Formation Of Nanorings Research Articles

Crystal Engineering and Self-Assembled Nanoring Formation with Purine-CdII/HgII Supramolecular Frameworks.

We report three complexes of CdII and HgII with two purine rare tautomers, N9-(pyridin-2-ylmethyl)-N6-methoxyadenine, L1 and N7-(pyridin-2-ylmethyl)-N6-methoxyadenine, L2, highlighting diverse crystallographic signatures exhibited by them. Influence of substituents, binding sites, steric effects and metal salts on the different modes of binding enabled an insight into metal-nucleobase interactions. L1 interacted with two and three equivalents of Cd(NO3)2.4H2O and HgCl2, respectively, while L2 interacted with two equivalents of HgCl2, altogether leading to three different complexes (1 [C48H48Cd6N34O50], 2 [C12H12Cl4Hg2N6O] and 3 [C12H12Cl2HgN6O]) possessing varied dimensionality and stabilising interactions. The photoluminescent properties of these coordination frameworks have also been probed. Notably, nanoring-like structures were obtained, as a result of self-assembly of 3 when investigated by transmission electron microscopy, additionally supported by molecular dynamics simulations.

In Situ and Ex Situ Studies of Ring-Like Assembly of Silica Nanoparticles in the Presence of Poly(propylene oxide)-Poly(ethylene oxide) Block Copolymers.

Block copolymer-mediated self-assembly of colloidal nanoparticles has attracted great attention for fabricating various nanoparticle arrays. We have previously shown that silica nanoparticles (SNPs) assemble into ring-like nanostructures in the presence of temperature-responsive block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (PEOVE-PMOVE) in an aqueous phase. The ring-like nanostructures formed within an aggregate of PEOVE-PMOVE when the temperature was increased to 45 °C, at which the polymer is amphiphilic. Herein, we report that SNPs assemble into ring-like nanostructures even with a different temperature-responsive, amphiphilic block copolymer poly(propylene oxide)-block-poly(ethylene oxide) (PPO-PEO) at 45 °C. Field-emission scanning electron microscopy for SNP assemblies that were spin-coated on a substrate indicated that SNP first assembled into chain-like nanostructures and then bent into closed loops over several days. In contrast, in situ small-angle X-ray diffraction measurements revealed the formation of SNP nanorings within 75 s at 45 °C in the liquid phase. These results indicated that ring-like assembly of SNPs occurs quickly in the liquid phase, but the slow formation of Si-O-Si bonds between SNPs leads to their structure being destroyed by spin-coating. Intriguingly, SNPs with a diameter of 15 nm form a well-defined nanoring structure, with five SNPs located at the vertex points of a regular pentagon. Additionally, small-angle neutron scattering, where the contrast of the solvent (a mixture of H2O and D2O) matches that of SNPs, clarified that SNPs are contained within the spherical micelle formed from PPO-PEO. This work offers a facile and versatile approach to preparing ring-like arrays from inorganic colloidal nanoparticles, leading to applications including sensing, catalysis, and nanoelectronics.

Hydrazine-induced synthesis of CdS nanorings for the application in photodegradation

In this paper, CdS nanorings synthesized by a facile hydrazine-induced microwave method for the photodegradation of pollutants were reported for the first time. Different reaction method, microwave power, the category and dosage of pH regulating reagent, reaction temperature and reaction time were investigated. The formation of CdS nanorings from the self-assembly of nanoparticles was attributed to the coordination of hydrazine producing the dipole–dipole interaction among the uniform nanoparticles prepared by microwave method. The crystal phase, composition, morphology and surface property of CdS nanorings were characterized. The results showed that 100 nm-sized wurtzite CdS nanorings generated with the self-assembly of 5–8 nm nanoparticles, which presented mesoporous structures. To study the influence of ring-like structures on the photocatalysis, the photodegradation of rhodamine B (RhB) with CdS nanorings and nanoparticles was compared. The results showed that, CdS nanorings displayed higher photodegradation efficiency, which were originated from more favorable band edge potential and effective electron–hole separation producing more superoxide radical and holes as active specifies. The photodegradation path of RhB contained the process of the demethylation, the decarboxylation process, the chromophore cleavage and ring-open reactions. Finally, the available photodegradation of multiple pollutants and reusability of CdS nanorings were carried out.

Spontaneous Condensation of RNA into Nanoring and Globular Structures.

