Self-assembled rings of EuBr2 nanostructures

The EuBr₂ nanostructures self-assembled (SA) in ring form are presented in this letter. The atomic force microscopy (AFM) images show rings of ~ 190 to 2500 nm diameter formed on [100] surface. The sample optical response with rings displays an emission band peak (EBP) at 435 nm. The europium absorption bands reveal structural changes and shift toward infrared wavelength. The emission bandwidth of EuBr₂ nanostructures in ring form is narrower than dispersed nanostructures of similar size. To our knowledge, is the first time that there is clear evidence of the arrangement in ring form in the KBr:Eu²⁺ crystal samples.     

Growth of single-crystalline AlZnO nanorods by simple vapor deposition method

Well-aligned AlZnO nanorod arrays with various Al concentrations and various diameters were prepared on silicon substrate by a simple vapor deposition with separate sources at different temperatures. Field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) were carried out to characterize morphology and microstructure. X-ray fluorescence shows that the atomic ratio of Al/(Al + Zn) of the arrays is determined to be about 3% and 1.6%, respectively. The Burstein-Moss (BM) shift of the strong ultraviolet emission is observed due to Al incorporation.     

Controllable growth of dendrite-like CuO nanostructures by ethylene glycol assisted hydrothermal process

The dendrite-like CuO nanostructures, consisting of a rod-like main stem and some rod-like sub-branches, have been synthesized by a simple ethylene glycol (EG) assisted hydrothermal method. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) patterns indicate that the dendrite-like CuO nanostructures are of monoclinic phase and the individual branch of CuO is single crystalline in nature. The effects of the growth conditions such as temperature and pH value on the morphology and structures of CuO have also been investigated. It is indicated that different temperature and pH value result in the morphology and structure evolution of CuO. Moreover, a possible mechanism for the morphology and structures evolution of CuO has been primarily presented.     

Heteroepitaxy of zinc-blende SiC nano-dots on Si substrate by organometallic ion beam

The self-assembled SiC nano-dots were fabricated on Si(111) substrate at low-temperatures using the organometallic ion beam deposition technique. The single precursor of methylsilicenium ions (SiCH₃⁺) with the energy of 100 eV was deposited on Si(111) substrate at 500, 550 and 600 °C. The characteristics of the self-assembled SiC nano-dots were analyzed by reflection high-energy electron diffraction (RHEED), Raman spectroscopy and atomic force microscope (AFM). The RHEED patterns showed that the crystal structure of the SiC nano-dots formed on Si(111) substrate was zinc-blende SiC (3C-SiC) and it was heteroepitaxy. The self-assembled SiC nano-dots were like a dome in shape, and their sizes were the length of 200-300 nm and the height of 10-15 nm. Despite the low-temperature of 500 °C as SiC crystallization the heteroepitaxial SiC nano-dots were fabricated on Si(111) substrate using the organometallic ion beam.     

A simple semi sol-gel method for preparation of alumina monoliths with hierarchical pore structures

A simple semi sol-gel method for preparation of stable alumina monoliths is presented. The approach is based on chemical binding of boehmite by hydrolysis products of aluminium nitrate. The crystalline phase of the monoliths depends on the calcination temperature, and the size and shape of the alumina crystallites were determined by transmission electron microscopy and modelling of X-ray diffraction patterns. The monoliths have bimodal pore size distributions with mesopores ranging from 3 to 20 nm and macropores ranging from 10 to 40 μm. Incipient wetness impregnation resulted in gold particles, ranging from 4 to 20 nm, supported on the monoliths. The size of the gold particles depended largely on the crystalline phase of the support, but also on the amount of gold precursor. The catalytic activity of the functionalised materials in liquid-phase oxidation of glucose was higher in continuously stirred batch reactor tests compared to continuous flow fix bed tests. In both cases the activity was improved as the size of gold particles decreased.     

