Large-Area Perovskite Nanocrystal Metasurfaces for Direction-Tunable Lasing.

Perovskite nanocrystals (PNCs) are attractive emissive materials for developing compact lasers. However, manipulation of PNC laser directionality has been difficult, which limits their usage in photonic devices that require on-demand tunability. Here we demonstrate PNC metasurface lasers with engineered emission angles. We fabricated millimeter-scale CsPbBr3 PNC metasurfaces using an all-solution-processing technique based on soft nanoimprinting lithography. By designing band-edge photonic modes at the high-symmetry X point of the reciprocal lattice, we achieved four linearly polarized lasing beams along a polar angle of ∼30° under optical pumping. The device architecture further allows tuning of the lasing emission angles to 0° and ∼50°, respectively, by adjusting the PNC thickness to shift other high-symmetry points (Γ and M) to the PNC emission wavelength range. Our laser design strategies offer prospects for applications in directional optical antennas and detectors, 3D laser projection displays, and multichannel visible light communication.

Sculpting the Electronic Nano-Terrain on a Perovskite Film for Efficient Charge Transport.

Nanopatterned halide perovskites have emerged to improve the performance of optoelectronic devices by controlling the crystallographic and optical properties via morphological modification. However, the correlation between the photophysical property and morphology transformation in nanopatterned perovskite films remains elusive, which hinders the rational design of nanopatterned halide perovskites for optoelectronic devices. In this study, we employed nanoimprinting lithography on a perovskite film to exert a precise control over grain growth and manipulate electronic structures at the level of individual grains. Surface-selective fluorescence lifetime imaging microscopy (FLIM) analyzes the spatiotemporally disentangled geometrical variations in carrier recombination rate and band structure modulation according to different pattern morphologies. Consequently, the stereoscopic mechanism of confined grain growth was unveiled, highlighting the quantitative grain size-based parameters that are crucial for nanoscale material engineering. Notably, the pattern-induced reduction of effective charge mass enabled exclusive control over the subdiffusive carrier transport dynamics on perovskite surfaces, ultimately realizing the surface-selective perovskite photodetectors. The implications of this study are expected to provide valuable guidelines, inspiring innovative design protocols for advancing the next-generation optoelectronic technologies.

Fourier Surfaces Reaching Full-Color Diffraction Limits.

Optical Fourier surfaces (OFSs), characterized by sinusoidally profiled diffractive optical elements, can outperform traditional binary-type counterparts by minimizing optical noise through selectively driving diffraction at desired frequencies. While scanning probe lithography (SPL), gray-scale electron beam lithography (EBL), and holographic inscriptions are effective for fabricating OFSs, achieving full-color diffractions at fundamental efficiency limits is challenging. Here, an integrated manufacturing process is presented, validated theoretically and experimentally, for fully transparent OFSs reaching the fundamental limit of diffraction efficiency. Leveraging holographic inscriptions and soft nanoimprinting, this approach effectively addresses challenges in conventional OFS manufacturing, enabling scalable production of noise-free and maximally efficient OFSs with record-high throughput (1010-1012 µm2 h-1), surpassing SPL and EBL by 1010 times. Toward this end, a wafer-scale OFSs array is demonstrated consisting of full-color diffractive gratings, color graphics, and microlenses by the one-step nanoimprinting, which is readily compatible with rapid prototyping of OFSs even on curved panels, demanding for transformative optical devices such as augmented and virtual reality displays.

Toward Defect-Free Nanoimprinting.