The effect of polyvalent cations, like spermine, on the condensation of DNA into very well-defined toroidal shapes has been well studied and understood. A great effort has been made to obtain similar condensed structures from RNA molecules, but so far, it has been elusive. In this work, we show that single-stranded RNA (ssRNA) molecules can easily be condensed into nanoring and globular structures on a mica surface, where each nanoring structure is formed mostly by a single RNA molecule. The condensation occurs in a concentration range of different cations, from monovalent to trivalent, but at a higher concentration, globular structures appear. RNA nanoring structures were observed on mica surfaces by atomic force microscopy (AFM). The samples were observed in tapping mode and were prepared by drop evaporation of a solution of RNA in the presence of one type of the different cations used. As far as we know, this is the first time that nanorings or any other well-defined condensed RNA structures have been reported in the presence of simple salts. The RNA nanoring formation can be understood by an energy competition between the hydrogen bonding forming hairpin stems—weakened by the salts—and the hairpin loops. This result may have an important biological relevance since it has been proposed that RNA is the oldest genome-coding molecule, and the formation of these structures could have given it stability against degradation in primeval times. Even more, the nanoring structures could have the potential to be used as biosensors and functionalized nanodevices.

Synthesis of silver nanorings through a glycerol-base polyol method

Silver nanoring, a new nanomaterial with special morphology, exhibits attractive potential in optoelectronics applications. In this work, a glycerol-base modified polyol method is investigated. Using this method, silver nanorings with perfect geometry and ring diameter range from 6.54 to 30.67ss μm, wire diameter of 66.7-115.5 nm were synthesized by replacing EG with glycerol and adjusting the molecular weight and concentration of polyvinylpyrrolidone (PVP). The growth mechanism and factors that affect the morphology were studied in detail. The formation of silver nanorings showed high dependence on the viscosity of solution, wire diameter of AgNWs and the molecular weight of PVP.

Silver plasmonic colour change due to chemical/mechanical reactions

Plasmonic colour from metals has been recently attracting attention because it is less likely to deteriorate due to environmental change. However, metals such as silver easily react chemically with the atmosphere. Although plasmonic colour in various materials and structures has been assessed, the effects of chemical changes on plasmonic properties have not been deeply investigated. In this paper, we have evaluated the changes in optical properties and structure of silver plasmonic colour from the viewpoint of a phase diagram. As a result, we report remarkable colour changes and the formation of nanorings with a diameter of approximately 100 nm by vacuum ultraviolet light irradiation and heat annealing.

Fabrication of nanorings from ultrathin layer of silver on zinc oxide-coated glass substrate

Fabrication of ring-like nanostructures of noble metal, particularly silver (Ag) nanostructures are challenging but long expected and suitable for various applications. Here, in this work, a strategy has been reported to fabricate Ag nanorings from ultrathin layer of the same. The edges of as-fabricated Ag nanorings were found continuous in nature rather than linear aggregation of adjacent nanoclusters as confirmed by high-resolution scanning electron microscope (SEM) micrographs. Interestingly, none of the Ag nanorings was found broken or cracked. Such clues led ones to a plausible hypothesis in demonstrating the fabrication mechanism. In this context, an in-depth morphological investigation and quantitative analysis have been carried out to understand the evolution of nanorings. SEM micrographs captured at the intermediate stage of Ag nanorings formation revealed that ultrathin layer of Ag turned into spherical nanoparticles before ending at the formation of such nanorings. High-resolution SEM micrographs confirmed that Ag nanoparticles were mostly spherical along with dark sheds at the center. A detailed morphological investigation of such Ag nanoparticles confirmed average estimated outer diameter of 376.74 ± 37.24 nm and average wall thickness of 102.89 ± 18.10 nm. Further estimation indicated Ag nanorings of 213.58 nm edge height which was verified in high-resolution SEM investigations. An attempt was taken to slice an individual Ag nanoparticle with SEM-aided focus ion beam (FIB) facility. A small deviation in heights was observed by high-resolution SEM micrographs of such SEM-aided FIB treated nanoparticles. Silver nanorings of different sizes and shapes (background) along with fractal features at the rim (inset) and plausible formation mechanism thereof (right).

Solid-state dewetting of silver-thin films: self-assembled nano-geometries

The study presents the dynamics of solid-state dewetting of silver (Ag)-film annealed in N2 ambient, analyzed by atomic force microscopy and scanning electron microscopy. Varying the annealing parameters (i.e. temperature and time) and Ag-film thicknesses were taken into account, to determine their effect over the solid-state dewetting of Ag-films. Several morphological evolutions from nanohole to the presence of metastable nanorings were observed. It was determined that structures annealed at high temperature (≥900 °C) and/or time (≥2 h) results in formation of metastable nanorings and whose geometrical aspects and population grew with increasing film thickness. Possible applications of the structures for fabrication of silicon nanowire arrays and photo-emitters are briefly described.

