3D Hybrid Small Scale Devices

Interfacing nano/microscale elements with biological components in 3D contexts opens new possibilities for mimicry, bionics, and augmentation of organismically and anatomically inspired materials. Abiotic nanoscale elements such as plasmonic nanostructures, piezoelectric ribbons, and thin film semiconductor devices interact with electromagnetic fields to facilitate advanced capabilities such as communication at a distance, digital feedback loops, logic, and memory. Biological components such as proteins, polynucleotides, cells, and organs feature complex chemical synthetic networks that can regulate growth, change shape, adapt, and regenerate. Abiotic and biotic components can be integrated in all three dimensions in a well‐ordered and programmed manner with high tunability, versatility, and resolution to produce radically new materials and hybrid devices such as sensor fabrics, anatomically mimetic microfluidic modules, artificial tissues, smart prostheses, and bionic devices. In this critical Review, applications of small scale devices in 3D hybrid integration, biomicrofluidics, advanced prostheses, and bionic organs are discussed.     

One-Dimensional （1D） ZnS Nanomaterials and Nanostructures

One-dimensional （1D） nanomaterials and nanostructures have received much attention due to their potential interest for understanding fundamental physical concepts and for applications in constructing nanoscale electric and optoelectronic devices. Zinc sulfide （ZnS） is an important semiconductor compound of Ⅱ-Ⅵ group, and the synthesis of 1D ZnS nanomaterials and nanostructures has been of growing interest owing to their promising application in nanoscale optoelectronic devices. This paper reviews the recent progress on 1D ZnS nanomaterials and nanostructures, including nanowires, nanowire arrays, nanorods, nanobelts or nanoribbons, nanocables, and hierarchical nanostructures etc. This article begins with a survey of various methods that have been developed for generating 1D nanomaterials and nanostructures, and then mainly focuses on structures, synthesis, characterization, formation mechanisms and optical property tuning, and luminescence mechanisms of 1D ZnS nanomaterials and nanostructures. Finally, this review concludes with personal views towards future research on 1D ZnS nanomaterials and nanostructures.     

3D Nanofabrication of Fluidic Components by Corner Lithography

A reproducible wafer‐scale method to obtain 3D nanostructures is investigated. This method, called corner lithography, explores the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as structural material or as an inversion mask in subsequent steps. The potential of corner lithography is studied by fabrication of functional 3D microfluidic components, in particular i) novel tips containing nano‐apertures at or near the apex for AFM‐based liquid deposition devices, and ii) a novel particle or cell trapping device using an array of nanowire frames. The use of these arrays of nanowire cages for capturing single primary bovine chondrocytes by a droplet seeding method is successfully demonstrated, and changes in phenotype are observed over time, while retaining them in a well‐defined pattern and 3D microenvironment in a flat array.     

Biomimetic approaches toward smart bio-hybrid systems

Bio-integrated materials and devices can blur the interfaces between living and artificial systems. Microfluidics, bioelectronics, and engineered nanostructures, with close interactions with biology at the cellular or tissue levels, have already yielded a spectrum of new applications. Many new designs emerge, including of organ-on-a-chip systems, biodegradable implants, electroceutical devices, minimally invasive neuro-prosthetic tools, and soft robotics. In this review, we highlight a few recent advances of the fabrication and application of smart bio-hybrid systems, with a particular emphasis on the three-dimensional (3D) bio-integrated devices that mimic the 3D feature of tissue scaffolds. Moreover,neurons integrated with engineered nanostructures for wireless neuromodulation and dynamic neural output are briefly discussed. We also discuss the progress in the construction of cell-enabled soft robotics, where a tight coupling of the synthetic and biological parts is crucial for efficient function. Finally, we summarize the approaches for enhancing bio-integration with biomimetic micro- and nanostructures.

