Large-area Patterning Research Articles

Accessible dynamic micropatterns in monolayer cultures via modified desktop xurography

Micropatterned cell cultures provide an important tool to understand dynamic biological processes, but often require specialized equipment and expertise. Here we present subtractive bioscribing (SuBscribing), a readily accessible and inexpensive technique to generate dynamic micropatterns in biomaterial monolayers on-the-fly. We first describe our modifications to a commercially available desktop xurographer and demonstrate the utility and limits of this system in creating micropatterned cultures by mechanically scribing patterns into a brittle, non-adhesive biomaterial layer. Patterns are sufficiently small to influence cell morphology and orientation and can be extended to pattern large areas with complex reproducible shapes. We also demonstrate the use of this system as a dynamic patterning tool for cocultures. Finally, we use this technique to explore and improve upon the well-established epithelial scratch assay, and demonstrate that robotic control of the scratching tool can be used to create custom-shaped wounds in epithelial monolayers, and that the scribing direction leaves trace remnants of matrix molecules that may significantly affect conventional implementations of this common assay.

Fabrication of High Aspect Ratio Micro-Structures with Superhydrophobic and Oleophobic Properties by Using Large-Area Roll-to-Plate Nanoimprint Lithography.

Bio-inspired surfaces with superamphiphobic properties are well known as effective candidates for antifouling technology. However, the limitation of large-area mastering, patterning and pattern collapsing upon physical contact are the bottleneck for practical utilization in marine and medical applications. In this study, a roll-to-plate nanoimprint lithography (R2P NIL) process using Morphotonics’ automated Portis NIL600 tool was used to replicate high aspect ratio (5.0) micro-structures via reusable intermediate flexible stamps that were fabricated from silicon master molds. Two types of Morphotonics’ in-house UV-curable resins were used to replicate a micro-pillar (PIL) and circular rings with eight stripe supporters (C-RESS) micro-structure onto polycarbonate (PC) and polyethylene terephthalate (PET) foil substrates. The pattern quality and surface wettability was compared to a conventional polydimethylsiloxane (PDMS) soft lithography process. It was found that the heights of the R2P NIL replicated PIL and C-RESS patterns deviated less than 6% and 5% from the pattern design, respectively. Moreover, the surface wettability of the imprinted PIL and C-RESS patterns was found to be superhydro- and oleophobic and hydro- and oleophobic, respectively, with good robustness for the C-RESS micro-structure. Therefore, the R2P NIL process is expected to be a promising method to fabricate robust C-RESS micro-structures for large-scale anti-biofouling application.

Large-Area Synthesis and Patterning of All-Inorganic Lead Halide Perovskite Thin Films and Heterostructures.

All-inorganic lead halide perovskites have attracted tremendous interest for their excellent stability when compared with hybrid perovskites. Here we report a large-area growth of monocrystalline all-inorganic perovskite thin films and further patterning them into heterostructure arrays. We show that highly oriented CsPbBr3 microcrystal domains can be readily grown on muscovite mica substrates with a well-defined epitaxial relationship, which can further expand and eventually merge into large-area monocrystalline CsPbBr3 thin films with an excellent optical quality. Taking a step further, we show the large-area CsPbBr3 thin film can be further patterned and selectively transformed into CsPbI3 using a selective anion-exchange process to produce CsPbBr3-CsPbI3 lateral heterostructure arrays with spatially modulated photoluminescence emission and an apparent current rectification behavior. The capability to grow large-area CsPbBr3 monocrystalline thin films and heterostructure arrays defines a robust material platform for both the fundamental investigations and potential applications in optoelectronics.

Boosting the performance of printed thermoelectric materials by inducing morphological anisotropy

Thermoelectrics can generate electrical energy from waste heat and work also as active coolers. However, their widespread use is hindered by their poor efficiency, which is aggravated by their costly and hard-to-scale fabrication process. Good thermoelectric performances require materials with high (low) electrical (thermal) conductivity. Inducing morphological anisotropy at the nanoscale holds promise to boost thermoelectric performances, in both inorganic and organic materials, by increasing the ratio electrical/thermal conductivity along a selected direction without strongly affecting the Seebeck coefficient. Recent advances in 2D/3D printed electronics are revealing new simple and inexpensive routes to fabricate thermoelectrics with the necessary morphological control to boost performance by inducing anisotropy.

