Nanotransfer Printing Research Articles

Controlled Formation of Porous Cross-Bar Arrays Using Nano-Transfer Printing.

Nano-transfer printing (nTP) has emerged as an effective method for fabricating three-dimensional (3D) nanopatterns on both flat and non-planar substrates. However, most transfer-printed 3D patterns tend to exhibit non-discrete and/or non-porous structures, limiting their application in high-precision nanofabrication. In this study, we introduce a simple and versatile approach to produce highly ordered, porous 3D cross-bar arrays through precise control of the nTP process parameters. By selectively adjusting the polymer solution concentration and spin-coating conditions, we successfully generated discrete, periodic line patterns, which were then stacked at a 90-degree angle to form a porous 3D cross-bar structure. This technique enabled the direct transfer printing of PMMA line patterns with well-defined, square-arrayed holes, without requiring additional deposition of functional materials. This method was applied across diverse substrates, including planar Si wafers, flexible PET, metallic copper foil, and transparent glass, demonstrating its adaptability. These well-defined 3D cross-bar patterns enhance the versatility of nTP and are anticipated to find broad applicability in various nano-to-microscale electronic devices, offering high surface area and structural precision to support enhanced functionality and performance.

Nanotransfer Printing of Functional Nanomaterials on Electrospun Fibers for Wearable Healthcare Applications (Adv. Funct. Mater. 33/2024)

Nanotransfer Printing of Functional Nanomaterials on Electrospun Fibers for Wearable Healthcare Applications (Adv. Funct. Mater. 33/2024)

Nanotransfer Printing for Synthesis of Vertically Aligned Carbon Nanotubes with Enhanced Atomic Penetration

AbstractVertically aligned carbon nanotubes (VACNTs) exhibit outstanding mechanical strength, chemical stability, and electrical characteristics; however, their constrained mechanical elasticity and chemical responsiveness spurred research on atomic decoration techniques for enhancing their mechanochemical attributes. Nevertheless, achieving uniform atomic decoration on the VACNT surface is difficult because of the high density and large aspect ratio of VACNT. Herein, a strategy to design and apply nanopatterned VACNTs (nVACNTs) based on a nanotransfer printing process is proposed to improve atomic penetrability. Nanopatterns inherent to nVACNTs facilitate atomic penetration, allowing for the more consistent and higher quality deposition of functional materials such as zinc oxide and alumina by atomic layer deposition. Furthermore, physical vapor deposition provides an improved coating of metal catalysts such as gold. The uniform deposition of ceramic layers on the entire surface of nVACNTs strengthens its mechanical resilience, owing to the diminished van der Waals forces of CNTs. Surface‐decorated nVACNTs display an increased sensitivity to NO2 gas, which is attributed to the enhanced quality of the reactive catalyst deposition and augmented permeability. This strategy achieves a larger decorated area while increasing a catalytically active reaction area. The obtained results promise that the enhanced nVACNTs will expand the industrial applications of carbon nanotubes.

Nanotransfer Printing of Functional Nanomaterials on Electrospun Fibers for Wearable Healthcare Applications

AbstractWith the advancement of functional textile technology, there is a growing demand for functional enhancements in textiles from both industrial and societal perspectives. Recently, nanopattern transfer technology has emerged as a potential approach for fabricating functional textiles. However, conventional transfer methods have some limitations such as transfer difficulties on curved fiber surfaces, polymer residues, and delamination of transferred nanopatterns. In this study, an advanced nanopattern transfer method based on surface modification and thermoforming principles is applied to microscale electrospun fibers. This transfer method utilizes covalent bonding and mechanical interlocking between nanopatterns and the fibers without requiring extra adhesives. Various nanopatterns transferred electrospun fibers possess significant potential for diverse wearable healthcare applications. This work introduces two specific application scenarios in the field of wearable healthcare, both of which leverage the light: diagnostics and antimicrobials. Versatile textile with silver nanogap‐pattern detects glucose in sweat, diagnosing hypoglycemia and diabetes by shifting Raman peaks from 1071.0 to 1075.4 cm−1 for 0 to 150 µm glucose. Additionally, a bactericidal mask using visible light to induce the photocatalytic degradation effect of titanium dioxide and silver nanopatterns is developed. Bactericidal efficacy against Escherichia coli and Staphylococcus aureus is 99.9% due to photolysis from visible light irradiation.

