Large-area Patterning Research Articles

Scalable Fabrication of Quasi-One-Dimensional Gold Nanoribbons for Plasmonic Sensing.

Plasmonic nanostructures have a wide range of applications, including chemical and biological sensing. However, the development of techniques to fabricate submicrometer-sized plasmonic structures over large scales remains challenging. We demonstrate a high-throughput, cost-effective approach to fabricate Au nanoribbons via chemical lift-off lithography (CLL). Commercial HD-DVDs were used as large-area templates for CLL. Transparent glass slides were coated with Au/Ti films and functionalized with self-assembled alkanethiolate monolayers. Monolayers were patterned with lines via CLL. The lifted-off, exposed regions of underlying Au were selectively etched into large-area grating-like patterns (200 nm line width; 400 nm pitch; 60 nm height). After removal of the remaining monolayers, a thin In2O3 layer was deposited and the resulting gratings were used as plasmonic sensors. Distinct features in the extinction spectra varied in their responses to refractive index changes in the solution environment with a maximum bulk sensitivity of ∼510 nm/refractive index unit. Sensitivity to local refractive index changes in the near-field was also achieved, as evidenced by real-time tracking of lipid vesicle or protein adsorption. These findings show how CLL provides a simple and economical means to pattern large-area plasmonic nanostructures for applications in optoelectronics and sensing.

Controlled patterning of upconversion nanocrystals through capillary force

Lanthanide-doped upconversion nanoparticles (UCNPs) can absorb near-infrared photons and convert them into visible and ultraviolet emissions. These nanomaterials possess extraordinary optical performance and hold potential as active platforms for a variety of technological applications. The ability to fabricate highly ordered nanoparticle-based photonic elements over a large area is of fundamental significance for luminescence tuning. Despite all the efforts made, however, large-area spatial patterning of UCNPs into ordered arrays with high controllability remains a challenge. In this study, we report a high-throughput strategy to pattern optical nanomaterials through the use of polymer microspheres and templated assembly of UCNPs. This technique utilizes capillary force to drive hybrid clusters into the physical template, resulting in large-area, spatially ordered arrays of particles. The findings reported in this work may promote the development of novel nonlinear optical devices, such as solid-state laser arrays, high-density optical storage, and anti-counterfeiting labels.

Multi-Step Crystallization of Self-Organized Spiral Eutectics.

A method for the solidification of metallic alloys involving spiral self-organization is presented as a new strategy for producing large-area chiral patterns with emergent structural and optical properties, with attention to the underlying mechanism and dynamics. This study reports the discovery of a new growth mode for metastable, two-phase spiral patterns from a liquid metal. Crystallization proceeds via a non-classical, two-step pathway consisting of the initial formation of a polytetrahedral seed crystal, followed by ordering of two solid phases that nucleate heterogeneously on the seed and grow in a strongly coupled fashion. Crystallographic defects within the seed provide a template for spiral self-organization. These observations demonstrate the ubiquity of defect-mediated growth in multi-phase materials and establish a pathway toward bottom-up synthesis of chiral materials with an inter-phase spacing comparable to the wavelength of infrared light. Given that liquids often possess polytetrahedral short-range order, our results are applicable to many systems undergoing multi-step crystallization.

Optimum design of a 740 mm-long lens mount for a large-area and high-speed line beam proximity exposure

Proximity exposure with line beam scanning can be an alternative to traditional proximity exposure for a fast, high-resolution, large-area patterning. The optical elements used for shaping the line beams have a very large length-to-cross-sectional area ratio, so even small misalignment has a large effect on the optical path. In this study, a lens mount system based on kinematic coupling was established to accurately locate and align the line beam lens. Finite element models of the line beam lens and the mount were constructed, and then static structural simulations were performed. Optical paths concerning lens deformation and misalignment were calculated based on the vector equations for lines, surfaces, and Snell's law. An optimum design process based on the Taguchi method was carried out to minimize the difference between the actual optical arrival location and the target location. The stiffness and clamping force of the clamp part and support positions were selected as design variables, and the geometrical uncertainties of the lens supports was treated as error factors. A cross product array was constructed for each design variable and error factor, and then a total of 36 simulations were performed. Finally, the influence of each design variable on the optical path was analyzed, and the optimum conditions for the design variables, minimizing the error factor, were determined. As a result, the optical path error due to the geometrical uncertainty was reduced by approximately 30% compared to initial design.

