Shape Evolution Mechanism Research Articles

Local corrosion mechanism of SiO2-based refractories caused by slag movement near solid–liquid–gas interface in different slag systems

Abstract Slag movement on SiO2-based prism refractories in different slag systems was observed. The cross section shape evolution mechanism was discussed. Two types of shape evolution appear. For PbO−SiO2 slag whose surface tension improves with SiO2 concentration, slag film flows up along four edges under axial Marangoni shear force and wettability. Then, it flows down along four lateral faces under gravity. Corrosion rate at edges is larger than that on lateral faces due to different SiO2 solubilities of ascending and descending flow. Prism cross section shape changes from square to round. For FetO−SiO2 slag whose surface tension reduces with the increase of SiO2 concentration, slag film flows up under the inflence of wettability. Then, it flows down under Marangoni shear force and gravity. Compared to four edges, slag is mainly up and down on four lateral faces due to larger surface tension and size. So, prism cross section shape keeps square.

High precision recognition and adjustment of complicated shape details in fine cold rolling process of ultra-thin wide strip

With development of the ultra-thin wide strip, more complicated shape problems begin to happen in the high-speed rolling process. A new shape method with high precision has to be proposed for recognition and adjustment of local composite shape defects, which is not only difficult to be detected exactly, but also easily affected by the various inevitable process factors in the practical rolling process. So, it is necessary to comprehensively take advantage of the deformation mechanism and the intelligent algorithm according to massive practical effective shape signals via focusing on the accurate shape signals and the exact local shape pattern as well as the co-regulation features. Just counting on combining the shape evolution mechanism and the intelligent property, more complicated local shape details can be revealed and controlled. Finally, many practical cases were calculated by the new model to verify the fine control effect of various shape defects, which is pretty helpful in recognition and adjustment of the ultra-thin wide strip.

Effect of sintering temperature on the emission-spectrum-shape-evolution of Sr2SiO4:Eu2+ phosphor

Color rendering index and color temperature are the key factors for the LEDs application. The two points are closely related to the emission spectrum shape of phosphors. As the key factors for the LEDs application, both the above aspects are closely dependent on the emission spectrum shape of phosphors. In this study, the emission spectrum shape has been adjusted via a home designed route. A combination of structural, morphological, and optical characterization techniques has been used to study the shape evolution mechanism. The structural results show that the Sr2SiO4 phase has not been changed with the sintering temperature increasing, but the emission spectrum shape has changed dramatically, meanwhile, the colorimetric coordinate moves from blue-green to green region. Gaussian fitting method has been used to treat the emission spectrum, and the as-obtained results indicate the emission spectrum contains two single bands, which come from the 4f7(7S7/2)–4f6(7FJ)5d1 transition of Eu2+ on the different Sr sites in the Sr2SiO4 crystal. The intensity of the two single bands is driven by sintering temperature, because of the difference between the energy barrier of the Eu2+ occupying the different Sr sites in the matrix crystal. Moreover, the mechanism of the above phenomenon has also been studied by means of first principles method, and the obtained results agree well with the former deduction.

Controlled synthesis of highly crystalline CVD-derived monolayer MoSe2 and shape evolution mechanism

Ultrathin two-dimensional transition metal dichalcogenides (TMDCs) have shown significant potential for diverse applications in semiconductor industry. The controlled synthesis of TMDCs is a prerequisite for its potential application. Unfortunately, controllable synthesis is still a great challenge. Here, we report an experimental method to induce a broad range of morphologies in highly crystalline, monolayer MoSe2 thin films by H2 content engineering. A growth mechanism was proposed to clarify the formation process for variable-shaped MoSe2 crystals. We attributed the evolution in morphologies to a result of the variable growth rates of two types of terminations that occur under different growth conditions. Our work provides a foundation for the controlled synthesis of MoSe2, reveals the shape evolution of CVD-derived MoSe2 and broadens the application range based on its shape-dependent properties.

