Cover Picture: Three‐Dimensional SiCN Ceramic Microstructures via Nano‐Stereolithography of Inorganic Polymer Photoresists (Adv. Funct. Mater. 9/2006)

An inorganic polymer photoresist was successfully synthesized for the first time with high photosensitivity and a high ceramic yield. Furthermore, it is shown by Kim, Yang, and co‐workers on p. 1235 that a nano‐stereolithography process linked with careful pyrolysis of this resin paves the way for the fabrication of 2D and 3D ceramic microstructures (examples of which are shown on the cover) with high spatial resolution. We report a newly synthesized inorganic polymer photoresist with a high ceramic yield by the functionalization of polyvinylsilazane (KiON VL20) with 2‐isocyanatoethyl methacrylate via linkage or insertion reaction routes. The chemistry of the synthesis and the pyrolytic conversion as well as the mechanical evaluation were investigated by using various analytical instruments. We show for the first time that this photosensitive resin is a novel precursor for the fabrication of complex 3D SiCN ceramic microstructures with a 210 nm resolution via a two‐photon absorbed crosslinking process and subsequent pyrolysis at 600 °C under a nitrogen atmosphere. Moreover, the dimensional deformation during pyrolysis was significantly reduced by adding silica nanoparticles as a filler. In particular, the ceramic microstructures containing 40 wt % silica nanoparticles exhibited a relatively isotropic shrinkage owing to its sliding free from the substrate during pyrolysis.     

Fabrication of Biofunctionalized Quasi‐Three‐Dimensional Microstructures of a Nonfouling Comb Polymer Using Soft Lithography

This paper describes a simple set of patterning methods that are applicable to diverse substrates and allow the routine and rapid fabrication of protein patterns embedded within a background that consists of quasi‐three‐dimensional microstructures of a cell‐resistant polymer. The ensemble of methods reported here utilizes three components to create topographically nonfouling polymeric structures that present cell‐adhesive protein patterns in the regions between the microstructures: the first component is an amphiphilic comb polymer that is comprised of a methyl methacrylate backbone and pendant oligo(ethylene glycol) moieties along the side chain, physically deposited films of which are protein‐ and cell‐resistant. The second component of the fabrication methodology involves the use of different variants of soft lithography, such as microcontact printing to create nonfouling topographical features of the comb polymer that demarcate cell‐adhesive regions of the third component: a cell‐adhesive extracellular protein or peptide. The ensemble of methods reported in this paper was used to fabricate quasi‐three‐dimensional patterns that present topographical and biochemical cues on a variety of substrates, and was shown to successfully maintain cellular patterns for up to two months in serum‐containing medium. We believe that this, and other such methods under development that allow independent and systematic control of chemistry, topography and substrate compliance will provide versatile “test‐beds” for fundamental studies in cell biology as well as allow the discovery of rational design principles for the development of biomaterials and tissue‐engineering scaffolds.     

Photodimerization of Coumarin‐Derived Pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane to Fabricate a Three‐Dimensional Organic–Inorganic Hybrid Material

An organic–inorganic hybrid material was prepared from a pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]octasiloxane bearing eight coumarin groups. The coumarin groups were photodimerized by UV‐light irradiation to connect the monomer units of the octasiloxane. Using a concentrated solution, the intermolecular photodimerization of these coumarin groups leaded to the cross‐linking of the octasiloxane, fabricating an organic–inorganic hybrid material with a three‐dimensional nanostructure. Whereas in dilute solution the intramolecular photodimerization was preferred to the intermolecular reaction, resulting in no formation of polymeric material.     