Significant Enhancement in Light Output of Photonic-Crystal-Based YAG:Ce Scintillator for Soft X-Ray Detectors

Because of its high light output, Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S:Tb (P43) phosphor powder is widely used in scintillator detectors for scanning transmission soft X-ray microscopy. However, the long decay time (>1 ms) of P43 phosphor powder limits the image scanning speed. Inorganic scintillators such as YAG:Ce are very suitable for fast scanning imaging due to their short decay time (tens of nanoseconds). Nevertheless, its light output is lower than that of P43 phosphor powder. Patterning photonic crystals (PhCs) on the output surface of an inorganic scintillator is a simple and efficient method to enhance its light output. In this article, we use a soft X-ray interference lithography technique to produce a large-area pattern of nanoscale PhCs on a 200-μm -thickness and 1-in-diameter YAG:Ce scintillator. Measurement of the enhancement ratio was performed on the soft X-ray beamline (BL08U1A) at the Shanghai Synchrotron Radiation Facility. The results show that the light output of the PhC-patterned YAG:Ce scintillator with air coupling is approximately 2.8 times higher than that of the unpatterned YAG:Ce scintillator. Meanwhile, the time-resolved emission with optical excitation showed that the PhC structures did not affect the spontaneous emission rate in the internal of scintillator crystal. This enhancement of the light output indicates that the PhC-patterned YAG:Ce scintillator is a good candidate for soft X-ray detection.

Ultrasmall Designed Plasmon Resonators by Fused Colloidal Nanopatterning.

This work presents a procedure for large-area patterning of designed plasmon resonators that are much smaller than possible with conventional lithography techniques. Fused Colloidal Nanopatterning combines directed self-assembly and controlled fusing of spherical colloidal nanoparticles. The two-step approach first patterns a surface covered with hydrogen silsesquioxane, an electron beam resist, forming traps into which the colloidal gold nanoparticles self-assemble. Second, the patterned nanoparticles are controllably fused to form plasmon resonators of any 2D designed shape. The heights and widths of the plasmon resonators are determined by the diameter of the nanoparticle building blocks, which can be well below 10 nm. By performing the fusing step with UV ozone and heat exposure, we demonstrate that the process is easily scalable to cover large areas on silicon wafers with designed gold nanostructures. The procedure neither requires adhesion layers nor a lift-off process, making it ideally suited for plasmonics, in comparison with regular electron beam lithography. We use monochromated electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy and boundary element method simulations to demonstrate that the designed plasmon resonators are directly tunable via the pattern design. We foresee future expansion of this approach for applications such as plasmon-enhanced photocatalysis and for large-scale patterning where chemical, optical, or confinement properties require sub-10 nm metal lines.

Plasma-based processes for planar and 3D surface patterning of functional nanoparticles

We present a gas-phase process for surface patterning and 3D self-assembly of nanoparticles (NPs) of functional materials such as metals, oxides, and nitrides. The method relies on electrostatic assembly of free-flying NPs with unipolar charge produced in plasma sources. We demonstrate the capability of the process in self-assembly of NPs, with the size in the range 10–60 nm, into arrays of free-standing 3D microstructures with complex morphologies. Considering that the plasma nanoparticle sources are compatible with synthesis of a large library of material NPs, the process introduces a novel approach for 3D printing of various functional NPs, high-precision device integration of NPs on sub-micrometer scales, and large-area parallel surface patterning of NPs.

"Double" displacement Talbot lithography: fast, wafer-scale, direct-writing of complex periodic nanopatterns.

We describe a new low-cost nanolithographic tool for creating periodic arrays of complex, nano-motifs, across large areas within minutes. Displacement Talbot lithography is combined with lateral nanopositioning to enable large-area patterning with the flexibility of a direct-write system. In this way, we can create different periodic patterns in short timescales using a single mask with no mask degradation. We demonstrate multiple exposures, combined with discrete lateral displacements, and single exposures, with continuous displacements, to achieve image inversion, pitch reduction, and nanogaps between metal nanoparticles. Our approach provides a flexible route to create large-area nanopatterned materials and devices in high volumes.

