Variety Of Nanostructures Research Articles

Rapid and Cyclable Morphology Transition of High-χ Block Copolymers via Solvent Vapor-Immersion Annealing for Nanoscale Lithography

The self-assembly of block copolymers (BCPs) has attracted considerable attention because it can effectively generate highly ordered nanostructures through a simple and cost-effective process. However, in BCP annealing systems, there remain several challenges and issues that must be resolved to achieve more rapid and tunable pattern formation of BCPs with a high Flory–Huggins parameter (χ) for next-generation lithography applications. Here, we introduce a useful annealing technique to induce a rapid morphological transition of sphere-forming poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) BCPs by employing multistep solvent vapor annealing (MSVA) and a combined annealing process of solvent vapor annealing (SVA) and immersion annealing (IA). We successfully obtained well-ordered sub-20 nm line, dot, core–shell dot, and core–shell line structures with a short annealing time (<25 min) based on the synergetic effects of the combined annealing method which provides both the fast self-assembly kinetics and a wide range of pattern geometries. Furthermore, we demonstrate how the repeated process of SVA and IA affects the morphological stability of self-assembled BCPs, showing highly ordered solid and core–shell BCP nanostructures even after ten cycles of the repeated annealing process. We expect that these results will provide a new guideline to manipulate diverse BCP nanostructures effectively for nanodevice fabrication by combining various annealing methods.

Pattern formation of metal-oxide hybrid nanostructures via the self-assembly of di-block copolymer blends.

The templated self-assembly of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) can effectively create ultrafine, well-ordered nanostructures in the range of 5-30 nm. However, the self-assembled BCP patterns remain limited to possible morphological geometries and materials. Here, we introduce a novel and useful self-assembly method of di-BCP blends capable of generating diverse hybrid nanostructures consisting of oxide and metal materials through the rapid microphase separation of A-B/B-C BCP blends. We successfully obtained various hybridized BCP morphologies which cannot be acquired from a single di-BCP, such as hexagonally arranged hybrid dot and dot-in-hole patterns by controlling the mixing ratios of the solvents with a binary solvent annealing process. Furthermore, we demonstrate how the binary solvent vapor annealing process can provide a wide range of pattern geometries to di-BCP blends, showing a well-defined spontaneous one-to-one accommodation in dot-in-hole nanostructures. Specifically, we show clearly how the self-assembled BCPs can be functionalized via selective reduction and/or an oxidation process, resulting in the excellent positioning of confined silica nanodots into each nanospace of a Pt mesh. These results suggest a new method to achieve the pattern formation of more diverse and complex hybrid nanostructures using various blended BCPs.

Chemical routes for synthesis of polypyrrole–based nanocomposites incorporating graphene platelets from natural Shungite

Polypyrrole (PPy)-based nanocomposites are synthesized by a micro-emulsion oxidative chemical polymerization of pyrrole monomer. Graphene platelets (GP), extracted from Shungite mineral powders through innovative procedures, are used as nanoinclusions to enhance the interesting properties of the pure polymer. SEM and HR-TEM analyses evidence that diverse PPy nanostructures are obtained in the presence of different dopant surfactants: globular grains with sodium dodecyl sulfate (SDS) anionic surfactant, and tubular features with hexadecyltrimethylammonium bromide (CTAB) cationic surfactant. Raman spectroscopy reveals that the polymer chains are in a semi-oxidized state. Functional characterizations evidence that the PPy-based nanocomposites doped with SDS are characterized by improved charge transport properties.

Imaging VIPER-labeled Cellular Proteins by Correlative Light and Electron Microscopy.

Advances in fluorescence microscopy (FM), electron microscopy (EM), and correlative light and EM (CLEM) offer unprecedented opportunities for studying diverse proteins and nanostructures involved in fundamental cell biology. It is now possible to visualize and quantify the spatial organization of cellular proteins and other macromolecules by FM, EM, and CLEM. However, tagging and tracking cellular proteins across size scales is restricted by the scarcity of methods for attaching appropriate reporter chemistries to target proteins. Namely, there are few genetic tags compatible with EM. To overcome these issues we developed Versatile Interacting Peptide (VIP) tags, genetically-encoded peptide tags that can be used to image proteins by fluorescence and EM. VIPER, a VIP tag, can be used to label cellular proteins with bright, photo-stable fluorophores for FM or electron-dense nanoparticles for EM. In this Bio-Protocol, we provide an instructional guide for implementing VIPER for imaging a cell-surface receptor by CLEM. This protocol is complemented by two other Bio-Protocols outlining the use of VIPER ( Doh et al., 2019a and 2019b).