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Dielectrophoretic self-assembly of polarized light emitting poly(9,9-dioctylfluorene) nanofibre arrays

Conjugated polymer based 1D nanostructures are attractive building blocks for future opto-electronic nanoscale devices and systems. However, a critical challenge remains the lack of manipulation methods that enable controlled and reliable positioning and orientation of organic nanostructures in a fast, reliable and scalable manner. To address this challenge, we explore dielectrophoretic assembly of discrete poly(9,9-dioctylfluorene) nanofibres and demonstrate site selective assembly and orientation of these fibres. Nanofibre arrays were assembled preferentially at receptor electrode edges, being aligned parallel to the applied electric field with a high order parameter fit (～ 0.9) and exhibiting an emission dichroic ratio of ～ 4.0. As such, the dielectrophoretic method represents a fast, reliable and scalable self-assembly approach for manipulation of 1D organic nanostructures. The ability to fabricate nanofibre arrays in this manner could be potentially important for exploration and development of future nanoscale opto-electronic devices and systems.     

Bio‐microfluidics: Biomaterials and Biomimetic Designs

Bio‐microfluidics applies biomaterials and biologically inspired structural designs (biomimetics) to microfluidic devices. Microfluidics, the techniques for constraining fluids on the micrometer and sub‐micrometer scale, offer applications ranging from lab‐on‐a‐chip to optofluidics. Despite this wealth of applications, the design of typical microfluidic devices imparts relatively simple, laminar behavior on fluids and is realized using materials and techniques from silicon planar fabrication. On the other hand, highly complex microfluidic behavior is commonplace in nature, where fluids with nonlinear rheology flow through chaotic vasculature composed from a range of biopolymers. In this Review, the current state of bio‐microfluidic materials, designs and applications are examined. Biopolymers enable bio‐microfluidic devices with versatile functionalization chemistries, flexibility in fabrication, and biocompatibility in vitro and in vivo. Polymeric materials such as alginate, collagen, chitosan, and silk are being explored as bulk and film materials for bio‐microfluidics. Hydrogels offer options for mechanically functional devices for microfluidic systems such as self‐regulating valves, microlens arrays and drug release systems, vital for integrated bio‐microfluidic devices. These devices including growth factor gradients to study cell responses, blood analysis, biomimetic capillary designs, and blood vessel tissue culture systems, as some recent examples of inroads in the field that should lead the way in a new generation of microfluidic devices for bio‐related needs and applications. Perhaps one of the most intriguing directions for the future will be fully implantable microfluidic devices that will also integrate with existing vasculature and slowly degrade to fully recapitulate native tissue structure and function, yet serve critical interim functions, such as tissue maintenance, drug release, mechanical support, and cell delivery.     

Advanced lithography simulation for various 3-dimensional nano/microstructuring fabrications in positive- and negative-tone photoresists

Photoresist lithography has been applied to the fabrication of micro/nano devices, such as microfluidic structures, quantum dots, and photonic devices, in MEMS (micro-electro mechanical systems) and NEMS (nano-electro-mechanical systems). In particular, nano devices can be expected to present different physical phenomena due to their three-dimensional (3D) structure. The flexible 3D micro/nano fabrication technique and its process simulation have become among the major topics needed to understand nano-mechanical phenomena. For this purpose, the moving-mask technology and the lithography processes for the positive- and negative-tone photoresists were modeled. The validity of the simulation of the proposed 3D nano/microstructuring was successfully confirmed by comparing the experiment results and the simulated results. Hence, the developed model and the simulation can present and optimize photoresist characteristics and lithography process conditions due to the various 3D nano/microstructures. They could be help in the understanding of nanomaterial and mechanical phenomena.     

One‐Dimensional Dielectric/Metallic Hybrid Materials for Photonic Applications

Explorations of 1D nanostructures have led to great progress in the area of nanophotonics in the past decades. Based on either dielectric or metallic materials, a variety of 1D photonic devices have been developed, such as nanolasers, waveguides, optical switches, and routers. What's interesting is that these dielectric systems enjoy low propagation losses and usually possess active optical performance, but they have a diffraction‐limited field confinement. Alternatively, metallic systems can guide light on deep subwavelength scales, but they suffer from high metallic absorption and can work as passive devices only. Thus, the idea to construct a hybrid system that combines the merits of both dielectric and metallic materials was proposed. To date, unprecedented optical properties have been achieved in various 1D hybrid systems, which manifest great potential for functional nanophotonic devices. Here, the focus is on recent advances in 1D dielectric/metallic hybrid systems, with a special emphasis on novel structure design, rational fabrication techniques, unique performance, as well as their wide application in photonic components. Gaining a better understanding of hybrid systems would benefit the design of nanophotonic components aimed at optical information processing.     

