Patterning of conjugated polymers for organic optoelectronic devices

Conjugated polymers have been attracting more and more attention because they possess various novel electrical, magnetical, and optical properties, which render them useful in modern organic optoelectronic devices. Due to their organic nature, conjugated polymers are light-weight and can be fabricated into flexible appliances. Significant research efforts have been devoted to developing new organic materials to make them competitive with their conventional inorganic counterparts. It is foreseeable that when large-scale industrial manufacture of the devices made from organic conjugated polymers is feasible, they would be much cheaper and have more functions. On one hand, in order to improve the performance of organic optoelectronic devices, it is essential to tune their surface morphologies by techniques such as patterning. On the other hand, patterning is the routine requirement for device processing. In this review, the recent progress in the patterning of conjugated polymers for high-performance optoelectronic devices is summarized. Patterning based on the bottom-up and top-down methods are introduced. Emerging new patterning strategies and future trends for conventional patterning techniques are discussed.     

Nanoscale fabrication by nonconventional approaches

An overview of three major nonconventional approaches in nanofabrication, scanning probe microscopy lithography, self-assembly, and imprint lithography, is presented. Typically, these nonconventional approaches are emerging technologies based on simple principles with potential cost-effective manufacturability, as compared to those conventional processes that are widely used and highly developed for making microelectronic circuits. Following the introduction of nonconventional technologies and their significances in nanofabrication, the details of each approach are presented. The lithographic applications of scanning probe microscopy, which involves three major variations: scanning tunneling microscopy, atomic force microscopy, and scanning near-field optical microscopy, are first evaluated with emphasis on their abilities in making structures with subnanoscale resolutions. The principles and processes for each technique are presented while their differences are also discussed. For the second approach, self-assembly, which uses a bottom-up fabrication strategy, is reported starting with an introduction of its basic principle. Self-assembly, with and without externally controlled forces for patterning nanoscale structures, is then examined. The associated principles and procedures of key assembling processes are presented. The third one, imprint lithography, is addressed with an emphasis on its recent progress and challenges. The nanolithographic abilities of different techniques developed using the general imprinting principle are examined. Finally, concluding remarks are provided to summarize the major technologies studied and to recommend the scopes for technology improvement and future research.     

Micro- and nanoscale modification of poly(2-hydroxyethyl methacrylate) hydrogels by AFM lithography and nanoparticle incorporation

Poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels are widely used as biomaterials. Due to their unique combination of biocompatibility and good mechanical properties, they have potential as scaffolds for tissue engineering applications. To this purpose, topographic and chemical patterning at the nano- to the mesoscale is crucial in order to favor and to characterize cell adhesion and proliferation. Here we report the characterization of as-prepared and patterned PHEMA hydrogels, produced by conventional radical polymerization in water and dimethylformamide. We have obtained chemical and morphological micro- and nanoscale patterning by atomic force microscopy based lithography. We also demonstrate that it is possible to incorporate carbon nanoparticles in the hydrogel matrix by supersonic cluster beam deposition.     

Patterning and Templating for Nanoelectronics

The semiconductor industry will soon be launching 32 nm complementary metal oxide semiconductor (CMOS) technology node using 193 nm lithography patterning technology to fabricate microprocessors with more than 2 billion transistors. To ensure the survival of Moore's law, alternative patterning techniques that offer advantages beyond conventional top‐down patterning are aggressively being explored. It is evident that most alternative patterning techniques may not offer compelling advantages to succeed conventional top‐down lithography for silicon integrated circuits, but alternative approaches may well indeed offer functional advantages in realising next‐generation information processing nanoarchitectures such as those based on cellular, bioinsipired, magnetic dot logic, and crossbar schemes. This paper highlights and evaluates some patterning methods from the Center on Functional Engineered Nano Architectonics in Los Angeles and discusses key benchmarking criteria with respect to CMOS scaling.     