Large area nanoscale patterning of functional materials using organosilicate ink based nanotransfer printing

This paper presents a versatile nanotransfer printing method for achieving large-area sub-micron patterns of functional materials. Organosilicate ink formulations combined with effective release layers have been shown to facilitate patterning of materials through the commonly used patterning approaches—lift off, physical etching and chemical etching. In this paper, we demonstrate that organosilicate ink formulations function as an effective resist owing to its superior physico-chemical stability whereas the release layers ensure clean removal of the resist post patterning. We successfully demonstrate patterning of sub-micron structures (800 nm feature sizes) of chromium metal through the lift off approach, silicon through reactive ion etching technique and silicon dioxide through wet chemical etching technique illustrating the versatility of the reported method. This patterning methodology represents a significant advancement in enabling nanostructure fabrication within resource-constrained laboratories. The approach requires nothing more than a master mold containing the desired structures, a spin coater, a low-temperature hotplate, and a desktop reactive ion etch tool.

Illuminating Recent Progress in Nanotransfer Printing: Core Principles, Emerging Applications, and Future Perspectives.

As the demand for diverse nanostructures in physical/chemical devices continues to rise, the development of nanotransfer printing (nTP) technology is receiving significant attention due to its exceptional throughput and ease of use. Over the past decade, researchers have attempted to enhance the diversity of materials and substrates used in transfer processes as well as to improve the resolution, reliability, and scalability of nTP. Recent research on nTP has made continuous progress, particularly using the control of the interfacial adhesion force between the donor mold, target material, and receiver substrate, and numerous practical nTP methods with niche applications have been demonstrated. This review article offers a comprehensive analysis of the chronological advancements in nTP technology and categorizes recent strategies targeted for high-yield and versatile printing based on controlling the relative adhesion force depending on interfacial layers. In detail, the advantages and challenges of various nTP approaches are discussed based on their working mechanisms, and several promising solutions to improve morphological/material diversity are presented. Furthermore, this review provides a summary of potential applications of nanostructured devices, along with perspectives on the outlook and remaining challenges, which are expected to facilitate the continued progress of nTP technology and to inspire future innovations.

Near-zero-adhesion-enabled intact wafer-scale resist-transfer printing for high-fidelity nanofabrication on arbitrary substrates

There is an urgent need for novel processes that can integrate different functional nanostructures onto specific substrates, so as to meet the fast-growing need for broad applications in nanoelectronics, nanophotonics, and flexible optoelectronics. Existing direct-lithography methods are difficult to use on flexible, nonplanar, and biocompatible surfaces. Therefore, this fabrication is usually accomplished by nanotransfer printing. However, large-scale integration of multiscale nanostructures with unconventional substrates remains challenging because fabrication yields and quality are often limited by the resolution, uniformity, adhesivity, and integrity of the nanostructures formed by direct transfer. Here, we proposed a resist-based transfer strategy enabled by near-zero adhesion, which was achieved by molecular modification to attain a critical surface energy interval. This approach enabled the intact transfer of wafer-scale, ultrathin-resist nanofilms onto arbitrary substrates with mitigated cracking and wrinkling, thereby facilitating the in situ fabrication of nanostructures for functional devices. Applying this approach, fabrication of three-dimensional-stacked multilayer structures with enhanced functionalities, nanoplasmonic structures with ∼10 nm resolution, and MoS2-based devices with excellent performance was demonstrated on specific substrates. These results collectively demonstrated the high stability, reliability, and throughput of our strategy for optical and electronic device applications.

