Nano Patterns Research Articles

Effect of metal ion concentration in Ni–W plating solution on surface roughness of Ni–W film

Since nanopatterns are used for various purposes including solar cells, super-hydrophilicity, and biosensors, it is necessary to miniaturize the patterns on glass devices from micro- to nano-order. We have studied glass imprinting as an excellent microfabrication technology for glass devices. Uniformity of the nanopattern height is required for a mold, since a nodular structure on the Ni–W surface is recognized as a problem in Ni–W nanopattern formation. We confirmed that the Ni–W plating bath increasing metal ion concentration is effective for inhibition of the nodular structure on the Ni–W film, and succeeded in Ni–W nano pattern formation with uniform height. However, the W content rate of plated Ni–W film was reduced in exchange for enhancing the flatness of the Ni–W film. It is necessary to examine the Ni–W plating condition for obtaining planarization of the Ni–W surface and a high content rate of W in the Ni–W film.

Electrolithography--A New and Versatile Process for Nano Patterning.

We report a new lithography technique based on electromigration driven material transport for drawing patterns at nanometer scales in ambient conditions. We use a thin metal film as a masking layer and a polymer layer beneath it as a pattern transfer layer. The desired pattern is drawn in the metal layer by etching the metal with a conducting scanning probe assisted by liquid electromigration. The pattern drawn on the metal layer is transferred to the polymer layer by etching the polymer with an appropriate solvent. Subsequently, the pattern is transferred to the desired material layer using a film deposition technique followed by conventional lift-off process. Using this simple technique, we have achieved pattern resolutions of 9 nm on the polymer and 40 nm on transferring the pattern to another material. Based on the ease of use and process costs, this technique promises to be competitive to e-beam lithography that employs high energy and ultra-high vacuum, or the industrial standard ultra-violet light photolithography that employs extremely expensive implements to reach nano-scale resolutions. We also demonstrate direct mask writing using this technique and explain the fundamentals behind the workings of the developed method.

Theoretical study of fabrication of line-and-space patterns with 7 nm quarter-pitch using electron beam lithography with chemically amplified resist process: III. Post exposure baking on quartz substrates

Electron beam (EB) lithography is a key technology for the fabrication of photomasks for ArF immersion and extreme ultraviolet (EUV) lithography and molds for nanoimprint lithography. In this study, the temporal change in the chemical gradient of line-and-space patterns with a 7 nm quarter-pitch (7 nm space width and 21 nm line width) was calculated until it became constant, independently of postexposure baking (PEB) time, to clarify the feasibility of single nano patterning on quartz substrates using EB lithography with chemically amplified resist processes. When the quencher diffusion constant is the same as the acid diffusion constant, the maximum chemical gradient of the line-and-space pattern with a 7 nm quarter-pitch did not differ much from that with a 14 nm half-pitch under the condition described above. Also, from the viewpoint of process control, a low quencher diffusion constant is considered to be preferable for the fabrication of line-and-space patterns with a 7 nm quarter-pitch on quartz substrates.

Theoretical study of fabrication of line-and-space patterns with 7 nm quarter-pitch using electron beam lithography with chemically amplified resist processes: II. Stochastic effects

Electron beam (EB) lithography is a core technology for nanofabrication. Owing to the increasing demand for high-resolution semiconductor lithography, the requirements for the resist processes of EB lithography for the photomasks used in ArF immersion and extreme ultraviolet lithographies and the mold fabrication of nanoimprints have also become stricter. In this study, the feasibility of single nano patterning by EB lithography with a chemically amplified resist process was investigated from the viewpoint of stochastic effects. The latent images of line-and-space patterns with a 7 nm quarter-pitch (7 nm space width and 21 nm line width) were calculated using a Monte Carlo method on the basis of the sensitization and reaction mechanisms of chemically amplified EB resists. Compared with the line-and-space pattern with a 7 nm half-pitch, line edge roughness (LER) and the stochastic pinching generation are considered to be significantly improved by increasing the pitch. It was found that the suppression of the stochastic generation of bridges is the critical issue in 7 nm quarter-pitch fabrication.

