Proximity Field Nanopatterning Research Articles

Metal Nanocomposites Reinforced by Ceramic Nanoarchitecture: Exploiting Extrinsic Size Effects for High Mechanical Strength.

The pursuit of harnessing superior mechanical properties achieved through the size effect on a macroscopic scale has been a prominent focus in engineering, as size-induced strengthening is enabled only in the nanoscale regime. This study presents a metal/ceramic/metal (MCM) nanocomposite reinforced by ceramic nanoarchitectures. Through proximity-field nanopatterning, the inch-scale production of nanoarchitecture films is enabled in a single fabrication step. The developed three-dimensional (3D) Ni/Al2O3/Ni nanocomposite film exhibits significantly high compressive strength, corresponding to an increase of approximately 30% compared with that calculated using the upper limits of the conventional rule of mixtures. The exceptional strength of the 3D MCM nanocomposite can be attributed to the extrinsic size effect of the ceramic nanoarchitectures. By combining size-induced strengthening of ceramics with the strengthening law for composites, a new type of strengthening model is derived and experimentally validated using the 3D MCM nanocomposite.

Towards optimal 3D battery electrode architecture: Integrating structural engineering with AI-driven optimization

The rapid evolution of energy storage devices, driven by increasing demands for prolonged battery life in electronics as well as sustainable energy solutions has elevated lithium-ion batteries (LIBs) to prominence in modern energy systems. With electric vehicle sales and LIB demand surging, the need for high-performing batteries is at an all-time high. However, critical issues with LIBs have become apparent, particularly in energy degradation due to poor mass transport, emphasising the need for advancements in electrode design. This review explores the influence of electrode structural factors on mass transport properties, with a specific focus on the latest developments in three-dimensional (3D) battery electrodes featuring diverse pore arrangements—ranging from random to ordered pores or porosity gradients. The review delves into recent breakthroughs achieved through structural diversification by applying an inverse design to Proximity-field nanoPatterning (PnP), laying the groundwork for collaborative efforts aimed at advancing energy storage technologies. Various fabrication methods for 3D electrodes are discussed, highlighting the promising role of integrating the PnP technique with computational algorithms to enhance the precision and design capabilities of 3D nanostructures.

Rational design of arbitrary topology in three-dimensional space via inverse calculation of phase modulation.

Recent advances in nanotechnology have led to the emergence of metamaterials with unprecedented properties through precisely controlled topologies. To explore metamaterials with nanoscale topologies, interest in three-dimensional nanofabrication methods has grown and led to rapid production of target nanostructures over large areas. Additionally, inverse design methods have revolutionized materials science, enabling the optimization of microstructures and topologies to achieve the desired properties without extensive experimental cycles. This review highlights the recent progress in inverse design methods applied in proximity-field nanopatterning. It introduces novel approaches, such as adjoint methods and particle swarm optimization, to achieve target topologies and high-resolution nanostructures. Furthermore, machine learning algorithms for inverse design are explored, demonstrating the potential efficacy of the phase-mask design. This comprehensive review offers insights into the progress of inverse design using phase modulation to realize target topologies of nanostructures.

Photolithographic realization of target nanostructures in 3D space by inverse design of phase modulation.

The mass production of precise three-dimensional (3D) nanopatterns has long been the ultimate goal of fabrication technology. While interference lithography and proximity-field nanopatterning (PnP) may provide partial solutions, their setup complexity and limited range of realizable structures, respectively, remain the main problems. Here, we tackle these challenges by applying an inverse design to the PnP process. Our inverse design platform based on the adjoint method can efficiently find optimal phase masks for diverse target lattices and motifs. We fabricate a 2D rectangular array of nanochannels, which has not been reported for conventional PnP with normally incident light, as a proof of concept. With further demonstration of material conversion, our work provides versatile platforms for nanomaterial fabrication.

Proximity-field nanopatterning for high-performance chemical and mechanical sensor applications based on 3D nanostructures

In this era of the Internet of Things, the development of innovative sensors has rapidly accelerated with that of nanotechnology to accommodate various demands for smart applications. The practical use of three-dimensional (3D) nanostructured materials breaks several limitations of conventional sensors, including the large surface-to-volume ratio, precisely tunable pore size and porosity, and efficient signal transduction of 3D geometries. This review provides an in-depth discussion on recent advances in chemical and mechanical sensors based on 3D nanostructures, which are rationally designed and manufactured by advanced 3D nanofabrication techniques that consider structural factors (e.g., porosity, periodicity, and connectivity). In particular, we focus on a proximity-field nanopatterning technique that specializes in the production of periodic porous 3D nanostructures that satisfy the structural properties universally required to improve the performance of various sensor systems. State-of-the-art demonstrations of high-performance sensor devices such as supersensitive gas sensors and wearable strain sensors realized through designed 3D nanostructures are summarized. Finally, challenges and outlooks related to nanostructures and nanofabrication for the practical application of 3D nanostructure-based sensor systems are proposed.