Large-area ultracompact pixelated aluminum-wire-grid-based metamaterials for Vis-NIR full-Stokes polarization imaging

The study of pixelated metamaterials that integrate both the functions of linear and circular polarization filters is rapidly growing due to the need for full-Stokes polarization imaging. However, there is a lack of large-area, ultracompact pixelated full-Stokes metamaterials with excellent performance, especially circular polarization filters with a high extinction ratio, a broad operating bandwidth, and a low-cost, high-quality, efficient manufacturing process, which limits the practical applications of pixelated full-Stokes metamaterials. In this study, we propose a universal design and fabrication scheme for large-area, ultracompact pixelated aluminum wire-grid-based metamaterials used in Vis-NIR full-Stokes polarization imaging. The aluminum wire-grid was designed as a linear polarization filter with an average linear polarization extinction ratio of 36,000 and a circular polarization filter with an average circular polarization extinction ratio of 110 in Vis-NIR. A large-area, ultracompact 320×320 pixelated aluminum wire-grid-based full-Stokes metamaterial was fabricated using nanoimprint lithography and nano transfer printing with the advantages of low cost and high efficiency. This metamaterial was used to achieve full-Stokes polarization imaging with errors within 8.77%, 12.58%, 14.04%, and 25.96% for Stokes parameters S0, S1, S2, and S3, respectively. The inversion errors of the compensated Stokes parameters can be reduced to 0.21%, 0.21%, 0.42%, and 1.96%, respectively.

Thermal-Assisted Multiscale Patterning of Nonplanar Colloidal Nanostructures for Multi-Modal Anti-Counterfeiting.

Nanotransfer printing of colloidal nanoparticles is a promising technique for the fabrication of functional materials and devices. However, patterning nonplanar nanostructures pose a challenge due to weak adhesion from the extremely small nanostructure-substrate contact area. Here, the study proposes a thermal-assisted nonplanar nanostructure transfer printing (NP-NTP) strategy for multiscale patterning of polystyrene (PS) nanospheres. The printing efficiency is significantly improved from ≈3.1% at low temperatures to ≈97.2% under the glass transition temperature of PS. Additionally, the arrangement of PS nanospheres transitioned from disorder to long-range order. The mechanism of printing efficiency enhancement is the drastic drop of Young's modulus of nanospheres, giving rise to an increased contact area, self-adhesive effect, and inter-particle necking. To demonstrate the versatility of the NP-NTP strategy, it is combined with the intaglio transfer printing technique, and multiple patterns are created at both micro and macro scales at a 4-inch scale with a resolution of ≈2757 pixels per inch (PPI). Furthermore, a multi-modal anti-counterfeiting concept based on structural patterns at hierarchical length scales is proposed, providing a new paradigm of imparting multiscale nanostructure patterning into macroscale functional devices.

Direct Printing of Ultrathin Block Copolymer Film with Nano-in-Micro Pattern Structures.

Nanotransfer printing (nTP) is one of the most promising nanopatterning methods given that it can be used to produce nano-to-micro patterns effectively with functionalities for electronic device applications. However, the nTP process is hindered by several critical obstacles, such as sub-20nm mold technology, reliable large-area replication, and uniform transfer-printing of functional materials. Here, for the first time, a dual nanopatterning process is demonstrated that creates periodic sub-20nm structures on the eight-inch wafer by the transfer-printing of patterned ultra-thin (<50nm) block copolymer (BCP) film onto desired substrates. This study shows how to transfer self-assembled BCP patterns from the Si mold onto rigid and/or flexible substrates through a nanopatterning method of thermally assisted nTP (T-nTP) and directed self-assembly (DSA) of Si-containing BCPs. In particular, the successful microscale patternization of well-ordered sub-20nm SiOx patterns is systematically presented by controlling the self-assembly conditions of BCP and printing temperature. In addition, various complex pattern geometries of nano-in-micro structures are displayed over a large patterning area by T-nTP, such as angular line, wave line, ring, dot-in-hole, and dot-in-honeycomb structures. This advanced BCP-replicated nanopatterning technology is expected to be widely applicable to nanofabrication of nano-to-micro electronic devices with complex circuits.

