Room-Temperature Ferromagnetism in Co-Doped In2O3 Nanocrystals

Co-doped In2O3 nanocrystals showing room-temperature ferromagnetism have been successfully prepared by a simple sol-gel synthesis route. The sample displays it clear ferromagnetism behavior above 300 K. Phase and structure analyses reveal that the nanocrystals are crystallized with Co ions substituted for In ions in the In2O3 matrix, and no trace of secondary phases or clusters is detected. The experimental results are explained theoretically by first-principles calculations based on density functional theory, which indicate that the native ferromagnetic behavior of Co-doped In2O3 could be mainly ascribed to the strong d-d coupling of the magnetic ions.

RECRYSTALLIZATION, IMPURITY MIGRATION AND OPTICAL ACTIVATION OF YB-IMPLANTED SILICON INDUCED BY RAPID THERMAL ANNEALING

The rapid thermal annealing temperature dependence of the recrystallization, Yb migration and its optical activation were studied for Yb-implanted silicon. For the annealing regime 800-1000-degrees-C, the Yb segregates both at the crystal/amorphous interface and at the surface, which is different from the usual segregation of Er at the crystal/amorphous interface, and the efficiency of optical activation also increases with annealing temperature. However, the amorphous layer regrows completely and no photoluminescence is observed after the annealing at 1200-degrees-C.

Carrier relaxation and thermal activation of localized excitons in self-organized InAs multilayers grown on GaAs substrates

We have investigated the temperature dependence of photoluminescence (PL) properties of a number of self-organized InAs/GaAs heterostructures with InAs layer thickness ranging from 0.5 to 3 ML. The temperature dependence of InAs exciton emission and linewidth was found to display a significant difference when the InAs layer thickness is smaller or larger than the critical thickness around 1.7 ML. The fast redshift of PL energy and an anomalous decrease of linewidth with increasing temperature were observed and attributed to the efficient relaxation process of carriers in multilayer samples, resulting from the spread and penetration of the carrier wave functions in coupled InAs quantum dots. The measured thermal activation energies of different samples demonstrated that the InAs wetting layer may act as a barrier for the thermionic emission of carriers in high-quality InAs multilayers, while in InAs monolayers and submonolayers the carriers are required to overcome the GaAs barrier to escape thermally from the localized states.

Catalytic Activation of Mg-Doped GaN by Hydrogen Desorption Using Different Metal Thin Layers

The annealing of Mg-doped GaN with Pt and Mo layers has been found to effectively improve the hole concentration of such material by more than 2 times as high as those in the same material without metal. Compared with the Ni and Mo catalysts, Pt showed good activation effect for hydrogen desorption and ohmic contact to the Ni/Au electrode. Despite the weak hydrogen desorption, Mo did not diffuse into the GaNepilayer in the annealing process, thus suppressing the carrier compensation phenomenon with respect to Ni and Pt depositions, which resulted in the high activation of Mg acceptors. For the GaN activated with the Ni, Pt, and Mo layers, the blue emission became dominant, followed by a clear peak redshift and the degradation of photoluminescence signal when compared with that of GaN without metal.

Low-temperature oxidation of methane to form formaldehyde: role of Fe and Mo on Fe-Mo/SiO2 catalysts, and their synergistic effects

The partial oxidation of methane with molecular oxygen was performed on Fe-Mo/SiO2 catalysts. Iron was loaded on the Mo/SiO2 catalyst by chemical vapor deposition of Fe-3(CO)(12). The catalyst showed good low-temperature activities at 723-823 K. Formaldehyde was a major condensable liquid product on the prepared catalyst. There were synergistic effects between iron and molybdenum in Fe-Mo/SiO2 catalysts for the production of formaldehyde from the methane partial oxidation. The activation energy of Mo/SiO2 decreased with the addition of iron and approached that of the Fe/SiO2. The concentration of isolated molybdenum species (the peak at 1148 K in TPR experiments) decreased as the ion concentration increased and had a linear relationship with the selectivity of methane to formaldehyde. The role of Fe and Mo in the Fe-Mo/SiO2 catalyst was proposed: Fe is the center for the C-H activation to generate reaction intermediates, and Mo is the one for the transformation of intermediates into formaldehyde. Those phenomena were predominant below 775 K.

