Ring-like Nanostructures Research Articles

Local Droplet Etching with Indium Droplets on InP(100) by Metal-Organic Vapor Phase Epitaxy.

The local droplet etching (LDE) by using indium droplets on bare InP(100) surfaces is demonstrated in a metal-organic vapor phase epitaxy (MOVPE) environment for the first time. The role of an arsenic flow applied to self-assembled metallic indium droplets is systematically studied. Increasing the arsenic supply leads to the formation of ring-like nanostructures and nanoholes. The results are analyzed with reference to LDE in a molecular beam epitaxy environment, where such a technique is well established, particularly for arsenide-based III-V semiconductors, and where only one group-V material is involved. Here, As-P exchange reactions at droplet sites are identified as the drivers for the formation of nanoholes. Such nanoholes can serve as nucleation sites for subsequent fabrication of highly symmetric QDs by nanohole-infilling or as a means for in situ surface nanopatterning. LDE on InP by MOVPE can thus be considered as a promising approach for the cost-effective fabrication of novel quantum emitters at the telecom C-band.

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.

Robust hollow Bowl-like α-Fe2O3 nanostructures with enhanced electrochemical lithium storage performance

The design and synthesis of hollow-nanostructured transition metal oxide-based anodes is of great importance for long-term operation of lithium ion batteries (LIBs). Herein, a special hollow bowl-like α-Fe2O3 nanostructure is controllably synthesized through a facile hydrothermal technique and exhibits great electrochemical lithium storage performance when used as LIBs anode. Under a facile hydrothermal condition, α-Fe2O3 nanostructures evolve from solid pie-like structure to hollow bowl-like structure and finally α-Fe2O3 nanorings through the regulation of HPO4- derived from ionized Na3PO4·12H2O and Ostwald ripening process. The designed hollow bowl-like α-Fe2O3 nanostructure not only has the merits of hollow structure, which can accelerate the diffusion of lithium ions and electrons, but also shows great mechanical strength to disperse stress when compared to solid pie-like and ring-like α-Fe2O3 nanostructures, which would avoid collapse during charge/discharge process. As a result, the as-synthesized hollow bowl-like α-Fe2O3 nanostructure displays an initial reversible capacity of 1616 mAh g−1 at a current density of 1 A g−1, an excellent cycling performance with a reversible capacity of 1018 mAh g−1 after 500 cycles and an outstanding rate capability (68.1% capacity retention at current densities from 100 to 2000 mA g−1). This work provides not only a novel hollow bowl-like α-Fe2O3 nanostructure with high specific surface area and stable structure as potential electrode materials for energy storage, but also a facile self-templated strategy free of any surfactants and templates for hollow nanostructures.

Self-Assembly of Flagellin into Immunostimulatory Ring-like Nanostructures as an Antigen Delivery System.

Proteinaceous nanoparticles represent attractive antigen carriers for vaccination as their size and repetitive antigen displays that mimic most viral particles enable efficient immune processing. However, these nanocarriers are often unable to stimulate efficiently the innate immune system, requiring coadministration with adjuvants to promote long-lasting protective immunity. The protein flagellin, which constitutes the primary constituent of the bacterial flagellum, has been widely evaluated as an antigen carrier due to its intrinsic adjuvant properties involving activation of the innate immune receptor Toll-like receptor 5 (TLR5). Although flagellin is known for its ability to self-assemble into micron-scale length nanotubes, few studies have evaluated the potential usage of flagellin-based nanostructures as immunostimulatory antigen carriers. In this study, we reported for the first time a strategy to guide the self-assembly of a flagellin protein from Bacillus subtilis, Hag, into lower aspect ratio nanoparticles by hindering non-covalent interactions responsible for its elongation into nanotubes. We observed that addition of an antigenic sequence derived from the influenza A virus (3M2e) at the C-terminus of this flagellin, as opposed to positioning the epitope into mid-sequence, precluded filament elongation and resulted in low aspect ratio ring-like nanostructures upon salting-out-induced self-assembly. These nanostructures displayed the antigen at their surface and shared morphological and structural characteristics with flagellin nanotubes, with a diameter of approximately 12 nm, and an α-helix-rich secondary structure. Flagellin ring-like nanostructures were efficiently internalized by antigen-presenting cells, and avidly activated the TLR5 in vitro as well as the innate and adaptive immune responses. Intranasal immunization of mice with these nanostructures resulted in the potentiation of the antigen-specific antibody response and protection against a lethal infection with the influenza A virus, illustrating the potential of these intrinsically immunostimulatory nanostructures as antigen carriers.