Nanoimprinting large-area structures, especially high-density features like meta lenses, poses challenges in achieving defect-free nanopatterns. Conventional high-resolution molds for nanoimprinting are often expensive, typically constructed from inorganic materials such as silicon, nickel (Ni), or quartz. Unfortunately, replicated nanostructures frequently suffer from breakage or a lack of definition during demolding due to the high adhesion and friction at the polymer-mold interface. Moreover, mold degradation after a limited number of imprinting cycles, attributed to contamination and damaged features, is a common issue. In this study, a disruptive approach is presented to address these challenges by successfully developing an anti-sticking nanocomposite mold. This nanocomposite mold is created through the co-deposition of nickel atoms and low surface tension polytetrafluoroethylene (PTFE) nanoparticles via electroforming. The incorporation of PTFE enhances the ease of polymer release from the mold. The resulting Ni-PTFE nanocomposite mold exhibits exceptional lubrication properties and a significantly reduced surface energy. This robust nanocomposite mold proves effective in imprinting fine, densely packed nanostructures down to 100 nm using thermal nanoimprinting for at least 20 cycles. Additionally, UV nanoimprint lithography (UV-NIL) is successfully performed with this nanocomposite mold. This work introduces a novel and cost-effective approach to reusable high-resolution molds, ensuring defect-reduction production in nanoimprinting.

Template-Confined Oriented Perovskite Nanowire Arrays Enable Polarization Detection and Imaging.

Polarized light detection can effectively identify the difference between the polarization information on the target and the background, which is of great significance for detection in complex natural environments and/or extreme weather. Generally, polarized light detection inevitably relies on anisotropic structures of photodetector devices, while organic-inorganic hybrid perovskites are ideal for anisotropic patterning due to their simple and efficient preparation by solution method. Compared to patterned thin films, patterned arrays of aligned one-dimensional (1D) perovskite nanowires (PNWAs) have fewer grain boundaries and lower defect densities, making them well suited for high-performance polarization-sensitive photodetectors. Here, we fabricated PNWAs crystallographically aligned with variable line widths and alignment densities employing CD-ROM and DVD-ROM grating pattern template-confined growth (TCG) methods. The photodetectors constructed from MAPbI3 PNWAs achieved responsivity of 35.01 A/W, detectivity of 6.85 × 1013 Jones, and fast response with a rise time of 172 µs and fall time of 114 µs. They were successfully applied to high-performance polarization detection with a polarization ratio of 1.81, potentially applicable in polarized light detection systems.

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.

Performance of Grating Couplers Used in the Optical Switch Configuration.

Surface plasmon resonance is an effect widely used for biosensing. Biosensors based on this effect operate in different configurations, including the use of diffraction gratings as couplers. Gratings are highly tunable and are easy to integrate into a fluidic system due to their planar configuration. We discuss the optimization of plasmonic grating couplers for use in a specific sensor configuration based on the optical switch. These gratings present a sinusoidal profile with a high depth/period ratio. Their interaction with a p-polarized light beam results in two significant diffracted orders (the 0th and the -1st), which enable differential measurements cancelling noise due to common fluctuations. The gratings are fabricated by combining laser interference lithography with nanoimprinting in a process that is aligned with the challenges of low-cost mass production. The effects of different grating parameters such as the period, depth and profile are theoretically and experimentally investigated.

Sub-30 nm 2D Perovskites Patterns via Block Copolymer Guided Self-Assembly for Color Conversion Optical Polarizer.

Despite the remarkable advances made in the development of 2D perovskites suitable for various high-performance devices, the development of sub-30 nm nanopatterns of 2D perovskites with anisotropic photoelectronic properties remains challenging. Herein, a simple but robust route for fabricating sub-30 nm 1D nanopatterns of 2D perovskites over a large area is presented. This method is based on nanoimprinting a thin precursor film of a 2D perovskite with a topographically pre-patterned hard poly(dimethylsiloxane) mold replicated from a block copolymer nanopattern consisting of guided self-assembled monolayered in-plane cylinders. 1D nanopatterns of various 2D perovskites (A'2 MAn -1 Pbn X3 n +1 ,A' = BA, PEA, X = Br, I) are developed; their enhanced photoluminescence (PL) quantum yields are approximately four times greater than those of the corresponding control flat films. Anisotropic photocurrent is observed because 2D perovskite nanocrystals are embedded in a topological 1D nanopattern. Furthermore, this 1D metal-coated nanopattern of a 2D perovskite is employed as a color conversion optical polarizer, in which polarized PL is developed. This is due to its capability of polarization of an incident light arising from the sub-30 nm line pattern, as well as the PL of the confined 2D perovskite nanocrystals in the pattern.

