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With BF(3)·OEt(2) as the catalyst, the glycosylation of phenols with glycosyl trichloroacetimidates (or N-phenyl trifluoroacetimidates) bearing 2-O-participating groups leads to the desired 1,2-trans-O-glycosides in generally excellent yields without formation of the 1,2-cis-anomers. However, with TMSOTf as the catalyst, the outcomes of the corresponding phenol O-glycosylation are highly dependent on the nucleophilicity of the phenols; less nucleophilic is the phenol, higher amounts of the 1,2-cis-O-glycoside together with more side-products are generated. 1,2-Orthoesters have been found to be the major products at a low temperature (<-70 °C) in all these phenol O-glycosylation reactions, which are transformed into the final products at a higher temperature. BF(3)·OEt(2) is an effective catalyst to promote the conversion of 1,2-orthoesters into the corresponding 1,2-trans-O-glycosides. However, the 1,2-orthoesters could be converted into the dioxolenium triflate and glycosyl triflate in the presence of TMSOTf, these intermediates which might be in equilibrium with the glycosyl oxocarbenium related species lead to the final mixture of the α/β-O-glycosides and side-products., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The microchemical and microstructural origins of insulation-resistance degradation in BaTiO3-based capacitors are studied by complementary impedance spectroscopy and analytical transmission electron microscopy. The degradation under dc-field bias involves electromigration and accumulation of oxygen vacancies at interfaces. The nonstoichiometric BaTiO3-δ becomes locally more conducting through increased oxygen vacancy concentration and Ti ion reduction. The symmetry across the dielectric layer and locally across each grain is broken during the degradation process. Locally, the nonstoichiometry becomes so severe that metastable lattice structures are formed. The degradation in insulation resistance at the grain boundaries and electrode interfaces is associated with the double Schottky-barrier potential lowering and narrowing. This may correlate with an effective decrease in net acceptor charge density at the grain boundaries. [ABSTRACT FROM AUTHOR]

By controlling the temperature and oxygen partial pressure, well polycrystalline Fe3O4 thin film on Pt substrate was fabricated, using a stoichiometric α-Fe2O3 target. A ferrimagnetic hysteresis loop and a Verwey transition at about 130 K were shown in the results of magnetic measurement. A sharp hysteretic resistance switching below Verwey transition temperature (Tv) was observed in I-V tests of the Au/Fe3O4/Pt heterostructure. Enlarged hysteresis by larger pulse delay and suppressed metal-insulator transition by larger source currents indicated that enhanced local Joule heating effect played an important role in the hysteresis of resistance switching. [ABSTRACT FROM AUTHOR]

Bipolar resistive switching (RS) behavior was observed in epitaxially deposited TiO2-δ/La2/3Sr1/3MnO3 stacks. An intermediate initial state of this device demonstrated that the original resistive state would switch to either the higher or the lower state, depending only on the electrical polarity of the initial measurement. As the analogue intermediate states were obtained by device fabrication, the direct observation of these switching states was possible, knowing the microscopic physical origin of the RS effect. Based on x-ray photoelectron spectroscopy analysis, an understanding of this interesting phenomenon was proposed, well supporting the oxygen vacancy formation and recombination mechanism. [ABSTRACT FROM AUTHOR]

Pronounced bipolar resistance switching with a good retention property has been observed in CeO2/PrBa2Cu3O7-δ/Pt heterostructure. The low resistance state and high resistance state exhibited distinguished ferromagnetic signals, as compared to the nearly non-magnetic initial state. It is found that the migration of the oxygen vacancies under electric field is mainly responsible for the electric and the magnetic changes. The modified interfacial electronic structure by the oxygen vacancy migration and the trapping/detrapping of the carriers leads to the resistance switching. The exchange interaction of the hydrogen-like orbitals formed around the singly occupied oxygen vacancies in CeO2 is accounting for the emerged and modulated ferromagnetic signals. Temperature dependence of resistance in the low resistance state follows a variable range hopping law, further confirming that the amount of oxygen vacancies in the CeO2 layer directly affects the hydrogen-like orbital radius, which determines the strength of the ferromagnetic coupling. [ABSTRACT FROM AUTHOR]