We report the synthesis of arrayed nanorings with tunable physical dimensions from thin films of polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) micelles. For accurate control of the inner and outer diameters of the nanorings, we added imidazolium-based ionic liquids (ILs) into the micellar solution, which were eventually incorporated into the micellar cores. We observed the structural changes of the micellar cores coated on a substrate due to the presence of ILs. The spin-coated micellar cores were treated with an acidic precursor solution and generated toroid nanostructures, of which size depended on the amount of IL loaded into the micelles. We then treated the transformed micellar films with oxygen plasma to produce arrays of various metal and oxide nanorings on a substrate. The spacings and diameters of nanorings were governed by the molecular weight of the PS-P4VP and the amount of IL used. We also demonstrated that arrayed Pt nanorings enabled the fabrication of reduced graphene oxide (rGO) anti-nanoring arrays via a catalytic tailoring process.
We report the growth and transfer of centimeter-sized, epitaxial hexagonal boron nitride (h-BN) few-layer films using Ni(111) single-crystal substrates. The h-BN films were heteroepitaxially grown on 10 × 10 mm2 or 20 × 20 mm2 Ni(111) substrates using atmospheric pressure chemical vapor deposition with a single ammonia-borane precursor. The grown films were transferred to arbitrary substrates via an electrochemical delamination technique, and the remaining Ni(111) substrates were repeatedly re-used. A careful analysis of the growth parameters revealed that the crystallinity and area coverage of the h-BN films were mostly sensitive to the sublimation temperature of the ammonia-borane source. Moreover, various physical characterizations confirmed that the grown films exhibited the typical characteristics of hexagonal boron nitride layers over the entire area. Furthermore, the heteroepitaxial relationship between h-BN and Ni(111) and the overall crystallinity of the film were thoroughly investigated using a synchrotron radiation X-ray diffraction analysis including θ–2θ scans, grazing incident diffraction, and reciprocal space mapping. The crystallinity at the microscopic scale was further investigated using transmission electron microscopy (TEM)-based techniques, including selective area electron diffraction pattern mapping, electron back-scattered diffraction, and high-resolution TEM.
In this study, the large-area tailoring of reduced graphene oxide (rGO) with tunable arrays of Pt nanostructures has been demonstrated. We synthesized arrays of catalytic Pt nanoparticles, nanowires, and their combined nanostructures from self-assembled thin films of polystyrene-block-poly(4-vinylpyridine) copolymers and their micelles. Then, rGO was transferred onto these Pt nanostructures, which were capable of catalyzing the oxidative elimination of carbon atoms from the rGO nanoregions in contact with the Pt, resulting in successful pattern transfer from the Pt nanoarrays onto the rGO, forming various nanostructures, such as nanoholes, nanoribbons, and perforated nanoribbons. Moreover, we transferred the tailored rGO onto a transparent and flexible polymeric substrate. The size and periodicity of the rGO nanostructures were controlled on the nanometer scale by adjusting those of the Pt nanostructures, which were strongly dependent on the molecular weights of the copolymers. In addition, arrayed Pt nanowires were aligned in a topographically patterned substrate by the directed self-assembly of the copolymers, enabling the fabrication of well-aligned rGO nanoribbon and nanosquare arrays.
We report controlled branching and eventual crosslinking in supracolloidal chains by introducing well-defined trifunctional patchy micelles. Uniform micelles having three patches were induced from core-crosslinked micelles of diblock copolymers. Three patches in the micelles served as functional groups for crosslinking as well as branching in supracolloidal polymerization.
We report the construction of non-hexagonal arrays of nanoparticles by the template-assisted self-assembly of polystyrene-block-poly(4-vinylpyridine) copolymer micelles. Diblock copolymers were spin-coated onto nanoscale TiO2 templates, which successfully guided the placement of the micelles to form unconventional assemblies such as linear, zigzag, and Kagome array structures. These arrangements, different from the usual quasi-hexagonal arrays of copolymer micelles spin-coated onto a flat substrate, greatly depended on the physical dimension of both the template and the micelles. Subsequent treatment of the copolymer micelles assemblies with oxygen plasma resulted in various non-hexagonal arrays of Au nanoparticles while preserving the arrangement of the original micelles on the template.
