Nanopillar Patterns Research Articles

Fabrication of Nanostructures on a Large-Area Substrate with a Minimized Stitch Error Using the Step-and-Repeat Nanoimprint Process.

Nanoimprint lithography (NIL) is suitable for achieving high uniformity and mass production. However, in conventional NIL, a stamp suitable for the substrate size is required to increase the substrate size. To address this issue, we fabricated nanostructures on a large-area substrate using step-and-repeat NIL after making a small stamp. A stamp was produced using glass, and a nano-pillar pattern with a diameter of 600 nm, an interval of 400 nm, and a height of 270 nm was used during the experiment. The area of the pattern on the stamp was 10 mm × 10 mm, and the step-and-repeat process was performed 25 times to transfer the nanostructures to a 4-inch substrate. In addition, stitch gaps were created between the patterns, which could decrease the performance upon future application. To minimize this stitch gap, a high-precision glass scale was attached to the stamp feeder to precisely control the position and to minimize the step difference. Moreover, an experiment was conducted to minimize the stitch gap by adjusting the movement interval of the stamp, and the stitch spacing was minimized by moving the stamp position by 9.97 mm. This approach will facilitate the manufacturing of large-area substrates and other structures in the future.

Study of the deposition of nanopillar-patterned 4H-SiC by molecular dynamics simulation

4H-SiC film growth is a key technology in device manufacturing, but the understanding of the substrate surface pattern on the deposition process of the 4H-SiC film at the atomic scale is still very poor. In this paper, the effect of nanopillar-patterned 4H-SiC substrate on the quality of the film is investigated by a series of molecular dynamics (MD) simulations, and the crystal structure, dislocation distribution, surface morphology, roughness, internal stress and density of the deposited film are analyzed at different growth temperatures. The results show that the substrate surface containing nanopillar pattern have lower dislocation density than that without pattern. The surface morphology and roughness of the deposited film are more sensitive to the growth temperature. The average mean atomic stress of the film is compressive and the value exhibits oscillatory behavior as the deposited atoms increase. The deposited film with nanopillar pattern has higher density compared to the one without pattern, resulting in lower volume fraction of defects in the film. The study of this work may provide a better understanding of film deposition at the nanoscale and the effect of substrate surface pattern on the deposited film.

Enhancement of Light Extraction from Organic Light-Emitting Diodes by SiO2 Nanoparticle-Embedded Phase Separated PAA/PI Polymer Blends

Using the phase separation of a binary immiscible polymer blend of poly(amic acid) and polyimide in combination with SiO2 nanoparticles, we have designed random nanopore and nanopillar patterns by a simple spin-coating technique. The spontaneously formed pattern structure was investigated by an atomic force microscope technique, which enhanced the external quantum efficiency of conventional green OLEDs up to a highest factor of 1.42. This enhancement is mainly attributed to the reduction of the total internal reflection at the interface of glass and air by the polymer hybrid layer on the backside of OLED devices. This work provides a new and practical approach to the development of efficient external outcoupling structures for OLEDs.

Nanopore-Templated Silver Nanoparticle Arrays Photopolymerized in Zero-Mode Waveguides.

In situ fabrication of nanostructures within a solid-polymer electrolyte confined to subwavelength-diameter nanoapertures is a promising approach for producing nanomaterials for nanophotonic and chemical sensing applications. The solid-polymer electrolyte can be patterned by lithographic photopolymerization of poly(ethylene glycol) diacrylate (PEGDA)-based silver cation (Ag+)-containing polyelectrolyte. Here, we present a new method for fabricating nanopore-templated Ag nanoparticle (AgNP) arrays by in situ photopolymerization using a zero-mode waveguide (ZMW) array to simultaneously template embedded AgNPs and control the spatial distribution of the optical field used for photopolymerization. The approach starts with an array of nanopores fabricated by sequential layer-by-layer deposition and focused ion beam milling. These structures have an optically transparent bottom, allowing access of the optical radiation to the attoliter-volume ZMW region to photopolymerize a PEGDA monomer solution containing AgNPs and Ag+. The electric field intensity distribution is calculated for various ZMW optical cladding layer thicknesses using finite-element simulations, closely following the light-blocking efficiency of the optical cladding layer. The fidelity of the polyelectrolyte nanopillar pattern was optimized with respect to experimental conditions, including the presence or absence of Ag+ and AgNPs and the concentrations of PEGDA and Ag+. The self-templated approach for photopatterning high-resolution photolabile polyelectrolyte nanostructures directly within a ZMW array could lead to a new class of metamaterials formed by embedding metal nanoparticles within a dielectric in a well-defined spatial array.