Increasing the Stability of Isolated and Dense High-Aspect-Ratio Nanopillars Fabricated Using UV-Nanoimprint Lithography.

Structural anti-reflective coating and bactericidal surfaces, as well as many other effects, rely on high-aspect-ratio (HAR) micro- and nanostructures, and thus, are of great interest for a wide range of applications. To date, there is no widespread fabrication of dense or isolated HAR nanopillars based on UV nanoimprint lithography (UV-NIL). In addition, little research on fabricating isolated HAR nanopillars via UV-NIL exists. In this work, we investigated the mastering and replication of HAR nanopillars with the smallest possible diameters for dense and isolated arrangements. For this purpose, a UV-based nanoimprint lithography process was developed. Stability investigations with capillary forces were performed and compared with simulations. Finally, strategies were developed in order to increase the stability of imprinted nanopillars or to convert them into nanoelectrodes. We present UV-NIL replication of pillars with aspect ratios reaching up to 15 with tip diameters down to 35 nm for the first time. We show that the stability could be increased by a factor of 58 when coating them with a 20 nm gold layer and by a factor of 164 when adding an additional 20 nm thick layer of SiN. The coating of the imprints significantly improved the stability of the nanopillars, thus making them interesting for a wide range of applications.

Nanoimprint Mold Consisting of an Adhesive Lap Joint between a Nanopatterned Metal Sleeve and a Carbon Composite Roll.

Roll-to-roll nanoimprinting is an emerging technology that has revolutionized the sectors of flexible electronics, thin films, and solar cells with its high throughput. However, there is still room for improvement. In this study, a FEM analysis (in ANSYS) was carried out on a large-area roll-to-roll nanoimprint system in which the master roller consists of a large nanopatterned nickel mold joined to a carbon fiber reinforced polymer (CFRP) base roller using epoxy adhesive. Deflections and pressure uniformity of the nano-mold assembly were analyzed under loadings of different magnitudes in a roll-to-roll nanoimprinting setup. Optimization of deflections was performed with applied loadings, and the lowest deflection value was 97.69 nm. The adhesive bond viability was assessed under a range of applied forces. Finally, potential strategies to reduce deflections were also discussed, which can be helpful in increasing pressure uniformity.

Electrochemical Nano-Imprinting of Trimetallic Dendritic Surface for Ultrasensitive Detection of Cephalexin in Pharmaceutical Formulations.

Cephalexin (CFX), a first-generation cephalosporin, is used to treat various infectious diseases. Although antibiotics have achieved considerable progress in the eradication of infectious diseases, their incorrect and excessive usage has contributed to various side effects, such as mouth soreness, pregnancy-related pruritus, and gastrointestinal symptoms, including nausea, epigastric discomfort, vomiting, diarrhoea, and haematuria. In addition to this, it also causes antibiotic resistance, one of the most pressing problems in the medical field. The World Health Organization (WHO) claims that cephalosporins are currently the most commonly used drugs for which bacteria have developed resistance. Hence, it is crucial to detect CFX in complex biological matrices in a highly selective and sensitive way. In view of this, a unique trimetallic dendritic nanostructure comprised of cobalt, copper, and gold was electrochemically imprinted on an electrode surface by optimising the electrodeposition variables. The dendritic sensing probe was thoroughly characterised using X-ray photoelectron spectroscopy, scanning electron microscopy, chronoamperometry, electrochemical impedance spectroscopy, and linear sweep voltammetry. The probe displayed superior analytical performance, with a linear dynamic range between 0.05 nM and 105 nM, limit of detection of 0.04 ± 0.01 nM, and response time of 4.5 ± 0.2 s. The dendritic sensing probe displayed minimal response to interfering compounds, such as glucose, acetaminophen, uric acid, aspirin, ascorbic acid, chloramphenicol, and glutamine, which usually occur together in real matrices. In order to check the feasibility of the surface, analysis of a real sample was carried out using the spike and recovery approach in pharmaceutical formulations and milk samples, yielding current recoveries of 93.29-99.77% and 92.66-98.29%, respectively, with RSD < 3.5%. It only took around 30 min to imprint the surface and analyse the CFX molecule, making it a quick and efficient platform for drug analysis in clinical settings.