Influence of spacer in the formation of nanorings by templateless electropolymerization

In this original work, we want to control the shape of the resulting porous structures by templateless electropolymerization, by adjusting the spacer (flexible alkyl chains or rigid aromatic groups) between thieno[3,4-b]thiophene and carbazole used as the monomer and the substituent, respectively. A huge change is especially observed from ribbon-like structures to nanorings as the alkyl spacer increases. The presence of a significant amount of water is necessary for the formation of these porous structures because it allows releasing a high amount of gas bubbles. The size and number of nanorings are dependent on both the alkyl spacer and electrochemical parameters such as the number of deposition scans. These surfaces could be used in the future in various potential applications such as in water harvesting, oil/water separation membranes, optical devices, sensors or photocatalysis.

Template/surfactant free and UV light irradiation assisted fabrication of Mn-Co oxides composite nanorings: Structure and synthesis mechanism

A facile, green, cost effective, and template or surfactant free strategy via a two-step route i.e. UV irradiation followed by dissolution-growth for the controlled synthesis of Mn-Co composite nanorings at room temperature was proposed. The nanorings structures and the process were systematically studied via TEM, HRTEM, EDX and XRD. Bir-MnO2 nanosheets first formed through the direct photolysis of KMnO4 under UV light irradiation. This was followed by a dissolution-growth process via the dissolution of Bir-MnO2 nanosheets by the generated H+ from the redox reaction between the added Co(NO3)2 and residual KMnO4, as well as the accompanied formation of CoOOH, and Mn-Co composite nanorings. It was found that a balance between the dissolution and growth rate was needed. Suitable pH, KMnO4 presence and the starting nanosheets like Bir-MnO2 were the key factors for the formation of nanorings. The obtained Mn-Co nanorings/TiO2 showed enhanced efficiency for the catalytic oxidation of HCHO. Based on the above understandings, it is believed that the developed dissolution-growth method can be adopted for the designing and preparation of other Mn-Co composite nanostructures which can be further applied for environmental pollution remediation.

Microstructure and plasmonic behavior of self-assembled silver nanoparticles and nanorings

Self-assembled nanoparticles were formed after annealing ultrathin Ag films, which were grown on glass and quartz by direct current magnetron sputtering, in a furnace in air at 420 °C, 500 °C, or 600 °C. Intense localized surface plasmon resonances were observed for these samples in the entire range of visible light spectrum depending on the annealing time and nanoparticle size. Prolonged annealing resulted in the formation of nanorings and the change of the position and shape of resonances. The nanoring formation is attributed to partial evaporation of silver due to trapping of electromagnetic field by the larger nanoparticles despite the relatively low annealing temperature. Finally, in order to gain a further physical insight, the experimental results are compared with respect to rigorous theoretical calculations.

Three-dimensional simulation of dual-scale deposition structures from evaporative self-assembly of nanofluid films

Self-assembly of nanomaterials from the drying of nanofluid films has aroused great interest due to its applications in micro/nano fabrication, ink-jet printing, and thin film coatings. Numerical models are developed to investigate the single-scale deposition structures from the drying of nanofluid films, including network structures, continuous labyrinthine, branched structures and micro-sized rings. In the case of the actual drying of nanofluid films, dual-scale cellular networks and nano-rings are also discovered. In order to study the formation mechanism of dual-scale deposition structures, a three-dimensional kinetic Monte Carlo model is developed based on two-dimensional lattice gas model, and the dynamic chemical potential which couples solvent evaporation rate is implemented. Different dynamic chemical potentials are defined for each layer of the thin-film in the model to mimic the real evaporation situation. Considering the Brownian motion and the interaction between particles, the formation of dual-scale cellular networks and nano-rings coexisting with small scale patternis achieved via coupling the chemical potential to the solvent evaporation rate. The simulation results accord well with the results from many experimentally studied de-wetting systems. The effects of the chemical potential sharpness and critical evaporation rate of fluids on the dual-scale deposition structures are discussed. It can be found that the evaporation mode of thin-film is dominated by nucleation and growth at the initial stage. If the spinodal point is passed, the residual solvent will evaporate suddenly, and the nanoparticles do not accumulate further but directly deposit into small-scale structures, thus forming a dual-scale deposition structures at the final stage of the evaporation. The simulation results also show that the chemical potential sharpness will affect the deposition structure after the mutation in a certain range. When the chemical potential sharpness equals zero, the sedimentary structure is the same as the single-scale sedimentary structure when the constant chemical potential is applied. When the chemical potential sharpness is small, the large-scale network structure interacts closely with the small-scale network structure. With the increase of chemical potential sharpness, the large-scale deposition structure remains unchanged, while the dense small-scale network structure becomes small-scale point structure. When the chemical potential sharpness exceeds a certain large value, the effect of chemical potential sharpness on the deposition structure will gradually decrease, and finally the dual-scale deposition structure will remain unchanged. The critical evaporation rate of fluids determines the area ratio of the two kind of structures in the dual-scale deposition. With the increase of the critical evaporation rate of fluids, the area ratio of small-scale structures decreases while that of the large-scale structure increases. When critical evaporation rate increases to a certain value, the final deposition structure will evolve into a single-scale deposition structure.