Morphology-controllable synthesis of highly ordered nanoporous diamond films

The remarkable functional properties of diamond depend not only on its physical and chemical properties but also on its surface morphology. Ordered porous diamond with hierarchical structures is used in various applications in the fields of environment and energy management. However, obtaining such micro- and nanostructures via conventional techniques has proven to be challenging because of the superhardness and extreme chemical inertness of diamond. In this study, a strategy to create highly textured diamond films structured by vertical columnar crystals was developed. The mechanism of shape-evolution of diamond grains was proposed to account for the changes in the crystal shape from octahedron through cubo-octahedron to cube, followed by oxidation and hydrogenation. Shape evolution of diamond crystals during the initial fabrication stages was assessed by scanning electron microscopy, which revealed that the surfaces of fabricated diamond consisted of rough octahedral {111} and smooth cubic {100} faces. The variation of the crystal shape depended on the relative growth rate of {111} faces to that of {100} faces during the growth process. Finally, highly ordered porous diamond films with switchable wettability properties were obtained by post-fabrication modification involving thermal etching in air followed by etching in hydrogen plasma.

Controlled growth of six-point stars MoS2 by chemical vapor deposition and its shape evolution mechanism

Monolayer semiconductors of molybdenum disulfide (MoS2) crystals have drawn tremendous attention due to their extraordinary electronic and optical properties. A uniform and high-quality crystalline MoS2 monolayer is greatly needed in fundamental studies and practical applications. Three-point star to six-point star MoS2 nanosheets are readily synthesized in a controlled manner using the chemical vapor deposition method. A possible coalescent model is proposed to study the evolution of the six-point star MoS2 domain. A comparative study of field effect transistors are performed to disclose the negative effect of grain boundaries on the transport properties based on six-point star MoS2.

Polymorphous ZnO Nanostructures: Zn Polar Surface‐Guided Size and Shape Evolution Mechanism and Enhanced Photocatalytic Activity

AbstractThis study proposes a simple, low‐temperature chemical etching method for selective preparation of monodispersed, hexagonal, single‐crystal ZnO nanostructures. The morphological evolution from nanoplates (NPs) to nanoseals (NSs), nanobowls (NBs), and nanorings (NRs) is initiated by positively charged (0 0 0 1) Zn polar surface and driven by the principle of minimum energy. The relationship among the morphology, dimensions, and function of ZnO was determined by investigating polar planes, surface areas, energy bands, defects, optical properties, and catalytic activity for rhodamine B degradation. The ZnO NBs and ZnO NRs exhibit improved photocatalytic performance because of enhanced light harvesting and plasmonic resonance enhanced absorption. Surface recombination plays a key role in the apparent rate constant k for ZnO NBs with small size and those formed at low reaction temperatures. The photocatalytic activity of ZnO NBs formed at high reaction temperatures decreases with increasing size because of the decreased surface area.

Controlled synthesis of β-NaGdF4 with nanosphere-, nanotube-, and nanorod-like morphology using solvents

NaGdF4 nanocrystals with controlled shapes were synthesized in an ethylene glycol/deionized water hydrothermal reaction system. Through adjusting the solvent composition, the nanocrystals with nanosphere-, nanotube-, and nanorod-like morphology have been selectively synthesized. The change in the nucleation speed, the growth rates in different crystallographic direction and the aggregation driving forces induced different morphologies of the resulting nanocrystals. A possible mechanism of shape evolution depending on solvent composition was proposed. Photoluminescence spectra of NaGdF4:Nd3+ nanocrystals exhibited characteristic emission of Nd3+ using an excitation wavelength of 794nm. Moreover, the nanotube-like nanocrystals exhibited the strongest fluorescence intensity and longest fluorescence decay time.