1D Carbon‐Based Nanocomposites for Electrochemical Energy Storage

Electrochemical energy storage (EES) devices have attracted immense research interests as an effective technology for utilizing renewable energy. 1D carbon‐based nanostructures are recognized as highly promising materials for EES application, combining the advantages of functional 1D nanostructures and carbon nanomaterials. Here, the recent advances of 1D carbon‐based nanomaterials for electrochemical storage devices are considered. First, the different categories of 1D carbon‐based nanocomposites, namely, 1D carbon‐embedded, carbon‐coated, carbon‐encapsulated, and carbon‐supported nanostructures, and the different synthesis methods are described. Next, the practical applications and optimization effects in electrochemical energy storage devices including Li‐ion batteries, Na‐ion batteries, Li–S batteries, and supercapacitors are presented. After that, the advanced in situ detection techniques that can be used to investigate the fundamental mechanisms and predict optimization of 1D carbon‐based nanocomposites are discussed. Finally, an outlook for the development trend of 1D carbon‐based nanocomposites for EES is provided.     

Controlled growth and characterization methods of semiconductor nanomaterials

One-dimensional (1D) semiconductor nanomaterials attract much attention because they are ideal systems for investigation and studying the relationship between properties and structures and having extensive application future in the high technical field. They are expected to play an important role in fabrication of the next generation nanocircuits, nanotools, nanowires lasers, photon tunneling devices, near-field photo-waveguide devices, etc. This article described controlled growth, characterization of structures and morphologies and properties of 1D semiconductor nanomaterials based on our previous works. This article is organized into two parts: The first part is complicated nanostructures of semiconductors, which includes coaxial nanocables, heterostructure nanowires and nanowires with metal-semiconductor junction behavior, hierarchical structures, doping of the nanowires and nanobelts, porous materials and periodically twined nanowires and asymmetrical polytypic nanobelts. The second part contains semiconductor nanoarrays based on anodic alumina membrane (AAM) templates. Finally, we propose that further investigation of the influence of nanomaterial morphologies on properties and how to design the morphology of nanostructures to meet the property requirements of nanodevices are our future research directions in this field.     

The Brownian and Flow‐Driven Rotational Dynamics of a Multicomponent DNA Origami‐Based Rotor

Nanomechanical devices are becoming increasingly popular due to the very diverse field of potential applications, including nanocomputing, robotics, and drug delivery. DNA is one of the most promising building materials to realize complex 3D structures at the nanoscale level. Several mechanical DNA origami structures have already been designed capable of simple operations such as a DNA box with a controllable lid, bipedal walkers, and cargo sorting robots. However, the nanomechanical properties of mechanically interlinked DNA nanostructures that are in general highly deformable have yet to be extensively experimentally evaluated. In this work, a multicomponent DNA origami‐based rotor is created and fully characterized by electron microscopy under negative stain and cryo preparations. The nanodevice is further immobilized on a microfluidic chamber and its Brownian and flow‐driven rotational behaviors are analyzed in real time by single‐molecule fluorescence microscopy. The rotation in previous DNA rotors based either on strand displacement, electric field or Brownian motion. This study is the first to attempt to manipulate the dynamics of an artificial nanodevice with fluidic flow as a natural force.     