Fabrication of graphitic carbon nitride films by inkjet printing

Graphitic carbon nitride (g‐C3N4) has recently arisen at the forefront of researching in many areas. For this reason, the establishment of attractive and functional methodologies for the preparation of g‐C3N4 films and coatings to develop novel applications is very important. Therefore, this paper is focused on taken advantage of the functionalities of ultrasound-assisted liquid-phase exfoliation (UALPE) process and inkjet printing (IJP) technique for the fabrication of g‐C3N4 films. By an integral analysis, a stable and printable colloidal ink containing exfoliated g‐C3N4 with an average particle size of 263 nm was formulated. Reproducible and well-defined g‐C3N4 films with 10, 20 and 30 printing-passes have been obtained where the distinctive characteristic related to the automatic droplets’ deposition provided by IJP technique allowed an easy control on the spatial uniformity, thickness and transparency. Additionally, the inkjet printed g‐C3N4 films were evaluated as a fluorescence sensor exhibiting a good response to the presence of Ag+ in aqueous solution. The strategy here reported can be exploited for the deposition of large-area and complex patterns of g‐C3N4 onto a variety of rigid and flexible substrates through the simple and low-cost UALPE and IJP approaches.

Scanning digital oil immersion lithography providing high-speed large area patterning with diffraction limited sub-micron resolution

A high numerical aperture (NA) scanning digital oil immersion lithography scheme is proposed and demonstrated in this study. To successfully conduct the scanning digital oil immersion lithography, immersion oil should be removed from the photoresist layer before the development process. Also, uniformity of the projected light patterns becomes crucial in the quality of this high NA photolithography. To solve these issues, we developed a cleaning procedure for the immersion oil and an intensity calibration scheme to achieve a highly uniform intensity distribution of the projected patterns. With these preparations, we were able to achieve 400 nm resolution large area patterning with the developed scanning digital oil immersion lithography system and a better than 200 nm resolution in the single line patterning. Also, with a double layered photoresist scheme and our lab-prepared photoresist, we successfully achieved large area lift-off patterns of 400 nm metallic dot arrays through the scanning digital oil immersion lithography system.

Large-Area Patterning of Oil-Based Inks on Superhydrophobic TiO2 Nanotubular Layers by Photocatalytic Wettability Conversion

Patterning an oil-based ink on a solid surface based on a wettability difference is of significant importance for the application of offset printing. Herein, we describe a large-area patterning of oil-based ink on a self-organized TiO2 nanotubular layer based on a photocatalytic wettability conversion. The TiO2 nanotubular layer was fabricated by electrochemical anodization, which demonstrated a superhydrophobic wettability after modification with a self-assembled molecular layer. Subsequently, area-selective ultraviolet (UV) irradiation through a pre-designed pattern of water-based UV-resistant ink formed by an ink-jet technique was used to form a wettability difference. After removing the water-based ink, an oil-based ink was capable of depositing selectively on the superhydrophobic area to form the same pattern as the pre-designed pattern of water-based ink. This large-area patterning of an oil-based ink based on the photocatalytic wettability conversion is potentially applicable in offset printing.

Controllable Heterogeneous Nucleation for Patterning High-Quality Vertical and Horizontal ZnO Microstructures toward Photodetectors.

High-quality crystalline micro- and nanostructures based on inorganic semiconductors including zinc oxide (ZnO) have attracted considerable interest in electronic and optoelectronic applications due to their outstanding properties. ZnO micro- and nanocrystals can be fabricated by the moderate and high throughput hydrothermal synthesis. Yet it is restricted by patterning large-area ZnO crystals with high-quality and programmable geometries through the hydrothermal process for the optoelectronic integration. Here, a capillary-bridge manipulation approach is demonstrated to control the dewetting process of ZnO precursor solution for patterning precursor arrays. Based on precursor arrays, vertically aligned high-quality ZnO microrod arrays with homogeneous morphology and pure crystallographic orientation are fabricated via a hydrothermal epitaxial method. Statistical results and crystallization theories guide the experimental optimization and discussion of the crystallization mechanism, dominated by the competition between homogeneous nucleation and heterogeneous nucleation. High-quality ZnO microbelt arrays are achieved through a surfactant-mediated hydrothermal method after ZnO microrod arrays are transferred to a polydimethylsiloxane substrate. Photodetectors based on ZnO microbelts exhibit a high responsivity of 2.3 × 104 A W-1 , a light on-off ratio exceeding 105 , and stable recyclability. It is anticipated that this work provides new insights into patterning inorganic high-quality micro- and nanostructures for multi-functional integrated devices.

