120 research outputs found
Doping, density of states and conductivity in polypyrrole and poly(p-phenylene vinylene)
The evolution of the density of states (DOS) and conductivity as function of
well controlled doping levels in OC_1C_10-poly(p-phenylene vinylene)
[OC_1C_10-PPV] doped by FeCl_3 and PF_6, and PF_6 doped polypyrrole (PPy-PF_6
have been investigated. At a doping level as high as 0.2 holes per monomer, the
former one remains non-metallic, while the latter crosses the metal-insulator
transition. In both systems a similar almost linear increase in DOS as function
of charges per unit volume c* has been observed from the electrochemical gated
transistor data. In PPy-PF_6, when compared to doped OC_1C_10-PPV, the energy
states filled at low doping are closer to the vacuum level; by the higher c* at
high doping more energy states are available, which apparently enables the
conduction to change to metallic. Although both systems on the insulating side
show log(sigma) proportional to T^-1/4 as in variable range hopping, for highly
doped PPy-PF_6 the usual interpretation of the hopping parameters leads to
seemingly too high values for the density of states.Comment: 4 pages (incl. 6 figures) in Phys. Rev.
High Electron Mobility in Vacuum and Ambient for PDIF-CN2 Single-Crystal Transistors
We have investigated the electron mobility on field-effect transistors based
on PDIF-CN single crystals. The family of the small molecules
PDI8-CN has been chosen for the promising results obtained for
vapour-deposited thin film FETs. We used as gate dielectric a layer of PMMA
(spinned on top of the SiO), to reduce the possibility of electron
trapping by hydroxyl groups present at surface of the oxide. For these devices
we obtained a room temperature mobility of 6 cm/Vs in vacuum and 3
cm/Vs in air. Our measurements demonstrate the possibility to obtain
n-type OFETs with performances comparable to those of p-type devices.Comment: published online in JAC
Greener Method to Obtain a Key Intermediate of Vitamin E over Cu-ZSM-5
The catalytic oxidation of 2,3,5-trimethylphenol was performed over transition metals modified ZSM-5 zeolites employing hydrogen peroxide as oxidant under mild reaction conditions. Catalysts samples were characterized by several techniques (XRD, FTIR, BET, AA) and cristallinity and orthorhombic symmetry were confirmed for all of them. Best catalytic results were obtained for Cu-ZSM-5 sample, so further activity studies were done over this material. 2,3,5-trimethyl-1,4-benzoquinone was obtained as the main product of the selective oxidation. Reaction parameters (nature of the solvent, hydrogen peroxide concentration, reaction time, catalyst mass, substrate initial concentration and reaction temperature) were evaluated to reach the optimum reaction conditions. According to the obtained results, an apparent activation energy of 52.33 kJ/mol was calculated.Fil: Saux, Clara. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina. Universidad Tecnologica Nacional. Facultad Regional Cordoba; ArgentinaFil: Renzini, Maria Soledad. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina. Universidad Tecnologica Nacional. Facultad Regional Cordoba; ArgentinaFil: Gómez, Silvina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina. Universidad Tecnologica Nacional. Facultad Regional Cordoba; ArgentinaFil: Pierella, Liliana Beatriz. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Centro de Investigacion y Tecnologia Quimica; Argentina. Universidad Tecnologica Nacional. Facultad Regional Cordoba; Argentin
The aldol condensation of acetaldehyde and heptanal on NiMg(Al)O mixed oxides obtained from LDH precursors
International audienc
Charge carrier properties below and above the metal-insulator transition in conjugated polymers : recent results
The strong doping dependence of the dc conductivity in conjugated polymers below the metal–insulator transition (MIT), illustrated for PPV, is argued to be due to an increase in the density of states and the growth in size of the regions, in which the charge is delocalized. Obviously in the metallic states these regions have to overlap. Phase sensitive dielectric spectroscopy data show that when this overlap is achieved less than 1% of the donated charges (at least in polypyrrole) participates in metallic transport. The data up to the MIT allow a tentative picture of the density of states
Zeolite Y Crystals with Trimodal Porosity as Ideal Hydrocracking Catalysts
Effektive Poren: Zeolith-Y-Kristalle mit Mikroporen (ca. 1 nm), kleinen (ca. 3 nm) und großen Mesoporen (ca. 30 nm) wurden aus zuvor mit Dampf und Säure behandeltem Material durch Auslaugen mit Base erhalten. Die Zeolith-Y-Kristalle mit trimodaler Porosität (siehe elektronentomographische Aufnahme) zeigen beim Hydrocracking eine nahezu ideale Selektivität für und erhöhte Ausbeuten an Kerosin und Diesel
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