A photolithographic method for fabricating electron devices based on MOCVD-grown MoS2

In modern electronics, two-dimensional (2D) materials which possess atomically thin layers and periodic network structures have emerged as a new paradigm of materials with a lot of potentials. To fully realize the important commercial applications that 2D materials in modern electronics, one of the key issues, such as development of adequate lithographic processing for 2D materials, must be resolved. Here, we report an unprecedented and reliable photolithographic process for large-area patterning of molybdenum disulfide (MoS2) films on both SiO2/Si and polymer substrates, as well as a lift-off of deposited metals on MoS2 films using an Irgacure 651-doped poly(methyl methacrylate) resist and a water-free developer. To verify the feasibility of our process, the fabrication and device performance of MoS2 field-effect transistors (FETs) is also presented. We expect the proposed method to provide a reliable route to device fabrication with 2D materials and to be an important step toward their commercialization.

Vertically Stacked CVD-Grown 2D Heterostructure for Wafer-Scale Electronics

This paper demonstrates, for the first time, wafer-scale graphene/MoS2 heterostructures prepared by chemical vapor deposition (CVD) and their application in vertical transistors and logic gates. A CVD-grown bulk MoS2 layer is utilized as the vertical channel, whereas CVD-grown monolayer graphene is used as the tunable work-function electrode. The short vertical channel of the transistor is formed by sandwiching bulk MoS2 between the bottom indium tin oxide (ITO, drain electrode) and the top graphene (source electrode). The electron injection barriers at the graphene-MoS2 junction and ITO-MoS2 junction are modulated effectively through variation of the Schottky barrier height and its effective barrier width, respectively, because of the work-function tunability of the graphene electrode. The resulting vertical transistor with the CVD-grown MoS2/graphene heterostructure exhibits a current density exceeding 7 A/cm2, a subthreshold swing of 410 mV/dec, and an on-off current ratio exceeding 103. The large-area synthesis, transfer, and patterning processes of both semiconducting MoS2 and metallic graphene facilitate construction of a wafer-scale array of transistors and logic gates such as NOT, NAND, and NOR.

Ablation and Patterning of Carbon Nanotube Film by Femtosecond Laser Irradiation

Carbon nanotube (CNT) film can be used as thin film electrodes and wearable electronic devices due to their excellent mechanical and electrical properties. The femtosecond laser has the characteristics of an ultra-short pulse duration and an ultra-high peak power, and it is one of the most suitable methods for film material processing. The ablation and patterning of CNT film are performed by a femtosecond laser with different parameters. An ablation threshold of 25 mJ/cm2 was obtained by investigating the effects of laser pulse energy and pulse number on ablation holes. Raman spectroscopy and scanning electron microscope (SEM) were used to characterize the performance of the pattern groove. The results show that the oligomer in the CNT film was removed by the laser ablation, resulting in an increase in Raman G band intensity. As the laser increased, the ablation of the CNTs was caused by the energy of photons interacting with laser-induced thermal elasticity when the pulse energy was increased enough to destroy the carbon–carbon bonds between different carbon atoms. Impurities and amorphous carbon were found at and near the cut edge while laser cutting at high energy, and considerable distortion and tensile was produced on the edge of the CNTs’ groove. Furthermore, appropriate cutting parameters were obtained without introducing defects and damage to the substrate, which provides a practical method applied to large-area patterning machining of CNT film.

Femtosecond laser irradiation of molecular excitonic films for nanophotonic response control and large-area patterning.

Molecular excitonic films such as J-aggregate thin films can show an optically metallic response in the visible region and can be considered as alternative materials for plasmonics. However, there was no direct, top-down method to modify the optical response over a large area. Here, we demonstrate the femtosecond (fs) laser processing of J-aggregate films on the centimeter scale. With proper laser conditions, optically metallic films (Re[ε] < 0) were modified to dielectric ones (Re[ε] > 0) with large changes in optical responses. We performed various optical spectrum measurements to investigate the effect of fs-laser irradiation. Our results demonstrate that the strong modification of the optical response can be induced over a large area by fs-laser processing and this can be useful for novel nanophotonic studies.

