Self-assembly Growth Mechanism Research Articles

General Synthesis of Metal Indium Sulfide Atomic Layers for Photocatalysis.

The metal indium sulfides have attracted extensive research interest in photocatalysis due to regulable atomic configuration and excellent optoelectronic properties. However, the synthesis of metal indium sulfide atomic layers is still challenging since intrinsic non-van-der-Waals layered structures of some components. Here, a surfactant self-assembly growth mechanism is proposed to controllably synthesize metal indium sulfide atomic layers. Eleven types of atomic layers with tunable compositions, thickness, and defect concentrations are successfully achieved namely In2S3, MgIn2S4, CaIn2S4, MnIn2S4, FeIn2S4, ZnIn2S4, Zn2In2S5, Zn4In16S33, CuInS2, CuIn5S8, and CdIn2S4. The typical CaIn2S4 shows a defect-dependence activity for CO2 photoreduction. The designed S vacancies in CaIn2S4 can serve as catalytic centers to activate CO2 molecules via localized electrons for π-back-donation. The engineered S vacancies tune the non-covalent interaction with CO2 and intermediates, manages to tune the free energy, and lower the reaction energy barrier. As a result, the defect-rich CaIn2S4 displays 2.82× improved reduction rate than defect-poor CaIn2S4. Meantime, other components also display promising photocatalytic performance, such as Zn2In2S5 with a H2O2 photosynthesis rate of 292µmolg-1h-1 and CuInS2 with N2-NH4 + conversion rate of 54µmolg-1h-1. This work paves the way for the multidisciplinary exploration of metal indium sulfide atomic layers with unique photocatalysis properties.

Self-assembled HVxOy nanobelts/rGO nanocomposite with an ultrahigh specific capacitance: Synthesis and promising applications in supercapacitors

Since the development of preparing vanadium oxide-graphene nanohybrids holds great promise recently, we report an HVxOy/rGO nanocomposite with novel microstructure assembling V3O7·H2O/V12O26 nanobelts and rGO nanosheets by a green facile one-step hydrothermal approach. The HVxOy nanobelts are self-assembled onto surfaces of rGO nanosheets intimately to develop a unique 3D microstructure through the in-situ and self-assembly growth mechanism. By taking full advantages of individual components, synergy has been created that HVxOy nanobelts offer abundant active sites whereas high conductive rGO nanosheets provide conductive bridges for charge transfer and act as conductive support skeletons to keep a robust structure. Evaluated as electrodes for SCs in a two-electrode system, the nanocomposite exhibits an ultrahigh specific capacitance of 813 F·g−1 at 0.5 A·g−1, a maximum power density of 3000 W·kg−1, a maximum energy density of 40.7 W·h·kg−1 as well as an ultralong lifespan up to 10,000 cycles with only 7% capacitance decline. As far as we know, the specific capacitance that we have obtained is higher than any of vanadium oxide-related materials which have been used for SCs in previous reports.

Microwave synthesis of chain-like zircona nanofibers through carbon-induced self-assembly growth

Chain-like zircona (ZrO2) nanofibers were prepared by microwave sintering without any surfactants or solid templates. Microwave sintering was conducted in a multimode microwave cavity with TE666 resonant mode at 2.45 GHz. Carbon particles were used to activate unique thermal processes when mixed with ZrO2 precursor. The sintering condition was at 1300°C for 10 min. Samples were characterized by XRD, SEM, TEM techniques. It was found that both monolithic and tetragonal ZrO2 co-existed in samples prepared fromthe mixture of ZrO2 precursors and carbon by either microwave or conventional sintering. Only m-ZrO2 exists in samples prepared by ZrO2 precursors without carbon. ZrO2 appeared as chain-like nanofibers, which might be attributed to a so-called carbon-induced self-assembly growth mechanism.

A novel route for synthesis and growth formation of metal oxides microspheres: Insights from V2O3 microspheres

Highly polydisperse V2O3 solid microspheres with large specific surface area were successfully synthesized via a facile hydrothermal decomposition of VOC2O4 solution. The morphology and composition were characterized by scanning electron microscopy (SEM), Energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). V2O3 microspheres display an obvious Mott phase transition at −128.5 °C (cooling curve) and −114.5 °C (heating curve). Some parameters including the reaction temperature, concentration of VOC2O4, reaction time, surfactant, H2C2O4 and precursor were briefly discussed to reveal the formation of V2O3 microspheres. It was found that the precursor is crucial for the fabrication of microsphere. A self-assembly growth mechanism was suggested to explain the growth process of microspheres and the autogenic CO and CO2 gas served as the soft templates. Furthermore, this route was developed to synthesize different metal oxides microspheres, and it was found that AlO(OH), Fe3O4, Fe2O3, Co3O4, Cr2O3, MoO2 and WO3 microspheres were obtained. All the results showed this process was successfully explored as a methodology to synthesize different metal oxides microspheres using the gas as the templates by this facile hydrothermal route.

