We report a one-step additive manufacturing process to fabricate metalenses for visible wavelengths. Nanostructures with aspect ratios larger than eight and critical dimensions smaller than 60 nm were produced using nanoimprint lithography and a titanium dioxide nanocrystal-based imprint material, resulting in inorganic structures exhibiting a refractive index of n = 1.9. As a demonstration, we fabricate metalenses with numerical apertures (NAs) of 0.2 and focusing efficiencies over 50%. Manufacturability was assessed by performing 15 manual imprints in 30 min (2 min of process time per imprint) with a single stamp. All imprinted lenses exhibit comparable performance, paving the way for high-throughput and low-cost manufacturing of flat optical devices. Metalenses with a diameter of 4 mm were also fabricated to investigate the success of large area replication using this process, showing efficiencies of 43%, indicating good macroscopic imprinting.
The [3 + 2] cycloaddition of azides and alkynes has proven invaluable across numerous scientific disciplines for imaging, cross-linking, and site-specific labeling among many other applications. We have developed a photoinitiated, benzyne-based [3 + 2] cycloaddition that is tolerant of a variety of functional groups as well as polar, protic solvents. The reaction is complete on the minute time scale using a single equivalent of partner azide, and the benzyne photoprecursor is stable for months under ambient light at room tempurature. Herein we report the optimization and scope of the photoinitiated reaction as well as characterization of the cycloaddition products.
Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V2O5 without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm2 and 126 F/cm3 (at 0.8 mA/cm2 using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V2O5 deposition yielded pseudocapacitors with 10-fold increase in energy density (20 μW h cm–2 μm–1) without adversely affecting the high power density (450 μW cm–2 μm–1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors.
Silicon carbide (SiC) and silicon oxycarbide (SiOC) ceramic/carbon (C) nanocomposites are prepared via photothermal pyrolysis of cross-linked polycarbosilanes and polysiloxanes using a high-intensity pulsed xenon flash lamp in air at room temperature to yield crystalline and amorphous phases of SiC and SiOC ceramics, graphitic, and amorphous carbon phases. The millisecond duration of the radiation pulse is shorter than the thermal equilibrium time of the preceramic polymers (PCPs), enabling pyrolysis of the precursor phase and crystallization of the product before significant energy transfer to the substrate, making this process uniquely amenable to ceramic processing on or adjacent to thermally sensitive materials. Rapid precursor pyrolysis and product crystallization during flash lamp processing, even in air, limit oxidation of the resulting ceramics. To prepare the nanocomposites, PCPs are coated onto woven carbon fiber fabrics, thermally cross-linked, and then flash-lamp-pyrolyzed. The resulting nanocomposites are thermally and oxidatively stable at extremely high temperatures. The nanocomposites exhibit excellent performance as supercapacitor electrodes with capacitance as high as 27.2 mF/cm2 at a 10 mV/s scan rate at room temperature, excellent stability over 1000 cycles, and Coulombic efficiency of 80%. Patterned nanocomposites are prepared via nanoimprint lithography, followed by photothermal processing of precursor films. These nanocomposites have potential applications in energy storage, catalysis, and separations.
The advanced optical and wetting properties of metamaterials, plasmonic structures, and nanostructured surfaces have been repeatedly demonstrated in lab-scale experiments. Extending these exciting discoveries to large-area surfaces can transform technologies ranging from solar energy and virtual reality to biosensors and anti-microbial surfaces. Although photolithography is ideal for nanopatterning of small, expensive items such as computer chips, nanopatterning of large-area surfaces is virtually impossible with traditional lithographic techniques due to their exceptionally slow patterning rates and high costs. This article presents a high-throughput process that achieves large-area nanopatterning by combining roll-to-roll (R2R) nanoimprint lithography (NIL) and nanocoining, a process that can seamlessly nanopattern around a cylinder hundreds of times faster than electron-beam lithography. Here, nanocoining is used to fabricate a cylindrical mold with nanofeatures spaced by 600 nm and microfeatures spaced by 2 μm. This cylindrical drum mold is then used on a R2R NIL setup to pattern over 60 feet of polymer film. Microscopy is used to compare the feature shapes throughout the process. This scalable process offers the potential to transfer exciting lab-scale demonstrations to industrial-scale manufacturing without the prohibitively high cost usually associated with the fabrication of a master mold.
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