Formation of nanopore and nanopillar patterned polymer films from mixed PAA-PI solutions by phase separation method

Random nanopore and nanopillar patterns were prepared by using simple spin-coating technique based on the phase separation of a binary immiscible polymer blend of poly(amic acid) (PAA) and polyimide (PI). The pattern structure was spontaneously formed upon spin-coating of a mixed solution of PAA and PI on a glass substarte followed by thermal annealing, whose morphology was investigated by atomic force microscope and field emission scanning electron microscope technique. The results showed that not only the size of the patterns was the nanoscale of around 200 nm but also their shape was very uniform without requiring conventional patterning or photolithography processes. Two different morphologies, nanopore and nanopillar arrays were obtained for the PAA:PI volume ratio of 1:9 and 9:1, respectively. The flexible characteristic of nanopore and nanopillar films could be an interesting feature to be applied to organic light-emitting diodes lighting and displays.

High performance microsupercapacitors based on a nano-micro hierarchical carbon electrode by direct laser writing

We have demonstrated a direct laser writing (DLW) process that uses a femtosecond laser to fabricate a nano-micro hierarchical structure for a large capacitance microsupercapacitor (MSC) electrode. By applying a two-photon polymerization-based DLW technique, a photoresist (PR) nano-pillar pattern was fabricated on a pre-defined PR interdigitated electrode (PR-IDE) pattern to form a nano-micro hierarchical structure. Carbon pyrolysis converted a PR-IDE with a nano-micro hierarchical structure to a PR derived carbon (PRC)-IDE while maintaining the aspect ratio of the pillar structure. The electrochemical performance of the PRC-MSC is improved by introducing the nano-pillar pattern to the PRC-IDE, resulting in larger areal capacitance of the as-fabricated PRC-IDE compared to the PRC-IDE with a micropattern only. The PRC-IDE with a nano-micro hierarchical structure in this study could be further applied as a backbone electrode structure for a high power pseudo-capacitor.

Comparative study on luminescence extraction strategies of LED by large-scale fabrication of nanopillar and nanohole structures

Light extraction and current injection are two important considerations in the development of high efficiency light-emitting-diodes (LEDs), but usually cannot be satisfied simultaneously in nanostructure patterned devices. In this work, we investigated near-UV LEDs with nanopillar and nanohole patterns to improve light extraction efficiency. Photoluminescence (PL) intensities were enhanced by 8.0 and 4.1 times for nanopillar and nanohole LEDs compared to that of planar LED. Nanopillar LED exhibits higher PL emission than that of the nanohole LED, attributing to a convex shape sidewall for more effective outward light scattering, and reduction of quantum-confined-stark-effect owing to strain relaxation. However, nanopillar LED exhibits lower electroluminescence intensity than the nanohole sample, which calls for further optimization in carrier distributions. Experimental results were further supported by near-field electric field simulations. This work demonstrates the difference in optical and electrical behaviors between the nanopillar and nanohole LEDs, paving the way for detailed understanding on luminescence extraction mechanisms of nanostructure patterned UV emitters.