Nano and Microscale Patterning on Soft Matters with Ion Beam Irradiation

Nano and Microscale Patterning on Soft Matters with Ion Beam Irradiation

(Invited) Imprinted Functional Nano-Structures for Highly Efficient Photonic Devices

Recently, nanoimprint lithography (NIL) has gained great attention as an effective patterning technology in the fields of light emitting diodes (LEDs), solar cells, and other optical devices, because of its simplicity and cost effectiveness. The aim of this research is the development of NIL based direct printing process with an imprint resist containing dispersed various metal oxide (ZnO, TiO2, and ATO) nano-particles. A functional nano pattern can be easily fabricated by this direct printing of functional materials. The properties of substrates, such as transmittance, diffraction, refractive index, and hydrophobicity, was successfully controlled by forming the functional nano-patterns. Finally, the efficiency of optoelectronic devices, such as solar cell and light-emitting diodes was drastically enhanced.

Ultrahigh precision low-cost pinpointed SiO2 patterns nanofabrication by using traditional MEMS fabrication processes

Recent years, nanoscale patterns transfer technique from DNA origami molecules to SiO2 layer has been a promising approach of silicon based nanofabrication process. However, researchers find it difficult to locate SiO2 nano patterns with origami's shapes. Here, we present a novel and low-cost approach of ultrahigh precision SiO2 patterns nanofabrication in target position. Traditional contact lithography process is used to fabricate nanoscale silicon oxide islands array in this paper, which are used to pinpoint the position of ultrahigh precision nano patterns. Precise controllability sacrificial layer etching is the key process to realize nanoscale control of islands in process. This fabrication method is a simple and cost-effective method with high yield, which will hopefully make contributions for higher precision nanofabrication technology in the future.

Theoretical study of fabrication of line-and-space patterns with 7 nm quarter-pitch (7 nm space width and 21 nm line width) using electron beam lithography with chemically amplified resist processes: I. Relationship between sensitivity and chemical gradient

Electron beam (EB) lithography used for mask and mold fabrication is an indispensable technology in the lithography used for high-volume production of semiconductor devices. With the reduction in the critical dimensions of semiconductor devices, the requirement for EB lithography also becomes severe. In this study, the feasibility of single nano patterning using EB lithography with a chemically amplified resist process was investigated. The latent images of line-and-space patterns with a 7 nm quarter-pitch (7 nm space width and 21 nm line width) were calculated on the basis of sensitization and reaction mechanisms of chemically amplified EB resists. Simulations indicated that the line-and-space patterns with 7 nm quarter-pitch can be resolved with line edge roughness of 0.9–1.9 nm with a sensitivity of 270 µC cm−2 using a 3 nm electron beam.

The role of bio-inspired hierarchical structures in wetting

Superhydrophobicity facilitates the development of self-cleaning, anti-biofouling, and anti-corrosion surfaces. The leaves of the lotus (Nelumbo nucifera) and taro (Colocasia esculenta) plants are well known for their self-cleaning properties. A hierarchical structure comprising papillae epidermal cells superimposed with epicuticular wax crystalloids of varying shapes, sizes, and orientations is an important aspect of the surface of these plant leaves. We fabricated two types of hierarchical structures biomimicking the surface topography of the lotus leaf. The hierarchical patterns successfully demonstrated the superhydrophobic state in comparison with nano and micro patterns. We used the finite element method (FEM) to simulate and understand the wetting process. The FEM simulations showed good correlation with the experimental results. FEM was helpful in understanding the wetting of enormously complex biological surfaces with relative ease, and it qualifies as a potential tool for designing superhydrophobic surfaces. Using the FEM framework, we further designed surfaces to optimize the order of the shapes in hierarchy. The results showed that the superhydrophobic surface with the lowest wetted area was obtained by placing shapes with smaller geometric angles at the top of the hierarchy. This arrangement of shapes provides the optimum combination of superhydrophobicity and surface integrity. This observation explains why the hierarchical structure of many superhydrophobic leaves follows this order. We also investigated the complex hierarchical structure of Salvinia minima. Owing to its remarkable ability to entrap air and pin the contact line, it exhibits superhydrophobicity along with the much-required Cassie state. These properties of Salvinia minima make it an excellent candidate for developing omniphobic surfaces.

