The effect of solvent upon molecularly thin rotaxane film formation

We have investigated variations in molecularly thin rotaxane films deposited by solvent evaporation, using atomic force microscopy (AFM). Small changes in rotaxane structure result in significant differences in film morphology. The addition of exo-pyridyl moietes to the rotaxane macrocycle results in uniform domains having orientations corresponding to the underlying substrate lattice, while a larger, less symmetric molecule results in a greater lattice mismatch and smaller domain sizes. We have measured differences in film heights both as a function of the solvent of deposition and as a function of surface coverage of rotaxanes. Based on these observations we describe how the use of solvents with higher hydrogen-bond basicity results in films which are more likely to favour sub-molecular motion.     

Fabrication of bismuth telluride nanotubes via a simple solvothermal process

The unique Bi₂Te₃ tubes were obtained via a simple solvothermal reaction in the presence of ethylenediaminetetraacetic acid disodium salt. The product was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Bi₂Te₃ nanosheets are vertically grown off the tube wall to form Bi₂Te₃ tubes. A possible formation mechanism is proposed.     

Fabrication of a complex InAs ring-and-dot structure by droplet epitaxy

An InAs ring structure accompanying the formation of quantum dots (QDs) was fabricated on (1 0 0)GaAs using droplet epitaxy. The QDs were located in the vicinity of the ring, due to the diffusion of In atoms from the In droplets. In addition, the dots were found to have distributed elliptically and preferentially along the [0 1 1] direction, implying that In itself prefers to diffuse along the [0 1 1] direction, which is the opposite of the favorable diffusion orientation of group III atoms on (1 0 0)GaAs under a commonly used As-stabilized growth condition. This is the first observation of a ring structure accompanying the formation of quantum dots in droplet epitaxy.     

Superhydrophobic surfaces prepared from water glass and non-fluorinated alkylsilane on cotton substrates

Superhydrophobic surfaces have been successfully prepared by sol-gel method using water glass as starting material. Such surfaces were obtained first by dip-coating the silica hydrosols prepared via hydrolysis and condensation of water glass onto cotton substrates, then the surface of the silica coating was modified with a non-fluoro compound, hexadecyltrimethoxysilane (HDTMS), to gain a thin film through self-assembly, superhydrophobicity with a water contact angle higher than 151° can be achieved. The morphology and surface roughness were characterized by SEM and AFM.     

Titanium-induced germanium nanocones synthesized by vacuum electron-beam evaporation: growth mechanism and morphology evolution

High-vacuum electron-beam evaporation method is used for large area, metal-nucleated germanium (Ge) nanodots and nanocones on Si₃N₄/Si preparation. Nanodot and nanocone arrays with uniform size in bulk-quantity are synthesized using titanium (Ti) nanocrystals as nucleating center at 750 °C with different Ge deposition amount, respectively. The morphology evolution from nanodot to nanocone is studied by atomic force microscopy (AFM). The structure of the prepared sample is characterized by X-ray diffraction (XRD) and Raman scattering. Ge nanocones formed by this convenient fabrication process could have potential applications on nanoelectronics and vacuum electron field emission.     

Fabrication of ZnO nanostructures of various dimensions using patterned substrates

ZnO nanostructures were grown on silicon, porous silicon, ZnO/Si and AlN/Si substrates by low-temperature aqueous synthesis method. The shape of nanostructures greatly depends on the underlying surface. Scattered ZnO nanorods were observed on silicon substrate, whereas aligned ZnO nanowires were obtained by introducing sputtered ZnO film as a seed layer. Furthermore, both the combination of nanorods and the bunch of nanowires were found on porous silicon substrates, whereas platelet-like morphology was observed on AlN/Si substrates. XRD patterns suggest the crystalline nature of aqueous-grown ZnO nanostructures and high-resolution transmission electron microscopy images confirm the single-crystalline growth of the ZnO nanorods along [0 0 1] direction. Room-temperature photoluminescence characterization clearly shows a band-edge luminescence along with a visible luminescence in the yellow spectral range.     

Study of DNA coated nanoparticles as possible programmable self-assembly building blocks

Nanoparticles coated with single stranded DNA have been shown to efficiently hybridize to targets of complementary DNA. This property might be used to implement programmable (or algorithmic) self-assembly to build nanoparticle structures. However, we argue that a DNA coated nanoparticle by itself cannot be used as a programmable self-assembly building block since it does not have directed bonds. A general scheme for assembling and purifying nanoparticle eight-mers with eight geometrically well-directed bonds is presented together with some preliminary experimental work.     

Synthesis of ZnO compound nanostructures via a chemical route for photovoltaic applications

A facile, low-temperature, and low-cost chemical route has been developed to prepare ZnO nanowire and nanosphere compound structures. The morphology, structure, and composition of the yielded products have been examined by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction measurements. We have systematically investigated the optical properties of the ZnO nanostructures by micro-Raman, photoluminescence, and transmission spectroscopy. The results demonstrate that the yielded ZnO nanostructures possess good optical quality with high light absorption. We have further successfully employed the obtained ZnO compound nanostructures in dye-sensitized solar cells. The light-to-electricity conversion results show that the compound nanostructure exhibits a significant enhancement of short-circuit current density due to the increased surface area and light scattering in the compound nanostructures. The present chemical route provides a simple way to synthesize various compound nanostructures with high surface area for nanodevice applications.     

