The growth of the flower-like ZnO structure using a continuous flow microreactor

ZnO is a valuable material for display devices, for catalytic chemical reactors, and as sorbents for desulfurizaton because of its excellent chemical and thermal stability. In this work, we report the synthesis of flower-like ZnO structures using a continuous flow microreactor over an oxidized silicon substrate. A chemical solution that employed zinc acetate [Zn(CH₃COO)₂ · 2H₂O] and sodium hydroxide [NaOH] was used as precursors. The effects of water bath temperature, impinging time and concentration of NaOH on the growth of the flower-like structure have been investigated in this study. It was confirmed that the size of the fabricated flower-like structure was increased as the impinging time and the water bath temperature were increased. Various flower-like morphologies were observed according to the different concentration of NaOH. Scanning electron microscope (SEM) was used to study the morphologies of the synthesized flower-like ZnO structures. X-ray diffraction (XRD) was used to characterize the crystal structures of the ZnO crystallites as a function of the concentration of sodium hydroxide.     

Probing pores using elementary quantum mechanics.

The relaxation of polarized spins in a porous medium has been utilized as a probe of its structure. We note that the governing diffusion problem has a close parallel to that of a particle in a box, an elementary Quantum mechanics toy model. Following the spirits of "free electron" model, we use generic properties of the eigen spectrum to understand features common to a wide variety of pore geometry, consistent with large scale numerical simulations and experimental data.     

Synthesis of CaWO<Subscript>4</Subscript> nanocolloidal suspension via pulsed laser ablation and its optical properties

Pulsed laser ablation (PLA) in the liquid phase was successfully employed to synthesize calcium tungstate (CaWO₄) nanocolloidal suspension. The crystalline phase, particle morphology and laser ablation mechanism for the colloidal nanoparticles were investigated using XRD, TEM and SEM. The obtained colloidal suspension consisted of well-dispersed CaWO₄ nanoparticles which showed a spherical shape with sizes ranging from 5 to 30 nm. The laser ablation and the nanoparticle forming process were discussed under consideration of the photo-ablation mechanism, where the nanoparticles were generated by rapid condensation of the plume in high pressured ethanol vapor. The optical properties of the prepared CaWO₄ colloidal nanoparticles were analyzed in detail using XPS, Raman spectroscopy, UV-Vis spectroscopy and PL spectrophotometry. The optical band gap was estimated by Tauc and Menths law. PACS 42.62.-b; 82.70.Dd; 78.55.Hx; 81.07.Wx     

Room-temperature laser deposition of GaAs nanocrystals on PMMA microspheres using particle fluidization

A modified pulsed laser deposition (PLD) was successfully employed to deposit GaAs nanocrystals on the surface of PMMA (polymethylmethacrylate) microspheres. This novel approach is distinguished by the fact that laser ablated materials are deposited uniformly onto the surface of spherical particles that are held constantly in a particle fluidization unit. The XRD, SEM, EDX, TEM, EDP, and XPS results confirmed that cubic structured GaAs nanocrystals was deposited uniformly on the surface of PMMA microspheres with an average diameter of about 15 nm. PACS 81.15.Fg; 78.55.Cr; 82.35.Np     

Pulsed laser induced synthesis of scheelite-type colloidal nanoparticles in liquid and the size distribution by nanoparticle tracking analysis

Pulsed laser ablation (PLA) of ceramic target in liquid phase was successfully employed to prepare calcium tungstate (CaWO₄) and calcium molybdate (CaMoO₄) colloidal nanoparticles. The crystalline phase, particle morphology and optical property of the colloidal nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The produced stable colloidal suspensions consisted of the well-dispersed nanoparticles showing a spherical shape. The mechanism for the laser ablation and nanoparticle forming was discussed under consideration of photo-ablation process. Nanoparticle tracking analysis using optical microscope combined with image analysis was proposed to determine the size distribution function of the prepared colloidal nanoparticles. The mean size of the CaWO₄ and CaMoO₄ colloidal nanoparticles were 16 and 29 nm, with a standard deviations of 2.1 and 5.2 nm, respectively.     

On the Washington subgroup of the unit group of certain abelian fields

For an abelian number field K, Sinnott defined the group C _S (K) of circular units of K and found the index formula for [E(K):C _S (K)], where E(K) is the group of units of K. Let C _W (K) be the subgroup of E(K) consisting of the cyclotomic units of $\mathbb{Q} (\zeta_{n} )$ fixed by $\mathrm{Gal}(\mathbb{Q}(\zeta_{n})/K)$ as was suggested by Washington. The aim of this paper is to find the index formula for [E(K):C _W (K)] when the conductor of K has two distinct odd prime divisors. To do this, we first exhibit a basis of C _W (K), and then describe the group structure of C _W (K)/C _S (K) by comparing the basis of C _W (K) with that of C _S (K) given by Dohmae, from which the index formula for [E(K):C _W (K)] can be derived.     

Conductance fluctuations in disordered superconductors with broken time-reversal symmetry near two dimensions

We extend the analysis of the conductance fluctuations in disordered metals by Altshuler, Kravtsov, and Lerner (AKL) to disordered superconductors with broken time-reversal symmetry in d=(2+?)$d=(2+\mathrm{?})$ dimensions (symmetry classes C and D of Altland and Zirnbauer). Using a perturbative renormalization group analysis of the corresponding non-linear sigma model (NLσM) we compute the anomalous scaling dimensions of the dominant scalar operators with 2s   gradients to one-loop order. We show that, in analogy with the result of AKL for ordinary, metallic systems (Wigner–Dyson classes), an infinite number of high-gradient operators would become relevant (in the renormalization group sense) near two dimensions if contributions beyond one-loop order are ignored. We explore the possibility to compare, in symmetry class D, the ?=(2−d)$\mathrm{?}=(2-d)$ expansion in d<2$d<2$ with exact results in one dimension. The method we use to perform the one-loop renormalization analysis is valid for general symmetric spaces of Kähler type, and suggests that this is a generic property of the perturbative treatment of NLσMs defined on Riemannian symmetric target spaces.     

Z2 topological term, the global anomaly, and the two-dimensional symplectic symmetry class of Anderson localization

We discuss, for a two-dimensional Dirac Hamiltonian with a random scalar potential, the presence of a Z2 topological term in the nonlinear sigma model encoding the physics of Anderson localization in the symplectic symmetry class. The Z2 topological term realizes the sign of the Pfaffian of a family of Dirac operators. We compute the corresponding global anomaly, i.e., the change in the sign of the Pfaffian by studying a spectral flow numerically. This Z2 topological effect can be relevant to graphene when the impurity potential is long ranged and, also, to the two-dimensional boundaries of a three-dimensional lattice model of Z2 topological insulators in the symplectic symmetry class.     

Experimental characterization of alpha spectrometer for optimization of operational parameters affecting energy resolution and detection efficiency

Journal of Radioanalytical and Nuclear Chemistry - The operational parameters of an alpha spectrometer equipped with a planar silicon semiconductor detector were characterized by measuring a mixed...