Zinc oxide nanowire gas sensors: fabrication,functionalisation and devices

With the progress in the synthesis of high quality ZnO nanowires, their implementation as gas sensors has gained popularity. Relying on the surface ionosorption, these devices have demonstrated exquisite sensitivity with further improvement achieved through various functionalisation methods. Both resistive and transistor based methodologies are employed for gas sensing while integration of micro-heaters has also been attempted for portability of the devices. In order to achieve successful inclusion amongst semiconductor fabrication processes, top-down approaches are being explored along with conventional bottom-up synthesis routes. Major challenge of low selectivity can be overcome by Electronic Nose systems. This article reviews the progress in synthesis, functionalisation, and device implementation of ZnO nanowire gas sensors, concluding with remarks on associated challenges and future prospects.     

Patterning surfaces with functional polymers

The ability to pattern functional polymers at different length scales is important for research fields including cell biology, tissue engineering and medicinal science and the development of optics and electronics. The interest and capabilities of polymer patterning have originated from the abundance of functionalities of polymers and a wide range of applications of the patterns. This paper reviews recent advances in top-down and bottom-up patterning of polymers using photolithography, printing techniques, self-assembly of block copolymers and instability-induced patterning. Finally, challenges and future directions are discussed from the point of view of both applicability and strategies for the surface patterning of polymers.     

Engineering III–V Semiconductor Nanowires for Device Applications

III–V semiconductor nanowires offer potential new device applications because of the unique properties associated with their 1D geometry and the ability to create quantum wells and other heterostructures with a radial and an axial geometry. Here, an overview of challenges in the bottom-up approaches for nanowire synthesis using catalyst and catalyst-free methods and the growth of axial and radial heterostructures is given. The work on nanowire devices such as lasers, light emitting nanowires, and solar cells and an overview of the top-down approaches for water splitting technologies is reviewed. The authors conclude with an analysis of the research field and the future research directions.     

可聚合表面活性剂在(微)乳液聚合中的应用

在(微)乳液聚合中用可聚合表面活性剂代替传统的表面活性剂,使提高胶乳的稳定性、得到透明高分子材料等成为可能。着重阐述了可聚合表面活性剂在(微)乳液聚合反应中的作用,介绍了用可聚合表面活性剂通过(微)乳液聚合法制备微孔高分子材料、薄膜材料、功能化材料和有机/无机杂化材料的性能和应用,展望了其研究趋势。     

Flexible Electronics Based on Organic Semiconductors: from Patterned Assembly to Integrated Applications

Organic flexible electronic devices are at the forefront of the electronics as they possess the potential to bring about a major lifestyle revolution owing to outstanding properties of organic semiconductors, including solution processability, lightweight and flexibility. For the integration of organic flexible electronics, the precise patterning and ordered assembly of organic semiconductors have attracted wide attention and gained rapid developments, which not only reduces the charge crosstalk between adjacent devices, but also enhances device uniformity and reproducibility. This review focuses on recent advances in the design, patterned assembly of organic semiconductors, and flexible electronic devices, especially for flexible organic field-effect transistors (FOFETs) and their multifunctional applications. First, typical organic semiconductor materials and material design methods are introduced. Based on these organic materials with not only superior mechanical properties but also high carrier mobility, patterned assembly strategies on flexible substrates, including one-step and two-step approaches are discussed. Advanced applications of flexible electronic devices based on organic semiconductor patterns are then highlighted. Finally, future challenges and possible directions in the field to motivate the development of the next generation of flexible electronics are proposed.     

Nanoelectronics from the bottom up

Electronics obtained through the bottom-up approach of molecular-level control of material composition and structure may lead to devices and fabrication strategies not possible with top-down methods. This review presents a brief summary of bottom-up and hybrid bottom-up/top-down strategies for nanoelectronics with an emphasis on memories based on the crossbar motif. First, we will discuss representative electromechanical and resistance-change memory devices based on carbon nanotube and core-shell nanowire structures, respectively. These device structures show robust switching, promising performance metrics and the potential for terabit-scale density. Second, we will review architectures being developed for circuit-level integration, hybrid crossbar/CMOS circuits and array-based systems, including experimental demonstrations of key concepts such lithography-independent, chemically coded stochastic demultipluxers. Finally, bottom-up fabrication approaches, including the opportunity for assembly of three-dimensional, vertically integrated multifunctional circuits, will be critically discussed.     