Fabrication and shape evolution of petal-like Cu2O nanocrystal toward enhanced photoactivity and stability for hydrogen generation under visible light irradiation

Controllable Cu2O nanocrystals with petal-like structure were successfully synthesized by the introduction of a concentrated ripening process into the methodology developed by the preparation of Cu2O nanocubes. The mechanism of shape evolution of petal-like Cu2O nanoflowers was proposed to reveal the concentrated ripening process as a novel strategy in the fabrication of special structured nanocrystals. Cu2O nanoflowers with petal-like structure exhibited enhanced activity and stability in hydrogen evolution compared with Cu2O naonocubes via the same route. The enhanced activity and stability of Cu2O nanoflowers was attributed to their unique petal-like sheet structure, which exhibited large BET surface area and pore volume. The results of cycle experiments also confirmed the enhanced stability of Cu2O nanoflower, which the H2 evolution rate of Cu2O nanoflower only decreased by 5.5% after the 4th cycles.

Shape Evolution of Platinum Nanocrystals by Electrochemistry

The high-index facets of face-centered cubic metal have high surface energy, and the thermodynamics of crystal growth makes the high-index facets disappear during the crystal growth. The surface energy of high-index facets can be reduced through adsorption of molecules during crystal growth, and metal nanoparticles with high-index facets are thus formed. The shape-controlled synthesis of metal nanocrystals remains a big challenge even today. The shape evolution mechanism of metal nanocrystals with different facets has not yet been well elucidated. In this work, platinum nanocrystals of different shapes, octahedra with low-index facets, tetrahexahedra and concave hexoctahedron enclosed with high-index facets, were synthesized by the square-wave-potential method (SWP). The same precursor and the same adsorption molecules were used to synthesize Pt nanocrystals, but a series of parameter were varied, such as precursor concentration, growth potential, oxidative etching potential, with/without electrolyte in solution, and frequency of the SWP. This paper discusses the details about shape-controlled synthesis and proposes the preliminary mechanism of formation of Pt nanocrystals. The current study has illustrated that the electrochemical approach is an effective and facile route in tuning Pt nanocrystals’ shape and corresponding properties, shedding lights on the design and preparation of Pt nanocatalysts.

Mechanism of Shape Evolution in Ag Nanoprisms Stabilized by Thiol-Terminated Poly(ethylene glycol): An in Situ Kinetic Study

Silver nanoprisms are found to undergo a shape transformation from triangular to disk-like upon functionalization with thiol-terminated poly(ethylene glycol) (PEG-SH). The shape transformation starts with a rounding of the nanoprism tips followed by a reduction in the overall particle size. The changes in nanoparticle morphology and surface chemistry during the PEGylation process are investigated by a combination of transmission electron microscopy, in situ UV–vis spectroscopy, and in situ solution-phase X-ray absorption near-edge structure at the Ag L3- and the S K-edge. We found that PEG-SH etches the Ag surface through a catalytic redox process, whereby oxidized surface atoms are first removed from the nanoprism tips (likely as the silver(I) thiolate complex) and then reduced back to elemental silver (in the form of small clusters) in the solution along with oxidation of the thiolate to the disulfide. The effect of PEG-SH concentration and molecular weight are investigated, along with the role of ambient oxygen in the etching process. The results have implications for the behavior of silver nanoprisms in various plasmonic applications (e.g., surface-enhanced Raman scattering and metal-enhanced fluorescence) and also provide insights into the degradation mechanism of silver nanomaterials in the environment.

Detecting intermediate particles in the growth of colloidal zinc oxide nanoparticles in different chemical routes using MCR–ALS

Zinc oxide (ZnO) nanoparticles have been used in a wide‐ranging of applications such as transparent UV protection, light emitting diodes, sensors and photovoltaic cells. Many applications of ZnO nanoparticles could be improved by changing the particle size, shape and morphology. Therefore, studying the mechanism of shape evolution is crucial for size and shape controlled synthesis of nanocrystaline ZnO particles. As an alternative to sophisticated techniques such as transmission electron microscopy (TEM) and X‐ray powder diffraction (XRD), commonly used for studying nanoparticles evolution, we herein employed UV/Vis spectroscopy for monitoring the evolution process of the ZnO nanocrystals coupled with chemometric methods for analyzing overlapped and complex spectral data. The evolutionary UV‐Visible absorbance data of ZnO nanoparticles through particle formation via precipitation methods in various solution conditions were analyzed using factor analysis, evolving factor analysis, and multivariate curve resolution‐alternative least‐squares analysis. Depending on chemical routs, three or four chemical factors that attributed to the ZnO nanoparticles of different size were detected and the concentration profiles and pure spectra of the particles were resolved. The interpretation of the evolution profiles of the detected ZnO nanoparticles were achieved by Ostwald ripening mechanism. Copyright © 2013 John Wiley & Sons, Ltd.