Hydrogen-bonding regulated assembly of molecular and macromolecular amphiphiles

Hydrogen bonding driven assembly of amphiphiles (small molecules and polymers) produce diverse nanostructures in aqueous medium.

Thin-film structural coloration from simple fused scales in moths.

The metallic coloration of insects often originates from diverse nanostructures ranging from simple thin films to complex three-dimensional photonic crystals. In Lepidoptera, structural coloration is widely present and seems to be abundant in extant species. However, even some basal moths exhibit metallic coloration. Here, we have investigated the origin of the vivid metallic colours of the wing scales of the basal moth Micropterix aureatella by spectrophotometry and scanning electron microscopy. The metallic gold-, bronze- and purple-coloured scales share a similar anatomy formed of a fused lower and upper lamina resulting in a single thin film. The optical response of this thin-film scale can be attributed to thin-film interference of the incident light, resulting in the colour variations that correlate with film thickness. Subtle variations in the wing scale thickness result in large visible colour changes that give Micropterix moths their colourful wing patterns. This simple coloration mechanism could provide a hint to understand the evolution of structural coloration in Lepidoptera.

2D Nanopatterning: 2D Metal Chalcogenide Nanopatterns by Block Copolymer Lithography (Adv. Funct. Mater. 50/2018)

In article number 1804508, Sang Ouk Kim and co-workers present a reliable and effective nanopatterning strategy for 2D transition metal dichalcogenides via block copolymer (BCP) lithography. By exploiting various BCP templates, diverse nanostructures, including nanomeshes, nanodots, and nanowire arrays, are demonstrated with wafer-scale scalability. Edge-exposed MoS2 nanomeshes exhibit superior sensitivity and reversibility for NO2 gas sensing.

A few rediscovered and challenging topics in polymer crystals and crystallization

This feature article discusses a few rediscovered and challenging topics in polymer crystals and crystallization. Among many research topics in this field, primary nucleation of polymers, twisted and curved polymer crystals, flow-induced crystallization, and supramolecular crystals are selected and illustrated. This selection includes traditional topics with yet to be solved critical questions, and relatively new topics that still call for more developments. Specific attention is paid to the supramolecular crystallization of a new class of macromolecules termed “giant molecules,” which show unusual self-assembly behaviors toward diverse hierarchical nanostructures. We believe that although being an old topic of long history, study on polymer crystallization will continue to flourish and will contribute to a more comprehensive understanding of self-assembly in polymers.

Fano resonances in near-field absorption in all-dielectric multilayer structures

Extending our previous studies on metal-dielectric multilayer structures, we demonstrate the feasibility of generating and controlling high-Q Fano resonances in all-dielectric multilayer structures. The structures studied consist of two waveguide layers (Ge-doped SiO2 and Al2O3 layers) separated by spacer layers (SiO2 layers) and arranged in the Kretschmann attenuated total reflection geometry. From analyses based on the electromagnetic theory, we reveal that the Fano resonance arises from the interaction between a broad waveguide mode supported by the Ge-doped SiO2 layer and a sharp waveguide mode supported by the Al2O3 layer. This mechanism allows us to generate similar Fano resonances with both the p- and s-polarized incident light. Although the Fano resonances based on radiative modes in a variety of nanostructures and metamaterials have been reported to appear only in the far-field responses, we show that the present Fano resonances appear not only in the far-field reflection spectra but also in the near-field absorption spectra.

PH-controlled surface engineering of nanostructured ZnO films generated via a sustainable low-temperature H2O oxidation process

Developing a consistent and sustainable protocol for fabricating predetermined ZnO nanostructures is of significant interest in materials science and industry, owing to the emergence of ZnO-based devices and applications. Herein, the design of novel nanostructured ZnO films via a green, sustainable and low-temperature H2O oxidation technique is presented. Surface engineering was achieved by controlling the pH value of H2O during oxidation of Zn thin films. Diverse ZnO nanostructures of high structural and optical qualities including nanoparticles, microparticles composed of smaller rods, columnar nanorods and nanotubes having different growth orientations emerged. The morphology, chemical composition, structure, surface chemistry and optical properties of the nanomaterials were comprehensively characterized as a function of pH value. The experimental results and proposed growth mechanism for each nanostructure were presented and thoroughly discussed to have a deeper understanding on the physical insights governing the pH-controlled development of the nanostructures. This in-depth examination could pave the way to pioneering properties and functionalities that could sustainably fulfill the requirements of next generation optoelectronic devices.

