1,721,025 research outputs found
Physicochemical evolution of nascent soot particles in a laminar premixed flame: From nucleation to early growth
No full textIn this work, particle inception and early growth stages were investigated in an ethylene/air premixed flame by the evolution of the particle size and structure with flame residence time. Particle size distribution was measured by a scanning mobility particle seizer and chemical-physical investigation was carried out by Raman microspectroscopy, UV-visible light absorption and cyclic voltammetry. From early inception of particles, just downstream the flame front, to the formation of primary soot particles, in the post-oxidation flame zone, particles participate in a series of chemical and physical reactions that strongly modify their nanostructure and physicochemical properties, resulting in different optical and electronic characteristics. The results presented in this study show that the evolution from a mono-modal to a bi-modal size distribution is associated to a particle graphitization process consisting of a slight increase of the in plane average size of the polyaromatic units within the particles, La, and on the formation of stacks of polyaromatic planes. These outcomes suggest that in our flame conditions particle coagulation/coalescence has a major role in the initial soot formation, affecting both physical and chemical particle properties. © 2015 The Combustion Institute
P3HT/CdSe/WS2 composites for hybrid photovoltaics: Structural and morphological properties
No full textOptical properties of ionic liquid passivated CdSe/ZnS quantum dots dispersed in POC copolymer
No full textA new blue emitter oxadiazole/carbazole copolymer has been synthesized and combined with CdSe/ZnS quantum dots (QDs). Surface passivation of the QDs by ionic liquids was crucial to improve their compatibility with the polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites have been characterized by thermogravimetric analysis, infrared, UV-visible absorption, and photoluminescence spectroscopy. The emission spectra of nanocomposites show a wide spectrum from blue to orange wavelengths due to the combination of colors emitted by the polymer and QDs, respectively. © 2013 Society of Plastics Engineers
Investigation of the optical characteristics of a combination of InP/ZnS-quantum dots with MWCNTs in a PMMA matrix
No full textIn the present study we investigated a combination of quantum dots with multi-walled carbon nanotubes as a possible future additive to the active layer of polymer solar cells. In this case the quantum dots should serve to enhance the long wavelength response of the solar cell, while the nanotubes enhance the charge carrier collection efficiency by favoring charge carrier separation and enhancement of the lateral conduction of the films. In order to clarify the interplay of the nanoparticles only, we deposited them into a non-conducting and transparent polymethyl-methalacrylate (PMMA) matrix. InP/ZnS quantum dots with an emission peak wavelength of 660 nm have been chosen in this study, because their addition can enhance the long wavelength response of conventional poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) bulk heterostructure polymer solar cells. In our study we kept the quantum dot concentration constant and varied the concentration of the carbon nanotubes (CNTs) in the deposited films. The characterization of the film morphology by scanning electron microscopy (SEM) imaging and of the optical properties by photoluminescence and transmittance revealed a rather complex interplay between nanotubes and quantum dots. In particular we found a strong quenching of the photoluminescence and an inhomogeneous CNT distribution for carbon nanotube concentrations exceeding 1%. The decrease in optical transmittance of the films with increasing CNT concentration is less pronounced, when quantum dots (QDs) are added. The optical transmittance in a wavelength range between 380 nm and 800 nm of the composites could be expressed empirically as a simple second order polynomial function. © 2013 Elsevier B.V. All rights reserved
Microscopic and spectroscopic investigation of MoS2 nanotubes/P3HT nanocomposites
No full textBlends of conductive polymer poly(3-hexylthiophene) (P3HT) and size controlled MoS2 nanotubes (NTs) were prepared focusing on procedures which do not alter the electrical and optical properties of nanotubes, i.e., without surfactants. After disassembly of as-grown hedgehog-like self-assemblies of the MoS2 NTs, relatively homogeneous dispersions of the NTs in P3HT were prepared. Thin films of these blends were prepared via spin coating. The NTs were found efficiently wetted by the P3HT and nearly completely immersed in the films. The surface structure was composed of pure P3HT lamellae. Photoluminescence spectra taken on P3HT/MoS2 NT thin films revealed a quenching effect, which depends on the concentration of NTs. Results of optical microscopy and spectroscopy investigations, scanning tunnelling microscopy and scanning electron microscopy studies are shown. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Preparation and catalytic properties of palladium(0) and rhodium(I) complexes containing new chiral P,N-ligands derived from carbohydrates
No full textMN COMPLEXES OF CHIRAL SALEN TYPE LIGANDS DERIVED FROM CARBOHYDRATES IN THE ASYMMETRIC EPOXIDATION OF ALKENES
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