Formation Mechanism Of Nanostructures Research Articles

Zirconia Nanostructures: Novel Facile Surfactant‐Free Preparation and Characterization

Zirconia nanostructures have been prepared via a facile precipitation route using Zirconium (IV) oxynitrate hydrate and tetraethylenepentamine (TEPA). Here, TEPA was used as novel precipitator to fabricate zirconia nanostructures. The influence of reaction time, dosage of TEPA, and solvent was also examined to control the shape and particle size. Results of this work indicate that these reaction parameters have important impact on the control of shape and grain size of the zirconia. To characterize the as‐synthesized nanostructures, techniques such as X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, energy dispersive X‐ray microanalysis (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT‐IR) spectroscopy, and photoluminescence (PL) spectroscopy were applied. In addition, the formation mechanism of zirconia nanostructures was discussed.

Study on the nanostructure formation mechanism of hypereutectic Al–17.5Si alloy induced by high current pulsed electron beam

This work investigates the nanostructure forming mechanism of hypereutectic Al–17.5Si alloy associated with the high current pulsed electron beam (HCPEB) treatment with increasing number of pulses by electron backscatter diffraction (EBSD) and SEM. The surface layers were melted and resolidified rapidly. The treated surfaces show different structural characteristics in different compositions and distribution zones. The top melted-layer zone can be divided into three zones: Si-rich, Ai-rich, and intermediate zone. The Al-rich zone has a nano-cellular microstructure with a diameter of ∼100nm. The microstructure in the Si-rich zone consists of fine, dispersive, and spherical nano-sized Si crystals surrounded by α(Al) cells. Some superfine eutectic structures form in the boundary of the two zones. With the increase of number of pulses, the proportion of Si-rich zone to the whole top surface increases, and more cellular substructures are transformed to fine equiaxed grain. In other words, with increasing number of pulses, more Si elements diffuse to the Al-rich zone and provide heterogeneous nucleation sites, and Al grains are refined dramatically. Moreover, the relationship between the substrate Si phase and crystalline phase is determined by EBSD; that is, (111)Al//(001)Si with a value of disregistry δ at approximately 5%. The HCPEB technique is a versatile technique for refining the surface microstructure of hypereutectic Al–Si alloys.

Direct Hydrothermal Synthesis of Carbonaceous Silver Nanocables for Electrocatalytic Applications.

This study demonstrates a facile but efficient hydrothermal method for the direct synthesis of both carbonaceous silver (Ag@C core-shell) nanocables and carbonaceous nanotubes under mild conditions (<180 °C). The carbonaceous tubes can be formed by removal of the silver cores via an etching process under temperature control (60-140 °C). The structure and composition are characterized using various advanced microscopic and spectroscopic techniques. The pertinent variables such as temperature, reaction time, and surfactants that can affect the formation and growth of the nanocables and nanotubes are investigated and optimized. It is found that cetyltrimethylammonium bromide plays multiple roles in the formation of Ag@C nanocables and carbonaceous nanotubes including: a shape controller for metallic Ag wires and Ag@C cables, a source of Br(-) ions to form insoluble AgBr and then Ag crystals, an etching agent of silver cores to form carbonaceous tubes, and an inducer to refill silver particles into the carbonaceous tubes to form core-shell structures. The formation mechanism of carbonaceous silver nanostructures depending upon temperature is also discussed. Finally, the electrocatalytic performance of the as-prepared Ag@C nanocables is assessed for the oxidation reduction reaction and found to be very active but much less costly than the commonly used platinum catalysts. The findings should be useful for designing and constructing carbonaceous-metal nanostructures with potential applications in conductive materials, catalysts, and biosensors.

Formation of GaAs nanostructures by droplet epitaxy—Monte Carlo simulation

Abstract A kinetic Monte Carlo model of droplet epitaxy is suggested and realized. A basis for the Monte Carlo model is the vapor–liquid–solid mechanism. The proposed model was used for the analysis of GaAs nanostructure formation mechanism during crystallization of Ga drops under the arsenic flux. The dependences of the grown structure morphology on temperature, As 2 flux intensity and GaAs substrate surface orientation were analyzed. Depending on temperature and arsenic flux intensity, different shapes of nanostructures (crystal dots, core–shell compact clusters, nanoholes and nanorings) were achieved. A lack of etching of GaAs substrates with (1 1 1)А and (1 1 1)В surface orientations by liquid gallium was revealed. Nanohole and nanoring formation was observed only on substrates with (0 0 1) surface orientation. The kinetics of nanoring formation was examined.

