Edge transfer lithography using alkanethiol inks

Edge lithographic patterning techniques are based on the utilization of the edges of micrometer-sized template features for the reproduction of submicrometer structures. Edge transfer lithography (ETL) permits local surface modification in a single step by depositing self-assembled monolayers onto a metal substrate selectively along the feature edges of an elastomeric stamp. In this report two stamp designs are described that now allow for the use of alkanethiol inks in ETL and their use as etch resists to reproduce submicrometer structures in gold. Anisotropically modified stamps are shown to combine the potential for very high-resolution patterning with the versatility and simplicity of microcontact printing.     

Electrochemical nanoimprinting with solid-state superionic stamps

This letter presents a solid-state electrochemical nanoimprint process for direct patterning of metallic nanostructures. It uses a patterned solid electrolyte or superionic conductor (such as silver sulfide) as a stamp and etches a metallic film by an electrochemical reaction. Our preliminary experiments demonstrate repeatable and high-fidelity pattern transfer with features down to 50 nm on silver films of thicknesses ranging from 50 to 500 nm. As the process is conducted in an ambient environment and does not involve the use of liquids, it displays potential for single-step, high-throughput, large-area manufacturing of metallic nanostructures. The use of superionic conductors in manufacturing opens up a new and potentially energy-efficient approach to nanopatterning and fabrication. It offers a highly competitive approach, both as a stand-alone process and as a complement of other nanofabrication techniques, to fabricating chemical sensors, photonic and plasmonic structures, and electronic interconnects.     

Direct printing of silver nanoparticles by an agarose stamp on planar and patterned substrates

In this study, we have used an agarose stamp to conduct direct printing of silver nanoparticles, nanowires and nanoplates on both planar and structured substrates. Nanoparticle solution could be first coated on an agarose stamp, and then transferred to a planar substrate. Micro-patterns comprising metal nanoparticles could be printed on planar substrates without the formation of residual layers. Thus a three-dimensional metal microstructure could be easily fabricated. The patterning of electrodes by printing Ag nanowires directly on TiO(2) was also demonstrated to fabricate resistive random access memory (RRAM) devices by all-solution-processing methods. By using a flat agarose stamp, the patterns printed on the microstructured substrates were quite different from those on the nanostructured substrates. On the microstructured substrates, direct printing could print silver nanoparticles onto the protrusion surface, and could print silver layers as thick as several microns, useful for high conductivity electrodes. On the substrates with nanostructures such as photonic crystals or nano-gratings, direct printing could transfer nanoparticles into the grooves or cavities only due to the contact of the agarose stamp with the groove or concavity surface. A new approach to fabricate metal wire grid polarizers was further demonstrated. A nanoporous agarose stamp has a good potential for printing using nanoparticle suspension.     

Microcontact Printing: Limitations and Achievements

Microcontact printing (µCP) offers a simple and low‐cost surface patterning methodology with high versatility and sub‐micrometer accuracy. The process has undergone a spectacular evolution since its invention, improving its capability to form sub‐100 nm SAM patterns of various polar and apolar materials and biomolecules over macroscopic areas. Diverse development lines of µCP are discussed in this work detailing various printing strategies. New printing schemes with improved stamp materials render µCP a reproducible surface‐patterning technique with an increased pattern resolution. New stamp materials and PDMS surface‐treatment methods allow the use of polar molecules as inks. Flat elastomeric surfaces and low‐diffusive inks push the feature sizes to the nanometer range. Chemical and supramolecular interactions between the ink and the substrate increase the applicability of the µCP process.     

The development of a finite element model for simulating the stamp forming of fibre–metal laminates

A finite element model for simulating the stamp forming of fibre–metal laminate material systems will encompass many aspects of both thermoplastic composite forming and metal stamp forming as well as interaction phenomenon between the laminate layers. This paper investigates the composite–metal interaction by studying the crystallisation behaviour of the interlayer adhesive and its shear stress transfer characteristics using lap-shear apparatus. A model utilising the data obtained from these tests is proposed and the underlying concept of shear stress transfer between laminate layers is justified by comparing results from a finite elements simulation incorporating an interface model with experimental results.     

