Acetylene-containing highly birefringent rod-type reactive liquid crystals based on 2-methylhydroquinone

<p>New highly birefringent reactive liquid crystal materials based on the 2-methylhydroquinone core were designed and synthesised. Rod-type liquid crystal compounds bearing photo-crosslinkable reactive group of acryloyl, methacryloyl, cinnamoyl, furylacryloyl group were synthesised by introducing acetylene groups via Sonogashira coupling to obtain high birefringence, and lateral groups such as fluoro and methyl to adjust the temperature of the liquid crystal phase. The synthesised compounds were characterised using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. In addition, their thermal behaviour was investigated using differential scanning calorimetry and polarised optical microscopy. After aligning the synthesised compounds, liquid crystal films were prepared by photo-irradiation. Photo-elastic modulator results showed that the obtained liquid crystal films had high birefringence (Δ<i>n</i>) values of 0.32–0.40.</p

Fabrication of 10 nm-Scale Complex 3D Nanopatterns with Multiple Shapes and Components by Secondary Sputtering Phenomenon

We introduce an advanced ultrahigh-resolution (∼15 nm) patterning technique that enables the fabrication of various 3D high aspect ratio multicomponents/shaped nanostructures. This methodology utilizes the repetitive secondary sputtering phenomenon under etching plasma conditions and prepatterned fabrication control. The secondary sputtering phenomenon repetitively generates an angular distribution of target particles during ion-bombardment. This method, advanced repetitive secondary sputtering lithography, provides many strategies to fabricate complex continuous patterns and multilayer/material patterns with 10 nm-scale resolution. To demonstrate the versatility of this method, we show induced vertical alignment of liquid crystals (LCs) on indium-tin-oxide (ITO) grid patterns without any alignment layers. The ITO grid pattern fabricated in this method is found to have not only an alignment capability but also electrode properties without electrical or optical damage

High birefringent reactive discotic liquid crystals based on asymmetrical triphenylene with phenyl-acetylene moieties

<p>Triphenylene (TP)-based liquid crystals, a category of discotic liquid crystals (DLCs), are easy to synthesise, thermally stable and can undergo self-assembly. A new DLC compound, 2,7,10-tris[4-(6-acryloyloxyhexyloxy)benzoate]-3,6,11-tris[(4-hexylphenyl)ethynyl]-triphenylene, was obtained with a 49% yield using catechol as a starting material and features acetylene groups on its TP core. This material can form films with high birefringence through its cross-linkable acrylate ends. Here, we synthesised this new compound and characterised it using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. The thermal behaviour was also investigated using differential scanning calorimetry and polarised optical microscopy. This new asymmetric TP-based DLC compound exhibited a nematic liquid-crystalline phase between −20 and 170°C and formed an optical anisotropic film with a high birefringence (Δ<i>n</i> = 0.21–0.25).</p

Electrical and Thermoelectric Transport by Variable Range Hopping in Thin Black Phosphorus Devices

The moderate band gap of black phosphorus (BP) in the range of 0.3–2 eV, along a high mobility of a few hundred cm² V^–1 s^–1 provides a bridge between the gapless graphene and relatively low-mobility transition metal dichalcogenides. Here, we study the mechanism of electrical and thermoelectric transport in 10–30 nm thick BP devices by measurements of electrical conductance and thermopower (<i>S</i>) with various temperatures (<i>T</i>) and gate-electric fields. The <i>T</i> dependences of <i>S</i> and the sheet conductance (σ_□) of the BP devices show behaviors of <i>T</i>^1/3 and exp­[−(1/<i>T</i>)^1/3], respectively, where <i>S</i> reaches ∼0.4 mV/K near room <i>T</i>. This result indicates that two-dimensional (2D) Mott’s variable range hopping (VRH) is a dominant mechanism in the thermoelectric and electrical transport in our examined thin BP devices. We consider the origin of the 2D Mott’s VRH transport in our BPs as trapped charges at the surface of the underlying SiO₂ based on the analysis with observed multiple quantum dots

Surface Modification of a Polyimide Gate Insulator with an Yttrium Oxide Interlayer for Aqueous-Solution-Processed ZnO Thin-Film Transistors

We report a simple approach to modify the surface of a polyimide gate insulator with an yttrium oxide interlayer for aqueous-solution-processed ZnO thin-film transistors. It is expected that the yttrium oxide interlayer will provide a surface that is more chemically compatible with the ZnO semiconductor than is bare polyimde. The field-effect mobility and the on/off current ratio of the ZnO TFT with the YO_<i>x</i>/polyimide gate insulator were 0.456 cm²/V·s and 2.12 × 10⁶, respectively, whereas the ZnO TFT with the polyimide gate insulator was inactive

Direct Observation of Highly Ordered Dendrimer Soft Building Blocks over a Large Area

Developing large-area, single domain of organic soft-building blocks such as block copolymers, colloids, and supramolecular materials is one of the most important issues in the materials science and nanotechnology. Owing to their small sizes, complex molecular architectures, and high mobility, supramolecular materials are not well-suited for building large area, single domain structures. In the described study, a single domain of supramolecular columnar dendrimers was created over large area. The columnar structures in these domains have smaller (4.5 nm) diameters, higher area densities (ca. 36 Tera-dots/in²) and larger domains (>0.1 × 0.1 mm²) than those of all existing BCP and colloidal assemblies. By simply annealing dendrimer thin films between two flat solid surfaces, single domains of hexagonal columnar structures are created over large macroscopic areas. Observations made in this effort should serve as the foundation for the design of new routes for bottom-up lithography based on supramolecular building blocks