Direct Observation of Magnetic Field Induced Ferroelectric Domain Evolution in Self-Assembled Quasi (0-3) BiFeO3–CoFe2O4 Thin Films

Strain-mediated magnetoelectric (ME) coupling effect is expected in self-assembly heterostructures engineered by ferroelectric and ferromagnetic materials, contributing to the enhanced overall magnetoelectric effect. Microstructures as well as the connectivity configuration are considered to play a significant role in achieving efficient magnetoelectric properties. Different from the conventional (1-3) and (2-2) type composite films, we fabricate BiFeO3-CoFe2O4 (BFO-CFO) composite thin films with a novel quasi (0-3) type connectivity via a dual-target pulsed laser deposition process. The self-assembly growth mechanism has been studied, which demonstrates that the perovskite (BFO) matrix segments the connectivity of spinel (CFO) resulting in a quasi (0-3) composite. Direct observation of ferroelectric domain wall motion under external magnetic fields proves a strong magnetoelectric coupling effect in these (0-3) thin films. Our preliminary findings reveal the promising application potential of this new structure as multiferroic domain wall devices.

A family of vertically aligned nanowires with smooth, hierarchical and hyperbranched architectures for efficient energy conversion

A powerful full solution-based process was demonstrated to synthesize various vertically aligned TiO2 wires/rods self-assembled arrays nanostructures on conductive substrates via a simple hydrothermal growth system. Demonstrated samples included a family of high-quality and high-crystallinity anatase nanowire arrays with smooth, hierarchical or hyperbranched architectures, thanks to oriented attachment and crystallization as well as a self-assembly growth mechanism. The proposed hyperbranched arrays, consisting of long TiO2 nanowire trunks, short TiO2 nanorod branches as well as tiny TiO2 nanorod leaves (recall a tree with luxuriant foliage) and thus possessing a microscopic feature size, overcome typical shortages of insufficient dye adsorption for conventional 1D smooth nanowire arrays or prototype hierarchical nanowire arrays when applied to DSSC, which achieved for the first time similar dye uptakes (i.e. 90.10nmolcm−2vs 88.62nmolcm−2) as nanoparticle counterparts under the same thickness. Dye-sensitized solar cell fabricated with an ~8μm long novel hyperbranched nanowire arrays photoelectrode yields an impressive power conversion efficiency (PCE) of 8.11%, which was much greater than that of anatase TiO2 nanoparticle (20nm in diameter) counterpart due to synergistic effects of high dye uptakes and superior broadband light scattering for improved light harvesting as well as fast charge transport for efficient charge collection for the former.

Solvothermal synthesis, characterisation and luminescent property of multilayered SnO 2 hollow microspheres

Multilayered nanocrystalline SnO2 hollow microspheres (MHS-SnO2) of a rutile structure with a controllable morphology have been successfully synthesised via a chemically induced self-assembly method by using tin chloride pentahydrate and sucrose as precursors in the glycol–water aided solvothermal synthesis. The morphology, composition, structure and luminescent properties of MHS-SnO2 are characterised by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction, X-ray diffraction, Raman spectroscopy and photoluminescence spectroscopy. The FESEM, TEM and HRTEM images indicate that the as-prepared microspheres show a multilayer structure and the walls of the hollow microspheres are composed of single crystalline nanoparticles . The effect of calcinating temperature on the Raman and optical properties of the product is analysed and a self-assembly growth mechanism of the MHS-SnO2 is proposed.

Insights into the Self-Assembly of Ferecrystalline Compounds from Designed Amorphous Precursors

Transition metal dichalcogenides, TSe2 with T = V, Ti, and Ta, were synthesized through self-assembly of designed amorphous precursors. All three compounds formed with the expected layered transition metal dichalcogenide structure with highly preferred orientation of the TSe2 layers aligned parallel with the substrate surface. VSe2 and TiSe2 self-assembled as the 1T polytype, which is the only known polytype found in the bulk form, while TaSe2 self-assembled into a new turbostratically disordered polytype. This turbostratic disorder is common among compounds made by self-assembly of designed amorphous precursors, also known as the modulated elemental reactant synthetic approach. The data obtained in this study on the formation of transition metal dichalcogenides suggest that templated nucleation at interfaces is the self-assembly growth mechanism that produces crystallographic alignment between structural units. If there is only one potential low energy orientation for the templated nucleation of the next layer, then a crystalline polytype is formed. If there is more than one low energy orientation for the templated nucleation of the next layer, a disordered polytype, referred to as a ferecrystal, is formed.