Fabrication of Transistors on Flexible Substrates: from Mass‐Printing to High‐Resolution Alternative Lithography Strategies

In this report, the development of conventional, mass‐printing strategies into high‐resolution, alternative patterning techniques is reviewed with the focus on large‐area patterning of flexible thin‐film transistors (TFTs) for display applications. In the first part, conventional and digital printing techniques are introduced and categorized as far as their development is relevant for this application area. The limitations of conventional printing guides the reader to the second part of the progress report: alternative‐lithographic patterning on low‐cost flexible foils for the fabrication of flexible TFTs. Soft and nanoimprint lithography‐based patterning techniques and their limitations are surveyed with respect to patterning on low‐cost flexible foils. These show a shift from fabricating simple microlense structures to more complicated, high‐resolution electronic devices. The development of alternative, low‐temperature processable materials and the introduction of high‐resolution patterning strategies will lead to the low‐cost, self‐aligned fabrication of flexible displays and solar cells from cheaper but better performing organic materials.     

Nanopatterning self-assembled nanoparticle superlattices by moulding microdroplets

Highly ordered arrays of nanoparticles exhibit many properties that are not found in their disordered counterparts. However, these nanoparticle superlattices usually form in a far-from-equilibrium dewetting process, which precludes the use of conventional patterning methods owing to a lack of control over the local dewetting dynamics. Here, we report a simple yet efficient approach for patterning such superlattices that involves moulding microdroplets containing the nanoparticles and spatially regulating their dewetting process. This approach can provide rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, we have patterned nanoparticle superlattices over large areas into a number of versatile structures with high degrees of internal order, including single-particle-width corrals, single-particle-thickness microdiscs and submicrometre-sized 'supra-crystals'. Remarkably, these features could be addressed by micropatterned electrode arrays, suggesting potential applications in bottom-up nanodevices.     

纤维材料表面图案化构筑及应用研究进展

自然界中生物体表面形形色色的图案赋予其减阻、强黏附、超疏水等多样的功能特性。受自然界的启发,研究者在平面基底表面构筑图案方面已经取得了很大研究进展。然而,纤维材料表面的图案化构筑及对纤维材料功能的影响等研究尚不深入。本文总结了目前纤维材料表面图案化的构筑方法,简述了三种“自下而上”策略的图案化形成机制;另外分析了纤维材料表面图案化对其功能的影响,展望了纤维材料表面图案化的潜在应用;最后对构筑方法、形成机制、应用领域提出了展望。本文旨在为纤维材料表面图案的构筑及功能纤维/织物更广阔的工程应用提供借鉴。      

Self‐Assembled Monolayers as Patterning Tool for Organic Electronic Devices

The patterning of functional materials represents a crucial step for the implementation of organic semiconducting materials into functional devices. Classical patterning techniques such as photolithography or shadow masking exhibit certain limitations in terms of choice of materials, processing techniques and feasibility for large area fabrication. The use of self‐assembled monolayers (SAMs) as a patterning tool offers a wide variety of opportunities, from the region‐selective deposition of active components to guiding the crystallization direction. Here, we discuss general techniques and mechanisms for SAM‐based patterning and show that all necessary components for organic electronic devices, i.e., conducting materials, dielectrics, organic semiconductors, and further functional layers can be patterned with the use of self‐assembled monolayers. The advantages and limitations, and potential further applications of patterning approaches based on self‐assembled monolayers are critically discussed.     

Unconventional layer-by-layer assembly: surface molecular imprinting and its applications

Layer-by-layer assembly (LbL) is a rich, versatile, and powerful technique for fabricating multilayer thin films with controlled architecture and functions. Singly charged, uncharged, or water-repellent molecules cannot be used directly in conventional LbL assembly. This problem can be solved with unconventional LbL methods, by employing the preassembly of building blocks in solution and the use of these assemblies for LbL formation at the interface. This Concept summarizes different methods of unconventional LbL assembly, including electrostatic complex formation, hydrogen-bonded complexes, block-copolymer micelles, and π-π interaction complexes. These preassembly treatments endow the building blocks with enhanced abilities for advanced functionality, in particular, surface molecular imprinting, a new concept emerging from unconventional LbL. Molecular imprinting approaches are thus conceptually described based on different types of interactions and their great potential in applications is demonstrated by examples such as selective surface patterning and selective filtration.     