Wafer‐Scale Patterning of Reduced Graphene Oxide Electrodes by Transfer‐and‐Reverse Stamping for High Performance OFETs

A wafer‐scale patterning method for solution‐processed graphene electrodes, named the transfer‐and‐reverse stamping method, is universally applicable for fabricating source/drain electrodes of n‐ and p‐type organic field‐effect transistors with excellent performance. The patterning method begins with transferring a highly uniform reduced graphene oxide thin film, which is pre‐prepared on a glass substrate, onto hydrophobic silanized (rigid/flexible) substrates. Patterns of the as‐prepared reduced graphene oxide films are then formed by modulating the surface energy of the films and selectively delaminating the films using an oxygen‐plasma‐treated elastomeric stamp with patterns. Reduced graphene oxide patterns with various sizes and shapes can be readily formed onto an entire wafer. Also, they can serve as the source/drain electrodes for benchmark n‐ and p‐type organic field‐effect transistors with enhanced performance, compared to those using conventional metal electrodes. These results demonstrate the general utility of this technique. Furthermore, this simple, inexpensive, and scalable electrode‐patterning‐technique leads to assembling organic complementary circuits onto a flexible substrate successfully.     

High-resolution patterning of silver thin films with a water-mediated metal transfer printing

We report a direct printing method, water-mediated metal transfer printing (mTP), for generating Ag patterns with a wide range of feature sizes. Water-mediated mTP is based on the direct transfer of a metal thin film from a stamp to a substrate via a water-mediated surface bonding. An Ag thin film is used as a solid "ink" in the mTP, which can be used for the formation of micro- and nanoscale Ag structures. To demonstrate its usefulness, we used the water-mediated mTP to fabricate low voltage ZnO thin-film transistors.     

Self-organized meso-patterning of soft solids by controlled adhesion: elastic contact lithography

The surface of a soft elastic film becomes unstable and deforms when a rigid flat plate is brought into its contact proximity, without application of any external pressure. These isotropic undulations have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. The wavelength is independent of the adhesive interactions and the mechanical properties of the film. We present here a mini-review of our recent work on techniques of aligning, modulating, and ordering the instability structures by the use of simple 1-D patterned stamps, by changing the stamp-surface separation, by slow shearing of a flat stamp and by confining the instability in soft narrow channels. The generality of the technique for different soft materials is illustrated by patterning cross-linked polydimethylsiloxane (PDMS), aluminum coated PDMS and hydrogels films. Use of a flexible stamp such as a metal foil provides enhanced conformal contact by adhesive forces, which aids large area patterning without critically maintaining a parallel configuration and uniform pressure between the stamp and the film. The technique has the potential to develop into a new soft lithography tool--"Elastic Contact Lithography" suitable for rapid, large area micron and sub-micron self-organized patterning of a variety of soft materials without any special equipments.     

Stretch forming studies on a fibre metal laminate based on a self-reinforcing polypropylene composite

This paper investigates the room temperature formability of a fibre metal laminate system comprised of aluminium and a self-reinforcing polypropylene composite. Blanks of varying geometry were stretch formed over a hemispherical punch in a custom built stamping press. A real-time three-dimensional photogrammetric measuring system was used to acquire the evolution of surface strain and the strain at failure during forming. The results from this work illustrate that these advanced light weight material systems are amenable to mass production through stamp forming. A significant finding from this work is that these material systems can exhibit forming characteristics that are comparable and sometimes superior to metal forming.     

Nasicon材料的制备及气敏特性研究

采用高温固相烧结方法,制备了Ｎａｓｉｃｏｎ固体电解质材料,并用ＩＲ、ＸＲＤ等手段对材料的组成和物相结构进行了表征。在材料电阻率随温度变化的测试结果基础上,进上步以所合成的Ｎａｓｉｃｏｎ材料作离子导体、ＢａＣＯ３－Ｌｉ２ＣＯ３复合盐作第三电极材料制成ＣＯ２传感器,考察了材料的气敏性能。结果表明材料对ＣＯ２具有良好的气敏特性及抗水蒸汽干扰性能。     

Quantitative characterizations of a nanopatterned bonded wafer: force determination for nanoimprint lithography stamp removal

