Sub-100 nm patterning with an amorphous fluoropolymer mold

A fluoropolymer mold is introduced and used to pattern sub-100 nm features with the characteristics that cause problems in patterning with a mold. The low surface energy and inertness, stiffness, and permeable nature of the mold material make it possible to pattern without surface treatment densely populated very fine features, mixed patterns of small and large features, and features with a high aspect ratio, when the mold is used with a polymer solution for the patterning. The ultraviolet transparency of the mold material also allows for patterning with photocurable pre-polymers.     

细胞图案化技术及其在胚胎干细胞研究中的应用

图案化技术的不断创新及在细胞领域研究中的应用使细胞图案化技术成为研究和控制细胞行为的有效实验工具.该技术结合微纳米制备、电化学、表面化学和光化学等手段与方法塑造和细胞相关的物理化学参量,如形貌、粗糙度、亲疏水性等,动态地控制细胞的粘附、脱附、迁移、分化及细胞间相互作用,为细胞生物学研究提供一个崭新的技术平台.本文从细胞...     

Development and research for applying innovative magnetic soft mold imprinting techniques in microstructure component manufacturing

The present study employs an innovative technique, which uses PDMS soft mold, blended with magnetic powder as the transmission and imprinting methods, and integrates features from soft micromolding PMMA, an electro‐magnetically controlled, well‐proportioned, pressing technique in order to study how to create microlens arrays through a magnetic soft mold imprinting resist technique. Thus, it renders nanometer imprinting applications, and its technology, more developed and mature. The research findings revealed that, PDMS, blended with magnetic powder, can accurately recast and duplicate nanometer microstructures. Under well‐proportioned magnetic pressing, controlled by an electro‐magnetic disk, it can effectively fill and shape resist microstructures. The composite material of PDMS, with added magnetic iron powder, can effectively improve mechanical strength properties of pure PDMS soft mold, which is easily transformed for imprinting. Meanwhile, owing to the unique features of PDMS soft mold, conformal contact with the base material is possible; therefore, the effective imprinting area and the duplicated representation are significantly improved. In addition, as magnetic PDMS soft mold is easily produced and fast in recasting, the costs can be effectively reduced. In addition, due to features such as low surface free energy and a tendency not to stick to resist in imprinting, the soft mold is evenly controlled by the electro‐magnetic disk for imprinting duplication, highlighting the advantages of microstructure imprinting procedures. Copyright © 2008 John Wiley & Sons, Ltd.     

Mold design rules for residual layer-free patterning in thermal imprint lithography

We present the mold design rules for assuring residual layer-free patterning in thermal imprint processes. Using simple relations for mass balance, structural stability, and work of adhesion, we derive the conditions with respect to the given single or multigeometrical feature of the mold, which are compared with simple thermal imprint experiments using soft imprint molds. Our analysis could serve as a guideline for designing the optimum mold geometry and selecting mold material in residual layer-free thermal imprint processes.     

Microscale features and surface chemical functionality patterned by electron beam lithography: a novel route to poly(dimethylsiloxane) (PDMS) stamp fabrication

Poly(dimethylsiloxane) (PDMS) has become a ubiquitous material for microcontact printing, yet there are few methods available to pattern a completed PDMS stamp in a single step. It is shown here that electron beam lithography (EBL) is effective in writing patterns directly onto cured PDMS stamps, thus overcoming the need for multiple patterning steps. Not only does this method allow the modification of an existing lithographic pattern, but new 3D features such as cones, pits, and channels can also be fabricated. EBL can also be used to fabricate PDMS masks for photolithography whereby 1:1 pattern transfer into a photoresist is achieved. Additionally, direct EBL writing of surface chemical features has been achieved using a PDMS stamp coated with a self-assembled monolayer. An electrostatic mechanism appears to be operative in the EBL patterning process, as supported by calculations, thermogravimetric analysis, time-of-flight secondary ion mass spectroscopy, optical and atomic force microscopy, and chemical functionalization assays.     

Pipette-friendly laminar flow patterning for cell-based assays

Laminar flow patterning (LFP) is a characteristic method of microfluidic systems that allows two (or more) different solutions to flow side-by-side in a channel without convective mixing. This fluid behavior can be used to pattern cell suspensions, particles, and treatments as well as to create chemical gradients. LFP is typically implemented using syringe pumps and, for this reason, is most effective in constant flow scenarios such as long-term gradient generation. However, the complexity of using syringe pumps for patterning cell suspensions typically makes it a less attractive option than other standard patterning methods. We present a passive microfluidic method that enables short-term LFP of multiple fluids using a single pipette and allows each sample to be loaded in any sequence, at any point in time relative to one another. The proposed method is well-suited for cell-based assays, reduces the complexity of LFP to be on a similar level as other cell patterning methods, can be scaled to include more than two streams of fluid, and enables arrays of individually addressable devices for LFP on a single chip.     