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).

One-step hydrothermal synthesis of high surface area m-ZrO2 nanorings with lower band gap, blue emission and high photocatalytic activity

Herein, monoclinic ZrO2 (m-ZrO2) nanostructures were prepared by a facile one-step hydrothermal method. As-prepared products showed ring-like nanostructures with an average size of ~ 23.1 nm and high surface area. The ring-like m-ZrO2 nanostructures exhibited broad absorption spectra in the visible region (400–800 nm) and a low band gap of 3.7 eV. Moreover, blue emission was also shown by m-ZrO2 nanostructures under the excitation of wavelength 300 nm. As-prepared m-ZrO2 nanostructures show high photocatalytic performance under UV irradiation. The lower band, high surface area and presence of oxygen vacancies may be attributed to the excellent performance of ring-like m-ZrO2 nanostructures as a photocatalyst.

Ring-Like Assembly of Silica Nanospheres in the Presence of Amphiphilic Block Copolymer: Effects of Particle Size.

Block copolymer-mediated self-assembly of colloidal nanoparticles has attracted great attention for the fabrication of a wide variety of nanoparticle arrays. We have previously shown that silica nanospheres (SNSs) 15 nm in diameter assemble into ring-like nanostructures in the presence of amphiphilic block copolymers poly[(2-ethoxyethyl vinyl ether)- block-(2-methoxyethyl vinyl ether)] (EOVE-MOVE) in an aqueous phase. Here, the effects of particle size of SNSs on this polymer-mediated self-assembly are studied systematically using scanning electron microscopy to observe SNSs of seven different sizes between 13 to 42 nm. SNSs of 13, 16, 19, and 21 nm in diameter assemble into nanorings in the presence of EOVE-MOVE. In contrast, larger SNSs of 26, 34, and 42 nm aggregate heavily, form chain-like networks, and remain dispersed, respectively, instead of forming ring-like nanostructures. The assembly trend for 26-42 nm-SNSs agrees with that expected from the increased colloidal stability for larger particles. Time-course observation for the assembled morphology of 16 nm-SNSs reveals that the nanorings, once formed, assemble further into network-like structures, as if the nanorings behave as building units for higher-order assembly. This indicates that the ring-like assembly is a fast process that can proceed onto random colloidal aggregation. Detailed analysis of nanoring structures revealed that the average number of SNSs comprising one ring decreased from 5.0 to 3.1 with increasing the SNS size from 13 to 21 nm. A change in the number of ring members was also observed when the length of EOVE-MOVE varied while the size of SNSs was fixed. Dynamic light scattering measurements and atomic force microscopy confirmed the SNSs/polymer composite structures. We hypothesize that a stable composite morphology may exist that is influenced by both the size of SNSs and the polymer molecular structures.

Template-free synthesis of mesoporous nanoring-like Zn-Co mixed oxides with high lithium storage performance

Mesoporous nanoring-like Zn-Co mixed oxides are synthesized via a simple template-free solvothermal method with a subsequent annealing process. The ring-like nanostructures with hollow interiors are formed under the complexing effects of potassium sodium tartrate. Numerous mesopores are generated after the precursor is annealed at 500 °C. When applied as anode materials, the mesoporous nanoring-like Zn-Co mixed oxides can deliver a high discharge capacity of 1102 mAh g−1 after 200 cycles at 500 mA g−1. Even when the current density is increased to 2 A g−1, the mixed oxides can still retain a reversible capacity of 761 mAh g−1. Such high cycling stability and rate capability are mainly derived from the unique mesoporous ring-like nanostructures and the synergistic effects between Zn and Co based oxides.

Effects of subphase pH, temperature and ionic strength on the aggregation behavior of PnBA-b-PAA at the air/water interface

Aggregation behavior of an amphiphilic diblock polyelectrolyte poly(n-butylacrylate)-b-poly(acrylic acid) (PnBA-b-PAA) at the air/water interface and morphologies of its LB films were characterized by the Langmuir monolayer technique and atomic force microscopy (AFM), respectively. Effects of subphase pH, temperature and ionic strength on the isotherms and hysteresis curves of the PnBA-b-PAA monolayers and the morphologies of its LB films were systematically studied. With the increase of subphase pH, the isotherms shift negatively and the quasi-plateaus disappear under neutral and alkaline conditions. Hysteresis phenomena of the PnBA-b-PAA monolayers on acidic and neutral subphases are quite obvious and similar, while the compression and expansion isotherms under alkaline condition are almost overlapped. The LB films of PnBA-b-PAA transferred from acidic subphase exhibit isolated circular micelles with large size, while those from alkaline subphase exhibit condensed ones with small size. With the rise in subphase temperature, PnBA blocks on the water surface are more likely to aggregate into large cores due to the higher molecular mobility. Furthermore, the totally ringlike nanostructures prepared from alkaline subphase with medium ionic strength are observed for the first time in LB films of block copolymers.