The nanoimprint lithography process consists of two mechanical steps: molding and stamp removal. While many publications dealing with anti-sticking layer properties or the understanding of polymer flow during imprinting have recently been published, only a few studies have been carried out to deeply characterize the demolding step. Regarding the small amount of theoretical work dedicated to this issue, in this paper both experimental and first theoretical approaches are proposed to characterize the demolding process in a peeling scheme. Full 200?mm stamp and imprinted wafers were used to identify the experimental limitation of such a full wafer peeling demolding scheme. A rectangular stamp and substrate samples with or without nanoscale features combined with an augmented beam theory are proposed to extract quantitative data for the required demolding force as well as the friction stress along the feature sidewall. Therefore both adhesion and friction forces were characterized on single stamp structures.     

Simultaneous self-assembly, orientation, and patterning of peptide-amphiphile nanofibers by soft lithography

Self-assembled nanofibers of peptide-amphiphile molecules have been of great interest because of their bioactivity both in vitro and in vivo. In this work, we demonstrate the simultaneous self-assembly, alignment, and patterning of these nanofibers over large areas by a novel technique termed sonication-assisted solution embossing. In this soft lithographic technique, the nanostructures self-assemble by solvent evaporation while under the influence of ultrasonic agitation and confinement within the topographical features of an elastomeric stamp. The nanofibers orient parallel to the channels as they assemble out of solution, yielding bundles of aligned nanofibers on the substrate after the stamp is removed. Alignment is likely a result of steric confinement and possibly a transition to a lyotropic liquid crystalline phase as solvent evaporates. This technique is not limited to uniaxial alignment and is shown to be able to guide nanofibers around turns. Alignment of nanostructures by this method introduces the possibility of controlling macroscale cellular behavior or material properties by tuning the directionality of interactions at the nanoscale.     

Design and fabrication of label-free biochip using a guided mode resonance filter with nano grating structures by injection molding process

This paper introduces technology to fabricate a guided mode resonance filter biochip using injection molding. Of the various nanofabrication processes that exist, injection molding is the most suitable for the mass production of polymer nanostructures. Fabrication of a nanograting pattern for guided mode resonance filters by injection molding requires a durable metal stamp, because of the high injection temperature and pressure. Careful consideration of the optimized process parameters is also required to achieve uniform sub-wavelength gratings with high fidelity. In this study, a metallic nanostructure pattern to be used as the stamp for the injection molding process was fabricated using electron beam lithography, a UV nanoimprinting process, and an electroforming process. A one-dimensional nanograting substrate was replicated by injection molding, during which the process parameters were controlled. To evaluate the geometric quality of the injection molded nanograting patterns, the surface profile of the fabricated nanograting for different processing conditions was analyzed using an atomic force microscope and a scanning electron microscope. Finally, to demonstrate the feasibility of the proposed process for fabricating guided mode resonance filter biochips, a high-refractive-index material was deposited on the polymer nanograting and its guided mode resonance characteristics were analyzed.     

Fabrication of an inorganic nano structure for a large area via electrohydrodynamic lithography (EHL)

Electrohydrodynamic lithography (EHL) is one of several unusual lithographic techniques for fabricating sub-micrometer structures over a large area. EHL uses the electrohydrodynamic (EHD) film instability induced by a laterally modulated electric field, which allows it to fabricate not only general organic structures but also structures of various components, such as diblock copolymers and inorganic materials, without contact between the resist and the stamp. Furthermore, EHL is a very special lithographic technique in that diverse structures are fabricated from one stamp via electric field modulation. The electric field is controlled by the replication time, air layer thickness, etc. A replicated inorganic structure was demonstrated from a hexagonal hole and line arrays. The heat treatment of the replicated pattern was carried out to obtain the crystalline phase, after which the samples were characterized via Raman spectroscopy. These values were ascertained using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The results will be useful in providing a facile route for patterning functional metal oxides over a large area. Such a technique can be used to produce photovoltaic cells, memory devices, display devices, etc.     

Fabrication of periodic metal nanowires with microscale mold by nanoimprint lithography

In this paper, a simple method is demonstrated for fabricating periodic metal nanowires based on the unconventional nanoimprint lithography (NIL) technique. Using this method, sub-100 nm metal nanowires with the rectangular cross-section are fabricated with microscale stamp. Furthermore, the metal nanowires with different widths and heights can be generated by adjusting the imprinting parameters with the same stamp. The metal nanowires prepared with this method can be used for chemical sensing, such as ammonia sensing, and it may have applications in optical signal processing.     