25th Anniversary Article: Hybrid Nanostructures Based on Two‐Dimensional Nanomaterials

Two‐dimensional (2D) nanomaterials, such as graphene and transition metal dichalcogenides (TMDs), receive a lot of attention, because of their intriguing properties and wide applications in catalysis, energy‐storage devices, electronics, optoelectronics, and so on. To further enhance the performance of their application, these 2D nanomaterials are hybridized with other functional nanostructures. In this review, the latest studies of 2D nanomaterial‐based hybrid nanostructures are discussed, focusing on their preparation methods, properties, and applications.     

Recent research progress of master mold manufacturing by nanoimprint technique for the novel microoptics devices

The consumer demand for emerging technologies such as augmented reality (AR), autopilot, and three-dimensional (3D) internet has rapidly promoted the application of novel optical display devices in innovative industries. However, the micro/nanomanufacturing of high-resolution optical display devices is the primary issue restricting their development. The manufacturing technology of micro/nanostructures, methods of display mechanisms, display materials, and mass production of display devices are major technical obstacles. To comprehensively understand the latest state-of-the-art and trigger new technological breakthroughs, this study reviews the recent research progress of master molds produced using nanoimprint technology for new optical devices, particularly AR glasses, new-generation light-emitting diode car lighting, and naked-eye 3D display mechanisms, and their manufacturing techniques of master molds. The focus is on the relationships among the manufacturing process, microstructure, and display of a new optical device. Nanoimprint master molds are reviewed for the manufacturing and application of new optical devices, and the challenges and prospects of the new optical device diffraction grating nanoimprint technology are discussed.     

Influence of hydrodynamic conditions on quantitative cellular assays in microfluidic systems

This study demonstrates the importance of the hydrodynamic environment in microfluidic systems in quantitative cellular assays using live cells. Commonly applied flow conditions used in microfluidics were evaluated using the quantitative intracellular Ca2+ analysis of Chinese hamster ovary (CHO) cells as a model system. Above certain thresholds of shear stress, hydrodynamically induced intracellular Ca2+ fluxes were observed which mimic the responses induced by chemical stimuli, such as the agonist uridine 5'-triphosphate tris salt (UTP). This effect is of significance given the increasing application of microfluidic devices in high-throughput cellular analysis for biophysical applications and pharmacological screening.     

Rapid Low‐Temperature 3D Integration of Silicon Nanowires on Flexible Substrates

The vertical integration of 1D nanostructures onto the 2D substrates has the potential to offer significant performance gains to flexible electronic devices due to high integration density, large surface area, and improved light absorption and trapping. A simple, rapid, and low temperature transfer bonding method has been developed for this purpose. Ultrasonic vibration is used to achieve a low temperature bonding within a few seconds, resulting in a polymer‐matrix‐free, electrically conducting vertical assembly of silicon nanowires (SiNWs) with a graphene/PET substrate. The microscopic structure, and mechanical and electrical characteristics of the interface between the transferred SiNW array and graphene layer are subsequently investigated, revealing that this creates a mechanically robust and electrically Ohmic contact. This newly developed ultrasonic transfer bonding technique is also found to be readily adaptable for diverse substrates of both metal and polymer. It is therefore considered as a valuable technique for integrating 1D vertical nanostructures onto the 2D flexible substrates for flexible photovoltaics, energy storage, and water splitting systems.     

Rapid and Low‐Cost Prototyping of 3D Nanostructures with Multi‐Layer Hydrogen Silsesquioxane Scaffolds

A layer‐by‐layer (LBL) method can generate or approximate any three‐dimensional (3D) structure, and has been the approach for the manufacturing of complementary metal‐oxide‐semiconductor (CMOS) devices. However, its high cost precludes the fabrication of anything other than CMOS‐compatible devices, and general 3D nanostructures have been difficult to prototype in academia and small businesses, due to the lack of expensive facility and state‐of‐the‐art tools. It is proposed and demonstrated that a novel process that can rapidly fabricate high‐resolution three‐dimensional (3D) nanostructures at low cost, without requiring specialized equipment. An individual layer is realized through electron‐beam lithography patterning of hydrogen silsesquioxane (HSQ) resist, followed by planarization via spinning SU‐8 resist and etch‐back. A 4‐layer silicon inverse woodpile photonic crystal with a period of 650 nm and a 7‐layer HSQ scaffold with a period of 300 nm are demonstrated. This process provides a versatile and accessible solution to the fabrication of highly complex 3D nanostructures.     