Controllable growth of zinc oxide nanosheets and sunflower structures by anodization method

Large scale of ZnO nanosheets and sunflower structures were fabricated by anodization of zinc in (NH₄)₂SO₄ and NH₄Cl aqueous electrolytes. The products were characterized via scanning electron microscope, transmission electron microscope and X-ray diffraction analysis. Results show that the sheets are about 20–50 μm in dimension and 20 nm in thickness. The sunflower microstructures are about 400–500 μm in dimension. The possible growth mechanism is suggested on the basis of experimental results.     

A simple template method for hierarchical dendrites of silver nanorods and their applications in catalysis

A novel strategy has been put forward to prepare hierarchical dendrites of silver nanorods via a simple integration method using “Devarda's template” as a reducing agent and architecture template with the assistance of ultrasonic waves, in which the template was firstly fabricated and employed. The individual silver dendrite is composed of a long central trunk with secondary branches, which preferentially grew in a parallel direction with a definite angle to the trunk. The results reveal that the dendrites are single crystalline in nature and interestingly prove that the silver single crystal has the preferential orientation in 〈1 1 1〉 direction in normal conditions. The contrast experiments demonstrated that both “Devarda's template” and the ultrasonic irradiation are necessary for building hierarchically silver dendrites in a water system. Moreover, the experimental results show that the dendrites of silver nanorods are the superior electrode materials for the electrochemical sensors to detect directly NO₂⁻ in aqueous solution.     

Fabrication of ZnS/ZnO hierarchical nanostructures by two-step vapor phase method

A simple two-step vapor phase method is presented to fabricate ZnS/ZnO hierarchical nanostructures in bulk quantities. That is ZnS nanobelts were first synthesized and then used as substrate for growth of ZnO nanorod arrays. Investigation results demonstrate that the polar surfaces of ZnS nanobelts could induce a preferred asymmetric growth of ZnO nanorods on the side surfaces. But it is believed that if the local concentration of ZnO was high enough, ZnO nanorods could also grow symmetrically on the top/bottom surface of the ZnS nanobelts. The optical property of the products was also recorded by means of photoluminescence (PL) spectroscopy.     

The influence of post deposition plasma treatment on SnOx structural properties

Thin tin-oxide (SnO_x) films were deposited by atmospheric pressure chemical vapor deposition (APCVD) and exposed to hydrogen plasma. The influence of such treatment on the films properties was investigated by X-ray diffraction (XRD), UV-visible spectroscopy, scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and grazing incidence small angle X-ray scattering (GISAXS). XRD showed that the deposited films are nano-crystalline, with a typical average of the individual crystal sizes between 15 and 40 nm and with a preferred orientation, depending on the parameters of the deposition. By exposure to the hydrogen plasma the micro-strain increased, the crystals became smaller and less preferentially oriented. The influence of the hydrogen plasma treatment, studied by SEM and XPS, indicated that part of the surface layer was etched away, presumably through the process of SnO_x reduction. The GISAXS results suggested that the nano-crystals in as-deposited samples had the shape of non-truncated pyramids. After plasma treatment, their shape is greatly rounded and the GISAXS signal becomes isotropic.     

ZnO nanowire growth by electric current heating method: A study on the effect of substrate temperature

In this study, we report the growth of ZnO nanowire on quartz glass substrates with Au-catalyst assistance by electric current heating of ZnO ceramic bar. The effect of substrate temperature on the properties of ZnO nanostructures has been investigated systematically. Structural analysis indicates that the grown ZnO crystals belong to hexagonal phase with preferential growth along (0 0 2) orientation. Scanning electron microscopic studies reveal the aligned ZnO nanowires were grown at 800 °C. The typical length and diameter of nanowires are in the uniform ranges of 4–20 μm and 20–100 nm, respectively, showing their high aspect ratio of about 1000. We have made an attempt to discuss about the change in ZnO nanostructures with different substrate temperatures and the possible mechanism for the growth of nanowires. Optical reflectance studies show the infrared reflectivity was controlled through the substrate temperature.     