Observation of particle assisted nano-ring, bump, pit structures on semiconductor substrates by dry laser exposure

We report on the generation of nano-structures on semiconductor substrates through particle assisted dry laser exposure technique. Of particular interest is the formation of nano rings in case of Silicon substrate following exposure with sub nano-second laser pulse at 532 nm wavelength. Usage of such a laser pulse enabled us to realise a condition wherein the dominating thermo-capillary force allowed the formation of nano rings. With gradual increase in the laser fluence the nano rings gave way to formation of nano bumps and nano pits. In case of GaAs, on the other hand, nano rings could be observed for irradiation at 1064 nm at substantially higher value of fluence, in line with its poor absorption in the substrate. For exposure to 532 nm wavelength, onset of ablation even for low incident fluence precluded the formation of rings or bumps.

Kinetics of nanoring formation on surfaces of stressed thin films

We model the kinetics of nanoring (NR) formation in stressed thin films and explore systematically the resulting nanoring structures upon variation of the film thermal processing parameters. We find that the thermal stress induced in the films during their thermal annealing can trigger the transformation of quantum dots on the film surface to simple NRs or multiple concentric NRs. Our analysis provides a comprehensive explanation of experimentally observed nanoring formation on stressed film surfaces, as well as a design rule for fabricating NRs with precisely controlled features and sizes.

Template-free synthesis of Co3O4 nanorings and their catalytic application

Co3O4 nanorings were prepared through the formation of CoOOH nanorings by oxidation of β-Co(OH)2 nanoplates with H2O2, followed by high-temperature calcination.

Solvent Assisted Tuning of Morphology of a Peptide-Perylenediimide Conjugate: Helical Fibers to Nano-Rings and their Differential Semiconductivity

Understanding the regulatory factors of self-assembly processes is a necessity in order to modulate the nano-structures and their properties. Here, the self-assembly mechanism of a peptide-perylenediimide (P-1) conjugate in mixed solvent systems of THF/water is studied and the semiconducting properties are correlated with the morphology. In THF, right handed helical fibers are formed while in 10% THF-water, the morphology changes to nano-rings along with a switch in the helicity to left-handed orientation. Experimental results combined with DFT calculations reveal the critical role of thermodynamic and kinetic factors to control these differential self-assembly processes. In THF, P-1 forms right handed helical fibers in a kinetically controlled fashion. In case of 10% THF-water, the initial nucleation of the aggregate is controlled kinetically. Due to differential solubility of the molecule in these two solvents, elongation of the nuclei into fibers is restricted after a critical length leading to the formation of nano-rings which is governed by the thermodynamics. The helical fibers show superior semi-conducting property to the nano-rings as confirmed by conducting-AFM and conventional I-V characteristics.

Direct Observation of Interactions between Nanoparticles and Nanoparticle Self-Assembly in Solution.