CTAB-assisted synthesis of unique 3D ZnO and the acetone sensing performances

Flower-like ZnO nanostructure composed of orderly nanoplates was synthesized by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. The unique ZnO nanostructure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy analysis. The possible formation mechanism of flower-like ZnO nanostructure is proposed. The positively charged CTA+ surfactant can act as an ionic carrier, as well as an agglomeration inhibitor in the orientation growth of ZnO nanoplates. Moreover, the gas sensing properties for acetone were also investigated. The sensor shows high response and good selectivity to acetone gas at the optimum operating temperature of 300°C. The excellent gas sensing performances of the flower-like ZnO indicate that ZnO sensor synthesized by the CTAB-assisted hydrothermal method can be used as a promising sensing material for fabricating acetone sensors.

Synthesis and characterization of carbon nanostructures by evaporating pure graphite and carbon black in detonation-gas arc discharge

Arc discharge experiments combined with explosive detonation have been carried out to probe the transformation of pure graphite and carbon black evaporated in detonation gas. Under respective conditions, different kinds of carbon nanostructures have been synthesized including few-layer graphene (FLG) nanosheets, polyhedral graphite particles (PGPs), carbonaceous monocrystals and graphene oxide (GO). The evaporation of graphite facilitates the formation of FLG and PGPs, which exhibits competitive growth according to the pressure of detonation gas. By evaporating carbon black, a considerable amount of high-crystalline GO with low oxygen concentration are acquired. The morphology, crystal structures, Raman spectroscopic fingerprints and chemical compositions of these products are investigated by the characterizations of transmission electron microscopy (TEM), high-resolution TEM, Raman spectra and X-ray photoelectron spectroscopy. The formation mechanisms of such carbon nanostructures in arc evaporation are discussed according to the chemical nature and pressure of detonation gas.

Synthesis of MOFs and Their Composite Structures through Sacrificial-Template Strategy

Exemplified by chemical conversion of ZnO nanostructures into zeolitic imidazolate framework-8 (ZIF-8) nanostructures, a sacrificial-template method has been demonstrated for the synthesis of metal–organic frameworks (MOFs) and their composite structures which may not be attainable by other methods. Their properties were investigated and the formation mechanism of ZIF-8 nanostructures was discussed. This method shows the potential of the formation of various-shaped MOFs and their composite nanostructures and will broad the applications of MOFs and their derivatives.

Hydrothermal synthesis of SnO2 nanocubes and nanospheres and their gas sensing properties

In this work, we reported successful synthesis of SnO2 nanocubes and nanospheres via a facile hydrothermal technique. The as-obtained SnO2 nanostructures have been characterized by X-ray diffraction and field-emission scanning electron microscopy. The formation mechanism of aforementioned SnO2 nanostructures has been proposed in detail, especially SnO2 nanaocubes, which has been systematically investigated by varying the reaction time and the surfactant SDS play a key role in growth process of nanocubes. Furthermore, the gas sensing properties of as-prepared SnO2 nanostructures have been tested towards ethanol. Interestingly, it is noted that gas sensing performance of nanocubes are superior to nanospheres, which certified that the gas sensing properties can be enhanced by controlling the morphologies and the SnO2 nanocubes maybe a promising candidate based materials in the fields of gas sensors.

Hybrid simulation research on formation mechanism of tungsten nanostructure induced by helium plasma irradiation

The generation of tungsten fuzzy nanostructure by exposure to helium plasma is one of the important problems for the use of tungsten material as divertor plates in nuclear fusion reactors. In the present paper, the formation mechanisms of the helium bubble and the tungsten fuzzy nanostructure were investigated by using several simulation methods. We proposed the four-step process which is composed of penetration step, diffusion and agglomeration step, helium bubble growth step, and fuzzy nanostructure formation step. As the fourth step, the formation of the tungsten fuzzy nanostructure was successfully reproduced by newly developed hybrid simulation combining between molecular dynamics and Monte-Carlo method. The formation mechanism of tungsten fuzzy nanostructure observed by the hybrid simulation is that concavity and convexity of the surface are enhanced by the bursting of helium bubbles in the region around the concavity.

