Effect of substrate temperature on the room-temperature ferromagnetism of Cu-doped ZnO films

Wurtzite structure ZnO films doped with ~2 at% Cu were deposited at substrate temperatures (T_s) from 350 to 600 °C by helicon magnetron sputtering. All the films exhibited room-temperature (RT) ferromagnetism (FM) and the maximum saturation magnetization (M_s) was 1.2 emu/cm³ (~0.15 μ_B/Cu). Cu ions were mainly in a divalent state as identified by X-ray photoelectron spectroscopy. FM tended to increase with decreasing T_s, and vacuum annealing enhanced the M_s. These results suggested that oxygen vacancies and/or zinc interstitials might contribute to the ferromagnetic performance. Thus, the observed FM was explained in terms of the defect related mechanism.     

Periodate oxidation analysis of carbohydrates: Part IX. Evaluation of the use of pyridine as reaction solvent for oxidation of water-insoluble carbohydrate materials

Oxidation of methyl glycopyranosides with periodic acid in pyridine was studied by analysis of the reaction products by the dithioacetal method. Both C₂—C₃ and C₃—C₄ bonds were cleaved yielding three types of dialdehydes;secondary attack of these dialdehydes by periodic acid did not occur. Oxidation in aqueous pyridine proceeded in normal Malapradian fashion, but more slowly than for oxidation in water. Molar proportions of aldehydes were theoretical, when methyl glycosides were oxidized with periodic acid in a 1:1 ($\text{v}\text{v}$) mixture of pyridine and water. The structures of carbohydrate moieties in a few saponins and glycolipids were confirmed by analysis of the oxidation products obtained under similar conditions.     

Aromatic hydroxylation with peroxymonophosphoric acid

Aromatic hydroxylation of mesitylene, phenol and anisole (ArH) with peroxymonosphosphoric acid (H₃PO₅) in acetonitrile has been studied. H₃PO₅ is shown to be an effective reagent for aromatic hydroxylation, the reactivity being comparable to that with CF₃CO₃H. Mesitylene gives mesitol (over 70%). The hydroxylation with H₃PO₅ is ca 100 fold faster than that with MeCO₃H or PhCO₃H. The rate equation is: v = k₂[ArH][H₃PO₅] instead of our previous one. The oxidation is catalyzed by H₂SO₄, giving a linear plot of log k₂ vs H₀ with a slope of 1.26 for phenol and 1.17 for mesitylene.     

Helical superstructures of fullerene peapods and empty single-walled carbon nanotubes formed in water

Aqueous dispersions of fullerene C70-filled carbon nanotubes (C70@SWNTs or peapods) and empty single-walled carbon nanotubes (empty SWNTs) were prepared with the aid of trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (1), which is a carbon nanotube solubilizer. This is the first report describing the preparation and characterization of the transparent dispersion/dissolution of the peapods. The UV-vis-near-IR spectra of C70@SWNTs-1 and empty SWNTs-1 were almost identical. We found by means of transmission electron microscopy and atomic force microscopy that the empty SWNTs and C70-peapods form helical nanostructures in the shapes of rings, irregular rings, lassos, handcuffs, catenanes, pseudorotaxanes, and figure-eight structures. The mechanism of the superstructure formation has been discussed in relation to the unique characteristics of stiff polymer chains with the aid of an off-lattice Monte Carlo simulation.     

Oxidative addition reactions of carbon diselenide and areneselenols to some iridium(I) and platinum(0) complexes

Reaction of carbon diselenide in 3 to 1 molar ratio, and areneselenols in equimolar ratio, with trans-IrCl(CO)(PPPh₃)₂ and PtL₄, gives oxidative addition products, IrCl(CO)CSe₂)(PPh₃)₂, Pt(CSe₂)L₂, IrHCl(CO)(SeC₆H₄Me-p)(PPh₃)₂, and PtH(SeR)L₂, respectively (R = Ph and p-MeC₆H₄; L = PPh₃ and PPh₂Me). However, reactions of PtL₄ with an excess of areneselenols afford bis(arylselenide) complexes Pt(SeR)₂L₂. The configurations of these complexes are discussed on the basis of their IR and PMR spectra. The carbon diselenide adducts are suggested to have configurations similar to the corresponding carbon disulfide adducts. The platinum hydrides are found to exist as a mixture of cis and trans isomers in solution, both the isomers being labile with regard to dissociative exchange of the tertiary phosphine ligands. The trans configurations of Pt(SeR)₂(PPh₂Me)₂ are unambiguously shown by the virtually coupled triplet pattern of the PPh₂Me signals.     

Electrochemical impedance spectroscopy study of a hydrogen electrode reaction at a Zn electrode in a molten LiCl-KCl-LiH system

The hydrogen electrode reaction involving hydride ion, H-, at a Zn electrode is investigated in a molten LiCl-KCl-LiH system at 673 K. The charge-transfer resistances were measured by electrochemical impedance spectroscopy in the overpotential region of 0.10 < or = eta < or = 0.35 V and over the H- concentrations of 1.5 x 10(-4) < or = C(H)- < or = 1.2 x 10(-3) mol cm(-3). The logarithm plot of the charge-transfer resistance against the overpotential at C(H)- = 3.0 x 10(-4) mol cm(-3) gives the symmetry factor, beta, of 0.50 and the exchange current density, j0, of 5.8 x 10(-3)A cm(-2), respectively. Analysis of the dependence of j0 on H- concentration independently gives a beta of 0.55. The reasonable beta values indicate that the H- <==> H(ad)(M) + e- step is rate-determining.     

Separation of vanadium isotopes by ion-exchange chromatography

Cation-exchange displacement chromatography of VO2+ was carried out for studying vanadium isotope effects in carboxylate ligand-exchange systems. The heavier isotope 51V was enriched in the carboxylate complex solution. The isotope separation coefficients epsilon(= alpha-1) for 50V/51V were 2.2 x 10(-4) and 2.4 x 10(-4) for citrate and lactate systems at 298 K, respectively. These values are much larger than those obtained in a previous study on the malate system. The existence of binuclear complexes of VO2+ may create the conditions for larger isotope fractionation. From the viewpoint of the process development of isotope separation, the heights equivalent to a theoretical plate of these processes were analyzed and found to be very small in each system due to the homogeneous, small and highly porous resin used. Citrate may be better than the other tested systems for the vanadium isotope separation.     

The effect of the anion fraction on the physicochemical properties of EMIm(HF)nF (n = 1.0-2.6)

A series of molten salts EMIm(HF)nF's with different n values has been synthesized by the reaction of EMImHF(2) and anhydrous hydrogen fluoride. The salts contain EMIm cation and some oligomeric fluorohydrogenate anions, (HF)nF-, of which the fraction changes with the change of n. A phase diagram of EMIm(HF)nF's (n = 1.0-2.6) has been constructed which suggests the presence of the stoichiometric compounds, EMIm(HF)1.5F and EMIm(HF)2F, in this range. Compared to the EMIm(HF)2.3F previously reported, EMIm(HF)nF's (n = 1.8-2.0) possess wider liquid temperature ranges because of their similar melting points and superior thermal stabilities at elevated temperatures. The electrochemical windows of EMIm(HF)nF's (n = 1.0-2.6) falls in the range of 2.9-3.4 V. The conductivity of EMIm(HF)nF's (n = 1.0-2.6) increases with the increase of n.