Density Multiplication of Highly Periodic Sub-5 nm Supramolecular Dendrimer Cylinders on Block Copolymer Lamellar-Assisted High-Resolution Patterns.

Density multiplication in nanopatterning is one of the most efficient techniques for increasing the resolution of the inherent patterns. Thus far, most of the density multiplication techniques integrate bottom-up (or top-down) patterning onto guide patterns prepared by the top-down approach. Although the bottom-up approach exhibits several advantages of cost-effectiveness and high resolution, very few studies have reported bottom-up patterning within a bottom-up template. In this study, the density multiplication of supramolecular cylinders into a block copolymer (BCP)-based guide lamellar pattern is demonstrated by the directed self-assembly (DSA) of a dendrimer and BCPs for the first time. Supramolecular cylinders of sub-5 nm scale are confined into trenches based on 50 and 100 nm scales of a lamellar polystyrene (PS)-poly(methyl methacrylate) (PMMA) BCP, which led to 10×-level to 20×-level density multiplication. Moreover, the orientation of the dendrimer is dependent on the dendrimer film thickness, and the corresponding mechanism is revealed. Notably, the strong guiding effect from the high-resolution guide patterns improved the ordering behavior in the highly curved pattern. Graphoepitaxy via the confinement of an ultrahigh-resolution dendrimer into the guide pattern based on BCP demonstrates promise as a density multiplication method for generating highly ordered nanostructures and complex structures.

Strong Bathochromic Shift of Conjugated Polymer Nanowires Assembled with a Liquid Crystalline Alkyl Benzoic Acid via a Film Dispersion Process.

We present aqueous dispersions of conjugated polymer nanowires (CPNWs) with improved light absorption properties aimed at aqueous-based applications. We assembled films of a donor-acceptor-type conjugated polymer and liquid crystalline 4-n-octylbenzoic acid by removing a cosolvent of their mixture solutions, followed by annealing of the films, and then formed aqueous-dispersed CPNWs with an aspect ratio >1000 by dispersing the films under ultrasonication at a basic pH. X-ray and spectroscopy studies showed that the polymer and liquid crystal molecules form independent domains in film assemblies and highly organized layer structures in CPNWs. Our ordered molecular assemblies in films and aqueous dispersions of CPNWs open up a new route to fabricate nanowires of low-band-gap linear conjugated polymers with the absorption maximum at 794 nm remarkably red-shifted from 666 nm of CPNWs prepared by an emulsion process. Our results suggest the presence of semicrystalline polymorphs ß1 and ß2 phases in CPNWs due to long-range π-π stacking of conjugated backbones in compactly organized lamellar structures. The resulting delocalization with a reduced energy bang gap should be beneficial for enhancing charge transfer and energy-conversion efficiencies in aqueous-based applications such as photocatalysis.

Wafer-Scale Unidirectional Alignment of Supramolecular Columns on Faceted Surfaces.

The long-range alignment of supramolecular structures must be engineered as a first step toward advanced nanopatterning processes aimed at miniaturizing features to dimensions below 5 nm. This study introduces a facile method of directing the orientation of supramolecular columns over wafer-scale areas using faceted surfaces. Supramolecular columns with features on the sub-5 nm scale were highly aligned in a direction orthogonal to that of the facet patterning on unidirectional and nanoscopic faceted surface patterns. This unidirectional alignment of supramolecular columns is also observed by varying the thickness of the supramolecular film or by altering the dimensions of the facet pattern. The ordering behavior of the supramolecular columns can be attributed to the triangular depth profile of the bottom facet pattern. Furthermore, this directed self-assembly principle allows for the continuous alignment of supramolecular structures across ultralarge distances on flexible patterned substrates.

Direct Growth of Highly Conductive Large-Area Stretchable Graphene.

