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.     

Chitosan Hydrogel‐Capped Porous SiO2 as a pH Responsive Nano‐Valve for Triggered Release of Insulin

A pH responsive, chitosan‐based hydrogel film is used to cap the pores of a porous SiO₂ layer. The porous SiO₂ layer is prepared by thermal oxidation of an electrochemically etched Si wafer, and the hydrogel film is prepared by reaction of chitosan with glycidoxypropyltrimethoxysilane (GPTMS). Optical reflectivity spectroscopy and scanning electron microscopy (SEM) confirm that the bio‐polymer only partially infiltrates the porous SiO₂ film, generating a double layer structure. The optical reflectivity spectrum displays Fabry–Pérot interference fringes characteristic of a double layer, which is characterized using reflective interferometric Fourier transform spectroscopy (RIFTS). Monitoring the position of the RIFTS peak corresponding to the hydrogel layer allows direct, real‐time observation of the reversible volume phase transition of the hydrogel upon cycling of pH in the range 6.0–7.4. The swelling ratio and response time are controlled by the relative amount of GPTMS in the hydrogel. The pH‐dependent volume phase transition can be used to release insulin trapped in the porous SiO₂ layer underneath the hydrogel film. At pH 7.4, the gel in the top layer effectively blocks insulin release, while at pH 6.0 insulin penetrates the swollen hydrogel layer, resulting in a steady release into solution.     

Direct Threat of a UV‐Ozone Treated Indium‐Tin‐Oxide Substrate to the Stabilities of Common Organic Semiconductors

Ultraviolet‐ozone treated indium‐tin‐oxide (UV‐ITO) glass substrates have been widely and unquestioningly used in the field of organic electronics to improve both device performance and stability. Evidence is presented here for rapid decay of common organic films such as N,N′‐bis(naphthalen‐1‐ yl)‐N,N′‐bis(phenyl)‐benzidine (NPB), tris(8‐hydroxy‐quinolinato)aluminum (Alq₃), and rubrene when they are in contact with an UV‐ITO substrate. While the photoluminescence (PL) of these organic films deposited on an UV‐ITO substrate decay rapidly under illumination; those on quartz substrates are comparatively much more stable. Results from X‐ray and UV photoemission spectroscopies (XPS and UPS) further suggest that degradations of the rubrene films on UV‐ITO substrate are mainly attributed to active oxygen species generated upon UV‐ozone treatment. These reactive oxygen species on the UV‐ITO surface behave as a reservoir of oxygen that interacts with rubrene and shifts its highest occupied molecular orbital (HOMO) level away from the Fermi level. This interaction induces a gap‐state in the energy gap of rubrene, which acts as a charge recombination center. More importantly, enhanced stabilities of rubrene‐based organic photovoltaic (OPV) devices are demonstrated when they are fabricated on gold‐coated or trifluoromethane (CHF₃) plasma‐treated ITO. The presented works shows that the commonly used UV‐ITO substrate is a threat to the stability of addlayer organic semiconducting films.     

Laser‐Induced Direct Lithography for Patterning of Carbon with sp3 and sp2 Hybridization

A new method of laser‐induced lithography for direct writing of carbon on a glass surface is described, in which deposition occurs from a transparent precursor solution. At the glass–solution interface where the laser spot is focused, a micro‐explosion process takes place, leading to the deposition of pure carbon on the glass surface. Transmission electron microscopy (TEM) analysis shows two distinct co‐existing phases. The dominant one shows a mottled morphology with diffraction typical of cubic (sp³) diamond. The other region shows an ordered array of graphene sheets with diffraction pattern typical of sp²‐bonded carbon. The sp³ crystallites range in size from 9 to 30 Å and are scattered randomly throughout the sample. A UV Raman spectrum shows a broad band at the location of the expected diamond peak, together with a peak corresponding to the graphite region. We conclude that the patterned carbon is composed of a mixture of nanocrystalline sp³ and sp² carbon forms.     

Cell Adhesion and Cellular Patterning on a Self‐Assembled Monolayer of Zeolite L Crystals

Chemically functionalized self‐assembled monolayers made by disk‐shaped zeolite L nanocrystals are used as models for biocompatible surfaces to study cell‐adhesion behavior. Different chemical groups lead to different cellular behavior and fluorescent‐molecule‐loaded zeolites allow the position of the cells to be determined. Furthermore, a patterned monolayer of asymmetrically functionalized zeolite L obtained by microcontact chemistry is used to grow cells. A spatial recognition of the cells, which proliferate only on the bioactive‐molecule‐functionalized stripes, is possible.     