Nanostructure formation mechanism and ion diffusion in iron–titanium composite materials with chemical looping redox reactions

Fe–Ti microparticles and their oxidation and redox processes in chemical looping.

Preparation of Nanostructured Microporous Metal Foams through Flow Induced Electroless Deposition

Monolithic nanostructured metallic porous structures with a hierarchy of pore size ranging from ca. 10 μm to 1 nm are processed for use as microreactors. The technique is based on flow induced electroless deposition of metals on a porous template known as PolyHIPE Polymer. The process is conducted in a purpose built flow reactor using a processing protocol to allow uniform and efficient metal deposition under flow. Nickel chloride and sodium hypophosphite were used as the metal and reducing agent, respectively. Electroless deposition occurs in the form of grains with a composition of NixPy in which the grain size range was ca. 20–0.2 μm depending on the composition of the metal deposition solution. Structure formation in the monoliths starts with heat treatment above 600°C resulting in the formation of a 3‐dimensional network of capillary‐like porous structures which form the walls of large arterial pores. These monoliths have a dense but porous surface providing mechanical strength for the monolith. The porous capillary‐like arterial pore walls provide a large surface area for any catalytic activity. The mechanisms of metal deposition and nanostructure formation are evaluated using scanning electron microscopy, energy dispersive X‐ray analysis, XRD, BET‐surface area, and mercury intrusion porosimetry.

Formation mechanism and optical characterization of polymorphic silicon nanostructures by DC arc-discharge

Polymorphic Si nanostructures (particle, sheet, ribbon) are generated through isotropic, anisotropic, and coalescence growth using a DC arc-discharge plasma method.

Vividly colorful hybrid perovskite solar cells by doctor-blade coating with perovskite photonic nanostructures

Efficient colorful perovskite solar cells are fabricated and the formation mechanism of the spontaneous photonic nanostructure is revealed.

Controlling DNA Bundle Size and Spatial Arrangement in Self-assembled Arrays on Superhydrophobic Surface

The use of superhydrophobic surfaces (SHSs) is now emerging as an attractive platform for the realization of one-dimensional (1D) nanostructures with potential applications in many nanotechnological and biotechnological fields. To this purpose, a strict control of the nanostructures size and their spatial arrangement is highly required. However, these parameters may be strongly dependent on the complex evaporation dynamics of the sessile droplet on the SHS. In this work, we investigated the effect of the evaporation dynamics on the size and the spatial arrangement of self-assembled 1D DNA bundles. Our results reveal that different arrangements and bundle size distributions may occur depending on droplet evaporation stage. These results contribute to elucidate the formation mechanism of 1D nanostructures on SHSs.

Facile synthesis of morphology- and size-controllable polythiophene/gold composites in aqueous medium

Polythiophene (PTh) nanomaterials and polythiophene/gold (PTh-Au) composites were successfully fabricated using chloroaurate acid (HAuCl4) as an oxidant in aqueous medium without using any templates or structure-directing agents. With increasing thiophene (Th) concentration from 0.5 to 50 mM at a fixed molar ratio of thiophene and HAuCl4 of 3:1, Au@PTh core–shell nanoparticles (~36 nm in diameter) and fibers, AuNPs-modified PTh nanospheres (~270 nm in diameter), flower-like gold microparticles, and gold microsheets were obtained. At a fixed thiophene concentration of 5.0 or 50 mM, the molar ratio of thiophene/HAuCl4 also affected the morphology and size of PTh–Au composites. The morphology of obtained nanostructures was determined by scanning electron microscope and transmission electron microscope. Furthermore, characterization experiments including FT-IR, UV–Vis spectrometry, energy-dispersive X-ray spectroscopy, and selected-area electron diffraction were utilized to investigate the chemical and electronic structures of PTh nanostructures and PTh–Au composites. The photoluminescent (PL) properties of PTh–Au composites have also been investigated to clarify the effectiveness of the morphology and composition of composites on the PL emission peaks. In addition, the formation mechanism of PTh nanostructures and PTh–Au composites is also proposed.

