Numerical simulation of the growth of ZnO nanostructures in a tube furnace by physical vapour deposition

Zinc oxide is a versatile II-VI naturally n-type semiconductor that exhibits piezoelectric properties. By controlling the growth kinetics during a simple carbothermal reduction process a wide range of 1D nanostructures such as nanowires, nanobelts, and nanotetrapods have been synthesized. The driving force: for the nanostructure growth is the Zn vapour supersaturation and supply rate which, if known, can be used to predict and explain the type of crystal structure that results. A model which attempts to determine the Zn vapour concentration as a function of position in the growth furnace is described. A numerical simulation package, COMSOL, was used to simultaneously model the effects of fluid flow, diffusion and heat transfer in a tube furnace made specifically for ZnO nanostructure growth. Parameters such as the temperature, pressure, and flow rate are used as inputs to the model to show the effect that each one has on the Zn concentration profile. An experimental parametric study of ZnO nanostructure growth was also conducted and compared to the model predictions for the Zn concentration in the tube. © 2008 Materials Research Society.

The behavior of a single pile under cyclic axial loads

Many piled foundations have been destroyed under significant cyclic loads in earthquakes. Centrifuge modelling of a single pile subjected to cyclic loads has been conducted to investigate the influence of cyclic loads on the axial performance of the single pile. Different pile installation procedures were applied to compare the axial behaviour of different piles under cyclic loads. Pile head permanent settlements accumulated due to cyclic axial loads, and these increased with the increasing load amplitude. Also the pile head axial secant stiffness decreased with the increasing number of axial load cycles, and with increasing amplitude. Furthermore, the axial pile performance is influenced significantly by different installation methods. © 2010 ASCE.

Self-assembled artificial pinning centres in thick YBCO superconducting films

Strong, artificial pinning centres are required in superconducting films of large thickness for power applications in high magnetic fields. One of the methods for the introduction of pinning centres in such films is substrate decoration, i.e., growing nanoscale islands of certain materials on the substrate prior to the deposition of the superconducting film. Two other methods are building up a layered distribution of a second phase and homogeneous incorporation of second phase inclusions from a compositional target. In this paper, we compare the effectiveness of these methods in terms of the type of the self-assembly of nanoparticles. The comparison is made over a large set of YBa2Cu3O7 films of thickness up to 6.6 μm deposited with Au, Ag, Pd, LaNiO3, PrBa2Cu 3O7, YBCO, BaZrO3 and Gd2Ba 4CuWOy nanoparticles. It is found that substrate-decoration self-assembly is able to provide higher critical current in low magnetic field than the incorporation of homogeneous second phase in the sample microstructure. By specific modification of substrate decoration we achieved the self-field critical current per centimetre of width of 896 A/cm at 77.3 K and 1620 A/cm at 65 K in a film of thickness of 4.8 μm. © 2010 IOP Publishing Ltd.