at doses of 25, 50 and 200 kGy, we attached amino groups onto GQDs in a single synthetic step. At the same time, a chemical reduction is achieved, too. Selected conditions induced incorporation of N-atoms within GDQs atomic lattice (around 3 at%), at all applied doses. Additionally, th…