Sacrificial layer-assisted nanoscale transfer printing

Transfer printing is an emerging assembly technique for flexible and stretchable electronics. Although a variety of transfer printing methods have been developed, transferring patterns with nanometer resolution remains challenging. We report a sacrificial layer-assisted nanoscale transfer printing method. A sacrificial layer is deposited on a donor substrate, and ink is prepared on and transferred with the sacrificial layer. Introducing the sacrificial layer into the transfer printing process eliminates the effect of the contact area on the energy release rate (ERR) and ensures that the ERR for the stamp/ink-sacrificial layer interface is greater than that for the sacrificial layer/donor interface even at a slow peel speed (5 mm s−1). Hence, large-area nanoscale patterns can be successfully transferred with a yield of 100%, such as Au nanoline arrays (100 nm thick, 4 mm long and 47 nm wide) fabricated by photolithography techniques and PZT nanowires (10 mm long and 63 nm wide) fabricated by electrohydrodynamic jet printing, using only a blank stamp and without the assistance of any interfacial chemistries. Moreover, the presence of the sacrificial layer also enables the ink to move close to the mechanical neutral plane of the multilayer peel-off sheet, remarkably decreasing the bending stress and obviating cracks or fractures in the ink during transfer printing.

Scalable fabrication of inkless, transfer-printed graphene-based textile microsupercapacitors with high rate capabilities

We have demonstrated the use of thermal transfer printing for scalable, inkless fabrication of a graphene-based textile microsupercapacitor (MSC). An adhesive film of a heat transfer paper was employed as a flat, buffer adhesive layer on a rough textile substrate. Laser-induced graphene (LIG) directly laser-written on polyimide (PI) films was transferred onto the adhesive film area of the textile substrates at elevated temperature and pressure. A thermally transfer-printed LIG pattern preserved porous structure with 3D interconnected pores and high electrical conductivity of LIG formed on PI films. The developed textile LIG-MSCs exhibit electrical double layer capacitive characteristics with areal capacitance of 0.76mFcm−2 and excellent capacitance retention of 96% after 1000 cycles of large bending (180°) deformation. Furthermore, scalable transfer of a large-area LIG pattern provided various array configurations of MSCs in series and in parallel to adjust the voltage and current for practical applications. Moreover, LIG-MSCs with a LIG-metal composite exhibit fast ion transport at a high scan rates of up to 20Vs-1, suggesting outstanding rate capability among graphene-based textile MSCs. In this regard, the proposed inkless transfer strategy provided low cost and scalable fabrication of a LIG composite electrode on a textile substrate without preparing costly graphene-based ink materials.

대면적 레이저 직접묘화 공정에서 비점수차 자동초점 기술 연구

We developed an astigmatic autofocus optics and a control unit which were implemented in a direct laser writing system for a large area patterning process. The autofocus module is comprised of a collimated laser, a quadrant photodiode, an astigmatic lens, and a few polarizing optics. This system has a 0.526 V/μm focus error signal resolution in the 50x objective lens and a surface tracking capability of under 1 mm/s XY translation stage speed. In this study, we conducted a patterning experiment using SU-8 photocurable resist on a silicon wafer to study the accuracy of the astigmatic autofocus system. We highlighted some features of this system for future improvement.

Experimental investigation of temperature and angular dependence of plasmonic structures on resonance and absorption properties

A metallic microcones array-based plasmonic strcture is presented as an example for the purpose of experimentally exploring the dependence of ambient temperature and incident angle on resonance and absorption properties. The microcones array is fabricated using the technique of heavy ion tracking. The technique has advantages of large-area patterning, high-aspect ratio of unit dimension, controllable length, and multichoice of materials. Fabrication steps, mathematical fitting, and experimental measurements of optical absorption spectra are presented. To analyze the experimental data regarding thetemperature-dependence effect, a theoretical formula, a quasi-Gauss model, is applied to describe the relationship between temperature (T) and plasmonic wavelength (λSP). Our experimental results demonstrate that the variation of temperature and incident angle strongly affect the sensitivity of λSP and its absorption properties. Our experimental results indicate that this structure is capbale of acting as an optical sensor for detection of temperature and angular denpendence.

Weak Antilocalization Tailor-Made by System Topography in Large Scale Bismuth Antidot Arrays.

Using a two-carriers model and the Hikami-Larkin-Nagaoka (HLN) theory, we investigate the influence of large area patterning on magnetotransport properties in bismuth thin films with a thickness of 50 nm. The patterned systems have been produced by means of nanospheres lithography complemented by RF-plasma etching leading to highly ordered antidot arrays with the hexagonal symmetry and a variable antidot size. Simultaneous measurements of transverse and longitudinal magnetoresistance in a broad temperature range provided comprehensive data on transport properties and enabled us to extract the values of charge carrier densities and mobilities. Weak antilocalization signatures observed at low temperatures provided information on spin-orbit scattering length ranging from 20 to 30 nm, elastic scattering length of approx. 60 nm, and strong dependence on temperature phase coherence length. We show that in the absence of antidots the charge carrier transport follow 2-dimensional behavior and the dimensionality for phase-coherent processes changes from two to three dimensions at temperature higher than 10 K. For the antidot arrays, however, a decrease of the power law dephasing exponent is observed which is a sign of the 1D-2D crossover caused by the geometry of the system. This results in changes of scattering events probability and phase coherence lengths depending on the antidot diameters, which opens up opportunity to tailor the magnetotransport characteristics.