Micro- and nanostripes of self-assembled Au nanocrystal superlattices by direct micromolding

A simple, inexpensive direct micromolding method for patterning Au nanocrystal superlattices using a polydimethylsiloxane (PDMS) stamp has been developed. The method involves in situ synthesis of Au(I) dodecanethiolate and its decomposition leading to Au nanocrystals in the microchannels of the stamp which order themselves to form patterned superlattice stripes, in conformity with the stamp geometry. Owing to its insolubility in common solvents, the dodecanethiolate was made by reacting Au(PPh₃)Cl and dodecanethiol in situ inside the microchannels, by injecting first the former solution in toluene at room temperature followed by the thiol solution at 120 °C. Annealing the reaction mixture at 250 °C, resulted in formation of nanocrystals (with a mean diameter of 7.5 nm) and hexagonal ordering. By using an external pressure while molding, parallel stripes with sub-100 nm widths were obtained. The choice of parameters such as injection temperature of the thiol and concentrations is shown to be important if an ordered superlattice is to be obtained. In addition, these parameters can be varied as a means to control the nanocrystal size.     

Simple colloidal lithography approach to generate inexpensive stamps for polymer nano-patterning

In this work we propose a simple method, based on colloidal crystal monolayer templating, to obtain good quality stamps for polymer patterning. By metal evaporation over colloidal monolayers we fabricate (i) metal-coated colloidal crystals, and (ii) arrays of triangular nanoparticles on glass substrate, obtained by subsequently removing the colloids. The applicability of these two types of nanostructured surfaces as lithographic stamps is demonstrated by transferring their patterns onto polyvinyl alcohol polymer surfaces. The morphology of the resulting polymer nanostructures is analyzed by atomic force microscopy. The proposed nanolithographic technique is remarkable for its simplicity, decreased cost of stamp fabrication, and high resolution of achievable nanopatterns.     

Ab initio self-consistent theory of ionic diffusion in superionic conductors with an internal interface

The kinetic equation of the hopping diffusion in a one-dimensional chain with an internal interface between a superionic conductor and an intercalate, is presented in a new form, which explicitly takes into account the effect of Coulomb correlations. Numerical results are presented for material parameters corresponding to the system: ternary borate glass-indium selenide, which is often used in solid microbatteries.     

Integration of copper multilevel interconnects with oxide and polymer interlevel dielectrics

Copper interconnect structures are being evaluated for 0.25 μm minimum feature size technology and below. This work focuses on fabrication of one- and two-level test structures with copper metallization and both oxide and polymer interlevel dielectrics to demonstrate the compatibility of unit processes being developed for future copper-based interconnects. Emphasis is placed on dual Damascene patterning and material and process compatibility with such patterning and the required barriers and passivation techniques required with copper. Future directions of this work are described in this invited review paper.     

High-Resolution 3D Deposition of Electrospun Fibers on Patterned Dielectric Elastomers

Electrostatic patterning has improved the performance of devices incorporating electrospun fibers in a wide variety of applications. However, the impact of process parameters on the final fiber pattern in these systems is rarely analyzed. Herein, a systematic analytical approach is developed to define quantitative metrics related to fiber patterning. Three-dimensional patterned dielectric elastomer collectors are fabricated via solution-casting polydimethylsiloxane with embedded carbon black or liquid metal droplets. Fiber patterning metrics are used to evaluate the effect of collector parameters such as insulating layer thickness, electrical ground surface area, and three-dimensional pattern geometry. Dielectric layer parameters such as conductive material concentration and particle diameter are also investigated. Using this framework, the best-performing collector is shown to improve selectivity 30-fold, uniformity ninefold, reproducibility eightfold, and increase fiber volume by one order of magnitude. Furthermore, eutectic gallium indium liquid metal and scaled-up pattern geometries demonstrate the tunability of this approach and broad applicability of systematic fiber pattern analysis. This rational approach to patterned fiber development can be applied to virtually any method or pattern to better understand the fiber patterning processes.