Synthesis of ThO2nanostructures through a hydrothermal approach: influence of hexamethylenetetramine (HMTA) and sodium dodecyl sulfate (SDS)

In this work, ThO2 nanostructures with various morphologies are synthesized through a hydrothermal approach. The influences of some experimental parameters, such as the concentration of hexamethylenetetramine (HMTA), the amount of sodium dodecyl sulfate (SDS) and the hydrothermal temperature, on the synthesis and morphologies of ThO2 nanostructures were systematically investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results showed that ThO2 nanospheres with a particle size of 59 +/- 9 nm could be synthesized at a molar ratio of Th4+/HMTA of 0.3 under the reaction temperature of 100 degrees C. Adding SDS could adjust the diameter of ThO2 nanospheres from 240 to 71 nm while keeping other parameters constant. Furthermore, nanoparticles and the aggregated nanostructures of ThO2 could be obtained by varying the concentration of HMTA and the amount of SDS. The possible formation mechanism of various ThO2 nanostructures was also proposed.

Polypyrrole single and double-shelled nanospheres templated by pyrrole–Hg(II) complex: Synthesis, characterization, formation mechanism and electrochemical performance

Spherical and yolk/shell nanostructures of pyrrole (Py)–Hg(II) complex have been formed by mixing Py monomer with HgCl2 in aqueous solution as white precipitation. Templated by spherical and yolk/shell nanostructures of Py–Hg(II) complex, polypyrrole (PPy) single and double-shelled hollow nanospheres have been successfully fabricated by simply introducing an oxidant to initial the polymerization of Py monomer on the surface of templates. Formation mechanisms of PPy nanostructures involved have been discussed in detail according to experimental observations. When hollow PPy spheres were used as the electrode materials for the supercapacitors, the specific capacity can achieve 252Fg−1 at the current density of 0.5Ag−1. Results indicated that the material has good cyclic stability, and is suitable to be applied as a good supercapacitor material.

Template-free sonochemical synthesis of flower-like ZnO nanostructures

Abstract Flower-like ZnO nanostructures have been successfully synthesized via a facile and template-free sonochemical method, using zinc acetate and potassium hydroxide as reactants only. The as-synthesized flower-like ZnO nanostructures were composed of nanorods with the width of ∼ 300 – 400 nm and the length of ∼ 2 – 3 μm . The structures, morphologies and optical properties of the as-prepared products were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV-Vis spectrophotometry and Raman-scattering spectroscopy. A plausible formation mechanism of flower-like ZnO nanostructures was studied by SEM which monitors an intermediate morphology transformation of the product at the different ultrasonic time ( t = 80 , 90 , 95 , 105 , and 120 min ).

Hydrothermal Synthesis of Rod-Like LaOCl Nanoparticles from New Precursors

Using the hydrothermal method, rod-like lanthanum oxychloride nanoparticles were synthesized by the reaction of LaCl3.7H2O, ethylenediamine, and hydrazine. Ethylenediamine and hydrazine with pH management can control the particle growth and have an important role in the formation of rod-like structures. The morphology and microstructure of the obtained products were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, fourier transformed infrared spectrum, and transmission electron microscopy The formation mechanism of the LaOCl nanostructures was also proposed.

Controllable synthesis of TiO2hierarchical and their applications in lithium ion batteries

In this article, TiO2 has been successfully fa in the Ti(SO4)2–CH3COOH system via a simple hydrothermal method. The formation mechanism of the TiO2 hierarchical nanostructures was also investigated in detail, which involved the complex reaction between Ti(SO4)2 and CH3COOH, hydrolysis of the complex, nucleation and self-assembly of TiO2 nanocrystals and anisotropic growth of these subunits. SO42− plays an important role in the self-assembly of subunits. In addition, controllable synthesis of TiO2 hierarchical nanostructures with tunable size can be realized just by changing experimental parameters, such as reaction time or Ti(SO4)2 concentration. When used as the anode in lithium ion batteries, these TiO2 hierarchical nanostructures present much higher specific capacity and better rate performances than TiO2 nanoparticles, which are attributed to the stability of the secondary-structure during the charge and discharge processes.