Hierarchically organized nanoparticles (NPs) possess unique properties and are relevant to various technological applications. An important "bottom-up" strategy for building such hierarchical nanostructures is to guide the individual NPs into ordered nanoarchitectures using intermolecular interactions and external forces. However, our current understanding of the nanoscale interactions that govern such self-assembly processes usually relies on post-synthesis/assembly or indirect characterization. Theoretical models that can derive these interactions are presently constrained to systems with only a few particles or on short time scales. Hence, except for a number of special cases, a description that captures the detailed mechanisms of NP self-assembly still eludes us. By imaging the assembly of NPs in solution with subnanometer resolution and in real-time, in situ liquid cell transmission electron microscopy (LC-TEM) can identify previously unknown intermediate stages and improve our understanding of such processes. Here, we review recent studies where we explored NP self-assembly at different organization length scales using LC-TEM: (1) we followed the transformation of atoms into crystalline NPs in solution, (2) we highlighted the role of solvation forces on interaction dynamics between NPs, and (3) we described the assembly dynamics of NPs in solution. In the case of nanocrystal nucleation, we identified the existence of three distinct steps that lead to the formation of crystalline nuclei in solution. These steps are spinodal decomposition of the precursor solution into solute-rich and solute-poor liquid phases, nucleation of amorphous clusters within the solute-rich liquid phase, followed by crystallization of these amorphous clusters into crystalline NPs. The next question we ask is how NPs interact in solution once they form. It turns out that the hydration layer surrounding each NP acts as a repulsive barrier that prevents NPs from readily attaching to each other due to attractive vdW forces. Consequently, two interacting NPs form a metastable pair separated by their one water molecule thick hydration shell and they undergo attachment only when this water between them is drained. Next, we explore the self-assembly of many NP systems where the formation of linear chains from spherical NPs or nanorods (NRs) is mediated by linker molecules. At low linker concentration, both spherical NPs and NRs tend to form linear chains because of the need to reduce electrostatic repulsion between NP building blocks. When the concentration of linkers is increased, the attachment of NPs is no longer linear. For example, we find that two NRs undergo side-to-side assembly due to decreased electrostatic repulsion and the anisotropic distribution of linkers on NR surfaces at high linker concentration. Lastly, we look at the formation of NP nanorings directed by ethylenediaminetetraacetic acid (EDTA) nanodroplets in water. Our study shows that nanoring assemblies form via sequential attachment of NPs to binding sites located along the circumference of the EDTA nanodroplet, followed by rearrangement and reorientation of the attached NPs. Our approach based on real-time visualization of nanoscale processes not only reveals all the intermediate steps of NP assembly, but also provides quantitative description on the interactions between nanoscale objects in solution.

Impact of cadmium and phosphate ions on the hematite nanorings formation

It has been suggested that the addition of divalent metal cations during the hydrothermal synthesis of hematite (α-Fe2O3) in the presence of phosphate ions has a strong impact on the hematite morphology, crystal growth and dissolution (Gotić et al., J. Mol. Struct. 993 (2011) 167). In this work, the same system was modified with divalent cadmium ions and the impacts of cadmium and phosphate ions on the hematite nanorings formation have been studied. It has been found that formed hematite and akaganeite (β-FeOOH) precipitates did not contain any trace of cadmium impurities. On the contrary, the modification with divalent cadmium cations changes the PO43−/Fe3+ molar ratio in the system. Upon the addition of cadmium ions the PO43−/Fe3+ molar ratio changes from 0.036 in a pure system to 0.051 in the cadmium modified system. The relative increase of phosphate concentration at early stage of precipitation induced the change of spindle to spherical morphology and formation of the poorly crystallised akaganeite-like phase. The appearance of akaganeite-like phase directly correlated with the delay in the crystallisation of hematite. Besides, the relative increase of phosphate concentration has the prevailing effect for the change of spindle to pseudosphere and nanotube to nanoring particle morphologies.

Monte Carlo simulation of the formation of AIIIBV nanostructures with the use of droplet epitaxy

A Monte Carlo lattice model is proposed to describe the formation of semiconductor nanostructures by the vapor–liquid–solid growth mechanism. This model is used to simulate the growth of GaAs nanostructures by the droplet epitaxy technique in the temperature range from 500 to 600 K in As2 fluxes with intensity of 0.005–0.04 ML/s. The morphology of the formed structures is demonstrated to depend on the growth parameters. Etching of the GaAs substrate by a gallium droplet is studied. The ranges of temperature and As flux rates necessary for the formation of GaAs nanorings are determined. The conditions of the formation of single and double concentric rings are analyzed.

Sonication‐induced self‐assembly of polymeric porphyrin–fullerene: Formation of nanorings

ABSTRACTIn this article, we detail the sonication‐induced self‐assembly of polymeric porphyrin and fullerenes into distinct nanorings in solution form. The formation of these trenchant superstructures was the result of the delicate choice of different assembly protocols, solvents, and polymeric tails associated with porphyrin and fullerene. In this study, the sonication supposedly directed the lateral aggregation into uniform ring formation. The sonication time was found to be the key parameter in ring formation. Furthermore, the flexibility of polymeric arms and electronic interactions of porphyrin–fullerene gave rise to synergistically enhanced molecular interactions, and this resulted in discrete morphologies. Key optical data, including the absorption maxima of the complexes, and microscopic studies attested to the nature and morphology of the self‐assembled complexes. This introduction of polymeric arms and sonication protocols in the porphyrin self‐assembly was expected to allow the easy formation of diverse morphologies. Because of the facile fabrication process and uniform morphology, the resulting composite architectures might show promising applications in drug‐delivery and advance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43537.