ChemNanoMat-A New Journal for Small Science with a Big Impact

<i>ChemNanoMat</i>-A New Journal for Small Science with a Big Impact

Research Highlight: Top-Down Nanomachining of Metals

Microand nanomachining technologies are commonly categorized into top-down and bottom-up approaches. Making nanoscale structures using top-down approach has been facing difficulties due to the limitation of optical lithography and the low throughput of electron beam and ion beam techniques. Soft lithography and hot embossing can transfer nanostructures across a large wafer. However, these techniques are limited to a soft substrate such as polymers only. A recent work by researchers from Purdue University, Harvard University, Madrid Institute for Advanced Studies, and the University of California, San Diego demonstrated a new embossing technology to create wafer-scale smooth three-dimensional nanoshapes on hard crystalline metal. Top-down micro/nanomaching approaches can either create a wafer-scale pattern with fast batch limited-resolution processes or a small-scale pattern with slow highresolution serial processes. Wafer-scale machining of nanostructures was made possible with soft lithography [1], which transfers patterns through direct contact of a soft stamp. Soft lithography, in particular the wafer-scale replication of elastomeric structures, has enabled the rapid development of the research areas of microfluidics and nanofluidics [2]. Although many microfluidic and nanofluidic devices were made of inorganic materials such as glass and silicon, the majority of these devices are made of elastomers and thermoplastics due to the simple replication processes such as molding and hot embossing [3]. The molding approach has been extended to hydrogels for biological applications such as cell culture [3]. Hot embossing and nano imprint techniques make role-to-role printing processes. The role-to-role technology allows for low-cost large-area fabrication of complex devices such as flexible thinfilm transistors for display applications [4]. Soft lithography and nano imprint lithography are suitable for making nanostructures in polymers [5]. However, the soft nature of polymers makes processes with high fidelity difficult. Often, subsequent processes such as bonding need to be carried out at low temperature and low pressure [6]. Nano patterning of metals through embossing has been impossible because of their low formability in the scale smaller than 1 micron. The extremely high strain rate and high temperature above the melting temperature are the main technological challenges for top-down nanomachining of metals. Nanomachining of hard and crystalline metals is even more challenging. Recently, Gao et al. [7] reported the laser shock imprinting (LSI) technology that can create smooth three-dimensional crystalline metallic structures in nanoscale under ambient conditions. The technology utilizes a laser to create shockwave impulses and ultrahigh strain rate to compress a metallic sheet into a silicon nanomold. The laser has a power of 0.3 to 1.4 GW/cm 2 , a wavelength of 1064 nm and a pulse duration of approximately 5 ns. The metal layer was prepared on a glass substrate that was coated with 10-μm graphite as the ablation coating layer. Under the laser irradiation, the graphite sublimates ad creates a shock wave that propagates through the metal layer and deforms it to conform the underlying silicon mold. The nanoscale resolution of the mold can be transferred accurately to the metal layer. The silicon mold surface was coated with 5 to 10 nm aluminum oxide to improve the abrasive resistance. Such as silicon nanomold can be reused for over a hundred times without reduction of patterning quality. Furthermore, coating a 1 to 5 nm polyvinylpyrrolidone (PVP) layer or a 5 to 10 nm gold layer on the metal reduces the friction during the imprinting process. The patterned nanostructures have an aspect ratio as high as 5. The technology allows for making nanoscale structures in titanium, aluminum, copper, gold and silver over a 6-inch wafer in only 30 seconds. The LSI technology has the potential to enable low-cost large-scale plasmonic metamaterials that have surfaces containing patterns on the scale of nanometers. The paper also reports the use of LSI for patterning the metal layer with graphene that represent a perfect absorber for metametrials with potential applications in nanoelectronics, optoelectronics and plasmonics. LSI also has the potential to be transferred to the roll-to-roll technology, which currently are limited to processing polymeric and organic materials.

누름가공과 AAO 공정을 이용한 나노-마이크로 복합패턴 제작방법 연구

Micro/nano patterns for optical concentration and diffusion have been studied in the various fields such as displays, optics, and sensors. Conventional micro patterns were continuous and linear shapes due to using linear-type light sources, however, recently non-continuous patterns have been applied as point sources are used for dot-type light sources such as LEDs and OLEDs. In this study, a hybrid machining technology combining an indentation machining method and an AAO process was developed for manufacturing the non-continuous micro patterns having nano patterns. First, mirror-like surfaces (R a <20nm) of pure Aluminum substrates were obtained by optimizing cutting conditions. Then, The letter of ‘K’ consisting of the arrays of the micro patterns was manufactured by the indentation machining method which has a similar principle to indentation hardness testing. Finally, nano patterns were machined by AAO process on the micro patterns. Conclusively, a specific letter having nano-micro hybrid patterns was manufactured in this study.