Structural properties and growth mechanism of flower-like ZnO structures obtained by simple solution method

Flower-shaped zinc oxide (ZnO) structures have been synthesized in the reaction of aqueous solution of zinc nitrate and NaOH at 90 °C. To examine the morphology of ZnO nanostructures, time-dependent experiments were carried out. Detailed structural observation showed that the flower-like structures consist of triangular-shaped leaves, having sharpened tips with wider bases. Photoluminescence spectrum measured at room temperature show a sharp UV emission at 381 nm and a strong and broad green emission at 480-750 nm attributed to structural defects. A possible growth mechanism for the formation of flower-shaped ZnO structures is discussed in detail.     

Optical response and surface morphology of crystalline Nd-doped fluoride films grown on monocrystalline LiYF4 substrates by pulsed laser deposition

The realization of crystalline films of Nd³⁺:YF₃ and Nd³⁺:LiYF₄ on a monocrystalline LiYF₄ substrate by pulsed laser deposition is reported. The films were obtained by laser ablation with 355 nm photons of a bulk LiYF₄ crystal doped with Nd³⁺ ions at 1.5% atomic concentration in the presence of different ablation/deposition parameters. The films optical characteristics, analyzed via laser induced polarized fluorescence spectroscopy upon IR excitation, are presented. Lifetime measurements of the fundamental Nd³⁺ ion transition in the film were also performed. All these results were compared with those obtained in the Nd³⁺:LiYF₄ bulk crystal. The surface morphology of the depositions was analyzed via a scanning electron microscope. When the production of the deposition took place in high vacuum (1 × 10^− 4 Pa) and the substrate temperature was 750 °C, the grown film was Nd³⁺:YF₃. A 1 Pa controlled atmosphere of He in the ablation chamber and a substrate temperature of 650 °C favoured the growth of a Nd³⁺:LiYF₄ film. In the latter case the film showed also a smoother surface.     

The synthesis of graphene oxide nanostructures for supercapacitors: a simple route

In this work, we report a simple strategy for synthesis of graphene oxide nanostructures with various morphologies including single-, few-layer, and three-dimensional networks. Morphology control is achieved by adding different amounts of Ni²⁺ into a one-step hydrothermal process. The involved growth mechanisms for the morphology control are discussed. A random arrangement of graphene oxide nanosheets is suggested to induce the networks’ formation. Ni²⁺ facilitates the formation of graphene oxide’s preferential face-to-face overlapping structure, and high Ni²⁺ concentrations render adjacent graphene oxide sheets to combine each other tightly to form closely packed, layered structures. Compared with single-, few-layer graphene oxide, the electrode prepared by three-dimensional networks has a mass specific capacitance of 352 F g^?1 at v = 5 mV s^?1, which is much higher than that of recently reported three-dimensional graphene oxide nanostructures (240 F g^?1).     

A simple method to ameliorate hierarchical porous structures of SiO2 xerogels through adjusting water contents

In this contribution, hierarchical micro-/meso-porous SiO₂ xerogels were successfully prepared through a Stöber methodology coupled with following drying process. The SiO₂ xerogels were consisted of nanoparticles of 20–40 nm in size with different contents of water. Fourier transform infrared spectroscopy proved that SiOC₂H₅ and SiOH groups could be formed in SiO₂ xerogels. Further analyses declared that the amount of the SiOC₂H₅ groups decreased while the concentration of SiOH was firstly increased and then suffered a decline with improving contents of water. Besides, the SiO₂ xerogels was endowed with controllable micro-/meso-porous structure. Furthermore, the formation mechanism of the micro-/meso-porous SiO₂ xerogels was tentatively put forward. As a consequence, SiO₂ xerogels with controllable hierarchical micro-/meso-porous structure could act as the smart material for huge development in catalytic fields.     

Synthetic hierarchical nanostructures: growth of carbon nanofibers on microfibers by chemical vapor deposition

In this paper the synthesis of three-dimensional hierarchical nanostructures by pyrolysis of acetylene to grow carbon nanofibers (CNFs) on carbon microfibers (CMFs) and glass microfibers (GMFs) is reported. The morphology and structure of the as-prepared CNFs were studied by scanning electron microscopy and high-resolution transmission electron microscopy. CNFs grown on both substrates typically exhibited two types of morphology: the coil-like CNFs with frequent change in orientation and the relatively straight and long CNFs with parallel graphene sheets. The ethanol pretreatment was effective at improving the yield and distribution of the as-grown CNFs on CMFs, but showed an adverse effect to the CNF growth on GMFs. The influence of different substrates and growth temperatures on CNF morphology and the possible growth mechanism for the observed microstructures was discussed.     