Periodically Ordered Meso‐ and Macroporous SiO2 Thin Films and Their Induced Electrochemical Activity as a Function of Pore Hierarchy

Silica thin films with variable pore hierarchy (different combinations of small meso‐, large meso‐, and macropores) were produced via evaporation induced self‐assembly in a one‐pot synthesis. A suitable block copolymer and an ionic liquid served as porogens for the generation of different types of mesopores whereas polymethylmethacrylate particles were used as macrotemplate. The silica architectures were characterized by various state‐of‐the‐art techniques, such as 2D‐SAXS, TEM, SEM, AFM, krypton and nitrogen sorption. Moreover, electrochemical functionalization was utilized as a tool to study the hierarchy‐property relationship. Thus, hierarchically porous films prepared on FTO‐coated glass were post‐synthetically silylated and electrochemically active ferrocene groups subsequently grafted onto the pore walls. Cyclic voltammetry was used to monitor the induced electrochemical activity as a function of variations in the pore hierarchy. It turned out that multimodal pore systems possess a relatively higher electrochemical response due to better connection between the pores and higher surface area.     

Highly Dispersed Mixed Zirconia and Hafnia Nanoparticles in a Silica Matrix: First Example of a ZrO2–HfO2–SiO2 Ternary Oxide System

ZrO₂ and HfO₂ nanoparticles are homogeneously dispersed in SiO₂ matrices (supported film and bulk powders) by copolymerization of two oxozirconium and oxohafnium clusters (M₄O₂(OMc)₁₂, M = Zr, Hf; OMc = OC(O)–C(CH₃)?CH₂) with (methacryloxypropyl)trimethoxysilane (MAPTMS, (CH2?C(CH₃)C(O)O)–(CH₂)₃Si(OCH₃)₃). After calcination (at a temperature ≥800 °C), a silica matrix with homogeneously distributed MO₂ nanocrystallites is obtained. This route yields a spatially homogeneous dispersion of the metal precursors inside the silica matrix, which is maintained during calcination. The composition of the films and the powders is studied before and after calcination by using Fourier transform infrared (FTIR) analysis, X‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS). The local environment of the metal atoms in one of the calcined samples is investigated by using X‐ray Absorption Fine Structure (XAFS) spectroscopy. Through X‐ray diffraction (XRD) the crystallization of Hf and Zr oxides is seen at temperatures higher than those expected for the pure oxides, and transmission electron microscopy (TEM) shows the presence of well‐distributed and isolated crystalline oxide nanoparticles (5–10 nm).     

Dual Roles of Graphene Oxide in Chondrogenic Differentiation of Adult Stem Cells: Cell‐Adhesion Substrate and Growth Factor‐Delivery Carrier

Here, it is shown that graphene oxide (GO) can be utilized as both a cell‐adhesion substrate and a growth factor protein‐delivery carrier for the chondrogenic differentiation of adult stem cells. Conventionally, chondrogenic differentiation of stem cells is achieved by culturing cells in pellets and adding the protein transforming growth factor‐β3 (TGF‐β3), a chondrogenic factor, to the culture medium. However, pellets mainly provide cell‐cell interaction and diffusional limitation of TGF‐β3 may occur inside the pellet both of these factors may limit the chondrogenic differentiation of stem cells. In this study, GO sheets (size = 0.5–1 μm) were utilized to adsorb fibronectin (FN, a cell‐adhesion protein) and TGF‐β3 and were then incorporated in pellets of human adipose‐derived stem cells (hASCs). The hybrid pellets of hASC‐GO enhanced the chondrogenic differentiation of hASCs by adding the cell‐FN interaction and supplying TGF‐β3 effectively. This method may provide a new platform for stem cell culture for regenerative medicine.     

Highly Robust Bendable Oxide Thin‐Film Transistors on Polyimide Substrates via Mesh and Strip Patterning of Device Layers

Advancement in thin‐film transistor (TFT) technologies has extended to applications that can withstand extreme bending or folding. The changes of the performances of amorphous‐indium‐gallium‐zinc‐oxide (a‐IGZO) TFTs on polyimide substrate after application of extreme mechanical bending strain are studied. The TFT designs include mesh and strip patterned source/drain metal lines as well as strip patterned a‐IGZO semiconductor layer. The robustness of the a‐IGZO TFTs with the strain of 2.17% corresponding to the radius of 0.32 mm is tested and no crack generation even after 60 000 bending cycles is found. The split of source/drain electrodes and semiconductor layer can improve the mechanical bending stability of the TFTs. This can be possible by using conventional TFT manufacturing process so that this technology can be easily applied to build robust TFT array for foldable displays.     