Synthesis and optical properties of CuS nanoplate-based architectures by a solvothermal method

The controlled synthesis of copper sulfide (CuS) nanoplate-based architectures in different solvents has been realized at low cost by simply reaction of Cu(NO₃)₂·3H₂O and S under solvothermal conditions without the use of any template. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectrometer and fluorescence measurement were used to characterize the products. The products were all in hexagonal phase with high crystallinity and the morphology was significantly influenced by the solvents. The CuS products synthesized in dimethylformamide (DMF) were nanoplates and the samples prepared in ethanol were flower-like morphology composed of large numbers of nanoplates, but those synthesized in ethylene glycol (EG) were CuS architectures with high symmetry made up of several nanoplates arranged in a certain mode. The optical properties were investigated and the growth mechanisms of these CuS crystals were also proposed.     

Bilayer ZnO nanostructure fabricated by chemical bath and its application in quantum dot sensitized solar cell

Chemical bath method was used to synthesize bilayer ZnO nanostructure on ITO glass in the alkaline solution. As revealed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), the product consists of a layered structure of ZnO nanorods at the bottom and nanoflower atop. The as-prepared sample was assembled in quantum dot sensitized solar cell (QDSSC), which obtained the incident photon to current conversion efficiency (IPCE) of 15% at 400 nm and power conversion efficiency (PCE) of 0.45%. Therefore, this novel bilayer ZnO nanostructure has the potential for application in solar cell device as the photoelectrode.     

Effect of growth time on the structure, Raman shift and photoluminescence of Al and Sb codoped ZnO nanorod ordered array thin films

Al and Sb codoped ZnO nanorod ordered array thin films have been deposited on glass substrate with a ZnO seed layer by hydrothermal method at different growth time. The effect of growth time on structure, Raman shift, and photoluminescence (PL) was studied. The thin films at growth time of 5 h consist of nanorods growth vertically oriented with ZnO seed layer, and the nanorods with an average diameter of 27.8 nm and a length of 1.02 μm consist of single crystalline wurtzite ZnO crystal and grow along [0 0 1] direction. Raman scattering analysis demonstrates that the thin films at the growth time of 5 h have great Raman shift of 15 cm⁻¹ to lower wavenumber and have low asymmetrical factor Г_a/Г_b of 1.17. Room temperature photoluminescence reveals that there is more donor-related PL in films with growth time of 5 h.     

Novel W-shaped and straight porous ZnO nanobelts

Novel W-shaped porous ZnO nanobelt with the periodical junction angles of about 118° and straight porous ZnO nanobelt have been successfully synthesized. The W-shaped structure growth changes from [0 0 0 1] to periodically. The straight nanobelt grows along [0 0 0 1] direction. Both of the structures have smooth surfaces with high porous density. Based on our X-ray diffraction (XRD), electron microscopy and photoluminescence (PL) spectrum study, the growth mechanism of the special ZnO nanostructures is discussed, emphasizing the effect of alteration of the reactant concentration for two different morphologies.     

Studies on surface modification of UHMWPE fibers via UV initiated grafting

In this research, the surface of ultra high molecular weight polyethylene (UHMWPE) fiber was modified by high energy ultraviolet (UV) initiated grafting reactions and acrylamide groups were grafted onto UHMWPE chains. The initiating and grafting mechanism of the reactions was studied. Some important factors influencing the grafting effect, e.g. crystallinity of UHMWPE fiber, concentration of the initiating reagent, grafting time and the concentration of grafting monomer (acrylamide) were discussed. Fourier transform infrared (FTIR) was used to manifest the mechanism of the grafting reaction. Scanning electron microscopy (SEM) was used to show the morphology changing of the fiber surface. Single fiber pull-out strength and ILSS tests of the composite showed that acrylamide grafted onto the surface of the fiber could improve the interfacial adhesion between treated fibers and matrices.     

Long term studies on the chemical stability of a superhydrophobic silicone nanofilament coating

We have performed extensive studies on the long term chemical stability of a superhydrophobic coating comprised of silicone nanofilaments. Durability was tested by immersion in various liquid media over a period of 6 months. The coating properties were monitored by static contact angle and sliding angle measurements. Changes in surface topography were examined by scanning electron microscopy. The coatings show an exceptional stability in organic solvents, neutral and mildly acidic aqueous solutions and mildly acidic detergent solutions. The superhydrophobic coating properties are stable for several days in mildly basic and strong acidic solutions but deteriorate fast under strong basic conditions.     

Self-assembled growth of MgO nanosheet arrays via a micro-arc oxidation technique

Unique magnesia (MgO) nanosheet arrays were fabricated via a promising micro-arc oxidation (MAO) technique on the surface of magnesium alloy. The non-uniform patterning of oxygen evolution on the sample surface and trapping of gas bubbles in the growing film are associated with the formations of the sheet and flower-like structures. These MgO structures may be useful in reinforcing composite materials or in further modifying other nanostructures.     