Synthesis and characterization of a hydrophilic conjugated 4+4 Re(I)-porphyrin metallacycle

The preparation and the full characterization, including the X-ray structure determination, of a polar trans-dipyridylporphyrin functionalized with two short polyoxyethylene chains is reported. Reaction of the porphyrin with a Re(I) complex yielded a 4+4 metallacycle showing an improved solubility and a lower tendency to aggregate with respect to analogous porphyrin cyclic derivatives. These properties allowed a full NMR characterization of the metallacycle including VT 1H DOSY-NMR experiments and, for the first time, the recording of a 13C-NMR spectrum giving further insight into the structural definition of these type of metallacycles. Spray deposition of the metallacycle on a heated mica substrate shows the formation of regular ring-like nano-structures which are not formed by the parent porphyrin.

Facile Hydrothermal Synthesis of Fe3O4/C Core–Shell Nanorings for Efficient Low-Frequency Microwave Absorption

Using elliptical iron glycolate nanosheets as precursors, elliptical Fe3O4/C core-shell nanorings (NRs) [25 ± 10 nm in wall thickness, 150 ± 40 nm in length, and 1.6 ± 0.3 in long/short axis ratio] are synthesized via a one-pot hydrothermal route. The surface-poly(vinylpyrrolidone) (PVP)-protected-glucose reduction/carbonization/Ostwald ripening mechanism is responsible for Fe3O4/C NR formation. Increasing the glucose/precursor molar ratio can enhance carbon contents, causing a linear decrease in saturation magnetization (Ms) and coercivity (Hc). The Fe3O4/C NRs reveal enhanced low-frequency microwave absorption because of improvements to their permittivity and impedance matching. A maximum RL value of -55.68 dB at 3.44 GHz is achieved by Fe3O4/C NRs with 11.95 wt % C content at a volume fraction of 17 vol %. Reflection loss (RL) values (≤-20 dB) are observed at 2.11-10.99 and 16.5-17.26 GHz. Our research provides insights into the microwave absorption mechanism of elliptical Fe3O4/C core-shell NRs. Findings indicate that ring-like and core-shell nanostructures are promising structures for devising new and effective microwave absorbers.

Excellent microwave-absorbing properties of elliptical Fe3O4 nanorings made by a rapid microwave-assisted hydrothermal approach

High-quality elliptical polycrystalline Fe3O4 nanorings (NRs) with continuously tunable size have been synthesized in large amounts via a rapid microwave-assisted hydrothermal approach. The surface-protected glucose reducing/etching/Ostwald ripening mechanism is responsible for the formation of NRs. Ring size can be modulated by selecting iron glycolate nanosheets with various sizes as precursors. The size-dependent magnetic behavior of the NRs was observed. Our research gives insights into the understanding of the microwave absorption mechanism of elliptical Fe3O4 NRs. Owing to their large specific surface area, shape anisotropy, and closed ring-like configuration, elliptical polycrystalline Fe3O4 NRs exhibited significantly enhanced microwave absorption performance compared with Fe3O4 circular NRs, nanosheets, microspheres, nanospindles, and nanotubes. An optimal reflection loss value of −41.59 dB is achieved at 5.84 GHz and RL values (≤−20 dB) are observed at 3.2–10.4 GHz. Some new mechanisms including multiple scattering, oscillation resonance absorption, microantenna radiation, and interference are also crucial to the enhanced absorption properties of NRs. These findings indicate that ring-like nanostructures are a promising structure for devising new and effective microwave absorbers.

Tunable dielectric properties and excellent microwave absorbing properties of elliptical Fe3O4 nanorings

Elliptical Fe3O4 nanorings (NRs) with continuously tunable axes that range from 40 nm to 145 nm in length were prepared through a precursor-directed synthetic route to determine the electromagnetic responses generated at 2–18 GHz. The tunability of the dielectric properties of Fe3O4 NRs depends on the long axis rather than on the specific surface area, internal stress, and grain size. Elliptical Fe3O4 NRs exhibit the excellent microwave absorbing properties due to the unique ring-like configuration, which significantly enhances permittivity, multiple scattering, oscillation resonance absorption, microantenna radiation, and interference. These findings indicate that ring-like nanostructures are promising for devising effective microwave absorbers.