Exploiting Super-Lithiation in 3D Mesostructured Polyimide Electrodes: Towards Practical Organic Batteries

Recent developments in redox-active organic molecules appear to be providing sustainable and cost-effective electrode materials as potential alternatives to conventional metal-based electrodes for lithium-ion batteries (LIBs). However, utilization of the organic battery electrodes in practical applications has been quite limited. The rational design principles of the electrode structure would be beneficial in concurrently achieving practical performance demands of high energy, fast charging rate, and long-term cyclability. In this work, we conceive a lithographic fabrication strategy for realizing a 3D mesostructured organic electrode that exploits a ‘super-lithiation’ phenomenon of nearly all unsaturated C=C bonds in multi-carbonyl polyimide. The polyimide layer grown on the ordered porous nickel current collector which is prepared via proximity-field nanopatterning (PnP), generates promoted super-lithiation and shows a much higher specific capacity of 1300 mAh g−1 compared to that of the 2D electrode (270 mAh g−1). We attribute the high electrochemical activity to fast reaction kinetics through the efficient pathways for Li-ions and electrons within the electrode, as well as pathways for rapid transport of ions within the interconnected, electrolyte-filled porous network. The effect of the 3D structure is further corroborated by the unprecedented high-rate capability (achieved rates up to 400 C) and 83% capacity retention at 10 C (15 A g−1) after 250 cycles. Finally, the full electrode-basis capacity reaches 2800 mAh cm−3, surpassing the target lines required to meet the energy density target of 1500 Wh L−1 (on half-cell level) for hybrid electric vehicles. Our findings suggest that our strategic electrode design may contribute to spurring the commercialization of organic electrodes for practical systems in near future. Furthermore, the 3D nickel with the continuous, periodic porous network used in this study is expected to accommodate the severe volume expansion and induce uniform Li deposition as an effective current collector. It could be further studied for the development of Si- and Sn-based anodes for advanced LIBs or dendrite-free Li anode for lithium-metal batteries.

Transparent polymer nanocomposite with three-dimensional ZnO thin-shell with high UV-shielding performance

This paper introduces a nontrivial concept of a transparent nanocomposite with a three-dimensional (3D) ZnO thin-shell, as an ultraviolet (UV)-shielding reinforcement which absorbs all ranges of UV light, including UV-A (320 nm–400 nm). The continuous and ordered geometry of the 3D ZnO thin-shell, uniformly distributed in an epoxy matrix, efficiently captures incident UV light by repeatedly scattering and absorbing UV light at the epoxy-ZnO interfaces. Proximity-field nanoPatterning and atomic layer deposition can be employed to produce a 3D ZnO thin-shell array on a large scale (>1 inch2). The fabricated 3D ZnO/epoxy nanocomposite film exhibits excellent UV-shielding performance, blocking 95.20% of UV-A light. Transmittance at the edge of the UV-A range (400 nm) is suppressed by 64% (from 86% to 31%), while transmittance in the visible range (550 nm) is retained (from 90% to 75%). Moreover, the UV-shielding capability of the 3D nanocomposite film can be tailored by controlling the ZnO shell thickness from 0 nm to 45 nm. The 3D ZnO/epoxy nanocomposite provides a good option for next-generation transparent UV-shielding films.