High-Resolution Nanotransfer Printing of Porous Crossbar Array Using Patterned Metal Molds by Extreme-Pressure Imprint Lithography.

High-resolution nanotransfer printing (nTP) technologies have attracted a tremendous amount of attention due to their excellent patternability, high productivity, and cost-effectiveness. However, there is still a need to develop low-cost mold manufacturing methods, because most nTP techniques generally require the use of patterned molds fabricated by high-cost lithography technology. Here, we introduce a novel nTP strategy that uses imprinted metal molds to serve as an alternative to a Si stamp in the transfer printing process. We present a method by which to fabricate rigid surface-patterned metallic molds (Zn, Al, and Ni) based on the process of direct extreme-pressure imprint lithography (EPIL). We also demonstrate the nanoscale pattern formation of functional materials, in this case Au, TiO2, and GST, onto diverse surfaces of SiO2/Si, polished metal, and slippery glass by the versatile nTP method using the imprinted metallic molds with nanopatterns. Furthermore, we show the patterning results of nanoporous crossbar arrays on colorless polyimide (CPI) by a repeated nTP process. We expect that this combined nanopatterning method of EPIL and nTP processes will be extendable to the fabrication of various nanodevices with complex circuits based on micro/nanostructures.

Formation of Multiscale Pattern Structures by Combined Patterning of Nanotransfer Printing and Laser Micromachining.

Various lithography techniques have been widely used for the fabrication of next-generation device applications. Micro/nanoscale pattern structures formed by lithographic methods significantly improve the performance capabilities of the devices. Here, we introduce a novel method that combines the patterning of nanotransfer printing (nTP) and laser micromachining to fabricate multiscale pattern structures on a wide range of scales. Prior to the formation of various nano-in-micro-in-millimeter (NMM) patterns, the nTP process is employed to obtain periodic nanoscale patterns on the target substrates. Then, an optimum laser-based patterning that effectively engraves various nanopatterned surfaces, in this case, spin-cast soft polymer film, rigid polymer film, a stainless still plate, and a Si substrate, is established. We demonstrate the formation of well-defined square and dot-shaped multiscale NMM-patterned structures by the combined patterning method of nTP and laser processes. Furthermore, we present the generation of unusual text-shaped NMM pattern structures on colorless polyimide (CPI) film, showing optically excellent rainbow luminescence based on the configuration of multiscale patterns from nanoscale to milliscale. We expect that this combined patterning strategy will be extendable to other nano-to-micro fabrication processes for application to various nano/microdevices with complex multiscale pattern geometries.

Thermal Nanoimprint Lithography-A Review of the Process, Mold Fabrication, and Material.

Micro- and nanopatterns perform unique functions and have attracted attention in various industrial fields, such as electronic devices, microfluidics, biotechnology, optics, sensors, and smart and anti-adhesion surfaces. To put fine-patterned products to practical use, low-cost patterning technology is necessary. Nanoimprint lithography (NIL) is a promising technique for high-throughput nanopattern fabrication. In particular, thermal nanoimprint lithography (T-NIL) has the advantage of employing flexible materials and eliminating chemicals and solvents. Moreover, T-NIL is particularly suitable for compostable and recyclable materials, especially when applying biobased materials for use in optics and electronics. These attributes make T-NIL an eco-friendly process. However, the processing time of normal T-NIL is longer than that of ultraviolet (UV) NIL using a UV-curable resin because the T-NIL process requires heating and cooling time. Therefore, many studies focus on improving the throughput of T-NIL. Specifically, a T-NIL process based on a roll-to-roll web system shows promise for next-generation nanopatterning techniques because it enables large-area applications with the capability to process webs several meters in width. In this review, the T-NIL process, roll mold fabrication techniques, and various materials are introduced. Moreover, metal pattern transfer techniques using a combination of nanotransfer printing, T-NIL, and a reverse offset are introduced.