Magnetic‐Core/Porous‐Shell CoFe2O4/SiO2 Composite Nanoparticles as Immobilized Affinity Supports for Clinical Immunoassays

This study demonstrates a novel approach towards the development of advanced protein assay systems based on physically functionalized, magnetic‐core/porous‐shell CoFe₂O₄/SiO₂ composite nanoparticles. The preparation, characterization, and measurement of the relevant properties of the protein assay system is discussed, and the system is used for the detection of cancer antigen 15‐3 (CA 15‐3, used as a model here) in clinical immunoassays. The protein assay system, based on nanometer‐sized magnetic cores and silica shells, shows good adsorption properties for the selective attachment of CA 15‐3 antibodies specific to CA 15‐3. The core/shell nanostructures exhibit good magnetic properties, which enables their integration into a quartz crystal microbalance (QCM) detection cell with the help of a permanent magnet. Under optimal conditions, the resulting immunoassay system presents a good QCM response for the detection of CA 15‐3, and allows the detection of CA 15‐3 at concentrations as low as 1.5 U mL^–1 (U: units). Importantly, the proposed protein assay system can be extended to the detection of other antigens and biological compounds.     

Growth Behavior of Cubic Boron Nitride Films in a Two‐Step Process: Changing Bias Voltage,Gas Composition,and Substrate Temperature

In the deposition of cubic boron nitride (cBN) films by DC‐bias‐assisted DC jet chemical vapor deposition in an Ar–N₂–BF₃–H₂ gas system, the balance between growth and etching and its relation to the deposition conditions were investigated. A two‐step process was designed to optimize the nucleation and growth separately, and a critical bias voltage for the growth of cBN after nucleation was observed. It was found that etching occurred when the bias voltage was below this critical value. Under optimized conditions, the crystallinity and crystal size of the cBN films were improved during the second step. Furthermore, cBN films showing clear crystal facets were obtained.     

Direct Patterning of Self‐Assembled Monolayers by Stamp Printing Method and Applications in High Performance Organic Field‐Effect Transistors and Complementary Inverters

Self‐assembled monolayer (SAM) is usually applied to tune the interface between dielectric and active layer of organic field‐effect transistors (OFETs) and other organic electronics, a time‐saving, direct patterning approach of depositing well‐ordered SAMs is highly desired. Here, a new direct patterning method of SAMs by stamp printing or roller printing with special designed stamps is introduced. The chemical structures of the paraffin hydrocarbon molecules and the tail groups of SAMs have allowed to use their attractive van der Waals force for the direct patterning of SAMs. Different SAMs including alkyl and fluoroalkyl silanes or phosphonic acids are used to stamp onto different dielectric surfaces and are characterized by water contact angle, atomic force microscopy, X‐ray diffraction, and attenuated total reflectance Fourier transform infrared. The p‐type dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) and n‐type F₁₆CuPc OFETs show competitive mobility as high as 3 and 0.018 cm² V^?1 s^?1, respectively. This stamp printing method also allows to deposit different SAMs on certain regions of same substrate, and the complementary inverter consists of both p‐type and n‐type transistors whose threshold voltages are tuned by stamp printing SAMs and shows a gain higher than 100. The proposed stamp or roller printing method can significantly reduce the deposition time and compatible with the roll‐to‐roll fabrication.     

Silica Nanocasting of Simple Cellulose Derivatives: Towards Chiral Pore Systems with Long‐Range Order and Chiral Optical Coatings

Aqueous solutions of hydroxypropyl cellulose with cholesteric superstructures were employed as templates in a silica nanocasting process, and the resulting pore structures were characterized by polarization microscopy, circular dichroism, X‐ray scattering, transmission electron microscopy, and sorption measurements. Whereas the local pore architecture corresponds to a cast of single cellulose strands and their statistical aggregates, the averaged structure on larger scales keeps the cholesteric character, with the cholesteric pitch just slightly shortened.     

