Dynamics of polymorphic nanostructures: from growth to collapse

Cobalt and sulfur co-doped nano-size TiO2 for photodegradation of various dyes and phenol

Various compositions of cobalt and sulfur co-doped titania nano-photocatalyst are synthesized via sol-gel method. A number of techniques including X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Rutherford backscattering spectrometry (RBS), thermal gravimetric analysis (TGA), Raman, N2 sorption, electron microscopy are used to examine composition, crystalline phase, morphology, distribution of dopants, surface area and optical properties of synthesized materials. The synthesized materials consisted of quasispherical nanoparticles of anatase phase exhibiting a high surface area and homogeneous distribution of dopants. Cobalt and sulfur co-doped titania demonstrated remarkable structural and optical properties leading to an efficient photocatalytic activity for degradation of dyes and phenol under visible light irradiations. Moreover, the effect of dye concentration, catalyst dose and pH on photodegradation behavior of environmental pollutants and recyclability of the catalyst is also examined to optimize the activity of nano-photocatalyst and gain a better understanding of the process.

Metastable adaptive orthorhombic martensite in zirconia nanoparticles

Reported here are observations of isolated orthorhombic (o) ZrO2nanoparticles (NPs) in thePbcaspace group under atmospheric conditions. These NPs are composed of o domains separated by internal semi-coherent boundaries. They are identified to transform from lamellar-twinned tetragonal (t) NPs. The constraining effect of the twin boundaries impedes a direct martensitic transformation to the monoclinic (m) phase but favours a transformation to the o phase. The internal boundaries are considered to evolve from the lamellar-twinning boundaries, playing an important role in the stabilization of the o structure under atmospheric conditions. The observed o structure should be an adaptive martensite transformed from the t phase, different from the general consideration of the o phase as an intermediate stage. A new lattice correspondence (LC) relationship of (011)o||(100)tand [100]o||[001]tis determined for the t-to-o transformation. A possible transformation path is proposed to be t (space groupP42/nmc) to o (PbcmorPbc21, named oA) to o (Pbca, named oB), and the LC relationship is identified to be (100)t||(100)oA||(011)oBand [001]t||[010]oA||[100]oB.

Fractal electronic devices: simulation and implementation

Many natural structures have fractal geometries that exhibit useful functional properties. These properties, which exploit the recurrence of patterns at increasingly small scales, are often desirable in applications and, consequently, fractal geometry is increasingly employed in diverse technologies ranging from radio antennae to storm barriers. In this paper, we explore the application of fractal geometry to electrical devices. First, we lay the foundations for the implementation of fractal devices by considering diffusion-limited aggregation (DLA) of atomic clusters. Under appropriate growth conditions, atomic clusters of various elements form fractal patterns driven by DLA. We perform a fractal analysis of both simulated and physical devices to determine their spatial scaling properties and demonstrate their potential as fractal circuit elements. Finally, we simulate conduction through idealized and DLA fractal devices and show that their fractal scaling properties generate novel, nonlinear conduction properties in response to depletion by electrostatic gates.

Tunable Nanostructures and Crystal Structures in Titanium Oxide Films

Controllable nanostructures in spin coated titanium oxide (TiO(2)) films have been achieved by a very simple means, through change of post deposition annealing temperature. Electron beam imaging and reciprocal space analysis revealed as-deposited TiO(2) films to be characterized by a dominant anatase phase which converts to the rutile form at 600 degrees C and reverts to the anatase modification at 1,200 degrees C. The phase changes are also accompanied by changes in the film microstructure: from regular nanoparticles (as-deposited) to nanowires (600 degrees C) and finally to dendrite like shapes at 1,200 degrees C. Photoluminescence studies, Raman spectral results, and X-ray diffraction data also furnish evidence in support of the observed solid state phase transformations in TiO(2).