Fabrication and Characterization of Three‐Dimensional Silver‐Coated Polymeric Microstructures

A method is reported for fabricating complex 3D silver‐coated polymeric microstructures. The approach is based on the creation of a crosslinked polymeric microscaffold via patterned multiphoton‐initiated polymerization followed by surface‐nucleated electroless deposition of silver. The conductivity and reflectivity of the resulting silver–polymer composites and the nanoscale morphology of the deposited silver are characterized. Sub‐micrometer thick layers of silver can be controllably deposited onto surfaces, including those of 3D microporous forms without occluding the interior of the structure. The approach is general for silver coating crosslinked polymeric structures based on acrylate, methacrylate, and epoxide resins and provides a new path to complex 3D micrometer‐scale devices with electronic, photonic, and electromechanical function.     

Dimer‐Based Three‐Dimensional Photonic Crystals

The self‐assembly of polystyrene dimer‐ and spherocylinder‐shaped colloids is achieved via controlled drying on glass and silicon substrates. 3D monoclinic colloidal crystal structures are determined from scanning electron microscopy images of sections prepared using focused ion‐beam (FIB) milling. Full photonic bandgaps between the eighth and ninth bands are found for a systematic range of colloidal dimer shapes explored with respect to the degree of constituent lobe fusion and radius ratio. The pseudogap between bands 2 and 3 for spherocylinder‐based monoclinic crystals is also probed using normal incidence reflection spectroscopy.     

Streptavidin‐Functionalized Three‐Dimensional Ordered Nanoporous Silica Film for Highly Efficient Chemiluminescent Immunosensing

A novel biofunctionalized three‐dimensional ordered nanoporous SiO₂ film is designed for construction of chemiluminescent analytical devices. The nanoporous SiO₂ film is prepared with self‐assembly of polystyrene spheres as a template and 5‐nm SiO₂ nanoparticles on a glass slide followed by a calcination process. Its functionalization with streptavidin is achieved by using 3‐glycidoxypropyltrimethoxysilane as a linker. Based on the high‐selectivity recognition of streptavidin to biotin‐labeled antibody a novel immunosensor is further constructed for highly efficient chemiluminescent immunoassay. The surface morphologies and fabrication processes of both the biofunctionalized film and the immunosensor are characterized using scanning electron microscopy, atomic‐force microscopy, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The three‐dimensional ordered nanopores have high capacity for loading of streptavidin and antibody and promote the mass transport of immunoreagents for immunoreaction, thus the resulting chemiluminescent immunosensor shows wide dynamic range for fast immunoassay, and good reproducibility and stability. Using carbohydrate antigen 125 (CA 125) as a model, the highly efficient chemiluminescent immunosensing shows a linear range of three orders of magnitude, from 0.5 to 400 U mL^?1. This work provides a biofunctionalized porous nanostructure for promising biosensing applications.     

3D Micro‐ and Nanostructures via Interference Lithography

Interference lithography (IL) holds the promise of fabricating large‐area, defect‐free 3D structures on the submicrometer scale both rapidly and cheaply. A stationary spatial variation of intensity is created by the interference of two or more beams of light. The pattern that emerges out of the intensity distribution is transferred to a light sensitive medium, such as a photoresist, and after development yields a 3D bicontinuous photoresist/air structure. Importantly, by a proper choice of beam parameters one can control the geometrical elements and volume fraction of the structures. This article provides an overview of the fabrication of 3D structures via IL (e.g., the formation of interference patterns, their dependence on beam parameters and several requirements for the photoresist) and highlights some of our recent efforts in the applications of these 3D structures in photonic crystals, phononic crystals and as microframes, and for the synthesis of highly non spherical polymer particles. Our discussion concludes with perspectives on the future directions in which this technique could be pursued.     

Multiphoton Lithography of Unconstrained Three‐Dimensional Protein Microstructures

Multiphoton lithography (MPL) is a highly versatile strategy for creating 3D microscale objects with complex geometrical arrangements, including nested boxes, interlocking blocks, and braided threads. Of the various chemistries used to produce solid forms in MPL, protein photocrosslinking has been of particular value in biological applications, yielding materials with high porosity, tunable elasticity, and a diverse set of chemical and biochemical properties. Unfortunately, the potential for object drift, and consequent distortion, during this direct‐write process has required that microforms be constructed in integral contact with an immobile surface, precluding fabrication of protein‐based objects that retain rotational and translational degrees of freedom. Here, the development of a high‐viscosity protein‐based reagent that can be used to fabricate complex 3D microstructures that are not adhered to a surface, including chains of Möbius strips, paddlewheels, and unconstrained (free‐floating) probes for bacterial motility, is reported.     

