Synthesis and evolution of hollow ZnO microspheres assisted by Zn powder precursor

Hollow ZnO microspheres with nanowires grown on the inner and outer surfaces (HZMSnws) have been successfully synthesized by a simple two-step thermal process approach, where pre-deposited Zn powder particles on Si substrates act as temporary templates to form hollow ZnO sphere shells, while additional Zn powder acts as a Zn source to grow single crystal nanowires on the surfaces of spherical shells. SEM, XRD, TEM and HRTEM were used to characterize the morphology and crystalline structure of the samples. Photoluminescence (PL) measurement shows strong UV emission (380 nm) of HZMSnws samples. Lacking the need for the additional template removal is an important advantage of this approach over others and it therefore can be used to prepare hollow ZnO nano/microsphere shells (HZMSs) and HZMSnws at low cost and at large scale. These kinds of special high surface area hollow spherical structures may find potential applications in photocatalysis, light-weight composite fillers, acoustic insulation, UV nano/micro-optoemission devices and photoanodes of dye-sensitized solar cells.     

A simple growth route towards ZnO thin films and nanorods

Highly orientated ZnO thin films and the self-organized ZnO nanorods can be easily prepared by a simple chemical vapor deposition method using zinc acetate as a source material at the growth temperature of 180 and 320 °C, respectively. The ZnO thin films deposited on Si (100) substrate have good crystallite quality with the thickness of 490 nm after annealing in oxygen at 800 °C. The ZnO nanorods grown along the [0001] direction have average diameter of 40 nm with length up to 700 nm. The growth mechanism for ZnO nanorods can be explained by a vapor-solid (VS) mechanism. Photoluminescence (PL) properties of ZnO thin films and self-organized nanorods were investigated. The luminescence mechanism for green band emission was attributed to oxygen vacancies and the surface states related to oxygen vacancy played a significant role in PL spectra of ZnO nanorods.     

Using sonochemistry for the fabrication of hollow ZnO microspheres

Hollow ZnO microspheres assembled by nanoparticles have been prepared by a sonochemical synthesis at room temperature using carbon spheres as template. The growth process of the precursor was investigated. The prepared hollow spheres were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM). The diameter of the obtained hollow spheres is about 500 nm, and the walls are composed of numerous ZnO aggregate nanocrystallines with diameters of 90 nm. A possible growth mechanism for the formation of ZnO microspheres has been proposed, in which carbon spheres play a crucial role in the formation of the wurtzite hollow ZnO microspheres. The specific structure of the hollow spheres may find applications in nanoelectronics, nanophotonics and nanomedicine.     

Studies of luminescence properties of ZnO and ZnO:Zn nanorods prepared by solution growth technique

Pyramidal ZnO nanorods with hexagonal structure having c-axis preferred orientation are grown over large area silica substrates by a simple aqueous solution growth technique. The as-grown nanorods were studied using XRD, SEM and UV-vis photoluminescence (PL) spectroscopy for their structural, morphological and optical properties, respectively. Further, the samples have also been annealed under different atmospheric conditions (air, O₂, N₂ and Zn) to study the defect formation in nanorods. The PL spectra of the as-grown nanorods show narrow-band excitonic emission at 3.03 eV and a broad-band deep-level emission (DLE) related to the defect centers at 2.24 eV. After some mild air annealing at 200 °C, fine structures with peaks having energy separation of ∼100 meV were observed in the DLE band and the same have been attributed to the longitudinal optical (LO) phonon-assisted transitions. However, the annealing of the samples under mild reducing atmospheres of N₂ or zinc at 550 °C resulted in significant modifications in the DLE band wherein high intensity green emission with two closely spaced peaks with maxima at 2.5 and 2.7 eV were observed which have been attributed to the V_O and Zn_i defect centers, respectively. The V-I characteristic of the ZnO:Zn nanorods shows enhancement in n-type conductivity compared to other samples. The studies thus suggest that the green emitting ZnO:Zn nanorods can be used as low voltage field emission display (FED) phosphors with nanometer scale resolution.     

A simple route to the synthesis of high-quality NiO nanoparticles

Dispersed nickel oxide nanoparticles were obtained by a simple and low-cost method using a mixture of gelatin as organic precursor and NiCl₂ · 6H₂O as Ni source. The average particle size was estimated from X-ray powder diffraction (XRPD) peaks using the Rietveld refinement. The values ranged from 3.2 to 79 nm. We observed that the particle size changes as a function of synthesis time, with a notable decrease after the addition of NaOH to the solution. Field emission scanning electron microscopy (FE-SEM) measurements show that particles have well defined shapes and are dispersed in an organic matrix. X-ray absorption near edge spectroscopy (XANES) shows also the formation of fcc NiO nanoparticles structures.     