Bird's‐Eye ‐ Large‐Scale Visual Analytics of City Dynamics using Social Location Data

AbstractThe analysis of behavioral city dynamics, such as temporal patterns of visited places and citizens' mobility routines, is an essential task for urban and transportation planning. Social media applications such as Foursquare and Twitter provide access to large‐scale and up‐to‐date dynamic movement data that not only help to understand the social life and pulse of a city but also to maintain and improve urban infrastructure. However, the fast growth rate of this data poses challenges for conventional methods to provide up‐to‐date, flexible analysis. Therefore, planning authorities barely consider it. We present a system and design study to leverage social media data that assist urban and transportation planners to achieve better monitoring and analysis of city dynamics such as visited places and mobility patterns in large metropolitan areas. We conducted a goal‐and‐task analysis with urban planning experts. To address these goals, we designed a system with a scalable data monitoring back‐end and an interactive visual analytics interface. The monitoring component uses intelligent pre‐aggregation to allow dynamic queries in near real‐time. The visual analytics interface leverages unsupervised learning to reveal clusters, routines, and unusual behavior in massive data, allowing to understand patterns in time and space. We evaluated our approach based on a qualitative user study with urban planning experts which demonstrates that intuitive integration of advanced analytical tools with visual interfaces is pivotal in making behavioral city dynamics accessible to practitioners. Our interviews also revealed areas for future research.

Top-down fabrication of high-uniformity nanodiamonds by self-assembled block copolymer masks

Nanodiamonds hosting colour centres are a promising material platform for various quantum technologies. The fabrication of non-aggregated and uniformly-sized nanodiamonds with systematic integration of single quantum emitters has so far been lacking. Here, we present a top-down fabrication method to produce 30.0 ± 5.4 nm uniformly-sized single-crystal nanodiamonds by block copolymer self-assembled nanomask patterning together with directional and isotropic reactive ion etching. We show detected emission from bright single nitrogen vacancy centres hosted in the fabricated nanodiamonds. The lithographically precise patterning of large areas of diamond by self-assembled masks and their release into uniformly sized nanodiamonds open up new possibilities for quantum information processing and sensing.

Production and Mechanical Characterization of Graphene Micro-Ribbons

Patterning of graphene into micro- and nano-ribbons allows for tunability in emerging fields such as flexible electronic and optoelectronic devices, and is gaining interest for the production of more efficient reinforcement for composite materials. In this work we fabricate micro-ribbons from graphene synthesized via chemical vapor deposition (CVD) by combining ultraviolet (UV) photolithography and dry etching oxygen plasma treatments. We used Raman spectral imaging to confirm the effectiveness of the patterning procedure, which is suitable for large-area patterning of graphene on wafer-scale, and confirms that the quality of graphene remains unaltered. The produced micro-ribbons were finally transferred and embedded into a polymeric matrix and the mechanical response was investigated by in-situ mechanical investigation combining Raman spectroscopy and tensile/compressive tests.

Use of beam-shaping optics for wafer-scaled nanopatterning in laser interference lithography

Laser interference lithography is a widely used technology for large-area patterning of surfaces on the micro- and nanoscale. It is mostly used for research purposes due to the limited area that can be uniformly patterned due to the Gaussian intensity profile of the laser. In the scope of this work, the lithography system was extended by a freeform refractive glass which provided a spatially uniform energy distribution for a homogenous structuring process. The energy variation of the introduced light was reduced to 2.6% for the exposed area (4 × 9 cm), which is one magnitude lower than the energy variation of a Gaussian beam. With the refractive beam shaper, it was possible to produce a uniform nanopattern with an absolute linewidth variation of 7 nm over an area of 4 × 9 cm2. The structurable area is limited by the mirror size of the Lloyd’s mirror device. The demonstrated LIL system was also able to generate variable light fields from Gaussian to flat-top as well as inverse Gaussian profiles. This paper demonstrates nanopatterning of negative resist with a square homogenous output profile of the beam shaper. The square shape of the beam profile gives the opportunity to efficiently structure substrates with a square shape. Apart from standard silicon-based photolithographic processes, this technique is also attractive for nanopatterning of organic light-emitting diodes on glass or graduated grid structures like polarizers. Consequently, the advantages of the LIL fabrication (high-throughput and low-cost fabrication) are extended by the opportunity to scale the single-exposure process to large areas with only small variations in the detail.

Scalable Nanoshaping of Hierarchical Metallic Patterns with Multiplex Laser Shock Imprinting Using Soft Optical Disks.