Study on the Adsorption and Activation of NO and CO over Mixed Oxide Catalysts Containing Cu by Means of TPSR

Adsorption and activation of small molecules NO, CO and CO+ NO on LaSrCuO4, La2CuO4 and La1.7Th0.3CuO4 which are typical samples in the sence of nonstoichiometric oxygen(lambda) anrong the series of La2-x(SrTh)(x)CuO4 +/-lambda mixed oxide catalysts were studied by means of MS- TPD (TPSR ), XRD, chemical analysis and so on. It was shown that the adsorption amount of NO can be correlated with the content of oxygen vacancy while the types and strength of adsorption of NO could be related to the oxidation state of the metallic ion. It was also found that CO molecule was first converted into CO32- and then desorbed in the form of CO2 at high temperature during the adsorption and desorption of CO on the mixed oxide with oxygen vacancy. The fact that the profiles of TPD(TPSR) of NO in co-adsorption of NO+CO and in single NO adsorption are similar shows that the adsorption of NO molecule not only has some priority to that of CO but also is stronger than that of CO. It seems that the adsorption of NO plays a dominate role in the activation and decomposition of NO.

Low-temperature oxidation of CO over Pd/CeO2-TiO2 catalysts with different pretreatments

A comprehensive study of the low-temperature oxidation of CO was conducted over Pd/TiO2, Pd/CeO2, and Pd/CeO2-TiO2 pretreated by a series of calcination and reduction processes. The catalysts were characterized by N-2 adsorption, XRD, H-2 chemisorption, and diffuse-reflectance infrared Fourier transform spectroscopy. The results indicated that Pd/CeO2-TiO2 has the highest activity among these catalysts, whether in the calcined state or in the reduced state. The activity of all of the catalysts can be improved significantly by the pre-reduction, and it seems that the reduction at low temperature (LTR. 150 degrees C) is more effective than that at high temperature (HTR, 500 degrees C), especially for Pd/CeO2 and Pd/TiO2. The catalysts with various supports and pretreatments are also different in the reaction mechanisms for CO oxidation at low temperature. Over Pd/TiO2, the reaction may proceed through a surface reaction between the weakly adsorbed CO and oxygen (Langmuir-Hinshelwood). For Ce-containing catalysts, however, an alteration of reaction mechanism with temperature and the involvement of the oxygen activation at different sites were observed, and the light-off profiles of the calcined Pd/CeO2 and Pd/CeOi-TiO2 show a distortion before CO conversion achieves 100%. At low temperature, CO oxidation proceeds mainly via the reaction between the adsorbed CO on Pd-0 sites and the lattice oxygen of surface CeO2 at the Pd-Ce interface, whereas at high temperature it proceeds via the reaction between the adsorbed CO and oxygen. The high activity of Pd/CeO2-TiO2 for the low-temperature CO oxidation was probably due to the enhancements of both CO activation, caused by the facilitated reduction of Pd2+ to Pd-0, and oxygen activation, through the improvement of the surface oxygen supply and the oxygen vacancies formation. The reduction pretreatment enhances metal-support interactions and oxygen vacancy formation and hence improves the activity of CO oxidation. (c) 2005 Elsevier Inc. All rights reserved.