Enhanced performance of organic light-emitting diodes by integrating quasi-periodic micro-nano structures.

To integrate a quasi-periodic micro-nano structure (PMS) to the organic light-emitting devices (OLEDs) is an efficient way to enhance the performance of OLEDs. In this paper, the PMS prepared by the phase separation of Polystyrene and Poly (methyl methacrylate) was integrated to the OLEDs with the structures of Glass/PMS/Ag (30 nm)/MoO3 (5 nm)/(NPB) (40 nm)/(Alq3) (60 nm)/LiF (0.5 nm)/Al (150 nm). The maximum luminance intensity and external quantum efficiency increased to 10700 cd/m2 and 1.11 %, which is 48 % and 44 % higher than that of 7209 cd/m2 and 0.77 % of the planar reference device. The enhanced performance of OLEDs was ascribed to the attenuation of surface plasmon polariton loss caused by the PMS, which was testified by the Finite-Difference Time-Domain (FDTD) simulation. The PMS was also transferred to the hole transfer layer (PEDOT: PSS) of OLEDs by nano-imprinting lithography with the structure of Glass/(ITO) (100 nm)/PEDOT: PSS (100 nm) (with PMS)/NPB (10 nm)/Alq3 (50 nm)/LiF (0.5 nm)/Al (100 nm). The performance was also improved by the optimized PMS and the light out-coupling efficiency increased to about 49.5 %, which is much higher than that of 28.8 % in the OLEDs with PMS Ag anode and 20 % in the planar reference devices. This suggests that the PMS can improve the OLED device performance regardless of the functional layer in which the PMS is integrated.

Nanoimprinted 2D-Chiral Perovskite Nanocrystal Metasurfaces for Circularly Polarized Photoluminescence.

The versatile hybrid perovskite nanocrystals (NCs) are one of the most promising materials for optoelectronics by virtue of their tunable bandgaps and high photoluminescence (PL) quantum yields. However, their inherent crystalline chemical structure limits the chiroptical properties achievable with the material. The production of chiral perovskites has become an active field of research for its promising applications in optics, chemistry, or biology. Typically, chiral halide perovskites are obtained by the incorporation of different chiral moieties in the material. Unfortunately, these chemically modified perovskites have demonstrated moderate values of chiral PL so far. Here, a general and scalable approach is introduced to produce chiral PL from arbitrary nanoemitters assembled into 2D-chiral metasurfaces. The fabrication via nanoimprinting lithography employs elastomeric molds engraved with chiral motifs covering millimeter areas that are used to pattern two types of unmodified colloidal perovskite NC inks: green-emissive CsPbBr3 and red-emissive CsPbBr1 I2 . The perovskite 2D-metasurfaces exhibit remarkable PL dissymmetry factors (glum ) of 0.16 that can be further improved up to glum of 0.3 by adding a high-refractive-index coating on the metasurfaces. This scalable approach to produce chiral photoluminescent thin films paves the way for the seamless production of bright chiral light sources for upcoming optoelectronic applications.

Triple and Quadruple Surface Pattern Memories in Nanoimprinted Polymer Blends.