Effects of surface topography on growth and osteogenic differentiation of human mesenchymal stem cells

The clinical success of an endosseous artificial implant is related to the quality of its osseointegration with the surrounding living bone. To achieve a stable anchorage, mesenchymal cells, migrating to the implant surface from the surrounding tissue, must differentiate towards mature osteoblasts rather than connective tissue cell types. It is well known that the cell response is affected by the physicochemical parameters of the biomaterial surface, such as surface energy, surface charges or chemical composition. Topography seems to be one of the most crucial physical cues for cells (1). In particular, interactions between mesenchymal stem cells (MSCs) and surfaces with specific micro and nano patterns can stimulate MSCs to produce bone mineral in vitro (2). Herein, stamps reporting different micro and nano features were fabricated in order to obtain several corresponding replicas in a short time through microinjec- tion molding. Then, the effects of the substrate topography on human bone marrowderived MSC adhesion, proliferation, and osteogenic differentiation were investigated in the absence of inductive growth factors. Collectively, our data show that both micro- and nano-structured surfaces possess osteoinductive properties. A relationship between dimensional feature of surface topography and differentiative potential was noted. On the contrary, cell adhesion and proliferation seemed to be unaffected. Further in vivo studies will be carried out to confirm the osteoinductive properties of selected surface geometries.

Simulation of nano-grating patterning based on X-ray Talbot effect

High aspect ratio gratings can be made by perpendicularly cutting in the growth direction of multilayers. X-ray exposure technique using a sectioned multilayer grating based on Talbot effect is a new type of nano patterning method. Although 300 nanometer gratings through the experiment are completed, some phenomena in the experiments cannot be satisfactorily explained and the factors influencing the nano pattern quality have not been fully understood yet. Here we use a rigorous coupled-wave theory to discuss several important factors, including grating thickness, the fraction of material thickness and multilayer period, which is the first time as far as we know for Talbot self-imaging in X-ray range. Simulation results show that the grating thickness affects both X-ray transmission efficiency and fringe contrast, while the fraction of material thickness determines the quality of fringes. And the position deviation of the best image plane in near field is related to both the thickness of the grating and the multilayer period. Moreover, the multilayer gratings with smaller periods can achieve higher resolution, indicating that the Talbot effect can be used to fabricate a more detailed structure.

Dip-pen nanolithography를 위한 이중 팁을 가진 질화규소 프로브의 설계 및 제조

We report the design, fabrication of a Si3N4 probe and calculation of its mechanical properties for DPN(dip pen nanolithography), which consists of dual tips. Concept of dual tip probe is to employ individual tips on probe as either an AFM tip for imaging or a writing tip for nano patterning. For this, the dual tip probe is fabricated using low residual stress Si3N4 material with LPCVD deposition and MEMS fabrication process. On the basis of FEM analysis we show that the functionality of dual tip probe for imaging is dependent on the dimensions of dual tip probe, and high ratio of widths of beam areas is preferred to minimize curvature variation on probe.

Effects of polycrystallinity in nano patterning by ion-beam sputtering

Employing graphites with distinctly different mean grain sizes, we study the effects of polycrystallinity on the pattern formation by ion-beam sputtering. The grains influence the growth of the ripples in a highly anisotropic fashion; both the mean uninterrupted ripple length along the ridges and the surface width depend on the mean size of the grains, which is attributed to the large sputter yield at the grain boundary compared with that on the terrace. In contrast, the ripple wavelength does not depend on the mean size of the grains, indicating that the mass transport across the grain boundaries should efficiently proceed by both thermal diffusion and ion-induced processes.

Capillary force lithography for cardiac tissue engineering.