The electrochemical oxidation of hydrogen at activated platinum electrodes in room temperature ionic liquids as solvents

The oxidation of hydrogen was studied at an activated platinum micro-electrode by cyclic voltammetry in the following ionic liquids: [C(2)mim][NTf2], [C(4)mim][NTf2], [N-6.2.2.2][NTf2], [P-14.6.6.6][NTf2], [C(4)mim][OTf], [C(4)mim][BF4] [C(4)mim][PF6], [C(4)mim][NO3], [C(6)mim]Cl and [C(6)mim][FAP] (where [C(n)mim](+) = 1-alkyl-3-methylimidazolium, [N-6,N-2,N-2,N-2](+) = n-hexyltriethylammonium, [P-14,P-6,P-6,P-6](+) = tris(n-hexyltetradecyl) phosphonium, [NTf2](-) = bis(trifluoromethylsulfonyl)amide, [OTf] = trifluoromethlysulfonate and [FAP](-) = tris(perfluoroethyl)trifluorophosphate). Activation of the Pt electrode was necessary to obtain reliable and reproducible voltammetry. After activation of the electrode, the H-2 oxidation waves were nearly electrochemically and chemically reversible in [C(n)mim][NTf2] ionic liquids, chemically irreversible in [C(6)mim]Cl and [C(4)mim][NO3], and showed intermediate characteristics in OTf-, [BF4](-), [PF6](-), [FAP](-) and other [NTf2](-)-based ionic liquids. These differences reflect the contrasting interactions of protons with the respective RTIL anions. The oxidation peaks are reported relative to the half-wave potential of the cobaltocenium/cobaltocene redox couple in all ionic liquids studied, giving an indication of the relative proton interactions of each ionic liquid. A preliminary temperature study (ca. 298-333 K) has also been carried out in some of the ionic liquids. Diffusion coefficients and solubilities of hydrogen at 298 K were obtained from potential-step chronoamperometry, and there was no relationship found between the diffusion coefficients and solvent viscosity. RTILs possessing [NTf2](-) and [FAP](-) anions showed the highest micro-electrode peak currents for the oxidation in H-2 saturated solutions, with[C(4)mim][NTf2] toeing the most sensitive. The large number of available RTIL anion/cation pairs allows scope for the possible electrochemical detection of hydrogen gas for use in gas sensor technology. (c) 2008 Elsevier B.V. All rights reserved.

Oxidation of several p-phenylenediamines in room temperature ionic liquids: Estimation of transport and electrode kinetic parameters

The electrochemical oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) has been studied by cyclic voltammetry and potential step chronoamperometry at 303 K in five ionic liquids, namely [C(2)mim] [NTf2], [C(4)mim] [NTf2] [C(4)mpyrr] [NTf2] [C(4)mim] [BF4], and [C(4)mim] [PF6] (where [C(n)mim](+) = 1-alkyl-3-methylimidazolium, [C(4)mpyrr](+) = N-butyl-N-methylpyrrolidinium, [NTf2](-) = bis(trifluoromethylsulfonyl)imide, [BF4](-) = tetrafluoroborate, and [PF6](-) = hexafluorophosphate). Diffusion coefficients, D, of 4.87, 3.32, 2.05, 1.74, and 1.34 x 10(-11) m(2) s(-1) and heterogeneous electron-transfer rate constants, k(0), of 0.0109, 0.0103, 0.0079, 0.0066, and 0.0059 cm s(-1) were calculated for TMPD in [C(2)mim] [NTf2], [C(4)mim] [NTf2], [C(4)mpyrr] [NTf2], [C(4)mim] [BF4], and [C(4)mim] [PF6], respectively, at 303 K. The oxidation of TMPD in [C4mim][PF6] was also carried out at increasing temperatures from 303 to 343 K, with an activation energy for diffusion of 32.3 kJ mol(-1). k(0) was found to increase systematically with increasing temperature, and an activation energy of 31.4 kJ mol(-1) was calculated. The study was extended to six other p-phenylenediamines with alkyl/phenyl group substitutions. D and k(0) values were calculated for these compounds in [C(2)mim] [NTf2], and it was found that k(0) showed no obvious relationship with the hydrodynamic radius, r.