Micro- and nanopatterned star poly(ethylene glycol) (PEG) materials prepared by UV-based imprint lithography

A UV-based imprint lithography method is used for the direct surface structuring of hydrogel-based biomaterials, which are prepared from a family of tailor-made star poly(ethylene glycol) formulations. Bulk star poly(ethylene glycol) (PEG) hydrogels are fabricated by cross-linking acrylate-functionalized star PEG macromolecules. Cross-linking is achieved by radical reactions initiated by UV irradiation. This UV-curable star PEG formulation allows templating of mold structures to yield a stable, stand-alone, elastomeric replica of the mold. In particular, when a secondary, soft mold is used that consists of a perfluorinated elastomer with inherent excellent release properties, nanometer-sized features (down to 100 nm) can be imprinted without specialized equipment. The applied UV-based imprint lithography is a fast and simple technique to employ for the direct topographic structuring of bulk PEG-based biomaterials. The UV-based imprinting into the star PEG prepolymer by means of a perfluorinated, soft mold can be carried out on the bench top, while nanoscale resolution is demonstrated.     

Micro patterning of active proteins with perforated PDMS sheets (PDMS sieve)

We propose a novel technique for patterning active proteins on a glass substrate using a perforated polydimethylsiloxane (PDMS) sheet-sieve. The sieve, which has tapering holes, is fabricated by spin-coating PDMS on a pyramidal-shaped mold. By means of this sieve, FITC (fluorescent isothiocyanate, bovine)-albumin was successfully spotted in a 5 x 5 microm(2) area in an array. The patterned spots were perfectly isolated, which eliminates the problem of non-specific binding of proteins to undesired areas. To show that proteins maintained their activity after the patterning, we used F(1)-ATPase biomolecular motors; their activity can easily be verified by observing their rotary motion after patterning. Selective patterning with three kinds of fluorescent micro beads indicated the possibility of patterning of different proteins on the same substrate by using the sieve.     

Patterned removal of molecular organic films by diffusion

We demonstrate that "contact patterning" subtractively patterns a wide range of molecular organic films of nanoscale thickness with nanometer-scale accuracy. In "contact patterning", an elastomeric stamp with raised features is brought into contact with the organic film and subsequently removed, generating patterns by the diffusion of the film molecules into the stamp. The mechanism of material removal via diffusion is documented over spans of minutes, hours, and days and is shown to be consistently repeatable. Contact patterning provides a photolithography-free, potentially scalable approach to subtractive patterning of a wide range of molecular organic films.     

Microscale patterning of thermoplastic polymer surfaces by selective solvent swelling

A new method for the fabrication of microscale features in thermoplastic substrates is presented. Unlike traditional thermoplastic microfabrication techniques, in which bulk polymer is displaced from the substrate by machining or embossing, a unique process termed orogenic microfabrication has been developed in which selected regions of a thermoplastic surface are raised from the substrate by an irreversible solvent swelling mechanism. The orogenic technique allows thermoplastic surfaces to be patterned using a variety of masking methods, resulting in three-dimensional features that would be difficult to achieve through traditional microfabrication methods. Using cyclic olefin copolymer as a model thermoplastic material, several variations of this process are described to realize growth heights ranging from several nanometers to tens of micrometers, with patterning techniques include direct photoresist masking, patterned UV/ozone surface passivation, elastomeric stamping, and noncontact spotting. Orogenic microfabrication is also demonstrated by direct inkjet printing as a facile photolithography-free masking method for rapid desktop thermoplastic microfabrication.     