Cardiovascular disease remains the leading cause of death worldwide(1). Cardiac tissue engineering holds much promise to deliver groundbreaking medical discoveries with the aims of developing functional tissues for cardiac regeneration as well as in vitro screening assays. However, the ability to create high-fidelity models of heart tissue has proven difficult. The heart's extracellular matrix (ECM) is a complex structure consisting of both biochemical and biomechanical signals ranging from the micro- to the nanometer scale(2). Local mechanical loading conditions and cell-ECM interactions have recently been recognized as vital components in cardiac tissue engineering(3-5). A large portion of the cardiac ECM is composed of aligned collagen fibers with nano-scale diameters that significantly influences tissue architecture and electromechanical coupling(2). Unfortunately, few methods have been able to mimic the organization of ECM fibers down to the nanometer scale. Recent advancements in nanofabrication techniques, however, have enabled the design and fabrication of scalable scaffolds that mimic the in vivo structural and substrate stiffness cues of the ECM in the heart(6-9). Here we present the development of two reproducible, cost-effective, and scalable nanopatterning processes for the functional alignment of cardiac cells using the biocompatible polymer poly(lactide-co-glycolide) (PLGA)(8) and a polyurethane (PU) based polymer. These anisotropically nanofabricated substrata (ANFS) mimic the underlying ECM of well-organized, aligned tissues and can be used to investigate the role of nanotopography on cell morphology and function(10-14). Using a nanopatterned (NP) silicon master as a template, a polyurethane acrylate (PUA) mold is fabricated. This PUA mold is then used to pattern the PU or PLGA hydrogel via UV-assisted or solvent-mediated capillary force lithography (CFL), respectively(15,16). Briefly, PU or PLGA pre-polymer is drop dispensed onto a glass coverslip and the PUA mold is placed on top. For UV-assisted CFL, the PU is then exposed to UV radiation (λ = 250-400 nm) for curing. For solvent-mediated CFL, the PLGA is embossed using heat (120 °C) and pressure (100 kPa). After curing, the PUA mold is peeled off, leaving behind an ANFS for cell culture. Primary cells, such as neonatal rat ventricular myocytes, as well as human pluripotent stem cell-derived cardiomyocytes, can be maintained on the ANFS(2).

Design of a fine alignment system featuring active orientation adjustment for nano imprint lithography

The fine alignment between a template with nano patterns and a wafer substrate, especially the parallelism between the two surfaces, is critical to Nano Imprint Lithography. A fine alignment system featuring active orientation adjustment which is composed of an imprint unit and a 6-DOF micromanipulator is proposed in this work. Deformations of a compact flexure layer caused by imprint loads are measured by four identical force sensors embedded in the imprint unit. The tilt of the flexure layer can thus be eliminated by adjusting the orientation of the 6-DOF micromanipulator. Kinematics and stiffness analysis are then developed, followed by dynamic performance evaluations. Based on the proposed system, an imprint tool is further developed and corresponding experiments are conducted. A saw shape grating pattern with 1.6 μm linewidth and a lattice pattern with 0.9 μm period are both imprinted with a minimum feature of 30 nm well reserved on the substrate. A maximum parallelism error of 14 nm across the template surface is also demonstrated by further section analyses on the imprinted patterns, hence the feasibility and superiority of the proposed method is verified.

Improvement of light out-coupling efficiency in organic light-emitting diodes with variable nanopatterns

We present a viable method to enhance the current efficiency of organic light-emitting diodes (OLEDs) by imprinting cylindrical nanopatterns (NPs) onto a glass substrate. Herein, OLEDs equipped with an optimum NP array having a diameter of 300 nm and a periodic distance of 500 nm show a 33.4% improvement in current efficiency compared with a device without NPs. The light extraction efficiency of OLEDs was enhanced using a nanopatterned glass substrate, without any electrical degradation owing to the formation of NPs on opposite sides of the organic layers. In addition, top-emitting OLEDs can be fabricated easily by patterning the encapsulation glass.

Recent Advances in Nano Patterning and Nano Imprint Lithography for Biological Applications

Nano patterning and Nanoimprint lithography [NIL] has advanced to great heights in recent years. Customizing the surface at micro and nano scale is of great demand. It facilitates the handling and working at micro and nano scale level. Its applications towards medical field are growing day by day. Precise surface patterning with nanometer resolution has great potential in many medical and biological applications. It also provides a platform for fundamental studies of molecular and cell biology. This review article comprises of current trends and future scope of nano patterning and NIL. In this article we particularly focus on biological applications.