Guiding the Dewetting of Thin Polymer Films by Colloidal Imprinting

Micropatterned surfaces are important in many biomedical and bioengineering applications, such as the development of biosensors. An approach for the creation of ordered surface patterns, fabricated combining colloidal crystals, consisting of ordered layers of micrometric particles, with dewetting of bilayers of thin polymer films is introduced. The produced patterns are both topographical and chemical in nature, consisting of ordered arrays of microscale holes imprinted in a polymer film, with tunable size. The spontaneous dewetting of the polymer film enables this tunability, with a maximum sevenfold increase in lateral size of the holes and sixfold increase in depth from imprinting to coalescence with neighboring holes. Polymer dewetting and layer inversion are seen to compete during the annealing of the polymer bilayers, and the optimal conditions for hole growth are identified. An in‐depth investigation highlights the effects of UV‐ozone treatment on the long‐range ordering of the colloidal crystals and on preventing the dewetting of the imprinted bilayers. Ordered patterns of different size and depth are produced over large areas by tuning of the colloidal crystal assembly, UV surface treatment and dewetting conditions. Potential applications of the micropatterns produced in the present work include microarrays for single cell studies and biosensors.     

Gold Binary‐Structured Arrays Based on Monolayer Colloidal Crystals and Their Optical Properties

A simple and flexible route is presented to fabricate a gold binary‐structured ordered array by one step based on non‐shadow deposition on a plasma etching‐induced dualistic monolayer colloidal crystal. Such a Au binary‐structure array is built of hexagonally arranged nanoshells and nanorings which stand between two adjacent nanoshells. Six gold nanorings surround each nanoshell. The obtained arrays exhibit both the controllable surface‐plasmon‐resonance (SPR) properties of Au nanoshells and the strong electromagnetic‐field‐enhancement effects of Au nanorings, with the high structural stability of ordered arrays, and show promising potential as the substrate of surface‐enhanced Raman scattering (SERS)‐based devices. The method could also be suitable for fabrication of other material binary‐structured arrays. This study is important in designing and fabricating basal materials for the next generation of multifunctional nanostructured devices.     

Colloidal Self‐Assembly Meets Nanofabrication: From Two‐Dimensional Colloidal Crystals to Nanostructure Arrays

Self‐assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self‐assembly with nanofabrication techniques, two‐dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as “colloidal lithography”, which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self‐assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal‐crystal‐assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.     

A Hierarchically Ordered TiO2 Hemispherical Particle Array with Hexagonal‐Non‐Close‐Packed Tops: Synthesis and Stable Superhydrophilicity Without UV Irradiation

A hierarchical TiO₂ ordered hemispherical particle array with hexagonal‐non‐close‐packed (hncp) tops is prepared by pulsed laser deposition (PLD) using a polystyrene colloidal monolayer as a template. Compared with conventional lithography, the route presented has the advantage of low cost for producing hncp nanostructured arrays. This hierarchical particle array exhibits excellent superhydrophilicity with a water contact angle of 0° without further UV irradiation. The superhydrophilic property originates from oxygen defects or vacancies on the surface of the TiO₂ nanoparticles produced by PLD and the increased roughness of the hierarchical particle arrays. More importantly, this property is very stable for half a year and could be used in self‐cleaning surfaces and microfluidic devices.     

Large‐Scale,Long‐Range‐Ordered Patterning of Nanocrystals via Capillary‐Bridge Manipulation

Deterministic assembly of nanoparticles with programmable patterns is a core opportunity for property‐by‐design fabrication and large‐scale integration of functional materials and devices. The wet‐chemical‐synthesized colloidal nanocrystals are compatible with solution assembly techniques, thus possessing advantages of high efficiency, low cost, and large scale. However, conventional solution process suffers from tradeoffs between spatial precision and long‐range order of nanocrystal assembly arising from the uncontrollable dewetting dynamics and fluid flow. Here, a capillary‐bridge manipulation method is demonstrated for directing the dewetting of nanocrystal inks and deterministically patterning long‐range‐ordered superlattice structures. This is achieved by employing micropillars with programmable size, arrangement, and shape, which permits deterministic manipulation of geometry, position, and dewetting dynamics of capillary bridges. Various superlattice structures, including one‐dimensional (1D), circle, square, pentagon, hexagon, pentagram, cross arrays, are fabricated. Compared to the glassy thin films, long‐range‐ordered superlattice arrays exhibit improved ferroelectric polarization. Coassembly of nanocrystal superlattice and organic functional molecule is further demonstrated. Through introducing azobenzene into superlattice arrays, a switchable ferroelectric polarization is realized, which is triggered by order–disorder transition of nanocrystal stacking in reversible isomerization process of azobenzene. This method offers a platform for patterning nanocrystal superlattices and fabricating microdevices with functionalities for multiferroics, electronics, and photonics.     

