ZnO Nanorods via Spray Deposition of Solutions Containing Zinc Chloride and Thiocarbamide

In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous solutions containing ZnCl2and thiocarbamide (tu) at different molar ratios. It has been observed that addition of thiocarbamide into the spray solution has great impact on the size, shape and phase composition of the ZnO crystals. Obtained layers were characterized by scanning electron microscopy (SEM) equipped with energy selected backscattered electron detection system (ESB), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). Small addition of thiocarbamide into ZnCl2solution (ZnCl2:tu = 1:0.25) supports development of significantly thinner ZnO nanorods with higher aspect ratio compared to those obtained from ZnCl2solution. Diameter of ZnO rods decreases from 270 to 100 nm and aspect ratio increases from ∼2.5 to 12 spraying ZnCl2and ZnCl2:tu solutions, respectively. According to XRD, well crystallized (002) orientated pure wurtzite ZnO crystals have been formed. However, tiny ‘spot’—like formations of ZnS were detected on the side planes of hexagonal rods prepared from the thiocarbamide containing solutions. Being adsorbed on the side facets of the crystals ZnS inhibits width growth and promotes longitudinalc-axis growth

Strangeness Suppression of q(q)over-bar Creation Observed in Exclusive Reactions

We measured the ratios of electroproduction cross-sections from a proton target for three exclusive meson-baryon final states: $\Lambda K^+$, $p\pi^0$, and $n\pi^+$, with the CLAS detector at Jefferson Lab. Using a simple model of quark hadronization we extract q-qbar creation probabilities for the first time in exclusive two-body production, in which only a single q-qbar pair is created. We observe a sizable suppression of strange quark-antiquark pairs compared to non-strange pairs, similar to that seen in high-energy production.Comment: 5pages, 2figure

Structural and process optimization of composite structures with resin transfer moldings.

International audienc

Multidisciplinary optimisation of composite laminates with resin transfer molding.

International audienc

Simultaneous optimization for structural design and manufacturing process of composite structures.

International audienc

Efficient crossover designs in the presence of interactions between direct and carry-over treatment effects

Crossover designs, or repeated measurements designs, are used for experiments in which t treatments are applied to each of n experimental units successively over p time periods. Such experiments are widely used in areas such as clinical trials, experimental psychology and agricultural field trials. In addition to the direct effect on the response of the treatment in the period of application, there is also the possible presence of a residual, or carry-over, effect of a treatment from one or more previous periods. We use a model in which the residual effect from a treatment depends upon the treatment applied in the succeeding period; that is, a model which includes interactions between the treatment direct and residual effects. We assume that residual effects do not persist further than one succeeding period.A particular class of strongly balanced repeated measurements designs with n=t2 units and which are uniform on the periods is examined. A lower bound for the A-efficiency of the designs for estimating the direct effects is derived and it is shown that such designs are highly efficient for any number of periods p=2,…,2

Metal-organic vapor phase epitaxial growth of high-quality ZnO on Al2O3(00.1)

High-quality ZnO thin films were grown epitaxially at 250-550 degreesC Al2O3(00.1) substrates using low-pressure metalorganic vapor phase epitaxy. The reactants for the growth were diethylzinc and oxygen. Growth temperature, one of the important experimental parameters for epitaxial layers, was optimized. The films grown at 500 degreesC exhibited good crystallinity and strong ultraviolet absorption and emission. Photoluminescence spectra of the films showed a dominant excitonic emission with a weak deep level emission. More importantly, a strong stimulated emission peak was observed even at room temperature.This research was sponsored by POSTECH BSRI Special Fund-2000, the Brain Korea 21 project, and the KISTEP through the National Research Laboratory program