The direct synthesis of inherently defect-free, large-area graphene on flexible substrates is a key technology for soft electronic devices. In the present work, in situ plasma-assisted thermal chemical vapor deposition is implemented in order to synthesize 4 in. diameter high-quality graphene directly on 10 nm thick Ti-buffered substrates at 100 °C. The in situ synthesized monolayer graphene displays outstanding stretching properties coupled with low sheet resistance. Further improved mechanical and electronic performances are achieved by the in situ multi-stacking of graphene. The four-layered graphene multi-stack is shown to display an ultralow resistance of ≈6 Ω sq-1, which is consistently maintained during the harsh repeat stretching tests and is assisted by self-p-doping under ambient conditions. Graphene-field effect transistors fabricated on polydimethylsiloxane substrates reveal an unprecedented hole mobility of ≈21 000 cm2 V-1 s-1 at a gate voltage of -4 V, irrespective of the channel length, which is consistently maintained during the repeat stretching test of 5000 cycles at 140% parallel strain.

Large-Area Alignment of Supramolecular Columns by Photothermal Laser Writing.

Controlling the orientation of highly periodic supramolecular structures of small feature size (<5 nm) is the first step for potential applications in optoelectronics, membranes, and template synthesis. A new method, namely, laser photothermal writing, is introduced to direct the orientation of supramolecular columns over a large area. Supramolecular columns consisting of taper-shaped molecules with long aliphatic tail groups are aligned by a thermal gradient, which is induced by exposing a near-infrared laser beam to a graphene photothermal conversion layer. Intriguingly, the orientation of the supramolecular columns can be controlled in a facile manner by varying the laser scanning velocity and power. In contrast to previous methodologies for aligning supramolecular structures, this laser photothermal mechanism allows the directional and continuous alignment of supramolecular structures over an arbitrary large area with the easy control of laser irradiation. Besides, the laser process also enables area-selective orientation of the supramolecular structures for device-oriented nanopatterning.

Hierarchical Self-Assembly of Perylene Diimide (PDI) Crystals.

Controlling molecular self-assembly of organic semiconductors is a key factor in enhancing the performance of organic electronics and optoelectronics. However, unlike various p-type organic semiconductors, it has proven elusive to control molecular self-assembly with about tens of nm dimensions using n-type organic semiconductors including perylene diimide (PDI), which is the most promising alternative to fullerene derivatives, without using an additional synthetic method or additives, thus far. Here, we developed a simple self-assembling method for the hierarchical self-assembly of PDI crystals with nanometer-to-micrometer scale features using pristine PDI-C8 without using an additional synthetic method or additive. Interestingly, we observed crystalline and optical properties of self-assembled PDI crystals depending on their size and structural features. In addition, we fabricated p-n junctions composed of PDI and poly(3-hexylthiophene) (P3HT), where the p-n junctions had coassembled and blended nanomorphologies, and confirmed that coassembled nanomorphologies enabled more effective energy transfer than the blended nanomorphologies.

Sculpted grain boundaries in soft crystals.

Engineering the grain boundaries of crystalline materials represents an enduring challenge, particularly in the case of soft materials. Grain boundaries, however, can provide preferential sites for chemical reactions, adsorption processes, nucleation of phase transitions, and mechanical transformations. In this work, "soft heteroepitaxy" is used to exert precise control over the lattice orientation of three-dimensional liquid crystalline soft crystals, thereby granting the ability to sculpt the grain boundaries between them. Since these soft crystals are liquid-like in nature, the heteroepitaxy approach introduced here provides a clear strategy to accurately mold liquid-liquid interfaces in structured liquids with a hitherto unavailable level of precision.

Ultra-dense (~20 Tdot/in2) nanoparticle array from an ordered supramolecular dendrimer containing a metal precursor.

The fabrication of an ultra-dense, highly periodic nanoparticle array from a soft template is one of the most important issues in the fields of material science and nanotechnology. To date, block copolymer (BCP) structures have been primarily used as templates for fabricating highly periodic nanoparticle arrays with high areal densities. Herein, we demonstrate for the first time the use of a supramolecular dendrimer assembly for the formation of a highly ordered nanoparticle array with a high areal density of ~20 Tdot/in2, four times larger than that of the currently reported BCP-based nanoparticle arrays. By the simple thermal annealing of a dendrimers containing a metal precursor between two flat, solid substrates, a hexagonal array of small gold nanoparticles (with a diameter of ~1.6 nm and center-to-center distance of ~5.3 nm), oriented normal to the bottom, was achieved. Density functional theory calculations demonstrated that the gold cation strongly bound to the head group of the dendrimer. This structure served as a building block for self-assembly into a stable cylindrical structure. We anticipate that this study will lead to the creation of a large family of supramolecular dendrimers that can be utilized as soft templates for creating periodic, ultra-dense nanoparticle arrays.

