Tetrapod Shape Research Articles

Understanding the piezoelectric response of ZnO nanotetrapods: Detailed numerical calculations

The complex tetrapod shape of zinc oxide nanostructure, which is constructed from four one-dimensional arms interconnected together via a central core, is a special 3D geometry with multifunctional applications in advanced technologies. The ZnO hexagonal wurtzite crystal lattice with a non-centrosymmetric structure introduces interesting piezoelectric property in nanorods in the bent state, which has been well reported and utilized in piezo- and tribo-electric nanogenerator applications. Considering the broad technological relevance of tetrapods, it is important to understand the piezoelectric response of zinc oxide tetrapods under different conditions. In this study, we explicate the fundamental mechanical and electrical properties of ZnO nanotetrapods (ZnO NTs) through a detailed finite element method analysis. On this basis, the effects of shape factors (including length, height, and aspect ratio) as well as connection strength and packing density on the deformation and piezoelectric potential of ZnO NTs are examined, offering guidance for the fabrication of ZnO NTs. This theoretical model and numerical simulation provide an avenue for further piezoelectric and piezotronic research of ZnO NTs.

Tuning of optical properties and phase behavior of Nanomaterial-stabilized blue phase liquid crystals

HypothesisNanoparticles of various shapes and sizes can affect the optical properties and blue phase (BP) stabilization of BP liquid crystals (BPLCs). This is because nanoparticles, which are more compatible with the LC host, can be dispersed in both the double twist cylinder (DTC) and disclination defects in BPLCs. ExperimentsThis study presents the first systematic study of the use of CdSe nanoparticles having various sizes and shapes (spheres, tetrapods and nanoplatelets) to stabilize BPLCs. Unlike previous studies using commercial nanoparticles (NPs), we custom-synthesized NPs with the same core and nearly identical long chain hydrocarbon ligand materials. Two LC hosts were used to investigate the NP effect on BPLCs. FindingsThe size and shape of nanomaterials greatly influence the interaction with LCs, and the dispersion of NPs in the LC medium affects the position of the BP reflection band and the stabilization of BPs. Spherical NPs were found to be more compatible with the LC medium than tetrapod shape and platelet shape NPs, resulting in a wider temperature range of BP and a redshift of the reflection band of BP. In addition, the inclusion of spherical NPs tuned the optical properties of BPLCs to a significant extent, whereas BPLCs with nanoplatelets displayed a limited influence on the optical properties and temperature window of BPs due to poor compatibility with LC hosts. The tunable optical behavior of BPLC as a function of the type and concentration of NPs has not been reported.

Magnetic Elastomers with Smart Variable Elasticity Mimetic to Sea Cucumber.

A magnetic-responsive elastomer consisting of magnetic elastomer and zinc oxide with a tetrapod shape and long arms was fabricated mimetic to the tissue of sea cucumber in which collagen fibrils are dispersed. Only the part of magnetic elastomer is active to magnetic fields, zinc oxide plays a role of reinforcement for the chain structure of magnetic particles formed under magnetic fields. The magnetic response of storage modulus for bimodal magnetic elastomers was measured when the magnetic particle was substituted to a nonmagnetic one, while keeping the total volume fraction of both particles. The change in storage modulus obeyed basically a mixing rule. However, a remarkable enhancement was observed at around the substitution ratio of 0.20. In addition, the bimodal magnetic elastomers with tetrapods exhibited apparent change in storage modulus even at regions with a high substitution ratio where monomodal magnetic elastomers consist of only magnetic particles with less response to the magnetic field. This strongly indicates that discontinuous chains of small amounts of magnetic particles were bridged by the nonmagnetic tetrapods. On the contrary, the change in storage modulus for bimodal magnetic elastomers with zinc oxide with irregular shape showed a mixing rule with a substitution ratio below 0.30. However, it decreased significantly at the substitution ratio above it. The structures of bimodal magnetic elastomers with tetrapods and the tissue of sea cucumber with collagen fibrils are discussed.

Improvement of Uniaxial Compression of Soil with ZnO tetrapods

With the limitation of the land availability in major population centers and the availability of the land to be used as waste management sites, incite is required in improving the ground. Many soil stabilization techniques are available using conventional method. Here, we intend to report a method applying the nanotechnology for ground improvement. T-ZnO is used to improve the uniaxial compressive strength of silty-clay at low liquid limit. Silt soil passing 1mm sieve and T-ZnO between 0-5 wt% is used. It was found that with increasing percentage of T-ZnO up to a threshold, a significant improvement in compressive strength is observed which may be attributed to the peculiar tetrapod shape that acts as reinforcement among silt and clay particles.