Transparent Nanocomposites of Radiopaque,Flame‐Made Ta2O5/SiO2 Particles in an Acrylic Matrix

Mixed Ta₂O₅‐containing SiO₂ particles, 6–14 nm in diameter, with closely controlled refractive index, transparency, and crystallinity are prepared via flame spray pyrolysis (FSP) at production rates of 6.7–100 g h^–1. The effect of precursor solution composition on product filler (particle) size, crystallinity, Ta dispersity, and transparency is studied using nitrogen adsorption, X‐ray diffraction, optical microscopy, high‐resolution transmission electron microscopy (HRTEM), and diffuse‐reflectance infrared Fourier‐transform spectroscopy (DRIFTS). Emphasis is placed on the transparency of the composite that is made with Ta₂O₅/SiO₂ filler and dimethylacrylate. Increasing Ta₂O₅ crystallinity and decreasing Ta dispersity on SiO₂ decreases both filler and composite transparencies. Powders with identical specific surface area (SSA), refractive index (RI), and Ta₂O₅ content (24 wt.‐%) show a wide range of composite transparencies, 33–78 %, depending on filler crystallinity and Ta dispersity. Amorphous fillers with a high Ta dispersity and an RI matching that of the polymer matrix lead to the highest composite transparency, 86 %. The composite containing 16.5 wt.‐% filler that itself contains 35 wt.‐% Ta₂O₅ has the optimal radiopacity for dental fillings.     

Original Fuel‐Cell Membranes from Crosslinked Terpolymers via a “Sol–gel” Strategy

Hybrid organic/inorganic membranes that include a functionalized (‐SO₃H), interconnected silica network, a non‐porogenic organic matrix, and a ‐SO₃H‐functionalized terpolymer are synthesized through a sol–gel‐based strategy. The use of a novel crosslinkable poly(vinylidene fluoride‐ter‐perfluoro(4‐methyl‐3,6‐dioxaoct‐7‐ene sulfonyl fluoride)‐ter‐vinyltriethoxysilane) (poly(VDF‐ter‐PFSVE‐ter‐VTEOS)) terpolymer allows a multiple tuning of the different interfaces to produce original hybrid membranes with improved properties. The synthesized terpolymer and the composite membranes are characterized, and the proton conductivity of a hybrid membrane in the absence of the terpolymer is promising, since 8 mS cm^?1 is reached at room temperature, immersed in water, with an experimental ion‐exchange‐capacity (IEC_exp) value of 0.4 meq g^?1. Furthermore, when the composite membranes contain the interfaced terpolymer, they exhibit both a higher proton conductivity (43 mS cm^?1 at 65 °C under 100% relative humidity) and better stability than the standard hybrid membrane, arising from the occurrence of a better interface between the inorganic silica and the poly[(vinylidene fluoride)‐co‐hexafluoropropylene] (poly(VDF‐co‐HFP)) copolymer network. Accordingly, the hybrid SiO₂‐SO₃H/terpolymer/poly(VDF‐co‐HFP) copolymer membrane has potential use as an electrolyte in a polymer‐electrolyte‐membrane fuel cell operating at intermediate temperatures.     

Autonomously Controlled Homogenous Growth of Wafer‐Sized High‐Quality Graphene via a Smart Janus Substrate

The work reports a new method for large‐area growth of graphene films, which have been predicted to have novel and broad applications in the future. While chemical vapor deposition (CVD) is currently the preferred method, it suffers from a rather narrow processing window, and there is also much to be desired in the electrical properties of the CVD films. A new method for large‐area growth of graphene films is reported to overcome the narrow processing window of the CVD method. A composite substrate made of a C‐dissolving top (Ni) layer and a C‐rejecting bottom (Cu) layer is designed, which evolves into a C‐rejecting mixture, to autonomously regulate the C content at an elevated yet stable level at and near the surface over an extended duration. This “smart” substrate promotes graphene formation over a wide temperature‐gas composition window, leading to reliable growth of wafer‐sized graphene films of defined layer‐thickness and superior electrical–optical properties. This “smart”‐substrate strategy can also be implemented on Si and SiO₂ supports, paving the way toward the direct fabrication of large area, graphene‐enabled electronic and photonic devices.     