Fundamental principles and development of proximity-field nanopatterning toward advanced 3D nanofabrication

Three-dimensional (3D) nanoarchitectures have offered unprecedented material performances in diverse applications like energy storages, catalysts, electronic, mechanical, and photonic devices. These outstanding performances are attributed to unusual material properties at the nanoscale, enormous surface areas, a geometrical uniqueness, and comparable feature sizes with optical wavelengths. For the practical use of the unusual nanoscale properties, there have been developments for macroscale fabrications of the 3D nanoarchitectures with process areas over centimeter scales. Among the many fabrication methods for 3D structures at the nanoscale, proximity-field nanopatterning (PnP) is one of the promising techniques that generates 3D optical holographic images and transforms them into material structures through a lithographic process. Using conformal and transparent phase masks as a key factor, the PnP process has advantages in terms of stability, uniformity, and reproducibility for 3D nanostructures with periods from 300 nm to several micrometers. Other merits of realizing precise 3D features with sub-100 nm and rapid processes are attributed to the interference of coherent light diffracted by phase masks. In this review, to report the overall progress of PnP from 2003, we present a comprehensive understanding of PnP, including its brief history, the fundamental principles, symmetry control of 3D nanoarchitectures, material issues for the phase masks, and the process area expansion to the wafer-scale for the target applications. Finally, technical challenges and prospects are discussed for further development and practical applications of the PnP technique.

Scalable Fabrication of High-Performance Thin-Shell Oxide Nanoarchitected Materials via Proximity-Field Nanopatterning.

Nanoarchitected materials are considered as a promising research field, deriving distinctive mechanical properties by combining nanomechanical size effects with conventional structural engineering. Despite the successful demonstration of the superiority and feasibility of nanoarchitected materials, scalable and facile fabrication techniques capable of macroscopically producing such materials at a low cost are required to take advantage of the nanoarchitected materials for specific applications. Unlike conventional techniques, proximity-field nanopatterning (PnP) is capable of simultaneously obtaining high spatial resolution and mass producibility in synthesizing such nanoarchitected materials in the form of an inch-scale film. Herein, we focus on the feasibility of using PnP as a scalable fabrication technique for three-dimensional nanostructures and the superiority of the resultant thin-shell oxide nanoarchitected materials for specific applications, such as lightweight structural materials, mechanically robust nanocomposites, and high-performance piezoelectric materials. This review will discuss and summarize the relevant results obtained for nanoarchitected materials synthesized by PnP and provide suggestions for future research directions for scalable manufacturing and application.

3D-ordered porous composite microparticles formed via substrate-free optical 3D lithography

This paper proposes a cutting-edge photolithography-based top-down approach to produce functional porous microparticles with three-dimensional (3D) periodic nanostructures. The developed fabrication process employs proximity-field nanopatterning (PnP), a representative optical 3D nanofabrication technique in which a new type of phase mask and exposure scheme have been introduced. In the modified PnP mode, where the photoresist is directly coated on the phase mask, a 3D nanostructured membrane detaches from the mask during the development process. The freestanding 3D nanostructured membrane is electromagnetically shredded through simple ultrasonication to produce a large amount of 3D-ordered porous microparticles. A Gaussian distribution of particle sizes with an average size of ∼37 µm can be obtained through an optimization of the sonication time. In addition, composite porous microparticles that exhibit exceptional magnetically responsive properties can be generated by incorporating iron oxide nanoparticles into the rinsing solution as nanofillers.

Breaking the elastic limit of piezoelectric ceramics using nanostructures: A case study using ZnO

Piezoelectric materials are suitable for haptic technology as they can convert mechanical stimuli into electrical signals and vice-versa. However, owing to their disadvantageous mechanical properties such as brittleness (in ceramics) and a low piezoelectric coefficient (in polymers), their application in haptic technology remains challenging. In this paper, we introduce a truss-like 3D hollow nanostructure using zinc oxide (ZnO) that exhibits a drastically improved elastic strain limit while maintaining a piezoelectric coefficient similar to that of single-crystal ZnO. The ZnO hollow nanostructure was fabricated using proximity field nanopatterning (PnP) and atomic layer deposition (ALD) at four different processing temperatures. The piezoelectric characteristics were analyzed through dual AC resonance tracking piezoresponse force microscopy (PFM), and the piezoelectric coefficient was measured to be up to 9.2 pm/V. The nanopillar compression test result showed that the measured elastic strain limit of approximately 10% was at least 3 times greater than the previously reported value. The extended elastic limit of the 3D hollow structure was further supported by finite element simulations. The ZnO hollow nanostructure shows excellent potential for its application to enhanced haptic devices, which mimic the human sense of touch.