Optical properties and the band-gap variation in diverse Zn1-xSnxO nanostructures

In this work, Zn1-xSnxO nanostructures with diverse morphological characters were prepared by hydrothermal technique. The morphology, structure, crystallization and the chemical states of the samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The characterization of UV–Vis spectra indicates that the optical transmittance of Zn1-xSnxO nanostructure is above 90% in the visible range. The optical absorption edge of the samples was determined according to the Tauc relationship, and a remarkable bule shift of the band-gap appeared for the Zn1-xSnxO nanomaterials. The fluorescence spectra were measured by using photoluminescence (PL) spectrometer. The pure ZnO nanostructure exhibits a strong yellow emission and a weak near-ultraviolet emission. The effect of CTAB is mainly on the photoluminescence intensity rather than the peak position. However, the introduction of stannum has an interesting effect on the PL of ZnO. The Zn1-xSnxO nanostructure exhibits a remarkable near-band-edge (NBE) emission with two peaks. The dependence of NBE emission spectra on excitation power was analyzed. Two radiative recombination channels of the NBE emission have been discussed in detail.

Digestive-Ripening-Facilitated Nanoengineering of Diverse Bimetallic Nanostructures.

From an ingenious methodology for obtaining monodispersity, digestive ripening has advanced to become an outstanding solution-based synthesis route to realizing various bimetallic heterostructures. This feature article attempts to provide an overview of the various facets of the codigestive ripening process and the array of heterostructures that could be achieved by this technique. We briefly discuss the mechanism of digestive ripening in the case of monometallic elements and use that understanding to elucidate the mechanism of the less well established codigestive ripening strategy for designing bimetallic nanostructures. The systems studied by our group in the past decade for the fabrication of diverse heterostructures are highlighted in this article. The exploitation of digestive ripening to realize monodisperse bimetallic nanostructures by several other groups is also featured. In addition to digestive ripening agents, the significance of tuning various reaction parameters and its consequences on the final structure and morphology have also been discussed. Additionally, efforts based on theoretical studies to gain insight into the factors which dominate the mechanism of the digestive ripening process have also been covered. This article is a contribution to the understanding of the codigestive ripening methodology and a demonstration of its tremendous potential in achieving the desired bimetallic heteronanostructures.

Utilization of Resist Stencil Lithography for Multidimensional Fabrication on a Curved Surface

The limited ability to fabricate nanostructures on nonplanar rugged surfaces has severely hampered the applicability of many emerging technologies. Here we report a resist stencil lithography based approach for in situ fabrication of multidimensional nanostructures on both planar and uneven substrates. By using the resist film as a flexible stencil to form a suspending membrane with predesigned patterns, a variety of nanostructures have been fabricated on curved or uneven substrates of diverse morphologies on demand. The ability to realize 4 in. wafer scale fabrication of nanostructures as well as line width resolution of sub-20 nm is also demonstrated. Its extraordinary capacity is highlighted by the fabrication of three-dimensional wavy nanostructures with diversified cell morphologies on substrates of different curvatures. A robust general scheme is also developed to construct various complex 3D nanostructures. The use of conventional resists and processing ensures the versatility of the method. Such an in situ lithography technique has offered exciting possibilities to construct nanostructures with high dimensionalities that can otherwise not be achieved with existing nanofabrication methods.

Morphological Control of Coil-Rod-Coil Molecules Containing m-Terphenyl Group: Construction of Helical Fibers and Helical Nanorings in Aqueous Solution.