Synthesis of needle- and flower-like ZnO microstructures by a simple aqueous solution route

Needle-like ZnO whiskers and flower-like ZnO microstructures composed of different building blocks were successfully prepared via a simple aqueous solution route at low temperature. To further understand the formation processes of these ZnO microparticles, concentration measurements of Zn(II) remaining in the solution as well as SEM and XRD analyses of the solid product have been made at regular intervals throughout the reactions. It is found that the solution basicity has determinative effects on the morphology of the obtained ZnO products by controlling the composition of the precursor and mediating the nucleation and crystal growth rate of ZnO.     

Preparation and characterization of Ag/ZnO composites via a simple hydrothermal route

Silver/zinc oxide (Ag/ZnO) composites were fabricated by a facile one-pot synthesis method under hydrothermal conditions. By choosing glucose as the reductant, metal Ag was fabricated from Ag₂O with the growth of the crystalline ZnO. Structure measurements revealed that obtained Ag/ZnO composites comprised wurtzite ZnO and face-centered cubic structure of nanosized Ag, which uniformly distributed in the composites. Moreover, the morphology of the ZnO was varied regularly with the formation of Ag nanoparticles from flower-like to rod-like and finally returned to flower-like. The optical properties of UV–Vis and surface-enhanced Raman scattering spectra of the composites as well as effects of the dimension of metal Ag fabricated during the prior period of reaction on the morphology of ZnO were discussed.     

Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm. PACS 81.05.Ys; 81.15.Gh; 78.66.Jg     

Majorons: A simultaneous solution to the large and small scale dark matter problems

It is shown that the existence of majorons, which enable a heavy neutrino, 500 eV ? m_νH ? 25 keV to decay into a light neutrino m_νL ? 8 eV and a majoron, with lifetime 10⁴ yr ? τ_νH ? 10⁸ yr can solve both the large and small scale dark matter problems. For a primordial “Zeldovich” spectrum of fluctuations the limits are $\text{m}{}_{\mathrm{<mtext>v</mtext><mtext>H</mtext>}}\text{?}\text{?}\text{550}\text{eV and}\text{τ}{}_{\mathrm{<mtext>v</mtext><mtext>H</mtext>}}$ > 10⁷ to 10⁸ yr (the ranges m_νH ? eV and τ_νH ? 10⁸ yr are allowed by the model but galaxy formation becomes problematic). The large scale dark matter problem is how to achieve the critical density as implied by inflation, the small scale problems deal with the halos of galaxies and galaxy formation and perturbation growth. The heavy neutrino could provide the solution to the small scale problem by initiating perturbation growth before decoupling. The decay products will be fast and thus not bound to the initial clumps, thus solving the large scale problem. The low mass relic neutrinos that were not decay products would remain bound in the gravitational potentials which grew from the initial perturbations. The resulting universe would be radiation dominated, which is consistent with present observations if H₀ ? 40 km/s/Mpc. An alternative solution can occur when m_νH ≈ 10 eV: the universe can again become matter dominated in the present epoch. This solution still allows H⁰ ～ 50 km/s/Mpc. The majoron model parameters which best fit the dark matter considerations are presented.     

A sonochemical route for the encapsulation of drug in magnetic microspheres

This study focused on the preparation and characterization of magnetic targeted antibiotic microspheres (MTAMs). MTAMs were prepared by a sonochemical method in the presence of hydrophobic Fe₃O₄ nanoparticles and tetracycline. The properties of MTAMs were characterized by transmission electron microscopy, Fourier-transform infrared spectrum, thermogravimetric analysis, vibration sample magnetometry, and bacteriostatic experiment. The results indicated that the superparamagnetic microspheres have ultrafine size (below 230 nm), high saturation magnetization (80.90 emu/g), high biocompatibility, biodegradability, controlled-release, and antibiotic effect. It has been proved that MTAMs can carry out the function of magnetic targeted drugs delivery system by putting together magnetic materials and antibiotics. The possible formation mechanism of MTAMs was also discussed. In summary, MTAMs had potential in medical imaging, drug targeting, and catalysis.     

Engineering the crystal growth behavior: “On substrate” MOD formation of ZnO hollow spheres

In this paper is described an easy, one-pot synthesis of ZnO hollow spheres with sizes ranging from 300 nm to 500 nm, by spin-coating deposition on aluminum substrate. Simplified models explaining the shape formation based on film-substrate interaction are discussed. The characteristic size and shape of the nanostructures obtained by the described method and the properties of ZnO as a low-cost biocompatible material make this methodology of synthesis interesting for a wide range of applications including optoelectronics, catalysis and (bio)sensors.     

From crystal to amorphous: A novel route to unjamming in soft disk packings

Numerical studies on the unjamming packing fraction of bi- and polydisperse disk packings, which are generated through compression of a monodisperse crystal, are presented. In bidisperse systems, a fraction f ₊ = 0.400 up to 0.800 of the total number of particles has their radii increased by D \Delta R , while the rest has their radii decreased by the same amount. Polydisperse packings are prepared by changing all particle radii according to a uniform distribution in the range [- D \Delta R,D \Delta R] . The results indicate that the critical packing fraction is never larger than the value for the initial monodisperse crystal, f₀ \phi_{0}^{} = p \pi/?{12} \sqrt{{12}} , and that the lowest value achieved is approximately the one for random close packing. These results are seen as a consequence of the interplay between the increase in small-small particle contacts and the local crystalline order provided by the large-large particle contacts.     