Plasmon-enhanced solar water splitting with metal oxide nanostructures: A brief overview of recent trends

In the last decade, the surface plasmon resonance-enhanced solar water splitting (SWS) has been actively investigated for improved hydrogen production. In this mini-review, we briefly introduce the mechanisms for plasmon-enhanced SWS and then review some representative studies related to these mechanisms. In addition, we also briefly discuss how metal oxide geometry affects the SWS activity in combined metal-semiconductor nanostructures. Finally, we summarize the recent discoveries and proposed a future vision for plasmon-enhanced SWS with metal oxide nanostructures.     

A simple numerical method of cycle jumps for cyclically loaded structures

A method for accelerated numerical simulations of structures subjected to cyclic loading is investigated. Of particular interest is a class of structures where the structural properties evolve with time. The proposed method is based on conducting detailed finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FEA simulations. This includes a control function that automatically monitors the length of the cycle jump to ensure a realistic solution. We compare the proposed method to a reference calculation, where all incremental cycles are conducted, and find that the cycle jump solution replicates the true solution.     

Development of a simple method for the preparation of novel egg-shell type Pt catalysts using hollow silica nanostructures as supporting precursors

A simple method for the preparation of novel egg-shell type platinum catalysts was developed and achieved by utilizing unique hollow silica nanostructures, i.e., hollow silica nanospheres and nanotubes, as supports. The observation by transmission electron microscopy indicated that the well-dispersed hollow silica supported Pt catalysts with a Pt particle diameter of 8-14 nm can be successfully prepared by wet impregnation process and heat treatment. The Pt-loaded hollow silica nanostructures were also characterized by inductively coupled plasma, X-ray diffraction, specific surface area, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive spectroscopy. It was thus demonstrated that a higher Pt loading amount (0.392%) could be obtained under the same conditions except the addition of ammonia, which was found to be more effective than that (0.061%) with the addition of HCl in the immobilization of Pt. In addition, the effect of soaking time, Pt precursor concentration and calcination temperature on the loading of Pt in hollow silica nanostructures were investigated as well.     

Large-scale growth and shape evolution of bismuth ferrite particles with a hydrothermal method

Large-scale polyhedral bismuth ferrite (BiFeO₃) particles were synthesized with a hydrothermal method under a series of experimental conditions. X-ray diffraction revealed that the BiFeO₃ powders had a perovskite structure. Scanning electron microscopy images showed different BiFeO₃ particles were formed, including sphere, octahedron, truncated octahedron, cubo-octahedron and truncated cube. The experimental results showed that the concentration of KOH, reaction time, heating and cooling rates had important impacts on the size and morphology of the BiFeO₃ particles. The formation mechanism and change process of the large-scale polyhedral BiFeO₃ particles were discussed in detail. The obtained BiFeO₃ showed ferroelectric behavior and magnetic response, which approved the multiferroic property of the BiFeO₃ crystallization. The optical behaviors of BiFeO₃ particles revealed the band gap energy of about 2 eV, which is smaller than the BiFeO₃ bulk due to the nano-crystallites.     

A simple method for the growth of high-quality GaN nanobelts

A simple method using two-step growth technology to successfully synthesize the high-quality single crystalline GaN nanobelts was employed in this paper. The as-prepared products are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results of XRD and the selective area electron diffraction (SAED) patterns indicate that the reflections of the samples can be indexed to the hexagonal GaN phase with single-crystal structure. From the SEM morphology, we can see that the width of the nanobelts is about 800 nm, and the ratio of thickness to width is about 1/10. The maximum length is up to several tens of micrometers. In the HRTEM image, the clear lattice fringes indicate the growth of good-quality hexagonal single-crystal GaN nanobelts. Finally, the growth mechanism is also briefly discussed.