Kinetics of interface state-limited hole injection in alpha-naphthylphenylbiphenyl diamine (alpha-NPD) thin layers

Injection-limited operation is identified in thin-film, alpha-NPD-based diodes. A detailed model for the impedance of the injection process is provided which considers the kinetics of filling/releasing of interface states as the key factor behind the injection mechanism. The injection model is able to simultaneously account for the steady-state, current-voltage (J-V) characteristics and impedance response. and is based on the sequential injection of holes mediated by energetically distributed surface states at the metal-organic interface. The model takes into account the vacuum level offset caused by the interface dipole, along with the partial shift of the interface level distribution with bias voltage. This approach connects the low-frequency (similar to 1 Hz) capacitance spectra, which exhibits a transition between positive to negative values, to the change in the occupancy of interface states with voltage. Simulations based on the model allow to derive the density of interface states effectively intervening in the carrier injection (similar to 5 x 10(12) cm(-2)), which exhibit a Gaussian-like distribution. A kinetically determined hole barrier is calculated at levels located similar to 0.4 eV below the contact work function. (C) 2008 Elsevier B.V. All rights reserved.

Disorder effects produced by the Mn and H incorporations on the optical absorption edge of Ga1-xMnxAs:H nanocrystalline films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The optical absorption edge of nanocrystalline Ga(1-x)Mn(x)N films deposited by reactive sputtering

We have focused on the optical absorption edge of nanocrystalline Ga(1-x)Mn(x)N (0.00 <= x <= 0.18) films deposited by reactive RF magnetron sputtering. The films obtained are nanocrystalline with grain sizes of about 25 nm, having wurtzite structure and strong orientation texture in the c-axis direction. The optical characterizations of the absorption edges were obtained in the 190-2600 nm spectral range. The increase of the Mn content causes an increase of the absorption coefficient which can be clearly noticed at low energies, and a quasi-linear decrease of the optical gap. Broad absorption bands observed around similar to 1.3 and similar to 2.2 eV were associated with transitions between the Mn acceptor level and the valence and conduction bands, respectively. The observed changes in the optical properties due to the Mn incorporation observed in these nanocrystalline films are similar to those reported for ferromagnetic GaMnN single-crystal films.

Structural Characterization of Nanocrystalline Sb-Doped SnO2 Xerogels by Multiedge X-ray Absorption Spectroscopy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Evaluation of Bulk and Surfaces Absorption Edge Energy of Sol-Gel-Dip-Coating SnO2 Thin Films

The absorption edge and the bandgap transition of sol-gel-dip-coating SnO2 thin films, deposited on quartz substrates, are evaluated from optical absorption data and temperature dependent photoconductivity spectra. Structural properties of these films help the interpretation of bandgap transition nature, since the obtained nanosized dimensions of crystallites are determinant on dominant growth direction and, thus, absorption energy. Electronic properties of the bulk and (110) and (101) surfaces are also presented, calculated by means of density functional theory applied to periodic calculations at B3LYP hybrid functional level. Experimentally obtained absorption edge is compared to the calculated energy band diagrams of bulk and (110) and (101) surfaces. The overall calculated electronic properties in conjunction with structural and electro-optical experimental data suggest that the nature of the bandgap transition is related to a combined effect of bulk and (101) surface, which presents direct bandgap transition.

Enhancement of optical absorption by modulation of the oxygen flow of TiO2 films deposited by reactive sputtering

Oxygen-deficient TiO2 films with enhanced visible and near-infrared optical absorption have been deposited by reactive sputtering using a planar diode radio frequency magnetron configuration. It is observed that the increase in the absorption coefficient is more effective when the O-2 gas supply is periodically interrupted rather than by a decrease of the partial O-2 gas pressure in the deposition plasma. The optical absorption coefficient at 1.5 eV increases from about 1 x 10(2) cm(-1) to more than 4 x 10(3) cm(-1) as a result of the gas flow discontinuity. A red-shift of similar to 0.24 eV in the optical absorption edge is also observed. High resolution transmission electron microscopy with composition analysis shows that the films present a dense columnar morphology, with estimated mean column width of 40nm. Moreover, the interruptions of the O-2 gas flow do not produce detectable variations in the film composition along its growing direction. X-ray diffraction and micro-Raman experiments indicate the presence of the TiO2 anatase, rutile, and brookite phases. The anatase phase is dominant, with a slight increment of the rutile and brookite phases in films deposited under discontinued O-2 gas flow. The increase of optical absorption in the visible and near-infrared regions has been attributed to a high density of defects in the TiO2 films, which is consistent with density functional theory calculations that place oxygen-related vacancy states in the upper third of the optical bandgap. The electronic structure calculation results, along with the adopted deposition method and experimental data, have been used to propose a mechanism to explain the formation of the observed oxygen-related defects in TiO2 thin films. The observed increase in sub-bandgap absorption and the modeling of the corresponding changes in the electronic structure are potentially useful concerning the optimization of efficiency of the photocatalytic activity and the magnetic doping of TiO2 films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4724334]

Respirometric techniques for assessment of biological kinetics in constructed wetland

The aim of this research was the development of a procedure to measure biological kinetics of organic matter oxidation and nitrification in constructed wetland, by using respirometric techniques. Columns simulating cores of vertical subsurface flow systems were investigated. The oxygen uptake rate (OUR) of the columns was calculated on the basis of the difference of DO concentrations measured continuously at the top and at the bottom of the column. From the respirogram, the following kinetic parameters have been evaluated: maximum rate of oxidation of readily biodegradable COD, maximum rate of nitrification, endogenous respiration of the biomass grown inside the bed. In order to improve the interpretation of the respirograms, additional respirometric tests were carried out on the wetland columns by using pure substrates, such as acetate (carbon source) and ammonium (substrate for nitrification). The kinetic parameters obtained from respirograms can be useful for control and design of constructed wetlands or for improving nutrient and carbon mass balances.