Highly transparent and conductive electrodes enabled by scalable printing-and-sintering of silver nanowires

Silver nanowires (Ag NWs) have good promised for flexible and transparent electronics. However, It remains an open question on how to achieve large-scale printing of Ag NWs with high optical transparency, electrical conductivity, and mechanical durability for practical applications, though extensive research has been conducted for more than a decade. In this work, we propose a possible solution that integrates screen printing of Ag NWs with flash-light sintering (FLS). We demonstrate that the use of low-concentration, screen-printable Ag NW ink enables large-area and high-resolution patterning of Ag NWs. A critical advantage comes from the FLS process that allows low-temperature processing, short operational time, and high output rate—characteristics that fit the scalable manufacturing. Importantly, we show that the resultant Ag NW patterns feature low sheet resistance (1.1–9.2 Ohm sq−1), high transparency (75.2–92.6%), and thus a remarkable figure of merit comparable to state of the art. These outstanding properties of Ag NW patterns, together with the scalable fabrication method we propose, would facilitate many Ag NW-based applications, such as transparent heaters, stretchable displays, and wearable devices; here, we demonstrate the novel design of flexible and transparent radio frequency 5G antennas.

Chemical Funneling of Colloidal Gold Nanoparticles on Printed Arrays of End-Grafted Polymers for Plasmonic Applications.

Spatially defined assembly of colloidal metallic nanoparticles is necessary for fabrication of plasmonic devices. In this study, we demonstrate high-resolution additive jet printing of end-functional polymers to serve as templates for directed self-assembly of nanoparticles into architectures with substantial plasmonic activity. The intriguing aspect of this work is the ability to form patterns of end-grafted poly(ethylene glycol) through printing on a hydrophobic layer that consists of fluoroalkylsilanes. The simultaneous dewetting of the underlying hydrophobic layer together with grafting of the printed polymer during thermal annealing enables fabrication of spatially defined binding sites for assembly of nanoparticles. The employment of electrohydrodynamic jet printing and aqueous inks together with reduction of the feature size during thermal annealing are critically important in achieving high chemical contrast patterns as small as ∼250 nm. Gold nanospheres of varying diameters selectively bind and assemble into nanostructures with reduced interparticle distances on the hydrophilic patterns of poly(ethylene glycol) surrounded with a hydrophobic background. The resulting plasmonic arrays exhibit intense and pattern-specific signals in surface-enhanced Raman scattering (SERS) spectroscopy. The localized seed-mediated growth of metallic nanostructures over the patterned gold nanospheres presents further routes for expanding the composition of the plasmonic arrays. A representative application in SERS-based surface encoding is demonstrated through large-area patterning of plasmonic structures and multiplex deposition of taggant molecules, all enabled by printing.

Trilayer Nanomesh Films with Tunable Wettability as Highly Transparent, Flexible, and Recyclable Electrodes

AbstractMetallic mesh materials are promising candidates to replace traditional transparent conductive oxides such as indium tin oxide (ITO) that is restricted by the limited indium resource and its brittle nature. The challenge of metal based transparent conductive networks is to achieve high transmittance, low sheet resistance, and small perforation size simultaneously, all of which significantly relate to device performances in optoelectronics. In this work, trilayer dielectric/metal/dielectric (D/M/D) nanomesh electrodes are reported with precisely controlled perforation size, wire width, and uniform hole distribution employing the nanosphere lithography technique. TiO2/Au/TiO2 nanomesh films with small hole diameter (≤700 nm) and low thickness (≤50 nm) are shown to yield high transmittance (>90%), low sheet resistance (≤70 Ω sq−1), as well as outstanding flexural endurance and feasibility for large area patterning. Further, by tuning the surface wettability, these films are applied as easily recyclable flexible electrodes for electrochromic devices. The simple and cost‐effective fabrication of diverse D/M/D nanomesh transparent conductive films with tunable optoelectronic properties paves a way for the design and realization of specialized transparent electrodes in optoelectronics.