Perfection in Nucleation and Growth of Blue-Phase Single Crystals: Small Free-Energy Required to Self-Assemble at Specific Lattice Orientation.

Chemically patterned surfaces can be used to selectively stabilize blue phases as macroscopic single crystals with a prescribed lattice orientation. By tailoring the interfacial free energy through the pattern characteristics, it is possible to set, with nanoscale precision, the optimal conditions to induce spontaneously blue-phase crystal nucleation on the patterned substrate where a uniform, defect-free, blue-phase single crystal is finally formed in a matter of seconds. The chemical patterns taken into consideration in this work are made up of alternated stripelike regions of homeotropic and planar anchoring. By varying the stripe pattern dimension, including the period and ratio of the planar/homeotropic anchoring width, it is possible to generate blue-phase I single crystals with (110) lattice orientation and blue-phase II single crystals with either the (100), (110), or (111) lattice orientation. Continuum mean-field calculations of the studied systems serve to explain, in terms of the free energy of the systems, how the pattern dimensions favor certain crystallographic orientations while penalizing the others. We found that a small free-energy difference is sufficient to drive the nucleation and growth of blue phases into a certain lattice orientation. Therefore, a processing window for obtaining arbitrary large blue-phase single crystals with predesigned lattice orientation, highly aligned reflective peaks, and significantly short forming time is provided here, which is essential for manufacturing and modulating optical devices and photonics.

Ultrasmall Grained Pd Nanopattern H2 Sensor.

Precise control of the size and interfaces of Pd grains is very important for designing a high-performance H2 sensing channel because the transition of the Pd phase from α to ß occurs through units of single grains. However, unfortunately, the grain controllability of previous approaches has been limited to grains exceeding 10 nm in size and simple macroscopic channel structures have only shown monotonic response behavior for a wide concentration range of H2. In this work, for the first time, we found that Pd channels that are precisely grain-controlled show very different H2 sensing behavior. They display dual-switching response behavior with simultaneous variation of the positive and negative response direction within single sensor. The Pd nanopattern channel having smallest grain size/interface among previous works could be fabricated via unique lithographic approaches involving low-energy plasma (Ar+) bombardment. The ultrasmall grain size (5 nm) and narrow interface gap (<2 nm) controlled by Ar+ plasma bombardment enabled both the hydrogen-induced lattice expansion (HILE) (Δ RH2 < 0) and surface electron scattering (Δ RH2 > 0) mechanisms to be simultaneously applied to the single Pd channel, thereby inducing dual-switching response according to the H2 concentration range. In addition, the unique high-aspect-ratio high-resolution morphological characteristics made it possible to achieve highly sensitive H2 detecting performance (limit of detection: 2.5 ppm) without any hysteresis and irreversible performance degradation. These noteworthy new insights are attributed to high-resolution control of the grain size and the interfaces with the Pd nanostructure channel.

Rational Design of Aminopolymer for Selective Discrimination of Acidic Air Pollutants.

Strong acidic gases such as CO2, SO2, and NO2 are harsh air pollutants with major human health threatening factors, and as such, developing new tools to monitor and to quickly sense these gases is critically required. However, it is difficult to selectively detect the acidic air pollutants with single channel material due to the similar chemistry shared by acidic molecules. In this work, three acidic gases (i.e., CO2, SO2, and NO2) are selectively discriminated using single channel material with precise moiety design. By changing the composition ratio of primary (1°), secondary (2°), and tertiary (3°) amines of polyethylenimine (PEI) on CNT channels, unprecedented high selectivity between CO2 and SO2 is achieved. Using in situ FT-IR characterizations, the distinct adsorption phenomenon of acidic gases on each amine moiety is precisely demonstrated. Our approach is the first attempt at controlling gas adsorption selectivity of solid-state sensor via modulating chemical moiety level within the single channel material. In addition, discrimination of CO2, SO2, and NO2 with the single channel material solid-state sensor is first reported. We believe that this approach can greatly enhance air pollution tracking systems for strong acidic pollutants and thus aid future studies on selective solid-state gas sensors.