Evaluation of the kinetics of xylose formation from dilute sulfuric acid hydrolysis of forest residues of Eucalyptus grandis

Dilute acid hydrolysis studies were performed on forest residues of Eucalyptus grandis, in a cylindrical reactor of stainless steel. The kinetics of this hydrolysis reaction was investigated employing 0.65% sulfuric acid, a residue/acid solution ratio of 1/9 (w/w), temperatures of 130, 140, 150, and 160 degrees C, and reaction times in the range 20-100 min. The results showed that, under the optimized conditions of acid hydrolysis employed in this study, the variables temperature and reaction time had a strong influence on hemicellulose removal and a small influence on the degree of lignin and cellulose removal. The highest xylose extraction yield was 87.6% attained at 160 degrees C, after 70 min reaction time, simultaneously with the formation of decomposition products, namely 2.8% acetic acid, 0.6% furfural, and 0.06% 5-hydroxymethylfurfural. A similar xylose extraction yield (82.8%) was observed at 150 degrees C after 100 min, with the formation of 3.2% acetic acid, 1.0% furfural, and 0.07% 5-hydroxymethylfurfural. The kinetic parameters determined at 130, 140, 150, and 160 degrees C for degradation of xylan present in the hemicellulose of the eucalyptus forest residue during the formation of xylose were the first-order reaction rate constants (k) for each temperature, 1.22 x 10(-4), 2.12 x 10(-4), 5.43 x 10(-4), and 9.05 x 10(-4) s(-1), respectively, and an activation energy (E-a) of 101.3 kJ mol(-1).

SURFACE MODIFICATION of SUGARCANE BAGASSE CELLULOSE and ITS EFFECT on MECHANICAL and WATER ABSORPTION PROPERTIES of SUGARCANE BAGASSE CELLULOSE HDPE COMPOSITES

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Crystallization kinetics in phosphate sodium-based glass studied by DSC technique

In this work, differential scanning calorimetry (DSC) was used to study the mechanism of crystallization of 5OP(2)O(5-)27.8Na(2)O-16ZnO-6.2Al(2)O(3) glass. DSC measurements were performed on bulk and powdered glasses with different particle size. The curve for bulk glass shows one crystallization peak while powdered glasses presented two distinct crystallization peaks. Based on DSC studies, the activation energies obtained were 336 +/- 6 and 213 +/- 3 U mol(-1), associated with first and second crystallization peaks, respectively. Analyzing the DSC parameters as a function of particle size, the Avrami n parameter suggests that the peak at low temperature may be associated with surface crystallization while the peak at high temperature is associated with bulk crystallization. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Controlled release system for ametryn using polymer microspheres: Preparation, characterization and release kinetics in water

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Banana Peel Applied to the Solid Phase Extraction of Copper and Lead from River Water: Preconcentration of Metal Ions with a Fruit Waste

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

4-amine-2-mercaptopyrimidine modified silica gel applied in Cd(II) and Pb(II) extraction from an aqueous medium

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Development of a method to determine Ni and Cd in biodiesel by graphite furnace atomic absorption spectrometry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese, caracterização e estudo cinético da degradação de quitosana impregnada em SBA-15

The recent interest in obtaining functionalized nanoporous materials for applications such as heterogeneous catalysts and adsorption of CO2 has increased today. In the latter application, the introduction of amino groups such as present in the chitosan (CS), in the nanoporous materials like SBA-15 to generate specific interactions with CO2 has gained importance. In this work were performed to hydrothermal synthesis of SBA-15 and subsequent impregnation of the CS in the support mesoporous by the method of the wet impregnation. The materials were characterized by TG/DTG, DSC, XRD, SEM, FTIR and adsorption / desorption of N2. The XRD showed that the ordered structure of the support SBA-15 was preserved after the impregnation and calculations have shown that the average pore diameter (Dp) and / or the average wall thickness (wt) have been changed due to introduction of the CS in the samples functionalized. The curves of TG and DSC data corroborates the XRD, indicating the presence of CS in the nanoporous structure of SBA-15, as well as micrographs of samples, which allowed the display state of aggregation of the material obtained. The characteristics of bands absorption in the region of the CS in the FTIR were identified and interpreted in the samples functionalized, confirming the further characterization. Measurements showed that the BET surface area decreases in the functionalized samples, indicating the successive incorporation of the polymer in the nanoporous support. The activation energy apparent (Ea) for the process of thermal degradation of CS in the impregnated support was determined by the methods of kinetic freedom Vyazovkin and Ozawa-Flynn-Wall with the results indicating that the sample functionalized CS/SBA-15 2,5 % was decrease of the Ea in their degradation of about 10% compared to 1,0 % CS/SBA-15 sample