Bio‐Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background

Inspired by Steller's jay, which displays angle‐independent structural colors, angle‐independent structurally colored materials are created, which are composed of amorphous arrays of submicrometer‐sized fine spherical silica colloidal particles. When the colloidal amorphous arrays are thick, they do not appear colorful but almost white. However, the saturation of the structural color can be increased by (i) appropriately controlling the thickness of the array and (ii) placing the black background substrate. This is similar in the case of the blue feather of Steller's jay. Based on the knowledge gained through the biomimicry of structural colored materials, colloidal amorphous arrays on the surface of a black particle as the core particle are also prepared as colorful photonic pigments. Moreover, a structural color on–off system is successfully built by controlling the background brightness of the colloidal amorphous arrays.     

Advanced colloidal lithography for sub-100 nm lift-off structures

We report on the fabrication of hexagonally ordered, sub-wavelength hole arrays (SWHA) by colloidal lithography combined with reactive ion etching and a lift-off process, and their characterization with scanning electron microscopy and ellipsometry.     

Self-assembled colloidal arrays as three-dimensional nanofluidic sieves for separation of biomolecules on microchips

We report on a biomolecular sieving system based on the use of ordered colloidal arrays to define the sieve structure within a microfluidic device. A facile microfluidic colloidal self-assembly strategy has been developed to create ordered, robust, three-dimensional nanofluidic sieves within microfluidic devices, with which fast separation of DNA and proteins of a wide size range was achieved. Compared to conventional colloidal deposition procedures, such as vertical deposition, this approach features much faster assembling speed, the absence of drying-caused cracks that may jeopardize the separation performance, and better flexibility to couple with current microfabrication techniques. The flexibility of pore size enabled by this methodology provides separation of biomolecules with a wide size distribution, ranging from proteins (20-200 kDa) to dsDNA (0.05-50 kbp). Under moderate electric fields, complete separation can be finished in minutes, with separation efficiency comparable to gel/polymer-filled or micro-/nanofabricated microsystems. To our knowledge, this is the first demonstration of size separation of biomolecules within self-assembled ordered colloidal lattices embedded within a microfluidic system.     

Growth of Large Colloidal Crystals with Their (100) Planes Orientated Parallel to the Surfaces of Supporting Substrates

Templating against two‐dimensional (2D) regular arrays of square pyramidal pits etched in Si(100) wafers has been exploited to fabricate colloidal crystals with their (100) planes oriented parallel to the substrates (see Figure for an SEM image). The capability and feasibility of this method have been demonstrated by crystallizing 1.0, 0.48, and 0.25 μm polystyrene beads into 3D opaline lattices having such an orientation over areas as large as several square centimeters. Like their (111)‐oriented cousins, these long‐range ordered lattices of spherical colloids are useful in many areas such as photonics and porous materials. In particular, the ability to generate large colloidal crystals with adjustable spatial orientations will allow one to systematically investigate their photonic band structures in an effort to elucidate the structure–property relationship.     

Physical Deposition Improved SERS Stability of Morphology Controlled Periodic Micro/Nanostructured Arrays Based on Colloidal Templates

An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal template induced precursor solution dipping strategy, different periodic arrays of semi‐hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb‐shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template‐induced chemical deposition. Additionally, a honeycomb‐shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb‐shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10^?11 M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.     