Hierarchical structured tungsten oxide nanocrystals via hydrothermal route: microstructure, formation mechanism and humidity sensing

Hierarchical structured tungsten oxide nanocrystals were synthesized via the hydrothermal route assisted by a capping agent of ammonium benzoate (AB). The products were characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that the crystal microstructures could be changed from flower-shape to star-shape by changing the mole ratio of ammonium benzoate to sodium tungstate (AB/ST). The crystal phases were changed from orthorhombic WO3⋅0.33H2O to hexagonal WO3 with the increase in the concentration of AB. Based on the results from Fourier transform infrared spectroscopy and time-dependent growth analysis, a self-assembly growth mechanism has been proposed for the formation of flower, spherical, and star-netted microstructures at different mole ratios of the AB/ST. The star-netted WO3 nanocrystals were applied as a sensitive layer for humidity sensing performed using a Love-mode ZnO/36∘ Y-cut LiTaO3 surface acoustic wave device, and a stable and sensitive response to the change of relative humidity was obtained.

Nitrate Ion Promoted Formation of Ag Nanowires in Polyol Processes: A New Nanowire Growth Mechanism

In polyol processes, it was widely accepted that Ag nanowires (NWs) were formed via uniaxial growth of multiple twinned decahedral particles (MTPs) along the {111} facets. Herein, we show that the above MTP uniaxial growth mechanism for growth of nanorods (NRs) and short nanowires (NWs) is different from that for the growth of long Ag NWs. We provide experimental evidence to show that polycrystalline long Ag NWs (up to ~100 μm) could be formed in high yield (~90%) by a completely different growth mechanism via self-assembly of Ag NPs/NRs. Transmission electron microscope (TEM) measurements show that long Ag NWs are composed of crystalline Ag NPs and NRs with multiple crystal orientations, and many NRs have crystalline structures with pentagonal cross section. Solution phase in situ X-ray diffraction (XRD) measurements show that a strained face-centered tetragonal (fct) phase was gradually formed during the formation and growth of long Ag NWs, in addition to the normal face-centered cubic (fcc) phase. The strained fct phase disappears after partial etching by HAuCl(4) and Fe(NO(3))(3). The working conditions for the MTP uniaxial growth mechanism and the current nitrate-promoted self-assembly growth mechanism will be compared and discussed.

A facile chemical route to α-Zn 3(PO 4) 2·4H 2O hierarchical sphere structures assembled by nanosheets

Novel α-Zn 3(PO 4) 2·4H 2O hierarchical sphere structures have been synthesized by a simple chemical method through the reaction between zinc acetate and orthophosphoric acid by using cetyltrimethylammonium bromide (CTAB) as capping reagent at room temperature. The structures and morphologies of the as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The influences of the synthetic parameters on the morphologies of the final products were investigated. The experimental results clearly show that both the concentration of CTAB aqueous solution and the concentration of initial reagents play important roles in the formation of the α-Zn 3(PO 4) 2·4H 2O hierarchical sphere structure. Detailed proofs indicated that the process of crystal growth was dominated by a self-assembly growth mechanism.

Controllable Synthesis of NIR-Luminescent ErQ3 Nano-/Microstructures through Self-assembly Growth

The NIR-luminescent ErQ3 nano-/microstructures have been successfully synthesized through a simple microemulsion route. Various morphologies, including nanorods, bundles, and urchins, have been achieved by tuning the fundamental experimental parameters, such as the organic solvents and the concentration of cetyltrimethylammonium bromide (CTAB). The results from SEM images indicate that a solvent with lower polar and higher boiling-point would result in nanorods, while higher concentrations of CTAB and solvents with higher polar and lower boiling-point would prefer the formation of bundles or urchins. The molecular formula of the products being ErQ3 can be deduced by the elemental analysis and thermal gravimetric analysis (TGA) and can be further confirmed by the X-ray powder diffraction (XRD) and Fourier-transform infrared spectra (FTIR). A self-assembly growth mechanism has been proposed to explain our system based on the obtained results. Following excitation of the absorption of the ligand, all the ErQ...