Hierarchically porous Au nanostructures with interconnected channels for efficient mass transport in electrocatalytic CO2 reduction

Electrocatalytic CO2 reduction is a promising way to provide renewable energy from gaseous CO2 The development of nanostructures improves energy efficiency and selectivity for value-added chemicals, but complex nanostructures limit the CO2 conversion rates due to poor mass transport during vigorous electrolysis. Herein, we propose a three-dimensional (3D) hierarchically porous Au comprising interconnected macroporous channels (200-300 nm) and nanopores (∼10 nm) fabricated via proximity-field nanopatterning. The interconnected macropores and nanopores enable efficient mass transport and large active areas, respectively. The roles of each pore network are investigated using reliable 3D nanostructures possessing controlled pore distribution and size. The hierarchical nanostructured electrodes show a high CO selectivity of 85.8% at a low overpotential of 0.264 V and efficient mass activity that is maximum 3.96 times higher than that of dealloyed nanoporous Au. Hence, the systematic model study shows the proposed hierarchical nanostructures have important value in increasing the efficiency of expensive Au.

Removing process of the three-dimension periodic nanostructure fabricated from KMPR photoresist

Three-dimensional (3D) periodic nanostructures with photonic and phononic crystals have enormous potential for new technology and research for example energy science, microfluidics and semiconductors. Previous studies have focused on using high pressure, high temperature and high cost processes like chemical vapor deposition or physical vapor deposition. In this work, 3D nanostructures were fabricated through a simple and cost effective method called the proximity field nano-patterning (PnP) process. Previous research has shown that 3D nanostructures can be fabricated via a PnP process using an SU-8 resist. Our research uses a KMPR (MicroChem) negative photoresist, which can be processed through an aqueous developer and removed by solution process. We investigated the Talbot distance, height, and periodicity of the KMPR periodic 3D nanostructure versus the SU-8 3D nanostructure. Furthermore, we demonstrate a facile solution removal process for the resist to fabricate inverse 3D nanostructures which can be extended to many applications.

Suppressing buoyant force: New avenue for long-term durability of oxygen evolution catalysts

Recent progress in the development of water oxidation electrocatalysts has mainly focused on achieving high performance in a single measurement, while the importance of durability has not yet been deeply studied. Additionally, oxygen evolution reaction (OER) involves a phase transition from a liquid to a gas, and thus, the removal of the generated oxygen bubble is an important factor for improving the activity or maintaining the performance. In this study, 3D ordered nanoporous nickel electrode is synthesized with a thickness of 5 µm by using a templating method composed of proximity field nanopatterning (PnP) and electrodeposition followed by introduction of NiFe(OH)2 on the nickel electrode to increase the OER activity. The unique nanopore array structure of the electrode has advantages of not only an enlarged active surface area but also the fast removal of oxygen bubbles by spatial confinement effect. Consequently, the NiFe-decorated 3D ordered nanoporous nickel electrode shows a highly efficient oxygen-evolving ability with a turnover frequency of 2.9 s−1 and an ultralong durability of 300 h.

Emergence of New Density-Strength Scaling Law in 3D Hollow Ceramic Nanoarchitectures.

Density-strength tradeoff appears to be an inherent limitation for most materials and therefore design of cell topology that mitigates strength decrease with density reduction has been a long-lasting engineering pursue for porous materials. Continuum-mechanics-based analyses of mechanical responses of conventional porous materials with bending-dominated structures often give the density-strength scaling law following the power-law relationship with an exponent of 1.5 or higher, which consequentially determines the upper bound of the specific strength for a material to reach. In this work, a new design criterion capable of significantly abating strength degradation in lightweight materials is presented, by successfully combining the size-induced strengthening effect in nanomaterials with the architectural design of cellular porous materials. Hollow-tube-based 3D ceramic nanoarchitectures satisfying such criterion are fabricated in large area using proximity field nano-patterning and atomic layer deposition. Experimental data from micropillar compression confirm that the strengths of these nanoarchitectural materials scale with relative densities with a power-law exponent of 0.93, a hardly observable value in conventional bending-dominated porous materials. This discovery of a new density-strength scaling law in nanoarchitectured materials will contribute to creating new lightweight structural materials attaining unprecedented specific strengths overcoming the conventional limit.