We demonstrate the large-area lithography-free ordered perforation of reduced graphene oxide (rGO) and graphene grown by chemical vapor deposition (CVD) with arrayed Pt nanoparticles (NPs) prepared by using self-patterning diblock copolymer micelles. The rGO layers were perforated by Pt NPs formed either on top or bottom surface. On the other hand, CVD graphene was perforated only when the Pt NPs were placed under the graphene layer. Various control experiments confirm that the perforation reaction of CVD graphene was catalyzed by Pt NPs, where the mechanical strain as well as the chemical reactivity of Pt lowered the activation energy barriers for the oxidation reaction of C═C bonds in graphene. Systematic atomic force microscopy and Raman analyses revealed the detailed perforation mechanism. The pore size and spacing can be controlled, and thus our present work may open a new direction in the development of ordered nanopatterns on graphene using metal NPs.
Superhydrophobic surfaces are normally fixed on the chosen materials. Here, we report transferrable superhydrophobicity which was enabled by fabricating TiO2 nanorods on a reduced graphene oxide (rGO) film. Superhydrophobic TiO2 nanorods were first synthesized from a nanoporous template of block copolymers (BCPs). The controllability over the dimension and shape of nanopores of the BCP template allowed for the adjustment of TiO2 nanostructures for superhydrophobicity. Since the rGO film provided effective transferring, TiO2 nanorods were conveyed onto a flexible polymer film and a metal substrate. Thus, the surface of the designated substrate was successfully changed to a superhydrophobic surface without alteration of its inherent characteristics.
We investigated the electrooxidative dissolution of uniformly distributed Au nanoparticles (NPs) without an extra adhesion layer or capping agent. Diblock copolymer micelles were exploited to fabricate the arrays of Au NPs where not only diameter of the particles but also inter-particle spacing, and thus coverage were finely controlled. The peak potential for electrochemical oxidation shifted greater as a function of coverage of NPs than the size.
We demonstrated the fabrication of ZnO nanorods and nanowalls directly on flexible substrates by combining a hydrothermal growth technique with nanoporous templates obtained from block copolymers. First, templates with cylindrical nanopores in two sizes and a template with nanogrooves were fabricated on flexible substrates by employing block copolymers with different molecular weights. From these nanotemplates, we synthesized vertically oriented ZnO nanorods with controlled diameters and ZnO nanostructures in a wall shape. Because the ZnO nanostructures were produced without an electrically insulating epitaxial layer, the semiconducting nature of the ZnO nanorods was characterized as synthesized. Thus, this combined method of hydrothermal growth and block copolymer templates for ZnO nanostructures can be directly applied to flexible electronic devices without alteration of the substrate.
We fabricated a single-layered film consisting of spherical micelles of diblock copolymers and one-dimensional Au nanorods that were surface modified with the same polymer as the corona block of the copolymers. When the diameters of micelles were larger than the lengths of the nanorods, spherical micelles arranged in a hexagonal configuration surrounded by nanorods with their long axes perpendicular to the radial direction of the micelles. This arrangement provided selective organization of the Au nanorods and Ag nanoparticles which were selectively synthesized within the cores of the copolymer micelles. Thus, position-selective arrangement of Au nanorods and Ag nanoparticles was demonstrated at the nanometer scale such that a homogenous distribution of two different nanomaterials over a large area without aggregation was achieved.