Long-range single domain array of a 5 nm pattern of supramolecules via solvent annealing in a double-sandwich cell.

In nanotechnology and microelectronics research, the generation of an ultradense, single-grain nanostructure with a long-range lateral order is challenging. In this paper, we report upon a new solvent-annealing method using a double-sandwich confinement to promote the formation of a large-area, single-domain array (>0.3 × 0.3 mm2) of supramolecular cylinders with a small feature size (4.7 nm). The in situ GISAXS experiment result shows the ordering process during solvent evaporation. The diffusion of the solvent molecules led to the disassembly of the supramolecules confined between the top and bottom surfaces and their subsequent mobilization, thereby producing a highly ordered hexagonal array of supramolecular materials under the double-sandwich confinement upon solvent evaporation. In addition, two key factors were found to be crucial in this process for generating highly-ordered supramolecular building blocks: (i) the presence of a top coat during solvent evaporation to provide a geometric confinement template, and (ii) the control of the solvent evaporation rate during the solvent evaporation step to provide the dendrimer sufficient time to self-assemble into the highly ordered state over a large area. Our developed approach, which can be extended to be used for a large family of supramolecules, is of critical importance in providing a new bottom-up lithographic method based on supramolecular self-assembly.

One dimensional building blocks for molecular separation: laminated graphitic nanoribbons.

Herein, a new carbon-based graphitic membrane composed of laminated graphitic nanoribbons with a nanometer-scale width and micrometer-scale length, the graphitic nanoribbon membrane, is reported. Compared to the existing graphitic membranes, such as those composed of graphene oxide and carbon nanotubes, the developed membrane exhibits several unique characteristics in pressure-driven systems. First, the short diffusion length through its interlayer and the free volume of its stacked nanoribbons result in high solvent flux regardless of solvent polarity (water: 25-250 L m-2 h-1 bar-1; toluene: ∼975 L m-2 h-1 bar-1; hexane: ∼240 L m-2 h-1 bar-1). The flux value for water is one order of magnitude higher, while that for nonpolar organic solvents is two to three orders of magnitude greater than the corresponding flux values obtained through commercially available nanofiltration membranes. Second, the membrane exhibits good separation performance, particularly with organic dye molecules (∼100%) and trivalent ions (∼60%), maintaining high solvent flux during extended filtration. Finally, the membrane exhibits high stability in various fluids, e.g., 1 M HCl solution, 1 M NaOH solution, toluene, ethanol, and water, as well as under hydraulic pressures of up to 50 bar. Electron microscopy observation and simulation results suggest that such distinctive features of the membrane are related to the entangled thin multilayers of the graphitic nanoribbons, which possibly originate from the high aspect ratio and narrow width of the nanoribbons.

Bio-information scanning technology using an optical pick-up head.

We have developed a low cost and a highly compact bio-chip detection technology by modifying a commercially available optical pick-up head for CD/DVD. The highly parallel and miniaturized hybridization assays are addressed by the fluorescence emitted by the DNA-chip using the optical pick-up head. The gap between the objective lens and the bio-chip is regulated by the focus servo during the detection of the fluorescence signal. High-resolution and high-speed scanning is effectively realized by this simple scanning system instead of utilizing high-precision mechanism. Regardless of achievement of effective detection mechanism, the technique of fluorescence detection can prove to be disadvantageous because of the low stability of the dyes with low S/N ratio and an expensive setup such as a PMT detector is always required for fluorescence detection. We propose, for the first time, a novel scanning scheme based on metal nanoparticles in combination with a bio-chip substrate having a phase change recording layer. We found that the phase change process is highly affected by the existence of the densely condensed metal nanoparticles on the phase change layer during the writing process of the pick-up head.