One‐Dimensional Nanostructures: Synthesis,Characterization, and Applications

This article provides a comprehensive review of current research activities that concentrate on one‐dimensional (1D) nanostructures—wires, rods, belts, and tubes—whose lateral dimensions fall anywhere in the range of 1 to 100 nm. We devote the most attention to 1D nanostructures that have been synthesized in relatively copious quantities using chemical methods. We begin this article with an overview of synthetic strategies that have been exploited to achieve 1D growth. We then elaborate on these approaches in the following four sections: i) anisotropic growth dictated by the crystallographic structure of a solid material; ii) anisotropic growth confined and directed by various templates; iii) anisotropic growth kinetically controlled by supersaturation or through the use of an appropriate capping reagent; and iv) new concepts not yet fully demonstrated, but with long‐term potential in generating 1D nanostructures. Following is a discussion of techniques for generating various types of important heterostructured nanowires. By the end of this article, we highlight a range of unique properties (e.g., thermal, mechanical, electronic, optoelectronic, optical, nonlinear optical, and field emission) associated with different types of 1D nanostructures. We also briefly discuss a number of methods potentially useful for assembling 1D nanostructures into functional devices based on crossbar junctions, and complex architectures such as 2D and 3D periodic lattices. We conclude this review with personal perspectives on the directions towards which future research on this new class of nanostructured materials might be directed.     

Three‐Dimensional Nanofabrication by Block Copolymer Self‐Assembly

Thin films of block copolymers are widely seen as enablers for nanoscale fabrication of semiconductor devices, membranes, and other structures, taking advantage of microphase separation to produce well‐organized nanostructures with periods of a few nm and above. However, the inherently three‐dimensional structure of block copolymer microdomains could enable them to make 3D devices and structures directly, which could lead to efficient fabrication of complex heterogeneous structures. This article reviews recent progress in developing 3D nanofabrication processes based on block copolymers.     

Synthesis and applications of one-dimensional semiconductors

Nanoscale inorganic materials such as quantum dots (0-dimensional) and one-dimensional (1D) structures, such as nanowires, nanobelts and nanotubes, have gained tremendous attention within the last decade. Among the huge variety of 1D nanostructures, semiconducting nanowires have gained particular interest due to their potential applications in optoelectronic and electronic devices. Despite the huge efforts to control and understand the growth mechanisms underlying the formation of these highly anisotropic structures, some fundamental phenomena are still not well understood. For example, high aspect-ratio semiconductors exhibit unexpected growth phenomena, e.g. diameter-dependent and temperature-dependent growth directions, and unusual high doping levels or compositions, which are not known for their macroscopic crystals or thin-film counterparts.This article reviews viable synthetic approaches for growing high aspect-ratio semiconductors from bottom-up techniques, such as crystal structure governed nucleation, metal-promoted vapour phase and solution growth, formation in non-metal seeded gas-phase processes, structure directing templates and electrospinning. In particular new experimental findings and theoretical models relating to the frequently applied vapour-liquid-solid (VLS) growth are highlighted. In addition, the top-down application of controlled chemical etching, using novel masking techniques, is described as a viable approach for generating certain 1D structures. The review highlights the controlled synthesis of semiconducting nanostructures and heterostructures of silicon, germanium, gallium nitride, gallium arsenide, cadmium sulphide, zinc oxide and tin oxide. The alignment of 1D nanostructures will be reviewed briefly. Whilst specific and reliable contact procedures are still a major challenge for the integration of 1D nanostructures as active building blocks, this issue will not be the focus of this paper. However, the promising applications of 1D semiconductors will be highlighted, particularly with reference to surface dependent electronic transduction (gas and biological sensors), energy generation (nanomechanical and photovoltaic) devices, energy storage (lithium storage in battery anodes) as well as nanowire photonics.