The Elastic Properties and Plastic Behavior of Two‐Dimensional Polymer Structures Fabricated by Laser Interference Lithography

The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern.     

Three‐Dimensional Inkjet‐Printed Interconnects using Functional Metallic Nanoparticle Inks

Inkjet‐printed gold nanoparticle pillars are investigated as a high‐performance alternative to conventional flip‐chip interconnects for electronic packages, with significant advantages in terms of mechanical/chemical robustness and conductivity. The process parameters critical to pillar fabrication are described and highly uniform pillar arrays are demonstrated. More generally, this work underscores the impact of sintering on the electrical, mechanical, structural, and compositional properties of three‐dimensional nanoparticle‐based structures. Using heat treatments as low as 200 °C, electrical and mechanical performance that outcompetes conventional lead‐tin eutectic solder materials is achieved. With sintering conditions reaching 300 °C it is possible to achieve pillars with properties comparable to bulk gold. This work demonstrates the immense potential for both inkjet printing and metal nanoparticles to become a viable and cost‐saving alternative to both conventional electronic packaging processes and application‐specific integration schemes.     

New TDOA‐Based Three‐Dimensional Positioning Method for 3GPP LTE System

Recently, mobile positioning enhancement has attracted much attention in the 3rd generation partnership project long‐term evolution system. In particular, for urban canyon environments, the need for three‐dimensional (3D) positioning has increased to enable the altitude of users to be measured. For several decades, several time difference of arrival (TDOA‐) based 3D positioning methods have been studied; however, they are only available when at least four evolved Node Bs (eNBs) exist nearby or when all eNBs have the same height. Therefore, in this paper, we propose a new 3D positioning method that estimates the 3D coordinates of a user using three types of two‐dimensional (2D) TDOAs. However, the give inaccurate results owing to the undefined axis of the 2D coordinate plane. Therefore, we propose a novel derivation of the hyperbola equation, which includes the undefined axis coordinate in the 2D hyperbola equation. Then, we propose an interaction algorithm that mutually supplies the undefined axis coordinate of users among 2D TDOAs. By performing extensive simulations, we verify that the proposed method is the only solution applicable by using three eNBs with different heights.     

Highly Conductive Nanocomposites with Three‐Dimensional,Compactly Interconnected Graphene Networks via a Self‐Assembly Process

Polymer‐based materials with high electrical conductivity are of considerable interest because of their wide range of applications. The construction of a 3D, compactly interconnected graphene network can offer a huge increase in the electrical conductivity of polymer composites. However, it is still a great challenge to achieve desirable 3D architectures in the polymer matrix. Here, highly conductive polymer nanocomposites with 3D compactly interconnected graphene networks are obtained using a self‐assembly process. Polystyrene (PS) and ethylene vinyl acetate (EVA) are used as polymer matrixes. The obtained PS composite film with 4.8 vol% graphene shows a high electrical conductivity of 1083.3 S/m, which is superior to that of the graphene composite prepared by a solvent mixing method. The electrical conductivity of the composites is closely related to the compact contact between graphene sheets in the 3D structures and the high reduction level of graphene sheets. The obtained EVA composite films with the 3D graphene structure not only show high electrical conductivity but also exhibit high flexibility. Importantly, the method to fabricate 3D graphene structures in polymer matrix is facile, green, low‐cost, and scalable, providing a universal route for the rational design and engineering of highly conductive polymer composites.     