The NanoTuFe — Fabrication of large area periodic nanopatterns with tunable feature sizes at low cost

Fabricating nanopatterns for large area and in small feature sizes is in general cost-intensive. In this paper, a cost-efficient process chain is demonstrated to fabricate periodic nanopatterns with tunable feature sizes (NanoTuFe) utilizing a series of well-known technologies such as soft UV Nanoimprint Lithography (NIL), dry and wet etching. An intermediate template featuring nanocone and nanopyramid is introduced to bridge the original and the final patterns. The feature size on the final fabricated substrate can be widely tuned and controlled. Wafers in diameter of 100mm full of square nanocavities with 130/160/190/220nm feature sizes, respectively, have been fabricated from a single master wafer containing nanocavities with 350nm diameter. Nanopillar patterns with diameters of 150/200/250nm, respectively, have been produced on wafer level from a single master with 450nm feature size. Cryogenic silicon etching based on SF6/O2 chemistry is employed to create the final shrunk nanopatterns with smooth and vertical profiles. The fabrication processes cope without costly electron beam or laser beam direct writings, achieving the nanopatterns with tunable feature sizes in a cost-efficient manner. In addition, the process chain grants the wafer-level production at a constant pitch, which is of importance for the stacked alignment of layers with varying feature sizes. The generated periodic nanopatterns can be applied for NIL templates, photonic crystals, optics, energy conversion and storage, sensing elements, etc.

Low-cost fabrication of nanoimprint templates with tunable feature sizes at a constant pitch

Nanoimprint lithography (NIL) templates are in general costly, especially for large area and small feature sizes. With a simple shrinking technique using a serial of well-known technologies, it has been feasibly realized to produce high-quality soft NIL templates with widely tunable feature sizes at a constant pitch from a single master at very low-cost and in a short processing cycle. The master featuring at sub-micron range has been replicated to new silicon NIL templates with feature sizes at, but not limited to, sub-200nm. soft UV-NIL combined with a dry etch process, were employed to fabricate an intermediate template of nanocone patterns that is further used for an imprint on the final substrate. The feature size of the SiO2 etch mask on the final substrate can be adjusted by varying the duration of mask formation etching. The final patterning of the template is realized by cryogenic etching based on SF6/O2 chemistry. Silicon NIL templates featuring nanopillar patterns with diameters of 150nm, 200nm and 250nm, respectively, have been fabricated on wafer level from the same master with 450nm feature size. The presented process flow avoids the time-consuming and cost-intensive electron beam writings and gives more flexibility in the fabrication of nanopatterns. The fabrication cycle for such NIL working templates with tunable feature sizes is maintained short and at a low cost. Moreover, the technique allows the fabrication of wafer level products at a constant pitch, which is of importance as well for the stacked large-area imprintings with varying feature sizes.

Cicada-inspired cell-instructive nanopatterned arrays.

Biocompatible surfaces hold key to a variety of biomedical problems that are directly related to the competition between host-tissue cell integration and bacterial colonisation. A saving solution to this is seen in the ability of cells to uniquely respond to physical cues on such surfaces thus prompting the search for cell-instructive nanoscale patterns. Here we introduce a generic rationale engineered into biocompatible, titanium, substrates to differentiate cell responses. The rationale is inspired by cicada wing surfaces that display bactericidal nanopillar patterns. The surfaces engineered in this study are titania (TiO2) nanowire arrays that are selectively bactericidal against motile bacteria, while capable of guiding mammalian cell proliferation according to the type of the array. The concept holds promise for clinically relevant materials capable of differential physico-mechanical responses to cellular adhesion.

Density of nanopatterned surfaces for designing bone tissue engineering scaffolds

Design and manipulation of scaffolds are essential to improve cellular functions for regeneration of functional bone constructs in tissue engineering and regenerative medicine. Here, we describe that the nanotopographical density may have great potentials as an effective strategy for modulating behavior of human osteoblast-like cells. Using capillary force lithography, nanopillar pattern arrays were fabricated to investigate the effect of nanotopographical density on the behaviors of MG-63 cells. It was found that the nanotopographical structures promoted the attachment of MG-63 cells compared to the flat substratum as well as influenced the shape of them. In particular, the cell differentiation study showed that the 1:3 nanopatterned substratum (width to spacing ratio, defined by the ridge width of 1:3) exhibited the highest bone mineralization compared to other nanopatterned substrata and the flat substratum. These results demonstrated that the nanotopographical density may play a crucial role in regulating cell behaviors as an important considering factor for scaffold fabrication for bone tissue engineering applications.