Electroreduction of sulfur dioxide in some room-temperature ionic liquids

The mechanism of sulfur dioxide reduction at a platinum microelectrode was investigated by cyclic voltammetry in several room-temperature ionic liquids (RTILs)-[C(2)mim][NTf2], [C(4)mim][BF4], [C(4)mim][NO3], [C(4)mim][PF6], and [C(6)mim][Cl] where [C(2)mim] is 1-ethyl-3-methylimidazolium, [C(4)mim] is 1-butyl-3-methylimidazolium, [C(6)mim] is 1-hexyl-3-methylimidazolium, and [NTf2] is bis(trifluoromethylsufonyl)imide-with special attention paid to [C(4)mim][NO3] because of the well-defined voltammetry, high solubility, and relatively low diffusion coefficient of SO2 obtained in that ionic liquid. A cathodic peak is observed in all RTILs between -2.0 and -1.0 V versus a silver quasi-reference electrode. In [C(4)mim][NO3], the peak appears at -1.0 V, and potential step chronoamperometry was used to determine that SO2 has a very high solubility of 3100 (+/-450) mM and a diffusion coefficient of 5.0 (+/-0.8) x 10(-10) m(2) s(-1) in that ionic liquid. On the reverse wave, up to four anodic peaks are observed at ca. -0.4, -0.3, -0.2, and 0.2 V in [C(4)mim][NO3]. The cathodic wave is assigned to the reduction of SO2 to its radical anion, SO2-center dot. The peaks at -0.4 and -0.2 V are assigned to the oxidation of unsolvated and solvated SO2-center dot, respectively. The peak appearing at 0.2 V is assigned to the oxidation of either S2O42- or S2O4-center dot. The activation energy for the reduction of SO2 in [C(4)mim][NO3] was measured to be 10 (+/-2) kJ mol(-1) using chronoamperometric data at different temperatures. The stabilizing interaction of the solvent with the reduced species SO2-center dot leads to a different mechanism than that observed in conventional aprotic solvents. The high sensitivity of the system to SO2 also suggests that [C(4)mim][NO3] may be a viable solvent in gas sensing applications.

An electrochemical study of the oxidation of hydrogen at platinum electrodes in several room temperature ionic liquids

The electrochemical oxidation of dissolved hydrogen gas has been studied in a range of room-temperature ionic liquids (RTILs), namely [C(2)mim][NTf2], [C(4)mim][NTf2], [N-6,N-2,N-2,N-2][NTf2], [P-14,P-6,P-6,P-6][NTf2], [C(4)mpyrr][NTf2], [C(4)mim][BF4], [C(4)mim][PF6], [C(4)mim][OTf], and [C(6)mim]Cl on a platinum microdisk electrode of diameter 10 mu m. In all cases, except [C(6)mim]Cl, a broad quasi-electrochemically reversible oxidation peak between 0.3 to 1.3 V vs Ag was seen prior to electrode activation ([C(6)mim]Cl showed an almost irreversible wave). When the electrode was pre-anodized (

Electroreduction of N-methylphthalimide in room temperature ionic liquids under insonated and silent conditions

The selective electroreduction N-methylphthalimide to 3-hydroxy-2-methyl-isoindolin-1-one has been performed in ionic liquids using phenol as a proton donor under silent and ultrasonic conditions. A significant increase in the rate of electroreduction is shown using ultrasonic activation and in addition high current efficiencies were observed. Some decomposition of the ionic liquid was found to have occurred under exposure to ultrasound. © 2004 Elsevier B.V. All rights reserved.

A comparative electrochemical study of diffusion in room temperature ionic liquid solvents versus acetonitrile

Measurements on the diffusion coefficient of the neutral molecule N,N,N',N'-tetramethyl-para-phenylenediamine and the radical cation and dication generated by its one- and two-electron oxidation, respectively, are reported over the range 298-348 K in both acetonitrile and four room temperature ionic liquids (RTILs). Data were collected using single and double potential step chronamperometry at a gold disk electrode of micrometer dimension, and analysed via fitting to the appropriate analytical expression or, where necessary, to simulation. The variation of diffusion coefficient with temperature was found to occur in an Arrhenius-type manner for all combinations of solute and solvent. For a given ionic liquid, the diffusional activation energies of each species were not only closely equivalent to each other, but also to the RTIL's activation energy of viscous flow. In acetonitrile supported with 0.1 M tetrabutylammonium perchlorate, the ratio in diffusion coefficients of the radial cation and dication tot he neutral molecule were calculated as 0.89 +/- 0.05 and 0.51 +/- 0.03, respectively. In contrast, amongst the ionic liquids the same ratios were determined to be on average 0.53 +/- 0.04 and 0.33 +/- 0.03. The consequences of this dissimilarity are considered in terms of the modelling of voltammetric data gathered within ionic liquid solvents.