Two-dimensional thermometry using temperature-induced line shifts of ZnO:Zn and ZnO:Ga fluorescence

Sensitive temperature-induced line shifts of the near-band-edge emission from ZnO:Ga and ZnO:Zn are investigated for two-dimensional (2D) thermometry with nanosecond time resolution. Spectral and temporal concerns for 2D measurements and the feasibility for utilizing the line shifts for temperature measurements using a spectral ratio are investigated. Owing to the high temperature sensitivity, a precision of 1% at 800 K is reported for spectral ratio measurements. The technique is demonstrated by 2D measurements of the liquid temperature of burning methanol droplets.     

Artificial intelligence and large scale computation: A physics perspective

We study the macroscopic behavior of computation and examine both emergent collective phenomena and dynamical aspects with an emphasis on software issues, which are at the core of large scale distributed computation and artificial intelligence systems. By considering large systems, we exhibit novel phenomena which cannot be foreseen from examination of their smaller counterparts. We review both the symbolic and connectionist views of artificial intelligence, provide a number of examples which display these phenomena, and resort to statistical mechanics, dynamical systems theory and the theory of random graphs to elicit the range of possible behaviors.     

A new simple route to grow Cu(In,Ga)Se2 thin films with large grains in the co-evaporation process

In the conventional three-stage co-evaporation process to grow Cu(In,Ga)Se₂ (CIGS) film, a large grain is achieved by the co-evaporation of Cu and Se on (In,Ga)₂Se₃ layer at 550 °C in the second stage and then a p-type is achieved by the co-evaporation of In, Ga, and Se in the third-stage. We reported a new process where a CIGS film with a large gain and p-type is achieved by evaporation of Cu only in the second stage at 400 °C and by the Se annealing in the third stage. In the new process, thermal budget was lowered and the third-stage co-evaporation process was eliminated. It was found that the CIGS gain size increased when the Cu/(In + Ga) ratio was above 0.7 and an addition thin CIGS layer appeared on the CIGS surface. The reaction path with Cu was described in the Cu-In-Se ternary phase diagram. The cell conversion efficiency increased from 9.6 to 15.4% as the Se annealing temperature increased from 400 to 550 °C in the third stage, mainly due to the increase of open-circuit voltage and fill factor. Our process demonstrated a new route to grow a CIGS film with a less thermal budget and simpler process in the co-evaporation process.     

Effect of growth temperature on the ZnO nanowires prepared by thermal heating of Zn powders

ZnO nanowires have been synthesized by heating Zn powders under nitrogen (N₂) gas atmosphere. The influence of the growth temperature on the morphology, structure, and photoluminescence (PL) properties of ZnO nanowires has been investigated. At the higher-temperature growth process, thinner nanowires have been obtained. Interestingly, it is observed that the variation of growth temperature has significantly affected the photoluminescence spectra of the ZnO nanowires, showing an enhancement in the relative intensity of the green to UV emission bands with the increase of the growth temperature. In addition, the oxygen sensing properties of the as-synthesized ZnO nanowires were tested.     

A Mulliken electronegativity scale and the structural stability of simple compounds

A new electronegativity scale is derived, in the spirit of Mulliken's original scheme, in terms of neutral atom spectroscopic data. The effect of changing the atomic configuration for C from covalent (sp³) to metallic (s²p²) is considered. Structural stability maps are presented for non-octet non-transition metal compounds, and for two classes of transition metal-non-transition-metal compounds.     

Investigation on simultaneous doping of Sn and F with ZnO nanopowders synthesized using a simple soft chemical route

ZnO nanopowders simultaneously doped with Sn and F are synthesized by employing a simple soft chemical route. The effect of simultaneous doping on the structural, optical and surface morphological properties are investigated in detail and reported. The structural, FTIR and Raman studies revealed the proper Sn and F incorporation into the ZnO matrix. The synthesized nanoparticles exhibit the Raman bands at 335, 386, 423, 440 and 553 cm⁻¹ which were assigned to wurtzite-type ZnO. The blue shift in the absorption spectrum, caused by the doping process suggests an increase in the optical band gap. The PL studies showed the occurrence of energy transition from ZnO to dopant sites. The surface morphological studies confirmed the nanosize of the obtained powder particles. The EDAX profiles confirmed the presence of expected elements in the final product. The characteristics of the synthesized nanopowders showed that they are potentially significant for several technological applications.     

分步加压法测量薄壁空心玻璃微球的耐压能力

 根据空心玻璃微球（HGM）耐内、外压能力与玻璃强度及形状因子的关系,用压力负荷分步增加的方法分别实验测量了直径为350μm～550μm、壁厚＜1.1μm的3种配方HGM的耐内、外压能力及HGM玻璃的杨氏模量和拉伸强度,并由强度测定值给出了不同直径与壁厚HGM的耐内、外压能力的计算式,分析了测量误差,提出了改进方案。