120 research outputs found
Bias-dependent Contact Resistance in Rubrene Single-Crystal Field-Effect Transistors
We report a systematic study of the bias-dependent contact resistance in
rubrene single-crystal field-effect transistors with Ni, Co, Cu, Au, and Pt
electrodes. We show that the reproducibility in the values of contact
resistance strongly depends on the metal, ranging from a factor of two for Ni
to more than three orders of magnitude for Au. Surprisingly, FETs with Ni, Co,
and Cu contacts exhibits an unexpected reproducibility of the bias-dependent
differential conductance of the contacts, once this has been normalized to the
value measured at zero bias. This reproducibility may enable the study of
microscopic carrier injection processes into organic semiconductors.Comment: 4 pages, 4 figure
Current saturation and Coulomb interactions in organic single-crystal transistors
Electronic transport through rubrene single-crystal field effect transistors
(FETs) is investigated experimentally in the high carrier density regime (n ~
0.1 carrier/molecule). In this regime, we find that the current does not
increase linearly with the density of charge carriers, and tends to saturate.
At the same time, the activation energy for transport unexpectedly increases
with increasing n. We perform a theoretical analysis in terms of a well-defined
microscopic model for interacting Frohlich polarons, that quantitatively
accounts for our experimental observations. This work is particularly
significant for our understanding of electronic transport through organic FETs.Comment: Extended version with 1 additional figure and an appendix explaining
the consistency of the theoretical calculatio
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
Tunable Frohlich Polarons in Organic Single-Crystal Transistors
In organic field effect transistors (FETs), charges move near the surface of
an organic semiconductor, at the interface with a dielectric. In the past, the
nature of the microscopic motion of charge carriers -that determines the device
performance- has been related to the quality of the organic semiconductor.
Recently, it has been appreciated that also the nearby dielectric has an
unexpectedly strong influence. The mechanisms responsible for this influence
are not understood. To investigate these mechanisms we have studied transport
through organic single crystal FETs with different gate insulators. We find
that the temperature dependence of the mobility evolves from metallic-like to
insulating-like with increasing the dielectric constant of the insulator. The
phenomenon is accounted for by a two-dimensional Frohlich polaron model that
quantitatively describes our observations and shows that increasing the
dielectric polarizability results in a crossover from the weak to the strong
polaronic coupling regime
Titanium dioxide doped with vanadium as effective catalyst for selective oxidation of diphenyl sulfide to diphenyl sulfonate
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
PEROXIDASE ELECTROPHORETIC PATTERN OF WHEAT AND TOMATO SEEDLINGS GROWN ON BIOLOGICALLY ACTIVE COMPOUNDS-CONTAINING MEDIUM
Heterogeneous sulfoxidation of thioethers by hydrogen peroxide over layered double hydroxides as catalysts
International audienceA new method for mild oxidation of thioethers with hydrogen peroxide in heterogeneous catalysis is described. The layered double hydroxides (or hydrotalcite-like materials) act as basic catalysts for the sulfoxidation reaction with hydrogen peroxide in the presence of acetonitrile. The influence of the nature of thioether, the type of catalyst, the reaction temperature and reaction time on the catalytic activity and selectivity in this reaction has been investigated. A mechanism of the sulfoxidation reaction is proposed. © 2001 Elsevier Science B.V
DETERMINATION OF MOLECULAR WIGHT OF ISOENZYMES IN A CRUDE EXTRACT BY THIN TAYER GEL FILTRATION AND POLYACRYLAMIDE GEL ELECTROPHORESIS
Acid-base properties of MgCuAl mixed oxides
International audienceMgCuAl layered double hydroxides (LDHs) with a hydrotalcite like structure containing different proportions of Mg2+ and Cu2+ cations have been prepared. Thermogravimetry and X-ray diffraction data indicated that the transformation of LDH into mixed oxides is effective after calcination at 723 K, irrespective of the composition. The acid-base properties of these mixed oxides have been investigated using adsorption microcalorimetry and X-ray photoelectron spectroscopy with NH3 (for acidity) and SO2 (for basicity) as probe molecules. Their catalytic behaviour for the conversion of cyclohexanol has been tested. The acid-base properties and the selectivity of catalysts has been related to their composition
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