Preparation of nano-hydroxyapatite particles with different morphology and their response to highly malignant melanoma cells in vitro

To investigate the effects of nano-hydroxyapatite (HA) particles with different morphology on highly malignant melanoma cells, three kinds of HA particles with different morphology were synthesized and co-cultured with highly malignant melanoma cells using phosphate-buffered saline (PBS) as control. A precipitation method with or without citric acid addition as surfactant was used to produce rod-like hydroxyapatite (HA) particles with nano- and micron size, respectively, and a novel oil-in-water emulsion method was employed to prepare ellipse-like nano-HA particles. Particle morphology and size distribution of the as prepared HA powders were characterized by transmission electron microscope (TEM) and dynamic light scattering technique. The nano- and micron HA particles with different morphology were co-cultured with highly malignant melanoma cells. Immunofluorescence analysis and MTT assay were employed to evaluate morphological change of nucleolus and proliferation of tumour cells, respectively. To compare the effects of HA particles on cell response, the PBS without HA particles was used as control. The experiment results indicated that particle nanoscale effect rather than particle morphology of HA was more effective for the inhibition on highly malignant melanoma cells proliferation.     

Nanowire manipulation on surfaces through electrostatic self‐assembly and magnetic interactions

A method for fabricating aligned nanowire arrays on surfaces is shown. Gold and segmented Au/Ni/Au nanowires of high aspect ratio have been prepared by template electrosynthesis, and functionalized with charged short alkanethiols that can be ionized in aqueous solutions. Different distributions of funtionalized nanowires could be obtained on large surfaces from nanowire aqueous suspensions, avoiding aggregation due to electrical repulsion. Due to the high magnetic anisotropy of segmented Au/Ni/Au nanowires chaining of aligned nanowires could be obtained by applying a low magnetic field. While electrostatics favours side wire interactions due to the high aspect ratio, concurrent electrostatics and applied magnetic field yields end‐to‐end interaction and linear alignment without bifunctionalization. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and room temperature photoluminescence of ZnO/CTAB ordered layered nanocomposite with flake-like architecture

Flake-like ZnO/surfactant ordered layered nanocomposite has been synthesized by self-assembly at room temperature with the presence of cetyltrimethylammonium bromide (CTAB, CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻) surfactant. The procedure described in this study is attractive since it gives high yields of ordered layered nanocomposite with flake-like architecture. XRD results showed the formation of a layered structure with two layered spacings ca. 18.56 Å. SEM and FT-IR spectroscopy were used to further characterize ZnO/CTAB nanolayered composite. The ZnO/CTAB-ordered layered nanocomposite exhibits the room temperature photoluminescence (RTPL) characteristics. It is inferred that the RTPL of ZnO/CTAB-layered nanocomposite might be induced by the interfacial effect between the ZnO and the surfactant.     

Fabrication of PECVD-grown fluorinated hydrocarbon nanoparticles and circular nanoring arrays using nanosphere lithography

Nanosphere lithography (NSL) masks were created by spin-coating of polystyrene particles onto silicon surfaces. Fluorinated hydrocarbon films were coated on the nanosphere lithography masks using plasma-enhanced chemical vapor deposition (PECVD) to obtain ordered arrays of fluorinated hydrocarbon. Atomic force microscope images show hexagonally ordered nanodots of dimension 225 ± 11 nm with a height of 23 ± 4 nm. Every hexagon encloses a circular ring of diameter 540 ± 24 nm having a height and width of 13.5 ± 0.6 nm and 203 ± 16 nm, respectively. FTIR analysis shows two distinct zones of atomic bonding of CH_x and CF_x in the plasma coated ordered fluorinated hydrocarbon films.     

Structural and photoluminescent properties of Ni doped ZnO nanorod arrays prepared by hydrothermal method

Self-assembled Ni-doped zinc oxide (Zn_1−xNi_xO, x = 0.05, 0.10, 0.15, i.e., ZnNiO, nominal composition) nanorod arrays vertically grown on the ZnO seed layer covered glass along [0 0 1] direction were synthesized by hydrothermal method. Their images and structures have been characterized by scan electron microscope (SEM), X-ray diffraction (XRD) and Raman spectra, showing that Ni doping is beneficial to the formation of ZnO nanorods with hexagonal cross section and the enhancement of ZnO crystal quality. X-ray photoemission spectroscopy (XPS) study further demonstrated that Ni atoms were successfully doped into ZnO lattices. The photoluminescence (PL) spectra of ZnNiO samples show near bandedge emission (NBE) peaks at about 380 nm at a low excitation power and the NBE peak position redshifts while its intensity continuously increases with the increase of Ni doping concentration. With the excitation power increasing, the NBE peak redshifts from 380 nm to about 400 nm for ZnNiO nanorod arrays. The NBE mechanisms for ZnNiO nanorod arrays have been discussed, which is helpful for understanding their room temperature ferromagnetisms.