Tools for synthesising and characterising Bragg grating structures in optical fibres and waveguides

Optical waveguide filters based on optical fibre Bragg gratings are used for a wide range of applications in communications systems, fibre lasers and optical fibre sensors. The technical specifications for many of these grating based devices are becoming increasingly challenging. To make technological advances in this area a number of tools, such as: grating synthesis, advanced fabrication techniques, characterisation and reconstruction techniques, are required to improve grating structures. Closing the loop between design and physical realisation has the potential to achieve an unprecedented degree of accuracy in device fabrication. Grating design, fabrication and characterisation has moved from merely an inexact experimental procedure to a highly controlled engineering process. The mathematical and physical tools to achieve this are described and examples of applications are used to illustrate the potential of these capabilities to accelerate further understanding and development of photosensitivity and gratings in novel optical fibres and waveguides in the future.     

Orchestrated structure evolution: modeling growth-regulated nanomanufacturing

Orchestrated structure evolution (OSE) is a scalable manufacturing method that combines the advantages of top-down (tool-directed) and bottom-up (self-propagating) approaches. The method consists of a seed patterning step that defines where material nucleates, followed by a growth step that merges seeded islands into the final patterned thin film. We develop a model to predict the completed pattern based on a computationally efficient approximate Green's function solution of the diffusion equation plus a Voronoi diagram based approach that defines the final grain boundary structure. Experimental results rely on electron beam lithography to pattern the seeds, followed by the mass transfer limited growth of copper via electrodeposition. The seed growth model is compared with experimental results to quantify nearest neighbor seed-to-seed interactions as well as how seeds interact with the pattern boundary to impact the local growth rate. Seed-to-seed and seed-to-pattern interactions are shown to result in overgrowth of seeds on edges and corners of the shape, where seeds have fewer neighbors. We explore how local changes to the seed location can be used to improve the patterning quality without increasing the manufacturing cost. OSE is shown to enable a unique set of trade-offs between the cost, time, and quality of thin film patterning.     

Synthesis of monolithic graphene-graphite integrated electronics

Encoding electronic functionality into nanoscale elements during chemical synthesis has been extensively explored over the past decade as the key to developing integrated nanosystems with functions defined by synthesis. Graphene has been recently explored as a two-dimensional nanoscale material, and has demonstrated simple device functions based on conventional top-down fabrication. However, the synthetic approach to encoding electronic functionality and thus enabling an entire integrated graphene electronics in a chemical synthesis had not previously been demonstrated. Here we report an unconventional approach for the synthesis of monolithically integrated electronic devices based on graphene and graphite. Spatial patterning of heterogeneous metal catalysts permits the selective growth of graphene and graphite, with a controlled number of graphene layers. Graphene transistor arrays with graphitic electrodes and interconnects were formed from the synthesis. These functional, all-carbon structures were transferable onto a variety of substrates. The integrated transistor arrays were used to demonstrate real-time, multiplexed chemical sensing and more significantly, multiple carbon layers of the graphene-graphite device components were vertically assembled to form a three-dimensional flexible structure which served as a top-gate transistor array. These results represent substantial progress towards encoding electronic functionality through chemical synthesis and suggest the future promise of one-step integration of graphene-graphite based electronics.     

Spatiotemporal micropatterning of cells on arbitrary substrates

This paper presents a readily accessible patterning platform--based upon geometric constraints, discrete cell suspension droplets, and controlled cell settling--that provides both temporal and spatial patterning capabilities. As a demonstration, single-cell (and bead) suspensions as well as multicellular human embryonic stem cell colonies are spatiotemporally patterned onto arbitrary substrates. These substrates include tissue culture surfaces, cell monolayers, protein-coated surfaces, and 3D gel matrices. The generation of soluble factor gradients is also demonstrated. This method is completely passive and does not require external power sources. Spatiotemporal patterning provides a foundation for future biological studies that explore the time-dependent relationships between cell-cell signaling and cellular responses.