Two-dimensional positive or negative patterning of submicrometer silica spheres on polyimide via ion implantation and selective adsorption

In this paper, we report a large-area 2D patterning technique via ion implantation and selective adsorption. It is found that the surface zeta potential (ξ) of polyimide (PI) can be changed by implanting different types of metal ions. On the surface of the Cu or Ni ion patterned implanted polyimide, both negative and positive adsorption patterns of submicrometer silica particles can be realized. The formation of different patterns is mainly decided by the surface zeta potential contrast ratio between implanted part and the unimplanted part of PI and the zeta potential of particles. Moreover, the shape of the patterns can be regulated by changing the liquid surface tension.

Designed growth and patterning of perovskite nanowires for lasing and wide color gamut phosphors with long-term stability

Abstract Hybrid halide perovskites are proposed for next-generation photovoltaics and lighting technologies due to their remarkable optoelectronic properties. In this study, we demonstrate printed perovskite nanowires (NWs) for lasing and wide-gamut phosphor using a combination of inkjet printing and nanoporous anodic aluminum oxide (AAO). The random lasing behaviors of the resulting perovskite NWs are analyzed and discussed. Moreover, by varying the composition of Cl−, Br−, and I− anions, we demonstrate tunable emission wavelengths of the perovskite NWs from 439 to 760 nm, with a large red-green-blue color space that extends to 117% of the color standard defined by the National Television Systems Committee (NTSC). Furthermore, we demonstrate passivation of the perovskite NWs against moisture due to their compact spatial confinement within the AAO template combined with a poly(methyl methacrylate) sealing process, resulting in highly stable emission intensity that degrades only 19% after continuous 250 h of 30 mW/cm2 UV excitation and degrades 30% after three months when stored in air at 50% humidity. This inkjet printing fabrication strategy involving AAO-confined perovskite NWs enables highly stable, large-area direct patterning and mass production of perovskite NWs, which is promising for modern lighting applications.

Symmetrical Wrinkles in Single-Component Elastomers with Fingerprint-Inspired Robust Isotropic Dry Adhesive Capabilities.

Robust and inexpensive dry adhesives have a great potential in multitudinous industrial applications. However, to date, the fabrication of dry adhesives, prepared using high aspect ratio structures in general, requires specific equipment and time-consuming processes, which limit their practicable utilization. Inspired from human fingerprints, in this study, we created durable single-component elastomer surfaces with symmetric and multiple concentric-shaped wrinkled patterns that exhibit isotropic dry adhesion capabilities. The dynamic interfacial release-induced surface wrinkling property of a rigid degradable polymeric capping layer [i.e., poly(l-lactide) (PLLA)] was exploited on a soft elastomer substrate [i.e., polydimethylsiloxane (PDMS)] to spontaneously form wrinkled PLLA/PDMS bilayer composites. After conducting a two-step thermal curing process on the composite and hydrolysis of the PLLA capping layer, a single-component microwrinkled PDMS surface with a large area and symmetric patterns could be generated. The patterns show flexible, durable, and isotropic dry adhesion capabilities that could be controlled by tuning their geometrical parameters (wrinkle wavelengths and amplitudes) and elastic modulus. In particular, the formation of symmetrically wrinkled patterns without using expensive lithography for patterning and costly material precursors is an advantage and could be extended to other industrial applications, such as damage-free transportation, biomimetic climbing robots, and biocompatible medical patches.

Replication of the Surface Wettability of Plant Leaves with Different Surface Morphologies Using Soft Lithography

Naturally occurring surfaces which display interesting surface wetting properties such as superhydrophobicity, superoleophobicity and directional wettability are found in most aquatic plants. These phenomena arise from the micro/nano structures present on these surfaces complimented by their surface chemistry. The replication of such surface structures is highly pursued due to their potential in applications such as self-cleaning (Lotus effect), microfluidic devices and antifouling surfaces. Soft lithography is a technique that has been used to replicate micro/nano structures with varying degrees of success. Nevertheless, in the context of natural surfaces, the technique has been mostly limited to the replication of the lotus leaf structure. Therefore, a systematic investigation could be fruitful since it has the potential to be scaled up to replicate different surface structures as well as large-area patterning. In this study, the feasibility of soft lithography technique on natural leaf surfaces was investigated using five plant species with different surface morphologies. The negatives of these primary molds were replicated using polydimethylsiloxane (PDMS) and the final positive replica was successfully replicated from PDMS while using hydroxypropyl methylcellulose (HPMC) as an anti-stick layer. The structures were characterized based on SEM images and contact angle measurements. Additionally, the effect of HPMC was also investigated. The technique can easily be extended to broader applications in other areas that require micro/nanostructured surfaces such as anti-reflection coatings, chemical sensors and anti-microbial surfaces.