Evaluating Internet Pricing Schemes: A Three‐Dimensional Visual Model

Traditional Internet pricing schemes are coming under continual pressure to adapt to, and encourage, a changing mix of Internet applications and consumer usage patterns. Much research effort over the last decade has been focused on developing more efficient and attractive charging schemes. However, none of the proposed models has been widely deployed. This raises questions regarding the inhibiting factors and missing pieces that make pricing the Internet such a challenge. In this paper, we discuss the problems with current Internet pricing schemes, review the history of Internet pricing research over the last ten years, and summarize the key features and motivations of the most significant models. We develop a novel visual approach to comparing and evaluating such schemes using a three‐dimensional (3D) metric encompassing technical efficiency, economic efficiency, and social impact. We address and discuss the important factors that have inhibited the deployment of the reviewed models and suggest productive areas of focus for future Internet pricing research.     

Dual‐Functionalized Polymer Nanotubes as Substrates for Molecular‐Probe and DNA‐Carrier Applications

Bifunctionalized polymer nanotubes have been fabricated using vapor‐deposition polymerization in FeCl₃‐adsorbed anodic aluminum oxide membranes followed by attachment of amine‐functionalized silica nanoparticles. The prepared bifunctionalized polymer nanotubes are applied as both a molecular probe and a DNA carrier by conjugating pyreneacetic acid with the amine groups and immobilizing DNA with the carboxylic acid groups on the surface. The number of amine functional groups on the nanotubes' surface can be measured by means of the photoluminescence intensity of pyreneacetic acid conjugated with amine groups, and the number of the residual carboxylic acid groups is calculated by titration with sodium hydroxide. Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy have been performed to confirm the complete polymerization of the monomer and the attachment of photoluminescent molecules and single‐stranded DNA.     

Three‐Dimensional Porous Copper–Tin Alloy Electrodes for Rechargeable Lithium Batteries

Three‐dimensional (3D) foam structure of a Cu₆Sn₅ alloy was fabricated via an electrochemical deposition process. The walls of the foam structure are highly porous and consist of numerous small grains. When used as a negative electrode for a rechargeable lithium battery, the Cu₆Sn₅ samples delivered a reversible capacity of about 400 mA h g^–1 up to 30 cycles. Further, these materials exhibit superior rate capability, attributed primarily to the unique porous structure and the large surface area for fast mass transport and rapid surface reactions. For instance, at a current drain of 10 mA cm^–2 (20C rate), the obtainable capacity (220 mA h g^–1) was more than 50 % of the capacity at 0.5 mA cm^–2 (1C rate).     

Three‐Dimensional Printing of Elastomeric,Cellular Architectures with Negative Stiffness

Three‐dimensional printing of viscoelastic inks to create porous, elastomeric architectures with mechanical properties governed by the ordered arrangement of their sub‐millimeter struts is reported. Two layouts are patterned, one resembling a “simple cubic” (SC)‐like structure and another akin to a “face‐centered tetragonal” (FCT) configuration. These structures exhibit markedly distinct load response with directionally dependent behavior, including negative stiffness. More broadly, these findings suggest the ability to independently tailor mechanical response in cellular solids via micro‐architected design. Such ordered materials may one day replace random foams in mechanical energy absorption applications.     

Fabrication of Hollow Inorganic Microspheres by Chemically Induced Self‐Transformation

Two contrasting approaches, involving either polymer‐mediated or fluoride‐mediated self‐transformation of amorphous solid particles, are described as general routes to the fabrication of hollow inorganic microspheres. Firstly, calcium carbonate and strontium tungstate hollow microspheres are fabricated in high yield using sodium poly(4‐styrenesulfonate) as a stabilizing agent for the formation and subsequent transformation of amorphous primary particles. Transformation occurs with retention of the bulk morphology by localized Ostwald ripening, in which preferential dissolution of the particle interior is coupled to the deposition of a porous external shell of loosely packed nanocrystals. Secondly, the fabrication process is extended to relatively stable amorphous microspheres, such as TiO₂ and SnO₂, by increasing the surface reactivity of the solid precursor particles. For this, fluoride ions, in the form of NH₄F and SnF₂, are used to produce well‐defined hollow spheroids of nanocrystalline TiO₂ and SnO₂, respectively. Our results suggest that the chemical self‐transformation of precursor objects under morphologically invariant conditions could be of general applicability in the preparation of a wide range of nanoparticle‐based hollow architectures for technological and biomedical applications.     