Molding block copolymer micelles: a framework for molding of discrete objects on surfaces

Soft lithography based on photocurable perfluoropolyether (PFPE) was used to mold and replicate poly(styrene-b-isoprene) block-copolymer micelles within a broad range of shapes and sizes including spheres, cylinders, and torroids. These physically assembled nanoparticles were first formed in a selective solvent for one block then deposited onto substrates having various surface energies in an effort to minimize the deformation of the micelles due to attractive surface forces. The successful molding of these delicate nanoparticles underscores two advantages of PFPE as a molding material. First, it allows one to minimize particle deformation due to adsorption by using low energy substrates. Second, PFPE is not miscible with the organic micelles and thus prevents their dissociation. For spherical PS-b-PI micelles, a threshold value of the substrate surface energy for the mold to lift-off cleanly, that is, the particles remain adhered to the substrate after mold removal was determined to be around gamma congruent with 54 mJ/m2. For substrates with higher surface energies (>54 mJ/m2), the micelles undergo flattening which increase the contact area and thus facilitate molding, although at the expense of particle deformation. The results are consistent with theoretical predictions of a molding range for substrate surface energies, which depends on the size, shape, and mechanical properties of the particles. In a similar fashion, cylindrical PS-b-PI micelles remain on the substrate at surface energies gamma>or=54 mJ/m2 after a mold removal. However, cylindrical micelles behaved differently at lower surface energies. These micelles ruptured due to their inability to slide on the surfaces during mold lift-off. Thus, the successful molding of extended objects is attainable only when the particle is adsorbed on higher energy substrates where deformation can still be kept at a minimum by using stronger materials such as carbon nanotubes for the master.     

Bio and soft-imprinting lithography on bacterial cellulose films

Bacterial cellulose (BC) is a biocompatible polysaccharide produced by bacteria currently used in packaging, cosmetics, or health care. A highly attractive feature of BC is the possibility of patterning the BC pellicle during its biosynthesis, a concept coined as bio-lithography. BC-patterned films have demonstrated improved properties for cellular-guided growth, implant protection, or wound dressing. However, aspects such as the diversity and size of the features patterned, how those features withstand postprocessing steps, or if large areas can be patterned remain unanswered. Gathering knowledge on these characteristics could extend the use of patterned cellulose-based materials in emerging fields such as transient devices, nanogenerators, or microfluidics. Here, we show that bio-lithographed BC films present good-quality micropatterned features for various motifs (wells, pillars, and channels) in a wide range of sizes (from 200 to 5 μm) and areas as large as 70 cm². Besides, we have studied the fidelity of the motifs and the fiber organization for wet, supercritical, and oven-dried films. When wells and pillars were patterned, the x and y dimensions were faithfully replicated in the wet and dried samples, but only wet and supercritically dried films afforded mold accuracy in the z-direction. In addition, x/z ratio should be carefully considered for obtaining self-standing pillars. Finally, we compared bio-lithography and soft-imprint lithography. In the latter case, fiber alignment was not observed and the depth of the resulting features dramatically decreased; however, this technique allowed us to produce submicron features that remain after the rewetting of the BC films.     

Fabrication of microfluidic chip using micro‐hot embossing with micro electrical discharge machining mold

This study develops an improved method for generating aluminum mold inserts used in the replication of polymer‐based microfluidic chip. Since molding masters that are suitable for microfluidic chip replication must have features whose dimensions are of the order of tens to hundreds of microns, micro electrical discharge machining is employed herein to fabricate an aluminum mold insert of a microfluidic chip. The width and depth of the aluminum mold insert for the microfluidic chip are 61.50 and 49.61 µm, respectively. The surface roughness values of the microchannel and the sample reservoir in aluminum mold insert for the microfluidic chip are 53.9 and 34.3 nm, respectively. PMMA material is adopted as the molded microfluidic chip that is produced by micro‐hot embossing molding. The PMMA material can replicate the microchannel and sample reservoir very well when the aluminum mold insert is used in micro‐hot embossing molding. The results indicate that the most important parameter in the replication of molded microfluidic chip is the embossing pressure, which is also the most important parameter in determining the surface roughness of the molded microfluidic chip. Copyright © 2010 John Wiley & Sons, Ltd.     

TiO2 nanotube layers: Flexible and electrically active flow-through membranes

In the present work we demonstrate the fabrication and use of a new generation of TiO₂ nanotube membranes. We show that anodic oxide nanotube growth can be performed through a patterned Ti foil into an underlying Al metal layer. After the selective dissolution of the Al/alumina layer, a very well defined both side open suspended TiO₂ nanotube layer can be obtained. Using lithographic patterning of the anodization area allows to achieve very large scale, flexible and well electrically connected nanotubular flow-through membranes with fast electrical switching features over the entire membrane.     