Fabrication of Nanoshell-Based 3D Periodic Structures by Templating Process using Solution-derived ZnO

Fabrication methods for a 3D periodic nanostructure with excellent and unique properties for various applications, such as photonic and phononic crystals, have attracted considerable interest. Templating processes using colloidal crystals have been proposed to create nanoshell-based 3D structures over a large area with ease. However, there are technical limitations in structural design, resulting in difficulties for structural flexibility. Here, we demonstrate a combination of proximity field nanopatterning and infiltration processes using solution-derived ZnO for a nanoshell-based 3D periodic structure with high structural flexibility and controllability. A unique process of infiltration of a solution-derived material into a polymeric template prepared by a proximity field nanopatterning process achieves the fabrication of a pre-formed layer that works as a protective layer for the template and framework for the inverse structure. Subsequently, this process shows the controllability of nanoshell thickness and significant improvement in the structure height shrinkage factor (16%) compared to those of a previous non-vacuum infiltration method (34%). The proposed method offers high controllability and flexibility in the design of structural sizes, leading to further development toward nanoshell-based 3D structures for various applications including energy devices and sensors.

Large-area metal foams with highly ordered sub-micrometer-scale pores for potential applications in energy areas

Nanoporous metallic foams with an exceptionally high specific surface area can be a perfect solution for advanced energy applications. There have been an increasing number of recent efforts to achieve nanoporous metallic foams, but the latest research has paid much attention to the processing and characterization of noble nanoporous metallic foams (Pt and Au) through the conventional dealloying technique. This study proposes a new and innovative method of processing non-noble nanoporous (sub-micrometer-scale) metallic foams: a technique that combines the conventional electroless plating and three-dimensional proximity-field nanopatterning. Copper and nickel foams with sub-micrometer-scale pores are processed and characterized in this study.

Monolithic 3D titania with ultrathin nanoshell structures for enhanced photocatalytic activity and recyclability

Titania has attracted considerable interest for use in water purification applications due to its excellent photocatalytic activity. To further improve the efficiency of photocatalysis, numerous nanostructures (i.e. nanoparticles, nanotubes, and nanowires) have been proposed to increase the surface area of titania. Despite the high photocatalytic performance of the nanostructured titania, subsequent difficulties encountered in recollection and reuse of titania inhibit the practical application for water purification systems. Here we successfully fabricate monolithic, three dimensional (3D) nanoshell titania with high uniformity over large areas (~1 × 1 inch(2)) through proximity field nanopatterning (PnP) and low-temperature atomic layer deposition (ALD) techniques. The higher surface area of 3D nanoshell titania increases the photocatalytic performance more than three-fold relative to that of a thin film of equivalent sample size. Also, the monolithic form of titania enables it to be reused without any degradation of photocatalytic activity. The newly developed nanomaterials in this study can serve as an efficient and reusable photocatalyst for water purification systems.

Rapid fabrication of 3D terahertz split ring resonator arrays by novel single-shot direct write focused proximity field nanopatterning

For the next generation of phoXonic, plasmonic, opto-mechanical and microfluidic devices, the capability to create 3D microstructures is highly desirable. Fabrication of such structures by conventional top-down techniques generally requires multiple time-consuming steps and is limited in the ability to define features spanning multiple layers at prescribed angles. 3D direct write lithography (3DDW) has the capability to draw nearly arbitrary structures, but is an inherently slow serial writing process. Here we present a method, denoted focused proximity field nanopatterning (FPnP), that combines 3DDW with single or multiphoton interference lithography (IL). By exposing a thick photoresist layer having a phase mask pattern imprinted on its surface with a tightly focused laser beam, we produce locally unique complex structures. The morphology can be varied based on beam and mask parameters. Patterns may be written rapidly in a single shot mode with arbitrary positions defined by the direct write, thus exploiting the control of 3DDW with the enhanced speed of phase mask IL. Here we show the ability for this technique to rapidly produce arrays of "stand-up" far IR resonators.

Triangular Elastomeric Stamps for Optical Applications: Near‐Field Phase Shift Photolithography, 3D Proximity Field Patterning, Embossed Antireflective Coatings, and SERS Sensing

AbstractThe use of a decal transfer lithography technique to fabricate elastomeric stamps with triangular cross‐sections, specifically triangular prisms and cones, is described. These stamps are used in demonstrations for several prototypical optical applications, including the fabrication of multiheight 3D photoresist patterns with near zero‐width features using near‐field phase shift lithography, fabrication of periodic porous polymer structures by maskless proximity field nanopatterning, embossing thin‐film antireflection coatings for improved device performance, and efficient fabrication of substrates for surface‐enhanced Raman spectroscopic sensing. The applications illustrate the utility of the triangular poly(dimethylsiloxane) decals for a wide variety of optics‐centric applications, particularly those that exploit the ability of the designed geometries and materials combinations to manipulate light–matter interactions in a predictable and controllable manner.