Resolving the Three‐Dimensional Microstructure of Polymer Electrolyte Fuel Cell Electrodes using Nanometer‐Scale X‐ray Computed Tomography

The electrodes of a polymer electrolyte fuel cell (PEFC) are composite porous layers consisting of carbon and platinum nanoparticles and a polymer electrolyte binder. The proper composition and arrangement of these materials for fast reactant transport and high electrochemical activity is crucial to achieving high performance, long lifetimes, and low costs. Here, the microstructure of a PEFC electrode using nanometer‐scale X‐ray computed tomography (nano‐CT) with a resolution of 50 nm is investigated. The nano‐CT instrument obtains this resolution for the low‐atomic‐number catalyst support and binder using a combination of a Fresnel zone plate objective and Zernike phase contrast imaging. High‐resolution, non‐destructive imaging of the three‐dimensional (3D) microstructures provides important new information on the size and form of the catalyst particle agglomerates and pore spaces. Transmission electron microscopy (TEM) and mercury intrusion porosimetry (MIP) is applied to evaluate the limits of the resolution and to verify the 3D reconstructions. The computational reconstructions and size distributions obtained with nano‐CT can be used for evaluating electrode preparation, performing pore‐scale simulations, and extracting effective morphological parameters for large‐scale computational models.     

Using SERS Tags to Image the Three‐Dimensional Structure of Complex Cell Models

Methods to image complex 3D cell cultures are limited by issues such as fluorophore photobleaching and decomposition, poor excitation light penetration, and lack of complementary techniques to verify the 3D structure. Although it remains insufficiently demonstrated, surface‐enhanced Raman scattering (SERS) imaging is a promising tool for the characterization of biological complex systems. To this aim, a controllable 3D cell culture model which spans nearly 1 cm² in surface footprint is designed. This structure is composed of fibroblasts containing SERS‐encoded nanoparticles (i.e., SERS tags), arranged in an alternating layered structure. This “sandwich” type structure allows monitoring of the SERS signals in the z‐axis and with mm dimensions in the xy‐axis. Taking advantage of correlative microscopy techniques such as electron microscopy, it is possible to corroborate nanoparticle positioning and distances in z‐depths of up to 150 µm. This study reveals a proof‐of‐concept method for detailed 3D SERS imaging of a complex, dense 3D cell culture model.     

Three‐Dimensional Bulk Heterojunction Morphology for Achieving High Internal Quantum Efficiency in Polymer Solar Cells

Here, an investigation of three‐dimensional (3D) morphologies for bulk heterojunction (BHJ) films based on regioregular poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) is reported. Based on the results, it is demonstrated that optimized post‐treatment, such as solvent annealing, forces the PCBM molecules to migrate or diffuse toward the top surface of the BHJ composite films, which induces a new vertical component distribution favorable for enhancing the internal quantum efficiency (η_IQE ) of the devices. To investigate the 3D BHJ morphology, novel time‐of‐flight secondary‐ion mass spectroscopy studies are employed along with conventional methods, such as UV‐vis absorption, X‐ray diffraction, and high‐resolution transmission electron microscopy studies. The η_IQE of the devices are also compared after solvent annealing for different times, which clearly shows the effect of the vertical component distribution on the performance of BHJ polymer solar cells. In addition, the fabrication of high‐performance P3HT:PCBM solar cells using the optimized solvent‐annealing method is reported, and these cells show a mean power‐conversion efficiency of 4.12% under AM 1.5G illumination conditions at an intensity of 100 mW cm^?2.