Humidity sensing properties of surface modified polyaniline ZnO nanocomposites

Purpose – The aim of this study is to investigate the humidity-sensing of polyaniline–zinc oxide (PANI–ZnO) nanocomposites. Humidity sensor has wide applications in drug industries, food industries and domestic purpose to regulate the humidity level. Design/methodology/approach – PANI–ZnO composites were prepared by in situ polymerization method, and further humidity response was tested by using a two-probe sensor setup. Findings – PANI-ZnO composites surface were modified by using camphor sulphonic acid. DC conductivity is due to the hopping of polorans. Thermal coefficient value varies from 1.7 to 2.3. The 30 weight per cent composite shows high sensitivity among other composites. Research limitations/implications – These composites can be used only at room temperature or moderate temperature, i.e. below 280°C. Practical implications – The composites are prepared in tetrapod shape that has a large surface area and more stability. Therefore, these materials would be the replacement for conventional materials. Social implications – These sensors have many applications in food and drug preservation, domestic purposes, etc. Originality/value – This work is original, and not being considered for publication elsewhere. In this work, the charge transport properties were evaluated based on the resistivity change when samples were exposed to humidity.

Size control and shape evolution of single-twinned platinum nanocrystals in a room temperature colloidal synthesis

Platinum nanocrystals in the size range of a few nanometers are especially interesting candidates for catalytic applications. We present an easy, low-temperature procedure, which allows for a precise size control of this material. Uniform platinum nanoparticles were obtained by reduction of platinum(IV)chloride with tetrabutylammonium borohydride in toluene solution at room temperature. Dodecylamine served as a ligand. The size of the resulting particles could be controlled in the range between 2 and 5 nm by slow addition of platinum monomers and the reducing agent to preformed 2 nm seeds. Furthermore, particles with a tetrapod shape could be synthesized. In contrast to the usual kinetic control leading to the formation of elongated structures, the analysis of the growth process of the tetrapods suggests a reaction-controlled growth process. Their structure was investigated by powder X-ray diffraction and high-resolution electron microscopy, which revealed that two branches of the tetrapods grow along the 〈111〉 direction, while the other two show growth in the 〈220〉 direction. This uncommon shape of the tetrapods is attributable to the presence of a twin defect parallel to the 〈220〉 direction. Thus, the method presented in the article allows for the formation of platinum particles with a single twin defect with a high yield.

X-ray scattering from immunostimulatory tetrapod-shaped DNA in aqueous solution to explore its biological activity-conformation relationship.

We carried out synchrotron X-ray scattering experiments from four DNA supermolecules designed to form tetrapod shapes; these supermolecules had different sequences but identical numbers of total base pairs, and each contained an immunostimulatory CpG motif. We confirmed that the supermolecules did indeed form the expected tetrapod shape. The sample that had the largest radius of gyration (Rg) induced the most cytokine secretion from cultured immune cells. Structural analysis in combination with a rigid tetrapod model and an atomic scale DNA model revealed that the larger Rg can be ascribed to dissociation of the DNA double strands in the central connecting portion of the DNA tetrapod. This finding suggests that the biological activity is related to the ease with which single DNA strands can be formed.

Formation of Tetrapod-Shaped Nanowires in the Gas Phase During the Synthesis of ZnO Nanostructures by Carbothermal Reduction

We experimentally confirmed that charged ZnO nanoparticles were generated abundantly in the gas phase using a differential mobility analyzer (DMA). When they were size-selected by the DMA and captured on a grid for transmission electron microscopy, particles of 10 nm had a rod or tetrahedron shape, while particles larger than 10 nm tended to have a tetrapod shape. The tetrahedral particles seemed to be a seed for the growth of tetrapod nanowires. Although the growth of a tetrahedron shape enclosed by a close-packed plane (0002) of the hexagonal close-packed ZnO can be explained by the classical crystal growth theory, the growth of tetrapod nanowires can be better explained by the building block of charged nanoparticles generated in the gas phase.

Shape Prediction for Supramolecular Organic Nanostructures: [4 + 4] Macrocyclic Tetrapods

Two [4 + 4] imine cages were synthesized with a unique macrocyclic tetrapod shape. The 3-dimensional structures of both molecules were predicted a priori by using conformer searching routines, illustrating a computational strategy with the potential to target new organic molecules with shape-persistent, intrinsic pores. These methods, in combination with crystal structure prediction, form part of a broader strategy for the computationally led synthesis of functional organic solids.

