407 research outputs found
Photoconductivity and optical properties of PPV and single-walled carbon nanotubes
No full textWe present photoconductivity and Raman scattering data obtained from composite films of poly(paraphenylene vinylene) (PPV) and single-walled carbon nanotubes at different weight concentrations from 0% to 64%. It is found that the introduction of nanotubes in the PPV precursor polymer solution, heated at 300 degrees C to perform conversion into PPV, yields drastic modifications in both the structural features of the composite components and in the electronic properties of the composites. The PPV polymer matrix becomes more disordered due to the introduction of nanotubes which induce a shortening of the polymer conjugated segments as shown by Raman scattering spectra. In addition, these spectra yield information about the evolution from small bundles to thick bundles of single-walled nanotubes as function of their concentration x. Photoconductivity data show that the percolation regime begins at x=2%, indicating that a migration network for the photogenerated charges is established above this threshold. By using a model based on distributions of PPV conjugated lengths and their changes as function of x, we calculate the Raman scattering band shapes and their relative intensities. The theoretical results lead to a comprehensive interpretation of experimental data
Long time decays of transient photoluminescence of Poly(para phenylene vinylene) films and nanofibers
No full textTheoretical and experimental investigation of the optical properties of poly(paraphenylene):evidence of chain length distribution
No full textThe optical properties of PPP have been investigated as function of the model based on distribution of conjugated segmentsof the polymer
Photoexcitations in composites of PPV and single-walled nanotubes
No full textAbsorption and photoluminescence (PL) studies have been carried out on pristine standard poly(paraphenylene vinylene) PPV and a series of PPV-single-walled carbon nanotubes (SWNT) composite films. Drastic changes in the PL and absorption spectra are observed with the increase of the SWNT fraction. A model is presented which is able to explain quantitatively the modification of absorption spectra, and particularly the new features in PL spectra as a function of SWNT percentages in the films. We provide evidence for strong electronic interaction between SWNT and the PPV polymer precursor precluding the complete thermal conversion of the polymer matrix
Optical properties of carbon nanotube-PPv composites : influence of the conversion temperature and nanotube concentration
No full textOptical absorption, photoluminescence,Raman scattering spectra of carbon nanotube-PPv composite films are studied as function of precursor conversion temperature in the range 120-300 C and nanotube concentration
Strain analysis of noble metal islands grown on multiwalled carbon nanotubes
No full textWe analyze the local microscopic deformation left by Au, Ag and Cu islands on carbon nanotube walls observed by transmission electron microscopy. We employ finite-element simulations within continuum elasticity theory to demonstrate that the observed deformation of the tube walls is the result of elastic strain energy relaxation induced by the nucleation of noble metal clusters on the graphene lattice. We find that the magnitude of the tube deformation is strictly correlated to the lattice mismatch of the metal/carbon system under study. In this context, the tube deformation under the island is a proof of the pseudomorphical character of the system, even in the case of high lattice misfit (similar to 15%) as for Au and Ag. (C) 2012 Elsevier Ltd. All rights reserved
In situ formation of noble metal nanoparticles on multiwalled carbon nanotubes and its implication in metal-nanotube interactions
No full textA simple method to decorate multiwalled carbon nanotubes (MWCNTs) with Au, Ag and Cu nanoparticles is illustrated. The method consists in directly depositing the selected metals by thermal evaporation on the carbon nanotubes. Comparative measurements carried out on samples that differ in the quantity and type of the deposited metal, reveal that isolated discrete particles form on the nanotube outer wall for all three metals. The CNT-based composites have been investigated by scanning and transmission electron microscopy to determine the size, shape and distribution of the nanoparticles. The results indicate that the quantity of evaporated metal only affects the nanoparticle size and not the average particle density. Particle composition was determined by X-ray photoelectron spectroscopy study. The results are discussed in terms of metal nanoparticle-tube interactions, an important issue for the fundamental and practical applications of similar MWCNT based composites. (C) 2011 Elsevier Ltd. All rights reserved
High coercivity of iron-filled carbon nanotubes synthesized on austenitic stainless steel
No full textMultiwalled carbon nanotubes synthesized directly on austenitic stainless steel result in being filled with pure iron nanoparticles. X-ray diffraction shows that the nanoparticles are either in the gamma- or alpha-phase, although iron in the original alloy is in gamma-phase because of the presence of nickel. This phase transformation is due to the selective extraction of iron, performed by carbon nanotubes during their growth. A high coercivity of iron-filled carbon nanotubes is measured although the starting steel is paramagnetic. The presence of the cc-phase, the magnetic anisotropy and the single domain character of the Fe nanoparticles explain their magnetic behavior. (C) 2011 Elsevier Ltd. All rights reserved
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