Size Control in ZnO Nanopillar Fabrication Using a Gel-Nanoimprint Process

We evaluated size controllability and size error occurrence in fabrication of ZnO nanopillar pattern by gel-nanoimprint process. The ZnO nanopillar patterning yielding smaller size error than the conventional nanoimprint process was achieved. The UV-O3treatment was also proposed to make precise patterning, but we found that this treatment could not hold the nanostructure patterned, though the clear shape could be obtained just after the treatment.

Reduction of proximity effect in fabricating nanometer-spaced nanopillars by two-step exposure

A two-step exposure method to effectively reduce the proximity effect in fabricating nanometer-spaced nanopillars is presented. In this method, nanopillar patterns on poly-methylmethacrylate (PMMA) were partly cross-linked in the first-step exposure. After development, PMMA between nanopillar patterns was removed, and hence the proximity effect would not take place there in the subsequent exposure. In the second-step exposure, PMMA masks were completely cross-linked to achieve good resistance in inductively coupled plasma etching. Accurate pattern transfer of rows of nanopillars with spacing down to 40 nm was realized on a silicon-on-insulator substrate.

Large Area High Density Sub-20 nm SiO2 Nanostructures Fabricated by Block Copolymer Template for Nanoimprint Lithography

We developed simple fabrication methods to effectively transfer the block copolymer nanopatterns to a substrate material. High aspect ratio, sub-20 nm nanopillar and nanohole structures are successfully fabricated in a SiO(2) layer in large area format, and the versatile utilities of these nanostructures as nanoimprint molds are studied. Nanoimprint lithography using these molds makes it possible to easily replicate densely packed block copolymer nanotemplate patterns on arbitrary substrates in a short processing time by using a large variety of polymer materials, including functional materials such as conjugated polymers. In addition, the PDMS soft stamps with both nanohole and nanopillar pattern polarities, which are useful tools for soft lithography and transparent template applications, are also successfully fabricated using the pillar- and hole-type SiO(2) molds. These soft stamps provide an effective way to fabricate controllable as well as reproducible plasmonic metal nanostructures with tunable surface plasmon resonances.

Design and Fabrication of Perpendicular Patterned Magnetic Media Using Nanoimprinted Nano Pillar Patterns

Perpendicular patterned magnetic media have been regarded as a one of candidate to achieve an ultrahigh density magnetic data storage media of over 1 Tb/in2 . One approach to producing patterned magnetic media is deposition of thin magnetic films on pre-etched nano pillar array prepared with nanoimprinting technology. In this paper, we have investigated the feasibility of the polymeric nano pillar patterns on glass substrate, which were replicated by UV nanoimprinting process with the polymeric nanostamp, and magnetic layer deposition technology without additional etching process to fabrication for perpendicular patterned magnetic media. The polymeric nano pillar patterns were replicated by 2-step UV nanoimprinting process by using a silicon nanomaster with nano pillar patterns. We deposited magnetic layers on the nanoimprinted nano pillar patterns to make the perpendicular patterned magnetic media. Finally, we show that the fabricated magnetic media could be used for perpendicular patterned magnetic media by measurement of magnetic characteristics.

Fabrication of Metallic Nano Stamp to Replicate Patterned Substrate Using Electron-Beam Recording, Nanoimprinting, and Electroforming

A cost-effective method to fabricate metallic nano stamp with full tracks of nano hole patterns with diameter of 30 nm and pitch of 50 nm was developed for nano replicating nano patterned substrate. Electron-beam recording (EBR) and inductively coupled plasma etching process were used in order to fabricate the original silicon master with hole patterns. Polymeric master with full tracks of nano pillar patterns was replicated from the original silicon master by UV nanoimprinting process. For the successful releasing during UV nanoimprinting process, self assembled monolayer of fluoroctatrichlorosilane was deposited on the original silicon master. With this approach, the expensive silicon master could be reused many times as a master mold. Nickel seed layer as conductive layer was deposited onto the polymeric master using sputtering process. Nano-electroforming process using nickel sulfamate solution was used to fabricate metallic nano stamp. Metallic nano stamp with full tracks of hole patterns having diameter of 30 nm, pitch of 50 nm, track width of 1.3 mm, and track inner diameter of 40 mm was successfully fabricated. The present method will provide an important mean to mass fabricate patterned media.