Growth orientation, shape evolution of monodisperse PbSe nanocrystals and their use in optoelectronic devices

A new facile solution method for the synthesis of high quality lead selenide (PbSe) nanocrystals with controllable size and shape was developed. A Pb–stearate complex and oleylamine–selenium (OLA–Se) were used as new precursors to prepare monodispersed nanocrystals instead of the traditional lead oxide (PbO) and trioctylphosphine–selenium (TOPSe). Both of the lead and chalcogenide precursors used in this method are inexpensive and air-stable, which largely reduces the cost of the reaction and simplifies the synthetic process. Five different shapes including quasi-spherical, cubic, octahedral, cuboctahedral and star shaped monodispersed PbSe nanocrystals were obtained, and the particle size can be easily tuned from ∼18 nm to ∼50 nm by varying the amount of oleic acid (OA) while keeping the amount of oleylamine (OLA) fixed. Oleic acid based growth orientation and shape evolution mechanism in double stabilizer surfactants was investigated in detail. The etching of PbSe nanocrystals was also observed when they were dispersed in toluene containing excessive amine over time, the etching process of oleylamine occurred on particle surfaces, and a new framework composed of nanorods formed around the nanocrystals. An ITO–PbSe–Al device based on a film of PbSe nanocrystals was constructed. The dark steadystate I–V characteristics of the films before and after ligand exchange revealed a broad prospect for the use of PbSe nanocrystals in light detection and infrared solar cells.

Growth of ZnO hemispheres on silicon by a hydrothermal method

This paper reports a hydrothermal method to control the morphology of hemisphere ZnO nanostructures (NSs) fabricated on a Si substrate by using surfactant additive molecules. The shape of ZnO NSs was controlled by the concentration of the trisodium citrate (TSC) added during the main growth step. With increasing the TSC concentration from 0 to 1.3 and 2.6mM, the shape of ZnO NSs changed from a bundle of nanorods to a flower-like-shape composed of merged large hexagonal crystals, and finally to ZnO hemispheres. X-ray diffraction and photoluminescence spectroscopy revealed that the ZnO NSs had a wurtzite crystalline structure. The shape evolution mechanism of ZnO NSs could be explained using the surfactant-mediated growth model.

Phase and Shape Evolution of CdS Nanocrystallites under Solvothermal Conditions

CdS nanocrystallites with different morphologies have solvothermally prepared with ethylenediamine (en) and glycol as solvents. Solvent-dependent experiments were carried out by adjusting the ratios of en/glycol to investigate the effects of the solvents on the product phase formation and morphology. It was found that the morphology of CdS nanocrystallite develops from a rough spherical nanoparticle to a rod-, twinrod-, and tetrapod-shaped nanoparticle by increasing the ratio of en/glycol, meanwhile the phase composition changes from coexistence of tetragonal zinc blende CdS and hexagonal wurtzite CdS to pure hexagonal wurtzite CdS. Based on the experimental results, a possible shape evolution mechanism of CdS nanocrystallites is simply discussed.

Delicate control of crystallographic facet-oriented Cu2O nanocrystals and the correlated adsorption ability

In this work, we demonstrate the systematic and delicate geometry control of Cu2O nanocrystals by taking advantage of the selective surface stabilization effect. A variety of Cu2O architectures, evolved from cubes through truncated cubes, cubooctahedrons, truncated octahedrons and finally to octahedrons, were achieved by simply adjusting the added PVP. Based on the understanding of the intrinsic structural features of the cuprite Cu2O and PVP, we elucidated the underlying shape evolution mechanism. The as-prepared products demonstrated a crystallography-dependent adsorption ability with methyl orange (MeO) as the pollutant. With the advantage of a low cost, high yield and straightforward procedure without pre-formed crystals as sacrificial templates, this method may provide a good starting point for the study of shape construction and morphology-dependent properties of other nanocrystals.