Development and evaluation of tetrapod-shaped granular artificial bones

We have developed a novel form of granular artificial bone “Tetrabones” with a homogeneous tetrapod shape and uniform size. Tetrabones are four armed structures that accumulate to form the intergranular pores that allow invasion of cells and blood vessels. In this study we evaluated the physicochemical characteristics of Tetrabones in vitro, and compared their biological and biomechanical properties in vivo to those of conventional β-tricalcium phosphate (β-TCP) granule artificial bone. Both the rupture strength and elastic modulus of Tetrabone particles were higher than those of β-TCP granules in vitro. The connectivity of intergranular pores 100, 300, and 400μm in size were higher in Tetrabones than in the β-TCP granules. Tetrabones showed similar osteoconductivity and biomechanical stiffness to β-TCP at 2months after implantation in an in vivo study of canine bone defects. These results suggest that Tetrabones may be a good bone graft material in bone reconstruction.

Self-Assembly of CdTe Tetrapods into Network Monolayers at the Air/Water Interface

Cadmium telluride (CdTe) tetrapods are synthesized with varying aspect ratios through multiple injections of the Te precursor, which provides an excellent means of controlling and tailoring the optical properties of the tetrapods. The self-assembly of CdTe tetrapods at the air/water interface is explored using the Langmuir-Blodgett (LB) technique due to potential use in solar cells arising from the intriguing tetrapod shape that improves charge transport and the optimum band gap energy of CdTe that enhances light absorption. Interestingly, the Langmuir isotherm shows two pressure plateau regions: one at approximately 10 mN/m with the other at the high surface pressure of approximately 39 mN/m. LB deposition at various pressures allows the discernment of the unique two-dimensional packing alluded in the isotherm. By placing CdTe at the air/water interface, it is revealed in the deposition that the tetrapods experienced a dewetting phenomenon, forming a ribbon structure at the onset of surface pressure with a height corresponding to the length of one tetrapod arm. With the increase of surface pressure, the ribbons widen to an eventual large-scale percolated network pattern. The packing density of tetrapods is successfully manipulated by controlling the surface pressure, which may find promising applications in optoelectronic devices.

Synthesis of Bottle-Shaped ZnO Particles through the Oxidation of a Mixture of Al-Zn-Au

ZnO particles with a bottle-like morphology were synthesized by direct melt oxidation of a source material mixed with Al, Zn, and Au in air at atmospheric pressure. The particles were synthesized when the source material contained Au. Without Au, only ZnO particles with a tetrapod shape were identified. The bottle-shaped particles consisted of a well-defined hexagonal faceted micro-rod stem and a bottleneck. It is proposed that the bottle-shaped morphology forms through a vapor-solid growth mechanism as no catalyst was used during the synthesis process.

Shape controlled ZnO nanoparticle prepared by microwave irradiation method

ZnO nanoparticle was successfully prepared by microwave irradiation method in various oxygen/nitrogen ratio atmospheres. In the present method, steel wool was used as a heat generator by microwave irradiation. The highest heating rate of ∼200°C/sec for the reaction was achieved under the highest oxygen concentration, 80%, whereas the lowest hating rate was ∼40°C/sec. The product prepared in a low oxygen ratio atmosphere showed tetra pod shape with high aspect ratio, c/a. On the other hand, the product prepared under high oxygen ratio atmosphere was relatively isotropic. PL spectra of the products with the higher aspect ratios showed higher UV emission intensity than the products with low aspect ratios i.e. isotropic shape.

Al-Zn 합금의 직접용융산화법을 이용한 ZnO 나노와이어의 제작

ZnO nanowires with tetrapod shape were formed on the surface of the sample by direct melt oxidation of Al-Zn alloy at <TEX>$1000^{\circ}C$</TEX> in air. X-ray diffraction (XRD) pattern revealed that the ZnO nanowires had wurtzite structure of hexagonal phase. Any other element except Zn and O was not detected in energy dispersive X-ray spectrum. The c- and a-axis lattice constants estimated from the XRD pattern were 0.520 and 0.325 nm, respectively. These are in well accordance with those of bulk ZnO single crystal, indicating high quality crystallinity. The green light emission at a wavelength of 510 nm was observed from the nanowires at room temperature, which was ascribed to high density of oxygen vacancies in nanowires.

Topology and electronic structure of nanotube junctions of tetrapod shape

We propose a series of carbon nanostructures in the shape of tetrapod as a kind of three-dimensional junction for carbon nanotubes. The tetrapod junctions are such open networks that are made of sp2 carbon atoms only, have negative Gaussian curvature, and connect four nanotubes together. We define the structure of standard tetrapod junctions, the simplest one, that have 12 heptagons other than hexagons and have the Td symmetry.Our tight-binding energy-band calculations for the standard tetrapod junctions of smaller sizes show that their electronic property mainly depends on one particular topological factor: the junctions having a carbon atom in the center of each triangular face of tetrahedron exhibit metallic band structure while the junctions having a benzene ring in the center of the faces are semiconductors. We also find that tetrapod junctions connecting (6,0) nanotubes exhibit a flat band near the Fermi energy in a particular momentum region. The origin of the flat band states can be figured out from the wavefunction distribution. We also show the possibility to extend the standard tetrapod junctions to some non-standard ones that can connect nanotubes of different kinds and/or radii.