The Reduction of Oxygen in Various Room Temperature Ionic Liquids in the Temperature Range 293-318 K: Exploring the Applicability of the Stokes-Einstein Relationship in Room Temperature Ionic Liquids

The voltammetry for the reduction of oxygen at a microdisk electrode is reported in six commonly used RTILs: [C(4)mim][NTf2], [C(4)mpyrr][NTf2], [C(4)dmim][NTf2], [C(4)mim][BF4], [C(4)mim][PF6], and [N-6.2.2.2][NTf2], where [C(4)mim](+) is 1-butyl-3-methylimidazolium, [NTf2](-) is bis(trifluoromethanesulfonyl)imide, [C(4)mpyrr](+) is N-butyl-N-methylpyrrolidinium, [C(4)dmim](+) is 1-butyl-2,3-methylimidazolium, [BF4](-) is tetrafluoroborate, [PF6](-) is hexafluorophosphate, and [N-6.2.2.2](+) is n-hexyltriethylammonium at varying scan rates (50-4000 mV s(-1)) and temperatures (293-318 K). Diffusion coefficients, D, of oxygen are deduced at each temperature from potential-step chronoamperometry, and diffusional activation energies are calculated. Oxygen solubilities are also reported as a function of temperature. In the six ionic liquids, the Stokes-Einstein relationship (D proportional to eta(-1)) was found to apply only very approximately for oxygen. This is considered in relationship to the behavior of other diverse solutes in RTILs.

Voltammetric Currents in Room Temperature Ionic Liquids Can Reflect Solutes Other Than the Electroactive Species and Are Influenced by Carbon Dioxide

The effects of such solutes such as halides and water on the physical properties of room temperature ionic liquids (RTILs) have been extensively studied, This work examines the effect of the solute carbon dioxide on the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide ([C(2)mim][NTf2]) and its influence on the electrochemical characterization of the important redox couple ferrocene/ferrocenium (Fc/Fc(+)). The system was studied using cyclic voltammetry, chronoamperometry, and electron spin resonance (ESR) spectroscopy. Addition Of 100% CO2 to a solution of Fc in [C(2)mim][NTf2] resulted in a substantial increase in both the limiting oxidative current and diffusion coefficient of Fc. Arrhenius plots of Fc diffusion coefficients in the pure and CO2-saturated ionic liquid revealed a decrease in activation energy of translational diffusion from 29.0 (+/- 0.5) kJ mol(-1) to 14.7 (+/- 1.6) kJ mol(-1), suggesting a reduction in the viscosity of the ionic liquid with addition Of CO2. ESR spectroscopy was then used to calculate the rotational correlation coefficients of a probe molecule, 2,2,6,6-tetramethyl-1-piperinyloxyl (TEMPO), to add supporting evidence to this hypothesis. Arrhenius plots of rotational correlation coefficients in the pure and CO2-saturated ionic liquid resulted in a similar drop in activation energy from 28.7 (+/- 2.1) kJ mol(-1) to 18.2 (+/- 5.6) kJ mol(-1). The effect of this solute on the ionic liquid [C(2)mim][NTf2] and on the electrochemical measurements of the Fc/Fc(+) couple emphasizes the necessity of fastidious sample preparation, as it is clear that the voltammetric currents of the electroactive species under study are influenced by the presence of CO2 in solution. The voltammetric response of the electroactive species in RTILs cannot be assumed to be independent of other solutes.