Rod-coil molecules, composed of rigid segments and flexible coil chains, have a strong intrinsic ability to self-assemble into diverse supramolecular nanostructures. Herein, we report the synthesis and the morphological control of a new series of amphiphilic coil-rod-coil molecular isomers 1-2 containing flexible oligoether chains. These molecules are comprised of m-terphenyl and biphenyl groups, along with triple bonds, and possess lateral methyl or butyl groups at the coil or rod segments. The results of this study suggest that the morphology of supramolecular aggregates is significantly influenced by the lateral alkyl groups and by the sequence of the rigid fragments in the bulk and in aqueous solution. The molecules with different coils self-assemble into lamellar or oblique columnar structures in the bulk state. In aqueous solution, molecule 1a, with a lack of lateral groups, self-assembled into large strips of sheets, whereas exquisite nanostructures of helical fibers were obtained from molecule 1b, which incorporated lateral methyl groups between the rod and coil segments. Interestingly, molecule 1c with lateral butyl and methyl groups exhibited a strong self-organizing capacity to form helical nanorings. Nanoribbons, helical fibers, and small nanorings were simultaneously formed from the 2a-2c, which are structural isomers of 1a, 1b, and 1c. Accurate control of these supramolecular nanostructures can be achieved by tuning the synergistic interactions of the noncovalent driving force with hydrophilic-hydrophobic interactions in aqueous solution.

Nanoformulation of metal complexes: Intelligent stimuli-responsive platforms for precision therapeutics

Precision medicine is a potential effective therapeutic for various human diseases. Currently, metal complex-based drugs are being successfully used in clinical applications owing to diverse properties such as multiple redox states, photo-induced ligand exchange, and preferential ligand and coordination numbers, which facilitate drug design and development. However, drawbacks such as toxicity, lack of specificity, and severe side effects have hampered their therapeutic outcome. Therefore, innovative strategies for improving the specificity and pharmacokinetics of conventional metal complex-based therapeutic agents are required. Recently, nanotechnology, which provides a unique toolbox for developing effective and safer medicine, has attracted considerable attention, mainly because of their ability to reduce side effects and enhance drug loading efficiency and pharmacokinetics. Considering the promising chemical and physical properties of diverse nanostructures, nanoformulation of metal complexes can be used to effectively address the problems associated with current metallodrug complexes, especially those based on stimuli-responsive therapeutic strategies, with excellent spatial, temporal, and dosage control. In this review, we have mainly focused on the specificity and environment-responsiveness of metallodrug nanoformulations as therapeutics, and summarized the recent strategies being used for developing metal complex-functionalized intelligent nanoplatforms, which respond to various types of stimuli, including endogenous signals (pH, redox conditions, and enzyme activities) or external triggers (light irradiation and magnetic field manipulations). In addition, we have also discussed the potential challenges associated with use of metallodrugs and their nanoformulations as effective precision therapy with improved specificity and minimal side effects.

Reversible Self-Assembly of Supramolecular Vesicles and Nanofibers Driven by Chalcogen-Bonding Interactions.

Chalcogen-bonding interactions have been viewed as new non-covalent forces in supramolecular chemistry. However, harnessing chalcogen bonds to drive molecular self-assembly processes is still unexplored. Here we report for the first time a novel class of supra-amphiphiles formed by Te···O or Se···O chalcogen-bonding interactions, and their self-assembly into supramolecular vesicles and nanofibers. A quasi-calix[4]chalcogenadiazole (C4Ch) as macrocyclic donor and a tailed pyridine N-oxide surfactant as molecular acceptor are designed to construct the donor-acceptor complex via chalcogen-chalcogen connection between the chalcogenadiazole moieties and oxide anion. The affinity of such chalcogen-bonding can dictate the geometry of supra-amphiphiles, driving diverse self-assembled nanostructures. Furthermore, the reversible disassembly of these structures can be promoted by introducing competing halide ions or by decreasing systemic pH.

He-Ion Microscopy as a High-Resolution Probe for Complex Quantum Heterostructures in Core-Shell Nanowires.