Microstructure and properties of tetrapod-like ZnO whiskers reinforced Al matrix composite

Aluminum matrix composites reinforced by one-dimension structure whiskers have a wide range of applications. The paper is concerned with ZnO whiskers with peculiar tetrapod shape which were introduced to 66-1 Al alloys. 25 vol.% tetrapod-like ZnO whiskers (ZnO w) reinforced 66-1 Al matrix composites were fabricated by a squeeze casting process. The tetrapod-like ZnO w are well dispersed in the Al matrix. There are dimples, a few whisker and whisker pull-out in fracture surfaces of the composites, showing a mixture of brittle failure and ductile failure. The prepared composites possess higher strength, hardness and density than the 66-1 Al matrix alloy due to the addition of tetrapod-like ZnO w as reinforcement, and isotropic properties which is superior to other whisker reinforced Al matrix composites can be achieved owing to the peculiar structure.

Optical properties of tetrapod-shaped CdTe nanocrystals

We studied the carrier confinement in tetrapod-shaped colloidal CdTe nanocrystals by means of absorption, photoluminescence, and photoluminescence excitation spectroscopy at room and cryogenic temperatures. The spectra show features characteristic of the tetrapod shape together with a clear dependence on the dominant confinement parameter, i.e., the diameter of the tetrapod arm. Theoretical calculations based on an envelope-function approximation and using the exact tetrapod shape have been performed to assign the observed spectral features. Oscillator strength and size dependence of the transitions energy have been calculated showing a direct correlation between the oscillator strength and the nanocrystal shape.

Preparation of tetrapod-like ZnO whiskers from waste hot dipping zinc

Large and uniform tetrapod-like ZnO whiskers (T-ZnO) were prepared from waste hot dipping zinc by vapor oxidation and examined by means of X-ray diffraction and ICP-AES analysis and scanning electron microscope. The products are pure hexagonal wurtzite crystals with tetrapod shape and edge size of center body 5–6 µm and needle length of 100–130 µm. The size and shape of ZnO particles are fully controlled by the growth conditions and T-ZnO can be obtained only at 850–1000 °C and total gas flow rate ranging from 40 to 250 L · h−1 in which the size of the T-ZnO particles varies slightly with temperature. The process of the formation of T-ZnO is that T-ZnO may nucleate at the initial stage with a complete tetrapod shape and develop to the large size, but not the process of preferential growth of octahedral nuclei and subsequent growth of the needles. The experiment presents a new method to prepare T-ZnO economically by using the waste hot dipping zinc.

Formation of tetrapod ZnO nanowhiskers and its optical properties

Nanopowder containing ZnO nanowhiskers and nanoparticles was synthesized by the oxidation of Zn vapor, at temperatures from 1050 to 1450 °C in a flow of Ar and O 2 gas mixture. The morphology and structure of the nanowhiskers were dependent on the synthesis parameters such as evaporation temperature and the gas pressure. The nanowhiskers formed had a tetrapod shape with needle-like feet that become shorter and fatter on increasing temperature under a certain pressure range. The amount of Zn phase inside the nanowhiskers increased with increasing temperature. The Zn phase melted at temperature of 420 °C, which was confirmed by differential scanning calorimetry (DSC). The nanopowders showed strong sintering activity after they were pressed. The far infrared light was intensely absorbed by the ZnO tetrapod nanowhiskers.

A New Preparation Method of ZnO Cubic Phase Particle and Its IR Spectrum

ZnO ultrafine particles were produced by dropping Zn powder into a nichrome boat heated above 1000°C in a mixture gas of argon and oxygen. Cubic ZnO particles were predominantly produced in the mixture gas of oxygen at 5 Torr and argon at 95 Torr. The well-known hexagonal smoke particles were predominantly produced in the mixture gas of oxygen partial pressure of more than 20 Torr in the total pressure of 100 Torr. The characteristic infrared (IR) spectra due to the cubic and hexagonal phase were observed experimentally. The IR spectra of samples embedded in KBr pellets exhibited a peak at 20.3 µm wavelength for the cubic phase, and 18.3 µm and 23.0 µm wavelength for the hexagonal phase. The existence of cubic nuclei at the center of the tetrapod shape has been confirmed from the IR spectra.