Trigger-responsive surfaces with multiple surface properties have wide-ranging application potential from surfaces with trigger-responsive fluid flow to cell culture to optical effects; such surfaces can be achieved through surface morphological changes. Although multiple shape-memory effects are successful in bulk polymers, there is limited programing and recovery of multiple surface memories due to the challenges in fabricating multiple surface topographies with good controllability. Here, we report the synergy between the polymer blend formulation and the thermal nanoimprinting process to achieve multiple microtopography memories. A series of immiscible blends consisting of poly(caprolactone) (PCL) and polyethylene (PE) with distinct thermal transitions governed by distinct crystallization events were augmented with improved elasticity through preferential cross-linking in the polymer blend. The effect of preferential cross-linking by dicumyl peroxide on the elastic property of the PCL/PE has been found to be nonlinearly dependent on the blend composition. This approach enabled triple and quadruple surface pattern fixity and recovery in nanoimprinted PCL/PE blends. Specifically, we demonstrated the recovery of a micropillar structure (diameter: 20 µm and height: 10 µm) from a hierarchical micrograting topography (width: 2 µm and height: 2 µm) when exposed to a thermal stimulus at 60 °C for 180 s. Furthermore, we also demonstrated the recovery of a deformed micrograting followed by a secondary recovery of the micropillar structure.

Curvature-Adjustable Polymeric Nanolens Fabrication Using UV-Controlled Nanoimprint Lithography.

Nanolenses are gaining importance in nanotechnology, but their challenging fabrication is thwarting their wider adoption. Of particular challenge is facile control of the lens' curvature. In this work, we demonstrate a new nanoimprinting technique capable of realizing polymeric nanolenses in which the nanolens' curvature is optically controlled by the ultraviolet (UV) dose at the pre-curing step. Our results reveal a regime in which the nanolens' height changes linearly with the UV dose. Computational modeling further uncovers that the polymer undergoes highly nonlinear dynamics during the UV-controlled nanoimprinting process. Both the technique and the process model will greatly advance nanoscale science and manufacturing technology.

Toward the Scalable Fabrication of Fully Bio-Based Antimicrobial and UVB-Blocking Transparent Polylactic Acid Films That Incorporate Natural Coatings and Nanopatterns.

Microbial transmissions via membrane surface and single-use plastic-induced pollution are two urgent societal problems. This research introduces a scalable fabrication strategy for fully biobased antibacterial and ultraviolet-B block polylactic acid (PLA) films integrating natural coatings and nanopatterns via ultrasonic atomization spray coating and thermal nanoimprinting lithography (TNIL) techniques, respectively. Tannic acid (TA) and gallic acid (GA) were formulated prior to TNIL using anode aluminum oxide template. Results reveal that TA and GA inks display intense adsorption in the UVB region. Plasma increases the hydrophilicity of PLA films for fast spreading of ink droplets. Micron-sized pillars observed on film confirm the successful structural replication. TA-coated PLA films display higher transparency than GA-coated ones. Nanopatterned PLA films have a modest antibacterial resistance of c. 45% against Escherichia coli. TA/GA coatings, however, impart PLA films with a bacterial reduction rate of over 80%. The integration of a TA or GA coating with nanopatterns further promotes the antibacterial rate up to 98%. The cytocompatibility of TA and GA demonstrates that the engineered film can potentially be applied as food packaging. Finally, a continuous mass production strategy is proposed along with an outline of the associated challenges and costs. This study provides a scalable strategy to the sustainable development of eco-benign and functional films.

Optical Manipulation of Incident Light for Enhanced Photon Absorption in Ultrathin Organic Photovoltaics.

We attempted to improve the photon absorption of the photoactive layer in organic photovoltaic (OPV) devices by device engineering without changing their thickness. Soft nanoimprinting lithography was used to introduce a 1D grating pattern into the photoactive layer. The increase in photocurrent caused by the propagating surface plasmon-polariton mode was quantitatively analyzed by measuring the external quantum efficiency in transverse magnetic and transverse electric modes. In addition, the introduction of an ultrathin substrate with a refractive index of 1.34 improved photon absorption by overcoming the mismatched optical impedance at the air/substrate interface. As a result, the power conversion efficiency (PCE) of an ultrathin OPV with a 400 nm grating period was 8.34%, which was 11.6% higher than that of an unpatterned ultrathin OPV, and the PCE was 3.2 times higher at a low incident light angle of 80°, indicating very low incident light angle dependence.