Core-shell semiconductor nanowires (NW) with internal quantum heterostructures are amongst the most complex nanostructured materials to be explored for assessing the ultimate capabilities of diverse ultrahigh-resolution imaging techniques. To probe the structure and composition of these materials in their native environment with minimal damage and sample preparation calls for high-resolution electron or ion microscopy methods, which have not yet been tested on such classes of ultrasmall quantum nanostructures. Here, we demonstrate that scanning helium ion microscopy (SHeIM) provides a powerful and straightforward method to map quantum heterostructures embedded in complex III-V semiconductor NWs with unique material contrast at ∼1 nm resolution. By probing the cross sections of GaAs-Al(Ga)As core-shell NWs with coaxial GaAs quantum wells as well as short-period GaAs/AlAs superlattice (SL) structures in the shell, the Al-rich and Ga-rich layers are accurately discriminated by their image contrast in excellent agreement with correlated, yet destructive, scanning transmission electron microscopy and atom probe tomography analysis. Most interestingly, quantitative He-ion dose-dependent SHeIM analysis of the ternary AlGaAs shell layers and of compositionally nonuniform GaAs/AlAs SLs reveals distinct alloy composition fluctuations in the form of Al-rich clusters with size distributions between ∼1-10 nm. In the GaAs/AlAs SLs the alloy clustering vanishes with increasing SL-period (>5 nm-GaAs/4 nm-AlAs), providing insights into critical size dimensions for atomic intermixing effects in short-period SLs within a NW geometry. The straightforward SHeIM technique therefore provides unique benefits in imaging the tiniest nanoscale features in topography, structure and composition of a multitude of diverse complex semiconductor nanostructures.

Thermodynamic and Kinetic Tuning of Block Copolymer Based on Random Copolymerization for High‐Quality Sub‐6 nm Pattern Formation

AbstractThe precisely controllable self‐assembly phenomenon of block copolymers (BCPs) has garnered much attention because it yields well‐defined periodic nanostructures with a periodicity of 5–50 nm. However, from both thermodynamic and kinetic viewpoints, it still remains a challenge to develop a BCP material that can provide sub‐10 nm resolution, high pattern quality, fast pattern formation, and sufficient etch selectivity. To address these challenges, this study reports a BCP system containing a random‐copolymerized block (poly(2‐vinylpyridine‐co‐4‐vinylpyridne)‐b‐poly(dimethylsiloxane) (P(2VP‐co‐4VP)‐b‐PDMS)) that can provide sub‐6 nm resolution, 3σ line edge roughness of 0.89 nm, sub‐1‐min assembly time, and a high etch selectivity over 10. Calculation of the Flory–Huggins interaction parameter (χ) based on Leibler's mean‐field theory and small‐angle X‐ray scattering measurement data confirms the gradual tunability of χ with the controlled addition of 4VP fraction in the P(2VP‐co‐4VP) block. While guaranteeing kinetically fast self‐assembly within one minute using microwave annealing, the best pattern quality resulting from the thermodynamic suppression of line edge fluctuation is achieved with a 4VP weight fraction of 33% in the random‐copolymerized block. This approach enables systematical control of sub‐6 nm scale BCP self‐assembly and will provide a practical patterning solution for diverse nanostructures and devices.

Nonviral Delivery Systems for Cancer Gene Therapy: Strategies and Challenges.

Gene therapy has been receiving widespread attention due to its unique advantage in regulating the expression of specific target genes. In the field of cancer gene therapy, modulation of gene expression has been shown to decrease oncogenic factors in cancer cells or increase immune responses against cancer. Due to the macromolecular size and highly negative physicochemical features of plasmid DNA, efficient delivery systems are an essential ingredient for successful gene therapy. To date, a variety of nanostructures and materials have been studied as nonviral gene delivery systems. In this review, we will cover nonviral delivery strategies for cancer gene therapy, with a focus on target cancer genes and delivery materials. Moreover, we will address current challenges and perspectives for nonviral delivery-based cancer gene therapeutics.

Self‐Assembly of Rod‐Coil Block Copolymers on Carbon Nanotubes: A Route toward Diverse Surface Nanostructures

In this work, it is reported that poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) rod-coil block copolymers (BCPs) can disperse carbon nanotubes (CNTs) in solution and form various surface nanostructures on the CNTs via solution self-assembly. In an organic solvent that dissolves the BCPs, the PBLG rod blocks adsorb on CNT surfaces, and the BCPs form conformal coatings. Then, by the introduction of water, a selective solvent for PEG blocks, the BCPs in the coatings further self-assemble into diverse surface nanostructures, such as helices (left-handed or right-handed), gyros, spheres, and rings. The morphology of the surface nanostructure can be tailored by initial organic solvent composition, preparation temperature, feeding ratio of BCPs to CNTs, degree of polymerization of PBLG blocks, and diameter of the CNTs.