Large-area patterning of metals in nanoscale has always been a challenge. Traditional microfabrication processes involve many high-cost steps, including etching and high-vacuum deposit, which limit the development of functional nanostructures, especially multiscale metallic patterns. Here, multiplex laser shock imprinting (MLSI) process is introduced to directly manufacture hierarchical micro/nanopatterns at a high strain rate on metallic surfaces using soft optical disks with 1D periodic trenches as molds. The unique metal/polymer layered structures in inexpensive soft optical disks make them strong candidates of molds for MLSI processes. The feasibility of MLSI on hard metals toward soft molds is studied using theoretical simulation. In addition, various types of hierarchical structures are fabricated via MLSI, and their optical reflectance can be modulated via a combination of depth (laser power density), width (types of molds), and angles (rotation between molds). The optical properties have been studied with surface plasmon polariton modes theory. This work opens a new way of manufacturing hierarchical micro/nanopatterns on metals, which is promising for future applications in fields of plasmonics and metasurfaces.

Submicrometer Top-Gate Self-Aligned a-IGZO TFTs by Substrate Conformal Imprint Lithography

Thin-film transistors (TFTs) are the fundamental building blocks of today's display industry. To achieve higher drive currents and device density, it is essential to scale down the channel lengths of TFTs. To be able to fabricate short-channel TFTs in large volumes is also equally important in order to realize lower fabrication costs and higher throughput. In this paper, we demonstrate the application of substrate conformal imprint lithography (SCIL) to pattern top-gate (TG) self-aligned (SA) amorphous indium gallium zinc oxide TFTs down to channel length LG = 450 nm with good device scaling properties resulting in average field-effect mobility (μFE) = ~10 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> = ~ 0.5 V, and subthreshold swing (SS) = ~0.3 V/decade. The device performance as a function of channel length outlines the importance of dopant diffusion control for realizing submicrometer SA TFTs. The results demonstrate the compatibility of SCIL-based large-area patterning for the realization of submicrometer TG SA TFTs with a potential for high throughput.

High-Resolution and Large-Area Patterning of Highly Conductive Silver Nanowire Electrodes by Reverse Offset Printing and Intense Pulsed Light Irradiation.

Conventional printing technologies such as inkjet, screen, and gravure printing have been used to fabricate patterns of silver nanowire (AgNW) transparent conducting electrodes (TCEs) for a variety of electronic devices. However, they have critical limitations in achieving micrometer-scale fine line width, uniform thickness, sharp line edge, and pattering of various shapes. Moreover, the optical and electrical properties of printed AgNW patterns do not satisfy the performance required by flexible integrated electronic devices. Here, we report a high-resolution and large-area patterning of highly conductive AgNW TCEs by reverse offset printing and intense pulsed light (IPL) irradiation for flexible integrated electronic devices. A conductive AgNW ink for reverse offset printing is prepared by carefully adjusting the composition of AgNW content, solvents, surface energy modifiers, and organic binders for the first time. High-quality and high-resolution AgNW micropatterns with various shapes and line widths are successfully achieved on a large-area plastic substrate (120 × 100 mm2) by optimizing the process parameters of reverse offset printing. The reverse offset printed AgNW micropatterns exhibit superior fine line widths (up to 6 μm) and excellent pattern quality such as sharp line edge, fine line spacing, effective wire junction connection, and smooth film roughness. They are post-processed with IPL irradiation, thereby realizing excellent optical, electrical, and mechanical properties. Furthermore, flexible OLEDs and heaters based on reverse offset printed AgNW micropatterns are successfully fabricated and characterized, demonstrating the potential use of the reverse offset printing for the conductive AgNW ink.

Large area patterning of residue-free metal oxide nanostructures by liquid transfer imprint lithography

One-dimensional (1D) and three-dimensional (3D) residue-free metal oxide patterns are directly fabricated over large areas using liquid transfer imprint lithography (LTIL) with an ultraviolet-curable metal oxide precursor resist. A 1D line or pillar array of metal oxides nano-patterns without a residual layer is formed by LTIL and annealing processes. A 3D layer-by-layer nanomesh structure is successfully constructed by repeating the LTIL method without a complex etching process. In addition, it is possible to form a hierarchical structure in which zinc oxide nanowires are selectively grown on a desired zinc oxide (ZnO) seed pattern formed by LTIL via a hydrothermal method. Unlike the pattern fabricated by the conventional nanoimprint lithography method, in the case of the pattern formed by LTIL the residues accumulated between the patterns during the patterning procedure can be removed, and thus it is possible to easily form various types of nanostructures.