Double‐Emulsion Globules as a Tool to Produce 2D Patterned Metal Deposits Using Electro‐Colloidal Lithography

A technique developed to self assemble solid colloidal particles under a sinusoidal electric field (AC field) is adapted to soft W/O/W double‐emulsion globules, and is exploited for surface patterning. Double‐emulsions containing cupric ions are prepared, placed between two planar ITO electrodes and submitted to a transversal AC field which induced their ordering into hexagonal 2D‐arrays. The characteristic spacing is monitored by varying the globule volume fraction. Such self‐assembly is used to fabricate copper‐depleted arrays, using globules as both a metal precursor reservoir/provider and as a mask. The ordered globule monolayer is then submitted to a DC field to induce metal precursor leakage and its reduction onto the electrode. The organized, oily and dielectric globules generate arrays of holes (c.a. 7 μm) into a thin copper deposit (thickness of 12 nm). Holes are shown to be formed below the globules, and their separation (from 10 to 30 μm) can be tuned as deduced from direct observations using optical and atomic force microscopy.     

Cover Picture: Templated Fabrication of Nanowire and Nanoring Arrays Based on Interference Lithography and Electrochemical Deposition (Adv. Mater. 19/2006)

On p. 2593, Ji and co‐workers report on a novel fabrication technique for ideally ordered lateral nanowire and nanoring arrays based on interference lithography and electrochemical deposition. This approach allows the fabrication of metallic and semiconductor nanowire or nanoring arrays over wafer‐scale areas and provides flexible control over shape, arrangement, and thickness of the nanowires and nanorings. The cover shows templated electrodeposited elliptical nanoring arrays and a cross‐section of electrodeposited nanowires.     

Inside Front Cover: Redox‐Tunable Defects in Colloidal Photonic Crystals (Adv. Mater. 20/2005)

The inside front cover illustrates reversible tuning of an intragap transmitting state induced by redox cycling, accomplished using a redox‐active polyferrocenylsilane polyelectrolyte multilayer planar defect embedded in a colloidal photonic crystal (CPC) synthesized by a bottom–up method combining colloidal self‐assembly and microcontact printing. In work reported on p. 2455 by Manners, Ozin, and co‐workers, the wavelength position of the defect state can be changed by changing the oxidation state of the ferrocene moieties in the polymer backbone. This could find applications in electrochemically tunable microcavities, and—if light emitters are incorporated—electrochemically tunable CPC‐based laser sources. Cover design by Ludovic Cademartiri.     

Interfacial Capillary‐Force‐Driven Self‐Assembly of Monolayer Colloidal Crystals for Supersensitive Plasmonic Sensors

Colloidal lithography technology based on monolayer colloidal crystals (MCCs) is considered as an outstanding candidate for fabricating large‐area patterned functional nanostructures and devices. Although many efforts have been devoted to achieve various novel applicatons, the quality of MCCs, a key factor for the controllability and reproducibility of the patterned nanostructures, is often overlooked. In this work, an interfacial capillary‐force‐driven self‐assembly strategy (ICFDS) is designed to realize a high‐quality and highly‐ordered hexagonal monolayer MCCs array by resorting the capillary effect of the interfacial water film at substrate surface as well as controlling the zeta potential of the polystyrene particles. Compared with the conventional self‐assembly method, this approach can realize the reself‐assembly process on the substrate surface with few colloidal aggregates, vacancy, and crystal boundary defects. Furthermore, various typical large‐scale nanostructure arrays are achieved by combining reactive ion etching, metal‐assisted chemical etching, and so forth. Specifically, benefiting from the as‐fabricated high‐quality 2D hexagonal colloidal crystals, the surface plasmon resonance (SPR) sensors achieve an excellent refractive index sensitivity value of 3497 nm RIU^?1, which is competent for detecting bovine serum albumin with an ultralow concentration of 10^?8 m . This work opens a window to prepare high‐quality MCCs for more potential applications.     

Ordered binary arrays of Au nanoparticles derived from colloidal lithography

By using angle-resolved colloidal lithography and O2-plasma etched bilayers of hexagonally packed spheres as templates, we succeeded in fabrication of highly ordered binary arrays of gold nanoparticles with varied shapes, for instance, with a shuttlecock-like shape composed of a small crescent-shaped nanoparticle and a big fan-shaped one. The size and shape of both small and big nanoparticles obtained were manipulated by the plasma etching period and the incidence angle of Au vapor flow. The subsequent thermal annealing led to binary arrays of round Au nanoparticles with a rather narrow distribution in terms of size and shape. Our approach should pave a simple and versatile colloidal way to form binary nanoparticle arrays, holding immense promise for technical applications such as nanoelectronics and nanophotonics.     