Roughness Suppression in Electrochemical Nanoimprinting of Si for Applications in Silicon Photonics.

Metal-assisted electrochemical nanoimprinting (Mac-Imprint) scales the fabrication of micro- and nanoscale 3D freeform geometries in silicon and holds the promise to enable novel chip-scale optics operating at the near-infrared spectrum. However, Mac-Imprint of silicon concomitantly generates mesoscale roughness (e.g., protrusion size ≈45 nm) creating prohibitive levels of light scattering. This arises from the requirement to coat stamps with nanoporous gold catalyst that, while sustaining etchant diffusion, imprints its pores (e.g., average diameter ≈42 nm) onto silicon. In this work, roughness is reduced to sub-10 nm levels, which is in par with plasma etching, by decreasing pore size of the catalyst via dealloying in far-from equilibrium conditions. At this level, single-digit nanometric details such as grain-boundary grooves of the catalyst are imprinted and attributed to the resolution limit of Mac-Imprint, which is argued to be twice the Debye length (i.e., 1.7 nm)-a finding that broadly applies to metal-assisted chemical etching. Last, Mac-Imprint is employed to produce single-mode rib-waveguides on pre-patterned silicon-on-insulator wafers with root-mean-square line-edge roughness less than 10 nm while providing depth uniformity (i.e., 42.9 ± 5.5 nm), and limited levels of silicon defect formation (e.g., Raman peak shift < 0.1 cm-1 ) and sidewall scattering.

Pillar-structured 3D inlets fabricated by dose-modulated e-beam lithography and nanoimprinting for DNA analysis in passive, clogging-free, nanofluidic devices.

We present the fabrication of three-dimensional inlets with gradually decreasing widths and depths and with nanopillars on the slope, all defined in just one lithography step. In addition, as an application, we show how these micro- and nanostructures can be used for micro- and nanofluidics and lab-on-a-chip devices to facilitate the flow and analyze single molecules of DNA. For the fabrication of 3D inlets in a single layer process, dose-modulated electron beam lithography was used, producing depths between 750 nm and 50 nm along a 30 µm long inlet, which is additionally structured with nanometer-scale pillars randomly distributed on top, as a result of incomplete exposure and underdevelopment of the resist. The fabrication conditions affect the slope of the inlet, the nanopillar density and coverage. The key parameters are the dose used for the electron beam exposure and the development conditions, like the developer's dilution, stirring and development time. The 3D inlets with nanostructured pillars were integrated into fluidic devices, acting as a transition between micro and nanofluidic structures for pre-stretching and unfolding DNA molecules, avoiding the intrusion of folded molecules and clogging the analysis channel. After patterning these structures in silicon, they can be replicated in polymer by UV nanoimprinting. We show here how the inlets with pillars slow down the molecules before they enter the nanochannels, resulting in a 3-fold decrease in speed, which would translate to an improvement in the resolution for DNA optical mapping.

Toward a Better Understanding of Shock Imprinting with Polymer Molds Using a Combination of Numerical Analysis and Experimental Research.

In the last decade, a new technique has been developed for the nanoimprinting of thin-metal foils using laser-induced shock waves. Recent studies have proposed replacing metal or silicone molds with inexpensive polymer molds for nanoimprinting. In addition, explosive-derived shock waves provide deeper imprinting than molds, greatly simplifying the application of this technology for mass production. In this study, we focused on explosive-derived shock waves, which persist longer than laser-induced shock waves. A numerical analysis and a set of simplified molding experiments were conducted to identify the cause of the deep imprint. Our numerical analysis has accurately simulated the pressure history and deformation behavior of the workpiece and the mold. Whereas a high pressure immediately deforms the polymer mold, a sustained pressure gradually increases the molding depth of the workpiece. Therefore, the duration of the pressure can be one of the conditions to control the impact imprint phenomenon.