Fabrication of large-area metal and semiconductor nanobridge arrays using nanotransfer printing and UV lithography

A new method for the fabrication of large-area metal and semiconductor nanobridge arrays is proposed. The method combines the possibilities offered by the nanotransfer printing technique and by UV lithography. The essence of the method consists in the formation of an array of metal or semiconductor nanostrips “imprinted” into a smooth layer of resist and in subsequent exposure of the resist to UV radiation through an additional mask defining the regions where the suspended nanostrip bridges will be formed during subsequent development of the resist layer. Large-area arrays of Au and Ti/Au nanobridge, 100 nm wide, 25–35 nm thick and 1–4 μm long, with their ends embedded into the SU-8 resist layer, were fabricated. SiGe nanobridge arrays of 18 nm thick and 1 μm long, with their ends embedded into the Shipley 1813 resist layer were fabricated. The proposed method is simple and low-cost, and it does not require using expensive reactive plasma-etching facilities and can be implemented both on solid and polymer substrates on the areas at the excess of 150 cm2.

Noninvasive Detection of Bladder Cancer Markers Based on Gold Nanomushrooms and Sandwich Immunoassays

Bladder cancer is one of the most common malignancies in the urinary system. Cystoscopy is the traditional standard diagnostic method for bladder cancer with subsequent biopsy or surgery. However, this method is uncomfortable for most patients because it requires anesthesia and possibly causes infections. Because of the high recurrence rate of bladder cancer, a rapid, low-cost, high-sensitivity, and noninvasive sensing method is needed. This study employed gold nanomushroom (AuNM) chips for bladder cancer biomarker detection, combining the benefits of sandwich immunoassay and localized surface plasmon resonance (LSPR) sensing. With a metal nanotransfer printing technique, which is cheap and straightforward, the AuNMs were patterned on flexible polycarbonate (PC) sheets. The gold caps stood above PC stems and provided ample spatial areas for capturing the biomarkers to be sensed. Three biomarkers served as the antigens and analytes, including human complement factor H (CFH), hyaluronic acid (HA), and nuclear matrix protein 22 (NMP22). Different antibodies, against the same biomarker, were covalently conjugated to AuNMs or gold nanoparticles, respectively. When the antibody–antigen–antibody sandwich structure formed, the plasmonic coupling between the AuNM surface and the gold nanoparticles significantly enhanced LSPR signals. The LSPR red shifts correlated quantitatively with the concentrations of the biomarkers. The limits of detection were 6.5, 8.3, and 7.0 pg/mL for CFH, HA, and NMP22, respectively. The chip’s specificity was tested and confirmed, excluding the nonspecific binding and false-positive possibility. The sensing performance of this sandwich immunoassay-based AuNM chip was better than that of the commercialized enzyme-linked immunosorbent assay. It provided a rapid, label-free, and easy operating platform for diagnosing and monitoring bladder cancer.

Nanotransfer-on-Things: From Rigid to Stretchable Nanophotonic Devices

The growing demand for nanophotonic devices has driven the advancement of nanotransfer printing (nTP) technology. Currently, the scope of nTP is limited to certain materials and substrates owing to the temperature, pressure, and chemical bonding requirements. In this study, we developed a universal nTP technique utilizing covalent bonding-based adhesives to improve the adhesion between the target material and substrate. Additionally, the technique employed plasma-based selective etching to weaken the adhesion between the mold and target material, thereby enabling the reliable modulation of the relative adhesion forces, regardless of the material or substrate. The technique was evaluated by printing four optical materials on nine substrates, including rigid, flexible, and stretchable substrates. Finally, its applicability was demonstrated by fabricating a ring hologram, a flexible plasmonic color filter, and extraordinary optical transmission-based strain sensors. The high accuracy and reliability of the proposed nTP method were verified by the performance of nanophotonic devices that closely matched numerical simulation results.