A Multiple‐Functional Ag/SiO2/Organic Based Biomimetic Nanocomposite Membrane for High‐Stability Protein Recognition and Cell Adhesion/Detachment

Biomimetic multilevel structured membrane materials have great potential for energy‐efficient chemical separations and biomedical applications. The current study represents a simple, yet efficient, method to obtain the biomimetic protein separation membrane and controllable cell culture substrate with high stability, selectivity, and antibacterial property. Here, a molecular imprinting methodology is reported to introduce the high‐biocompatible protein ovalbumin (Ova) to a multilevel Ag/SiO₂/organic based molecularly imprinted membranes (ASO‐MIMs), which have made significant achievements in protein identification and controllable growth of liver cells in vitro platform. Interestingly, the relative morphological observations of the adhered cells and in vitro viability tests show no significant difference between the ASO‐MIMs binding with 13.6 mg g^?1 Ova (13.6‐ASO‐MIMs) and bare glass, indicating the excellent biocompatibility of the 13.6‐ASO‐MIMs. Here, the results on largely enhanced adsorption capacity, perm‐selectivity (β values are more than 2.2), regeneration ability (still maintained 90% of the maximum adsorption capacity after 10 cycling operation), and high‐performance cell adhesion system (controlled by the binding amount of template protein) are shown, which clearly demonstrates the potential value of this method in smart biomaterials and biosensors.     

Tuning Anionic Redox Activity and Reversibility for a High‐Capacity Li‐Rich Mn‐Based Oxide Cathode via an Integrated Strategy

When fabricating Li‐rich layered oxide cathode materials, anionic redox chemistry plays a critical role in achieving a large specific capacity. Unfortunately, the release of lattice oxygen at the surface impedes the reversibility of the anionic redox reaction, which induces a large irreversible capacity loss, inferior thermal stability, and voltage decay. Therefore, methods for improving the anionic redox constitute a major challenge for the application of high‐energy‐density Li‐rich Mn‐based cathode materials. Herein, to enhance the oxygen redox activity and reversibility in Co‐free Li‐rich Mn‐based Li_1.2Mn_0.6Ni_0.2O₂ cathode materials by using an integrated strategy of Li₂SnO₃ coating‐induced Sn doping and spinel phase formation during synchronous lithiation is proposed. As an Li⁺ conductor, a Li₂SnO₃ nanocoating layer protects the lattice oxygen from exposure at the surface, thereby avoiding irreversible oxidation. The synergy of the formed spinel phase and Sn dopant not only improves the anionic redox activity, reversibility, and Li⁺ migration rate but also decreases Li/Ni mixing. The 1% Li₂SnO₃‐coated Li_1.2Mn_0.6Ni_0.2O₂ delivers a capacity of more than 300 mAh g^?1 with 92% Coulombic efficiency. Moreover, improved thermal stability and voltage retention are also observed. This synergic strategy may provide insights for understanding and designing new high‐performance materials with enhanced reversible anionic redox and stabilized surface lattice oxygen.     

Generation of Monodisperse,Shape‐Controlled Single and Hybrid Core–Shell Nanoparticles via a Simple One‐Step Process

In nano‐biotechnology, optoelectronics, and energy research areas, various fabrication methods have been developed for hybrid nanoparticles. A method is developed here for fabricating highly monodisperse three‐dimensional hybrid nanoparticles using a unique top‐down method based on secondary sputtering lithography. Nanostructures that have been formed on a PEDOT sacrificial layer are transferred from the substrate to an aqueous solution in a process that could be used to successfully disperse a variety of nanoparticle shapes and hybrid nanoparticles. By this method, a fluorescent dye could be encapsulated within the fabricated hybrid nanoparticles for use in bio‐sensing and drug‐delivery applications     

On‐the‐Spot Immobilization of Quantum Dots,Graphene Oxide,and Proteins via Hydrophobins

Class I hydrophobin Vmh2, a peculiar surface active and versatile fungal protein, is known to self‐assemble into chemically stable amphiphilic films, to be able to change wettability of surfaces, and to strongly adsorb other proteins. Herein, a fast, highly homogeneous and efficient glass functionalization by spontaneous self‐assembling of Vmh2 at liquid–solid interfaces is achieved (in 2 min). The Vmh2‐coated glass slides are proven to immobilize not only proteins but also nanomaterials such as graphene oxide (GO) and quantum dots (QDs). As models, bovine serum albumin labeled with Alexa 555 fluorophore, anti‐immunoglobulin G antibodies, and cadmium telluride QDs are patterned in a microarray fashion in order to demonstrate functionality, reproducibility, and versatility of the proposed substrate. Additionally, a GO layer is effectively and homogeneously self‐assembled onto the studied functionalized surface. This approach offers a quick and simple alternative to immobilize nanomaterials and proteins, which is appealing for new bioanalytical and nanobioenabled applications.