A general strategy to incorporate a wide range of metallic salts into ring-like organized nanostructures via polymer self-assembly

We present a general strategy for incorporating metallic precursors into ring-like nanostructures. The method is promising for the fabrication of multifunctional materials.

Aharonov-Bohm effect for excitons in a semiconductor quantum ring dressed by circularly polarized light

We show theoretically that the strong coupling of circularly polarized photons to an exciton in ring-like semiconductor nanostructures results in physical nonequivalence of clockwise and counterclockwise exciton rotations in the ring. As a consequence, the stationary energy splitting of exciton states corresponding to these mutually opposite rotations appears. This excitonic Aharonov-Bohm effect depends on the intensity and frequency of the circularly polarized field and can be detected in state-of-the-art optical experiments.

Aharonov–Bohm effect induced by circularly polarized light

We demonstrated theoretically that the strong electron interaction with circularly polarized photons in ring-like nanostructures changes the phase of electron wave. This optically-induced effect is caused by the breaking of time-reversal symmetry and is similar to the Aharonov–Bohm effect. As a consequence of this phenomenon, the conductance of mesoscopic rings irradiated by a circularly polarized electromagnetic wave behaves as an oscillating function of the intensity and frequency of the wave.

Tetraphenylethene-based star shaped porphyrins: synthesis, self-assembly, and optical and photophysical study.

Supramolecular self-assembly and self-organization are simple and convenient ways to design and create controlled assemblies with organic molecules, and they have provoked great interest due to their potential applications in various fields, such as electronics, photonics, and light-energy conversion. Herein, we describe the synthesis of two π-conjugated porphyrin molecules bearing tetraphenylethene moieties with high fluorescence quantum yield. Photophysical and electrochemical studies were conducted to understand the physical and redox properties of these new materials, respectively. Furthermore, these derivatives were used to investigate self-assembly via the solvophobic effect. The self-assembled aggregation was performed in nonpolar and polar organic solvents and forms nanospheres and ring-like nanostructures, respectively. The solution based aggregation was studied by means of UV-vis absorption, emission, XRD, and DLS analyses. Self-assembled ring-shape structures were visualized by SEM and TEM imaging. This ring-shape morphology of nanosized macromolecules might be a good candidate for the creation of artificial light-harvesting nanodevices.

Synchronization of two assembly processes to build responsive DNA nanostructures.

Herein, we report a strategy for the synchronization of two self-assembly processes to assemble stimulus-responsive DNA nanostructures under isothermal conditions. We hypothesized that two independent assembly processes, when brought into proximity in space, could be synchronized and would exhibit positive synergy. To demonstrate this strategy, we assembled a ladderlike DNA nanostructure and a ringlike DNA nanostructure through two hybridization chain reactions (HCRs) and an HCR in combination with T-junction cohesion, respectively. Such proximity-induced synchronization adds a new element to the tool box of DNA nanotechnology. We believe that it will be a useful approach for the assembly of complex and responsive nanostructures.

Essential properties of a [formula omitted] molecular complex confined in ring-like nanostructures under external probes: Magnetic field and hydrostatic pressure

A rigorous adiabatic approximation is used to investigate the energy states of the singly ionized double-donors D2+ complex formed by the coupling of a conduction band electron and two donor centers in a quantum ring with rectangular cross-section. The effects of changing the relative position between the Coulombic centers and the quantum ring geometry parameters, as well as the influence of external probes such as applied magnetic fields and hydrostatic pressure, are particularly studied, highlighting the important contribution of the repulsive inter-center interaction. The suppression of the Aharonov–Bohm ground state oscillations associated with the localization of the electron by the fixed donors is discussed. Comparison between the essential properties of an actual hydrogen ion H2+ and those of the D2+ complex trapped within a quantum ring shows that the strong electron confinement substantially increases the D2+ stability effects.

Synthesis of near-infrared fluorescent, elongated ring-like Ag2Se colloidal nanoassemblies

A low-temperature, air-exposed, hot-injection process has been developed for the synthesis of water-dispersible Ag2Se quantum dots. The 3-mercaptopropionic acid capped quantum dots were shown to be elongated ring-like self-assembled nanostructures with prominent near-infrared fluorescent absorptions and emissions.