Investigating the Shape Evolution Mechanism of CdSe Quantum Dots by Chemometrics Analysis of Spectrophotometric Data

The study on the mechanism of the shape evolution of nanocrystaline particles is an important and emerging field, which is applicable in the shaped control synthesis of nanoparticles. As an alternative to transmittance electron microscopy (TEM), which is already used in the study of nanoparticles, in this article a simple spectrophotometric method has been proposed utilizing the advantages of chemometrics methods in analyzing overlapped and complex spectral data. The evolutionary visible absorbance data of CdSe quantum dots through particle formation were analyzed by factor analysis, evolving factor analysis, and multivariate curve resolution−alternative least-squares analysis, by which four chemical factors, attributed to the CdSe nanoparticles of different shapes, were detected and the concentration profiles and pure spectra of these particles were resolved. The interpretation of the evolution profiles of the detected nanocrystaline CdSe particles was easily achieved by using the existing shape evolution mechanism. The formation of magic size nanoclusters was detected at the beginning of the reaction, which was followed by the formation of rods and other elongated particles. At the end of the reaction, the formation of thermodynamically stable quantum dots nanoparticles was identified.

Shape Evolution of α-Fe2O3 and Its Size-Dependent Electrochemical Properties for Lithium-Ion Batteries

Crystalline with different particle shapes and sizes was selectively synthesized by a simple hydrothermal method. By carefully tuning the concentration of the reactants and the reaction time, cuboid particles and nanowires can be obtained. Based on the evidence of electron microscope images, a shape evolution mechanism for the nanowire structure is proposed. Electrochemical performance as an anode material for lithium-ion batteries was further evaluated by cyclic voltammetry, electrochemical impedance, and charge–discharge measurements. It was demonstrated that both the morphology and the particle size had an influence on the performance. Compared with the electrode made from the cuboid material, the nanowire electrode displayed higher discharge capacity and better cycling reversibility, which may be a result of the one-dimensional nanostructure and high surface area.

Thiol-Frozen Shape Evolution of Triangular Silver Nanoplates

The structural and optical stability of nanoparticles directly influences their applications. The shape evolution of silver nanoplates synthesized in the presence of bis(2-ethylhexyl) sulfosuccinate (AOT) could be effectively frozen using thiols in aqueous solution. These thiols (e.g., 1-hexanethiol, 1-octanethiol, 1-dodecanethiol, and 1-hexadecanethiol) exhibit stronger surface affinity on the silver crystalline surfaces. This is evidenced from both the unchanged shape/size of nanoplates and their unshifted plasmon resonances in optical absorption. To quantitatively explain the thiol-frozen shape evolution mechanism of silver nanoplates at molecular scale, molecular dynamics simulation was performed. The results show that these thiols exhibit larger interaction energies than AOT molecules on the silver atomic surfaces and hence freeze the shape evolution of silver nanoparticles. This thiol-frozen strategy would not only be useful for stabilizing nanoparticles but would also allow the introduction of a wide range of surface chemical functionalities to the nanoparticles for potential applications in nanosensors.

Structure of neutron-rich nuclei around A ⋍ 100

Neutron-rich isotopes of Mo (Z=42) around A ⋍ 100 have been investigated within the formalisms of cranked Nilsson Strutinsky and CHFB, to study several interesting features of nuclear structure in this mass region. The total energy/routhian surfaces have been generated for the isotopes of Mo ranging from A ⋍ 96 − 112, as a function of deformation (β 2 and γ) for ground state and higher angular momentum states. Results of calculations using two different formalisms have been compared and combined to have a better understanding of the underlying mechanism of shape evolution.