Direct Observation of Molybdenum Disulfide, MoS₂, Domains by Using a Liquid Crystalline Texture Method

Because the properties of molybdenum disulfide (MoS₂) are strongly influenced by the sizes and boundaries of its domains, the direct visualization of large-area MoS₂ domains is one of the most important challenges in MoS₂ research. In the current study, we developed a simple and rapid method to observe and determine the boundaries of MoS₂ domains. The technique, which depends on observations of nematic liquid crystal textures on the MoS₂ surface, does not damage the sample and is not limited by domain size. Thus, this approach should significantly aid not only efforts aimed at gaining an understanding of the relationships between grain boundaries and properties of MoS₂ but also those focusing on how domain sizes are controlled during large-area synthesi

Enhanced Performance of Solution-Processed Organic Thin-Film Transistors with a Low-Temperature-Annealed Alumina Interlayer between the Polyimide Gate Insulator and the Semiconductor

We studied a low-temperature-annealed sol–gel-derived alumina interlayer between the organic semiconductor and the organic gate insulator for high-performance organic thin-film transistors. The alumina interlayer was deposited on the polyimide gate insulator by a simple spin-coating and 200 °C-annealing process. The leakage current density decreased by the interlayer deposition: at 1 MV/cm, the leakage current densities of the polyimide and the alumina/polyimide gate insulators were 7.64 × 10^–7 and 3.01 × 10^–9 A/cm², respectively. For the first time, enhancement of the organic thin-film transistor performance by introduction of an inorganic interlayer between the organic semiconductor and the organic gate insulator was demonstrated: by introducing the interlayer, the field-effect mobility of the solution-processed organic thin-film transistor increased from 0.35 ± 0.15 to 1.35 ± 0.28 cm²/V·s. Our results suggest that inorganic interlayer deposition could be a simple and efficient surface treatment of organic gate insulators for enhancing the performance of solution-processed organic thin-film transistors

High performance carbon nanotubes thin film transistors by selective ferric chloride doping

Single wall carbon nanotubes (SWNT) have been a significant research topic as active layers for thin film transistors (TFTs) due to their high charge carrier mobility beyond that of crystalline silicon. In this study, we report an effective approach to achieve a very high field-effect mobility and on/off ratio for solution processed semiconducting SWNT TFTs, by selective doping through contact with a thin ferric chloride (FeCl3) dopant layer. The semiconducting layer is formed by a double spin coating of the highly purified (>99%) high pressure carbon mono oxide (HiPCO) SWNT sorted by wrapping of poly (3-dodecylthiophene-2,5-diyl) (P3DDT). In order to achieve effective hole injection from the top Au source electrode without increasing the off-state drain current, less purified (98-99%) SWNTs produced by the plasma discharge process sorted by wrapping of poly (9,9-di-n-dodecylfluorene) (PFDD) are formed on the top of HiPCO film. Significantly improved TFT performance is achieved by the insertion of a few nanometers of a FeCl3 dopant layer at the semiconductor-contact interface. A significant high hole field-effect of 48.35 ± 3.11 cm2V−1s−1 (bare: 6.18 ± 0.87 cm2V−1s−1) with a reasonable on/off current ratio of 105, and low off current of ∼80 pA, are obtained by controlling the concentration of FeCl3 dopant (thickness = 1.5 nm) at the contact. Mobility is improved further at 2.5 nm thickness of the FeCl3 dopant layer resulting in a hole mobility of 177 ± 13.2 cm2 V−1s−1, an on/off ratio of 7.4 × 103, and off state current of 1.2 × 10−9 A.</p

Controlling Smectic Liquid Crystal Defect Patterns by Physical Stamping-Assisted Domain Separation and Their Use as Templates for Quantum Dot Cluster Arrays

Controlling the organization of self-assembling building blocks over a large area is crucial for lithographic tools based on the bottom-up approach. However, the fabrication of liquid crystal (LC) defect patterns with a particular ordering still remains a challenge because of the limited close-packed morphologies of LC defects. Here, we introduce a multiple-stamping domain separation method for the control of the dimensions and organization of LC defect structures. Prepatterns with various grid shapes on planar polyimide (PI) surfaces were fabricated by pressing a line-shaped stamp into the PI surfaces in two different directions, and then these surfaces were used to prepare LC defect structures confined to these grid domains. The dimensions of the LC defect structures, namely, the equilibrium diameter and the center to center spacing, are controlled by varying the line spacing of the stamps and the film thickness. A variety of arrangements of LC defects, including square, rhombic, hexagonal, and other oblique lattices, can be obtained by simply varying the stamping angle (Ω) between the first and second stamping directions. Furthermore, we demonstrate that the resulting controllable LC defect arrays can be used as templates for generating various patterns of nanoparticle clusters by trapping quantum dots (QDs) within the cores of the LC defects