Reduced graphene oxide (rGO) films are decorated with non-overlapping Au nanoparticles using diblock copolymer micelles that provide controllability over the number density as well as the diameter of the nanoparticles. This synthetic process produces a pure Au surface without extra layers. Furthermore, the rGO film enables the transferability of the Au nanoparticles without deterioration of their arrays. Thus, the controllability of the Au nanoparticles and their transferability with rGO films allow the effective modification of electrochemical electrodes. With a glassy carbon electrode modified with an rGO film with Au nanoparticles, high electrochemical activity is observed in the oxygen reduction reaction (ORR). Furthermore, it is possible to identify a size-dependent ORR mechanism, showing that Au nanoparticles with an average diameter of 8.6 nm exhibit a 4-electron direct reduction of O2 to H2O.
We report the density- and size-controlled growth of zinc oxide (ZnO) nanorod arrays on arbitrary substrates using reduced graphene oxide (rGO) nanodot arrays. For the controlled growth of the ZnO nanorod arrays, rGO nanodot arrays with tunable density and size were designed using a monolayer of diblock copolymer micelles and oxygen plasma etching. While the diameter and number density of the ZnO nanorods were readily determined by those of the rGO nanodots, the length of the ZnO nanorods was easily controlled by changing the growth time. x-ray diffraction and electron microscopy confirmed that the vertically well-aligned ZnO nanorod arrays were heteroepitaxially grown on the rGO nanodots. Strong, sharp near-band-edge emission peaks with no carbon-related peak were observed in the photoluminescence spectra, implying that the ZnO nanostructures grown on the rGO nanodots were of high optical quality and without carbon contamination. Our approach provides a general and rational route for heteroepitaxial growth of high-quality inorganic materials with tunable number density, size, and spatial arrangement on arbitrary substrates using rGO nanodot arrays.
We have investigated the effect of argon (Ar) plasma treatment on the surface of graphite and the hydrothermal growth of zinc oxide (ZnO) microstructures. With the plasma treatment, the growth behavior of ZnO microrods on the graphite substrates changed drastically. After the graphite surface was exposed to the Ar plasma, the number density of ZnO was one order of magnitude higher than that on the pristine graphite without plasma treatment. Raman spectroscopy revealed that Ar plasma treatment created the structural defects on the graphite surfaces and decreased the mean distance of defects. Surface characterization through atomic force microscopy and X-ray photoelectron spectroscopy showed that the graphite surface was roughened and that oxygen–carbon bonding was formed. The enhanced nucleation of ZnO can be explained by the generation of structural defects, surface roughness, and surface functional groups on the graphite substrate. Therefore, Ar plasma treatment can be used as a simple method to engineer the surface properties of graphite substrates and to control the crystal nucleation and growth of inorganic materials on their surface.
Three-dimensional nanostructures of TIO2 related materials including nanotubes, electron acceptor materials in hybrid polymer solar cells, and working electrodes of dye sensitized solar cells (DSSCs) were visualized by electron tomography as well as TEM micrographs. The regions on the wall of TIO2 nanotubes where the streptavidins were attached were elucidated by electron tomogram analysis. The coverage of TIO2 nanotubes by streptavidin was also investigated. The TIO2 nanostructures in hybrid polymer solar cells made by sol–gel and atomic layer deposition (ALD) methods and the morphologies of pores between TIO2 particles in DSSCs were also observed by reconstructed three-dimensional images made by electron tomography.
Nanostructured graphenes such as nanoribbons, nanomeshes, and nanodots have attracted a great deal of attention in relation to graphene-based semiconductor devices. The block copolymer micellar approach is a promising bottom-up technique for generating large area nanostructures of various materials without using sophisticated electron-beam lithography. Here we demonstrate the fabrication of an array of graphene nanodots with tunable size and inter-distance with the utilization of a monolayer of diblock copolymer micelles. Au nanoparticles were synthesized in the micellar cores and effectively worked as shielding nanostructures in generating graphene nanodots by oxygen plasma etching. We also controlled the radius and inter-distance of graphene nanodots simply through the molecular weight of the copolymers.