Synthesis,microstructure and optical characterization of zirconium oxide nanostructures

Zirconium oxide (ZrO₂) nanostructures were synthesized by hydrothermal route. Surface morphology analysis depicts the formation of the nanobars and hexagonal-shaped nanodiscs at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO₂ product is of pure monoclinic phase (m-ZrO₂) with crystallite size of about 25 nm. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of the m-ZrO₂. The UV–vis absorption spectrum showed a strong absorption peak at about 292 nm and the estimated optical band gap was around 3.57 eV. Photoluminescence (PL) spectrum of ZrO₂ nanostructure showed a strong and broad emission peak at around 410 nm at room temperature, which can be attributed to the ionized oxygen vacancy in the material.     

Zinc oxide micro- and nanoparticles: Synthesis, structure and optical properties

Zinc oxide (ZnO) spherical nanoparticles (SNPs) and bitter-melon-like (BML) microparticles were synthesized by a hydrothermal route using a zinc (Zn) plate as a source and substrate at various synthesis conditions. The structural analysis confirmed the formation of ZnO with hexagonal wurtzite phase on the hexagonal Zn substrate with growth of the ZnO microparticles along the [1 0 1] direction. The UV-vis absorption spectra of the ZnO microparticles indicated absorption peaks in the UV region which can be attributed to the band gap of ZnO. The room temperature photoluminescence (PL) of the ZnO microparticles exhibited a broad emission band, which is fitted with four Gaussian peaks and were assigned to transitions involving free excitons and various defect centers. The growth model for the formation of ZnO micro- and nanoparticles is presented.     

Influence of soil grading on the characteristics of cement stabilised soil compacts

The paper deals with experimental investigations aiming at specifying optimum soil grading limits for the production of cement stabilised soil bricks (CSSB). Wide range of soil grading curves encompassing both fine and coarse grained soils were considered. Strength, durability and absorption characteristics of CSSB were examined considering 14 different types of soil grading curves and three cement contents. The investigations show that there is optimum clay content for the soil mix which yields maximum compressive strength for CSSB and the optimum clay content is about 10 and 14 % for fine grained and coarse grained soils respectively. Void ratio of the compacted specimens is the lowest at the optimum clay content and therefore possesses maximum strength at that point. CSSB using fine grained soils shows higher strength and better durability characteristics when compared to the bricks using coarse grained soils.     

A single-molecule potentiometer

Controlling electron transport through a single-molecule device is key to the realization of nanoscale electronic components. A design requirement for single molecule electrical devices is that the molecule must be both structurally and electrically connected to the metallic electrodes. Typically, the mechanical and electrical contacts are achieved by the same chemical moiety. In this study, we demonstrate that the structural role may be played by one group (for example, a sulfide) while the electrical role may be played by another (a conjugated chain of C═C π-bonds). We can specify the electrical conductance through the molecule by modulating to which particular site on the oligoene chain the electrode binds. The result is a device that functions as a potentiometer at the single-molecule level.     

Single-molecule circuits with well-defined molecular conductance

We measure the conductance of amine-terminated molecules by breaking Au point contacts in a molecular solution at room temperature. We find that the variability of the observed conductance for the diamine molecule-Au junctions is much less than the variability for diisonitrile- and dithiol-Au junctions. This narrow distribution enables unambiguous conductance measurements of single molecules. For an alkane diamine series with 2-8 carbon atoms in the hydrocarbon chain, our results show a systematic trend in the conductance from which we extract a tunneling decay constant of 0.91 +/- 0.03 per methylene group. We hypothesize that the diamine link binds preferentially to undercoordinated Au atoms in the junction. This is supported by density functional theory-based calculations that show the amine binding to a gold adatom with sufficient angular flexibility for easy junction formation but well-defined electronic coupling of the N lone pair to the Au. Therefore, the amine linkage leads to well-defined conductance measurements of a single molecule junction in a statistical study.     

Strategies for stereocontrol at C1 or C2 in syntheses of α-glucosaminides

The C1 and C2 stereocenters of α-glucosaminides can be prepared by establishing the stereocenters in either order. For the former, a C2-azido glucosyl donor is prepared first, and the restraining effect of a 4,6-O-benzylidene ring is used to induce α-coupling. For the latter, the C1 linkage is prepared first by use of an n-pentenyl-manno-1,2-orthoester donor which ensures (a) clean α-coupling and (b) a convenient C2-ester. The C2-ester is replaced with a triflate leaving group, and nucleophilic displacement is effected by use of a hypervalent silicon azide.