(00l)-oriented Bi2Sr2Co2Oy and Ca3Co4O9 films: Self-assembly orientation and growth mechanism by chemical solution deposition

Abstract In this study, two typical cobaltate-based thermoelectric films, Bi 2 Sr 2 Co 2 O y (BSC) and Ca 3 Co 4 O 9 (CCO), with structures of [Bi 2 Sr 2 O 4 ][CoO 2 ] 2 and [Ca 2 CoO 3 ] RS [CoO 2 ], respectively, are prepared by a simple chemical solution deposition on SrTiO 3 (1 0 0), (1 1 0), and (1 1 1) single crystal substrates. X-ray results reveal that all films are c -axis oriented regardless of the orientation of the substrate, suggesting self-assembly orientation. Transmission electron microscopy reveals amorphous/delamination regions for BSC film on SrTiO 3 (1 1 0), and the c -axis stripes of CCO on SrTiO 3 (1 1 1) are inclined at 30° to the interface, whereas the c -axis stripes are parallel to the interfaces for other films. The growth mechanism is established, and the driving force for self-assembly c -axis orientation is attributed to the syneresis stress due to solvent evaporation. The microstructures and properties are also studied and discussed, with the conclusion that self-assembly c -axis oriented layered cobaltates films are good candidates for thermoelectric applications.

La2Sn2O7:Eu3+ Micronanospheres: Hydrothermal Synthesis and Luminescent Properties

La2Sn2O7:Eu3+ micronanospheres were prepared by a simple and facile hydrothermal synthesis method. Well-crystallized and phase-pure La2Sn2O7:Eu3+ solid micronanospheres of ∼400 nm in size can be readily obtained after calcination at 900 °C for 3 h. The prepared samples were systematically characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and photoluminescent excitation spectra (PLE). Detailed proofs indicated that the process of La2Sn2O7:Eu3+ micronanospheres growth was dominated by a crystallization−dissolution−recrystallization−self-assembly growth mechanism. Furthermore, photoluminescent properties were also investigated.

Synthesis of BaMoO4 Nestlike Nanostructures Under a New Growth Mechanism

Novel BaMoO4 nestlike nanostructures assembled with single-crystal nanosheets have been successfully synthesized by using PVP (K30) as capping reagents under hydrothermal conditions. Detailed proofs indicated that the process of crystal growth was dominated by a crystallization−dissolution−recrystallization−self-assembly growth mechanism. The morphology of BaMoO4 evolved from several micro-compressed decahedrons to two-dimensional (2-D) nanoplates and to three-dimensional (3-D) nestlike nanostructures. The compressed decahedrons with rough surfaces synthesized in a very short time should have larger numbers of lattice defects which induce its state to be metastable. Room-temperature photoluminescence (PL) spectra also reflected the evolution of intrinsic lattice and morphology. Both the concentration of PVP aqueous solutions and the concentration of initial reagents play important roles in the formation of the BaMoO4 nestlike nanostructure.

Self-assembly of versatile tubular-likeIn2O3 nanostructures

Versatile indium oxide tubular nanostructures (well-aligned nanotube arrays, flower-liketubular structures, and square nanotubes) were fabricated by a facile and reliable chemicalvapor deposition (CVD) technique, taking advantage of the self-assembly property andsubstrate-induced epitaxial growth mechanism. The technique has a few advantages, suchas low growth temperature, nonexistence of catalyst, template-free synthesis, directbonding to the semiconductor substrates, etc. This strategy might extend the approach ofsynthesizing desirable nanostructures of other important low-melting metal oxides forpotential applications.

Surfactant-assisted self-assembly growth of single-crystalline ZnO microflowers at low temperature

Uniform single-crystalline ZnO microflower with well-defined multilayer spiny petals and hexangular prism pistil have been successfully prepared through the surfactant-assisted self-assembly route at 60°C. For the as-prepared product, three emitting bands were observed, of which included a very strong and broad green light emission at around 580nm, and two shoulders emission at 404nm and 439nm, respectively. ESR experiments confirm that there existed a great fraction of oxygen vacancies in the ZnO microflowers. The possible self-assembly growth mechanism has also been proposed.

Formation and stabilization of nanosize grains in ferromagnetic thin films by dispersed C60

Thermal stability and formation of the nanostructured metal–C60 films have been studied. Comparative grain growth kinetic studies at 450 °C between Co–C60 and Co films show higher thermal stability and significantly slower grain growth in the Co–C60 thin film than in the Co film. Atomic force microscope observation shows that the surface of the Co film is coarsened by severe grain growth and formation of surface thermal grooves after annealing at 450 °C while the surface of the Co–C60 film remains smooth due to high thermal stability and slow grain growth in the film. A self-assembly grain growth mechanism is proposed to explain the formation of the uniform columnar nanosize grain structures in these ferromagnetic metal–C60 thin films. Estimated grain sizes based on this mechanism agree with the experimental measurement and give a relationship between the grain size and the C60 concentration in these films. These results indicate that C60 has a dual function of forming and stabilizing the nanosize grains in the metal–C60 films.