Electrochemical deposition of silver nanoparticles on TiO2/FTO thin films

Silver nanoparticles were deposited on titanium oxide^IV (TiO₂) thin films supported on FTO (fluorine-doped tin oxide^IV) glass using a double pulse electrochemical deposition method. A systematic study of particle nucleation and growth is presented as a function of applied potential and time. Samples were analyzed by grazing-angle X-ray diffraction (GIXRD) technique and morphology was observed using Scanning Electron Microscopy and Energy Dispersive Spectroscopy device (SEM-EDS). Our results confirm the possibility of controlled electrochemical homogeneous deposition of metallic silver particles over TiO₂ surface, which exhibit a potential application in catalytic processes.     

N-Biphenyl thioureas as carboxylate receptors. Effect of the ligand substituents on the geometry of the complexes

Six new biphenyl thiourea derivatives have been prepared to be used in carboxylate sensing. Experiments carried out with these ligands have demonstrated that the type of interaction with TBA carboxylates is strongly dependent on the substituents in the thiourea moiety. These interactions go from the formation of 1:1 hydrogen-bonded complexes to acid-base reactions. In addition, different geometries have been observed for the complexes being dependent on the conformations of the free ligands in solution.     

Limewashing paintings in Alentejo urban heritage: pigment characterization and differentiation by WDXRF and XRD

Pigments used in traditional limewashing paintings in Alentejo urban Heritage are inorganic materials and can be grouped into four categories: a) reds – red ochre (from terras rossas, red schists and iron ore deposits weathering), almagres, terra roxa (natural processed red ochres) and synthetic red iron oxides; b) yellows – yellow ochre (from schists and iron ore deposits), processed natural ochres, yellow iron synthetic oxides, c) blacks – black earths and black iron synthetic oxides and d) blues – artificial ultramarine. The present work proposes to characterize natural, natural processed and synthetic pigments by comparing phase and elemental compositions. The results reveal differences in Fe, Si, K and Al total content according to their origin and fabrication process and reveal intentional addition of white charges like carbonates. Elements like Zr, Ti, Cr, Mn, Ca and Zn are present in all categories. Under optical microscopy, some samples of processed natural pigments do not exhibit optical activity, thus revealing mixtures with synthetic pigments, while natural pigments present a strong birefringence colorless due to optically active minerals. PACS 78.70.En; 07.60.Pb; 61.10.Nz; 81.70.-q; 91.60.-x     

Fabrication of a Cu‐Cone‐Shaped Cation Source Inserted Conductive Bridge Random Access Memory and Its Improved Switching Reliability

Conductive bridge random access memory (CBRAM) has been regarded as a promising candidate for the next‐generation nonvolatile memory technology. Even with the great performance of CBRAM, the global generation and overinjection of cations after much repetitive switching cannot be prevented. The overinjection of cations into an electrolyte layer causes high‐resistance‐state resistance (R_HRS) degradation, on/off ratio reduction, and eventual switching failure. It also degrades the switching uniformity. In this work, a Cu‐cone‐structure‐embedded TiN/TiO₂/Cu cone/TiN device is fabricated to alleviate the problems of Cu‐based CBRAM, mentioned above. The fabrication method of the device, which is useful for laboratory scale experiment, is developed, and its superior switching performance and reliability compared with the conventional planar device. The insertion of the Cu cone structure allows the placement of only a limited amount of cation source in each cell, and the embedded conical structure also concentrates the applied electric field, which enables filament growth control. Furthermore, the concentrated field localizes the resistive switching on the tip area of the cone structure, which makes the effective switching area about tens of nanometers even for the much larger area of the entire electrode (several µm²).     

Photocontrolled Cobalt Catalysis for Selective Hydroboration of α,β-Unsaturated Ketones

Selectivity between 1,2 and 1,4 addition of a nucleophile to an α,β-unsaturated carbonyl compound has classically been modified by the addition of stoichiometric additives to the substrate or reagent to increase their “hard” or “soft” character. Here, we demonstrate a conceptually distinct approach that instead relies on controlling the coordination sphere of a catalyst with visible light. In this way, we bias the reaction down two divergent pathways, giving contrasting products in the catalytic hydroboration of α,β-unsaturated ketones. This includes direct access to previously elusive cyclic enolborates, via 1,4-selective hydroboration, providing a straightforward and stereoselective route to rare syn-aldol products in one-pot. DFT calculations and mechanistic experiments confirm two different mechanisms are operative, underpinning this unusual photocontrolled selectivity switch.