Ordered Arrays of Nanostructures and Applications in High‐Efficient Nano‐Generators

Large‐scale ordered nanostructure arrays on substrates, including nanowires, nanotubes, nanodots, and nano‐holes, can be fabricated using template fabrication processes. The controllable structural parameters and properties of the ordered nanostructure arrays make them quite suitable to be used in many device‐related application areas. It is shown that large‐scale nanowire arrays are good candidates for the realization of a nano‐generator based on the piezoelectric effect of ZnO nanowires. The mechanism of a proposed high‐efficient nano‐generator based on an assembled nanowire/nanohole embedded structure shows high application potentials for biological and nanometer‐sized devices.     

Nanodomain Swelling Block Copolymer Lithography for Morphology Tunable Metal Nanopatterning

Ordered metal nanopatterns are crucial requirements for electronics, magnetics, catalysts, photonics, and so on. Despite considerable progress in the synthetic route to metal nanostructures, highly ordered metal nanopatterning over a large‐area is still challenging. Nanodomain swelling block copolymer lithography is presented as a general route to the systematic morphology tuning of metal nanopatterns from amphiphilic diblock copolymer self‐assembly. Selective swelling of hydrophilic nanocylinder domains in amphiphilic block copolymer films during metal precursor loading and subsequent oxygen based etching generates diverse shapes of metal nanopatterns, including hexagonal nanoring array and hexagonal nanomesh and double line array in addition to common nanodot and nanowire arrays. Solvent annealing condition of block copolymer templates, selective swelling of hydrophilic cylinder nanodomains, block copolymer template thickness, and oxygen based etching methods are the decisive parameters for systematic morphology evolution. The plasmonic properties of ordered Au nanopatterns are characterized and analyzed with finite differential time domain calculation. This approach offers unprecedented opportunity for diverse metal nanopatterns from commonly used diblock copolymer self‐assembly.     

Self-assembly of colloidal crystals from polystyrene emulsion at elevated temperature by dip-drawing method

The self-assembly of colloidal crystal arrays from polystyrene (PS) sphere emulsion at elevated temperature by dip-drawing method was investigated. The dependence of effective sphere transfer in the meniscus of emulsion on temperature was discussed. The results show that the assembled arrays formed at 50 °C have fewer defects than those at room temperature. The elevated emulsion temperature during the ordered arrangement of colloidal crystals causes quicker solvent evaporation, hence quicker sphere transfer. However, exceeding solvent flux and crystal growth induced by over high temperatures result in more fracture lines displayed in arrays. At 50 °C, the effective sphere transfer by the solvent flux to the array edge can also be enhanced by increasing the PS volume fraction of emulsion, which obviously reduces fracture lines on the surface of multilayer.     

Colloidal lithography and Metal-Organic Chemical Vapor Deposition process integration to fabricate ZnO nanohole arrays

A complete set up of optimal process conditions for an effective colloidal lithography/catalyst assisted MOCVD process integration is presented. It mainly focuses on the determination of the deposition temperature threshold for ZnO Metal-Organic Chemical Vapour Deposition (MOCVD) as well as the concentration of metal-organic silver (Ag) catalyst. Indeed, the optimization of such process parameters allows to tailor the ZnO film morphology in order to make the colloidal lithography/catalyst assisted MOCVD approach a valuable bottom up method to fabricate bi-dimensional ordered ZnO nanohole arrays.     

Tunable surface plasmon resonance and strong SERS performances of Au opening-nanoshell ordered arrays

Au opening-nanoshell ordered arrays with tunable local surface plasmon resonance (SPR) property have been fabricated based on sputtering deposition onto monolayer colloidal crystal. The changes in local SPR peak for the arrays can be well tuned from visible to near-infrared region with decreasing of the spacing between two neighbor opening-nanoshells. It has been revealed that the changes of SPR peak originate from the electromagnetic coupling between two adjacent Au opening-nanoshells. This study is important to design and fabricate surface-enhanced Raman scattering substrates with high activity and practical application.