Heat-Free Biomimetic Metal Molding on Soft Substrates

Fabrication of bio-templated metallic structures is limited by differences in properties, processing conditions, packing, and material state(s). Herein, by using undercooled metal particles, differences in modulus and processing temperatures can be overcome. Adoption of autonomous processes such as self-filtration, capillary pressure, and evaporative concentration leads to enhanced packing, stabilization (jamming) and point sintering with phase change to create solid metal replicas of complex bio-based features. Differentiation of subtle differences between cultivars of the rose flower with reproduction over large areas shows that this biomimetic metal patterning (BIOMAP) is a versatile method to replicate biological features either as positive or negative reliefs irrespective of the substrate. Using rose petal patterns, we illustrate the versatility of bio-templated mapping with undercooled metal particles at ambient conditions, and with unprecedented efficiency for metal structures.     

Microscale patterning of organic films on carbon surfaces using electrochemistry and soft lithography

We have demonstrated three simple strategies employing poly(dimethylsiloxane) (PDMS) molds for patterning carbon surfaces with two different modifiers in an 18 microm line pattern. The PDMS molds are patterned with microfluidic channels (approximately 22 microm wide and 49 microm deep) and form a reversible, conformal seal to the pyrolyzed photoresist film (PPF) and modified PPF surfaces. Modifiers are electrochemically grafted to the PPF surface by the reduction of aryl diazonium salts and the oxidation of primary amines. For the fill-in patterning approach, the first modifier is electrografted to the PPF surface exposed within the microchannels, and in a second grafting step after removal of the PDMS mold, the second modifier fills in the remaining surface. The selective conversion strategy involves electrografting a continuous film of the modifier to the PPF surface, sealing the PDMS mold to the modified surface and carrying out an irreversible electrochemical reaction of the modifier exposed within the microchannels. In the build-up patterning approach, the PDMS mold is sealed to the modified PPF surface, and a chemical coupling reaction is effected in the microchannels to build up the pattern. The patterns are characterized using SEM, optical microscopy, the formation of condensation figures, and SEM imaging after the assembly of Au nanoparticles.     

Heat‐Free Biomimetic Metal Molding on Soft Substrates

Fabrication of bio‐templated metallic structures is limited by differences in properties, processing conditions, packing, and material state(s). Herein, by using undercooled metal particles, differences in modulus and processing temperatures can be overcome. Adoption of autonomous processes such as self‐filtration, capillary pressure, and evaporative concentration leads to enhanced packing, stabilization (jamming) and point sintering with phase change to create solid metal replicas of complex bio‐based features. Differentiation of subtle differences between cultivars of the rose flower with reproduction over large areas shows that this biomimetic metal patterning (BIOMAP) is a versatile method to replicate biological features either as positive or negative reliefs irrespective of the substrate. Using rose petal patterns, we illustrate the versatility of bio‐templated mapping with undercooled metal particles at ambient conditions, and with unprecedented efficiency for metal structures.     

Electro-optical properties of holographically patterned polymer-stabilized cholesteric liquid crystals

Electro-optical properties of cholesteric liquid crystals (LCs) with holographically patterned polymer stabilization were examined. It is hypothesized that increasing the LC domain size in a single dimension, relative to a random three-dimensional network of LC pockets separated by polymer strands, will allow enhanced electro-optical properties of the final device. Prior to holographic patterning, polymer stabilization with large elastic memory was generated by way of high irradiation intensities and optimized material choices. High irradiation intensities are required for the holographic patterning process to maintain polymer layer formation. At optimized conditions, polymer patterning of the stabilization allowed for an approximate 20% increase in the clear state transmission of the device, and allowed for an approximate 3 V µm^-1 reduction in the overall switching voltage as compared to an analogous floodlit irradiated sample. Switching times were increased at most threefold with holographic patterning, but all relaxation times were below 20 ms. The enhanced electro-optical properties appear to stem from a single dimension domain size increase, which allows for a reduction in the LC/polymer interaction.     

Interfacial chemistries for nanoscale transfer printing

We describe a patterning technique that uses self-assembled monolayers and other surface chemistries for guiding the transfer of material from relief features on a stamp to a substrate. This purely additive contact printing technique is capable of nanometer resolution. Pattern transfer is fast and it occurs at ambient conditions. We illustrate the versatility of this method by printing single-layer metal patterns with feature sizes from a few tens of microns to a few tens of nanometers. We also demonstrate its use for patterning, in a single step, metal/dielectric/metal multilayers for functional thin film capacitors on plastic substrates.