Customized Patterning of Deep Nanowell Structures in Polymer Electrolyte Membranes for Highly Enhanced Fuel Cell Performances

Surface microstructuring of polymer electrolyte membranes (PEMs) has been considered as an effective strategy to extend the three-phase boundary in PEM fuel cells (PEMFCs). However, it is still unclear which parameters are the most critical for maximizing cell performance. In this study, in order to elucidate the correlation between the membrane surface topography and PEMFC performances, we employed solvent-assisted nanotransfer printing and plasma deep etching techniques, which allow independent control of structural parameters. This approach enables the formation of various catalyst–membrane interface structures with controlled pattern periods and aspect ratios. Our systematic customization reveals that nanowell patterned membranes partially filled with carbon-supported platinum (Pt/C) can significantly improve fuel cell performance, which is driven by both reducing kinetic resistance and mass transport resistance. In particular, the sample with a pattern period of 1200 nm and a well depth of 1100 nm exhibited the best performance, a current density of 1000 mA/cm2 at a cell voltage of 0.6 V, and a maximum power density of 583 mW/cm2. These values are 53 and 41% higher than those with unpatterned membranes, respectively, at the same Pt loading.

Silver pattern transfer technique using concave region of mold and silver ink

In this study, we performed two-tone transfer using silver ink by the nano-transfer printing process, which does not involve a vacuum deposition step. To achieve a two-tone transfer, it is necessary to separate the metal film from the top surface of the mold and the metal part at the bottom of the hole. However, in the case of silver ink, the hole is often completely filled, therefore, separation between the top surface and the bottom of the hole is difficult. We performed spin coating to thin out the silver ink in the mold, confirmed that the silver ink can be separated at the top and bottom of the mold by baking, and investigated the relationship between the number of spin coating revolutions and the pattern success rate. The success rate for scooping the bottom silver from the 2 cm × 2 cm line-and-space mold was ∼85%.

Broadband Vis–NIR Circular Polarizer with Cascaded Aluminum Wire‐Grid

AbstractA universal design and fabrication scheme is proposed for a cascaded aluminum wire‐grid‐based vis–NIR circular polarizer. The aluminum wire‐grid is designed as a broadband circular‐linear polarization converter and a broadband linear polarizer, which is further cascaded to form a circular polarizer with strong circular polarization transmittance difference (CPTD) and circular polarization extinction ratio (CPER) in vis–NIR. By increasing the distance between the circular‐linear polarization converter and the linear polarizer, the redshift of the CPTD and CPER peaks is realized and used to design a novel circular polarizer to work better in the operating wavelength. Anisotropic thin‐film interference is revealed to be responsible for the redshift phenomenon. Furthermore, the circular polarizer is fabricated by nano imprint lithography and nano transfer printing with the merits of relatively low cost, and high production efficiency. With such flexibility in the design and fabrication, cascaded aluminum wire‐grid may serve as a tunable compact circular polarizer, and it is also easy to integrate with the wire‐grid‐based linear polarizer to realize the fabrication of the division‐of‐focal‐plane full Stokes polarimeter.

Stretchable and Transparent Interconnects With Hybrid Ag-Nanomesh/Indium Tin Oxide Structure

We demonstrate a hybrid structure for both transparent and stretchable interconnects, that provides high conductance, stretchability, and transparency simultaneously. In this structure, a serpentine-shaped discrete Ag nanomesh formed by the nanotransfer printing technique works as the primary conducting layer, while an indium tin oxide thin film covering it allows planar contact with other devices for proper functions as interconnects. We have confirmed that the hybrid serpentine interconnects provide high conductance and stretching reliability comparable to that of opaque ductile metals, and the transmittance and sheet resistance can be controlled independently by modifying the structural parameters of the mesh layer. Based on conventional photolithography and etching processes compatible with the current flexible circuit technology, the new hybrid interconnect can be utilized in various devices requiring highly integrated transparent and stretchable circuits.