Search results for " GAP"
showing 10 items of 811 documents
Ligand removal from soluble CdTe nanocrystals evidenced by time-resolved photoluminescence spectroscopy
2008
We present experimental studies on the effect of pyridine treatment on the optical properties of ligand-stabilized colloidal CdTe nanocrystals. We demonstrate, by quasi-stationary and time-resolved photoluminescence (PL) spectroscopy, a drastic reduction in the PL lifetime and a concomitant decrease in the PL yield by more than 90% when dissolving the nanocrystals in pyridine. The pyridine solvent efficiently removes the ligand shell and thus enables a rapid energy transfer from the quantum dot to optically dark surface states or into the solvent. The demonstrated removal of the ligand shell is a key step towards integrating such CdTe nanocrystals in hybrid organic/inorganic nanocomposites,…
Nonlocal dispersion anomalies of Dyakonov-like surface waves at hyperbolic media interfaces
2016
Dyakonov-like surface waves (DSWs) propagating obliquely on an anisotropic nanostructure have been theoretically proved in a few cases including 2D photonic crystals and metal-insulator (MI) layered metamaterials. Up to now, the long-wavelength approximation has been employed in order to obtain effective parameters to be introduced in the Dyakonov equation, which is largely restricted to material inhomogeneities of a few nanometers when including metallic elements. Here, we explore DSWs propagating obliquely at the interface between an insulator and a hyperbolic metamaterial, the latter consisting of a 1D MI bandgap grating using realistic slab sizes. We found unexpected favorable condition…
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology
2016
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered,…
Controlled hydrodynamic conditions on the formation of iron oxide nanostructures synthesized by electrochemical anodization: Effect of the electrode …
2017
[EN] Iron oxide nanostructures are of particular interest because they can be used as photocatalysts in water splitting due to their advantageous properties. Electrochemical anodization is one of the best techniques to synthesize nanostructures directly on the metal substrate (direct back contact). In the present study, a novel methodology consisting of the anodization of iron under hydrodynamic conditions is carried out in order to obtain mainly hematite (alpha-Fe2O3) nanostructures to be used as photocatalysts for photoelectrochemical water splitting applications. Different rotation speeds were studied with the aim of evaluating the obtained nanostructures and determining the most attract…
Structural and electronic properties of single-walled AlN nanotubes of different chiralities and sizes
2006
Four models of single-walled AlN nanotubes (NTs), which possess (i) two different chiralities (armchair or zigzag type) and (ii) two different uniform diameters for both types of NTs (1 or 6 nm) have been constructed, in order to analyse the dependence of their properties on both morphology and thickness. Periodic one-dimensional (1D) DFT calculations performed on these models have allowed us to analyse how the chirality and curvature of the NT change its properties as compared to both AlN bulk with either wurtzite or zinc-blende structures and their densely packed surfaces. We have found that the larger the diameter of the AlN NT, the smaller the width of its bandgap, the strengths of its …
Titania nanotubes modeled from 3- and 6-layered (101) anatase sheets: Line group symmetry and comparative ab initio LCAO calculations
2010
Abstract The formalism of line groups for one-periodic (1D) nanostructures with rotohelical symmetry has been applied for construction of TiO 2 nanotubes (NTs). They are formed by rolling up the stoichiometric two-periodic (2D) sheets cut from the energetically stable (1 0 1) anatase surface, which contains either six (O–Ti–O_O–Ti–O) or three (O–Ti–O) layers. After optimization of geometry the former keeps the centered rectangular symmetry of initial slab while the latter is spontaneously reconstructed to the hexagonal fluorite-type (1 1 1) sheet. We have considered the four sets of TiO 2 NTs with optimized 6- and 3-layered structures, which possess the two pairs of either anatase (− n , n …
Electronic properties of single-walled carbon nanotubes inside cyclic supermolecules
2006
Possible ways for manipulating carbon nanotubes (CNTs) with cyclic supermolecules are studied using density functional theory. Electronic structure calculations with structure optimizations have been performed for the (4,4) and (8,0) single-walled carbon nanotubes (SWNTs) complexed with crown ethers as well as for the (4,0) SWNT with beta-cyclodextrin. A slight polarization of charge in both the nanotube and the supermolecule is observed upon rotaxane complexation, but the interaction is mainly repulsive, and the systems stay 2.8-3.5 A apart. The supermolecule does not affect the electronic band structure of the nanotube significantly within such a configuration. The situation differs notic…
First principles modeling of 3d-metal doped three-layer fluorite-structured TiO2 (4,4) nanotube to be used for photocatalytic hydrogen production
2017
This study has been supported by the EC ERA.Net RUS Plus project No. 237 WATERSPLIT, Russian Basic Research Foundation No. 16-53-76019, and additionally by the IMIS2 Program (Latvia). The authors are also indebted to R. A. Evarestov and O. Lisovski for stimulating discussions as well as to A. Chesnokov for technical assistance.
Symmetry and Models of Double-Wall BN and TiO2 Nanotubes with Hexagonal Morphology
2011
The line symmetry groups for one-periodic (1D) nanostructures with rotohelical symmetry have been applied for symmetry analysis of double-wall boron nitride and titania nano- tubes (DW BN and TiO2 NTs) formed by rolling up the stoichiometric two-periodic (2D) slabs of hexagonal structure with the same or opposite orientation of translation and chiral vectors. We have considered the two sets of commensurate DW BN and TiO2 NTs with either armchair- or zigzag-type chiralities, i.e., (n1,n1)@(n2,n2 )o r (n1,0)@(n2,0), respectively. To establish theequilibriuminterwalldistancescorrespondingtotheminimaof energy, we have varied chiral indices n1 and n2 of the constituent single-wall (SW) nanotubes…
Photoluminescence excitation spectroscopy in boron nitride nanotubes compared to microcrystalline h‐BN and c‐BN
2005
Photoluminescence spectra and photoluminescence excitation spectra have been measured on samples of hexagonal boron nitride microcrystalline powder, cubic boron nitride single crystal, and boron nitride nanotubes (mixture of single-walled and multi-walled with some h-BN precursor). The reason for studying these 3 samples in a comparative fashion is that nanotube BN, while based on a rolled hexagonal-BN (sp2-bonded) sheet, is expected to take on more sp3 bond-character reminiscent of cubic-BN as the curvature becomes tighter. With some simplicity of statement, this study was planned to view spectroscopy of nanotube BN with respect to its two limiting cases of bond character, all measured in …