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1. Engineered telecom emission and controlled positioning of Er3+ enabled by SiC nanophotonic structures

   https://doi.org/10.1515/nanoph-2019-0535  

   Tabassum, Natasha ; Nikas, Vasileios ; Kaloyeros, Alex E. ; Kaushik, Vidya ; Crawford, Edward ; Huang, Mengbing ; Gallis, Spyros ( April 2020 , Nanophotonics)

   Abstract High-precision placement of rare-earth ions in scalable silicon-based nanostructured materials exhibiting high photoluminescence (PL) emission, photostable and polarized emission, and near-radiative-limited excited state lifetimes can serve as critical building blocks toward the practical implementation of devices in the emerging fields of nanophotonics and quantum photonics. Introduced herein are optical nanostructures composed of arrays of ultrathin silicon carbide (SiC) nanowires (NWs) that constitute scalable one-dimensional NW-based photonic crystal (NW-PC) structures. The latter are based on a novel, fab-friendly, nanofabrication process. The NW arrays are grown in a self-aligned manner through chemical vapor deposition. They exhibit a reduction in defect density as determined by low-temperature time-resolved PL measurements. Additionally, the NW-PC structures enable the positioning of erbium (Er 3+ ) ions with an accuracy of 10 nm, an improvement on the current state-of-the-art ion implantation processes, and allow strong coupling of Er 3+ ions in NW-PC. The NW-PC structure is pivotal in engineering the Er 3+ -induced 1540-nm emission, which is the telecommunication wavelength used in optical fibers. An approximately 60-fold increase in the room-temperature Er 3+ PL emission is observed in NW-PC compared to its thin-film analog in the linear pumping regime. Furthermore, 22 times increase in the Er 3+more »PL intensity per number of exited Er ions in NW-PC was observed at saturation while using 20 times lower pumping power. The NW-PC structures demonstrate broadband and efficient excitation characteristics for Er 3+ , with an absorption cross-section (~2 × 10 −18 cm 2 ) two-order larger than typical benchmark values for direct absorption in rare-earth-doped quantum materials. Experimental and simulation results show that the Er 3+ PL is photostable at high pumping power and polarized in NW-PC and is modulated with NW-PC lattice periodicity. The observed characteristics from these technologically friendly nanophotonic structures provide a promising route to the development of scalable nanophotonics and formation of single-photon emitters in the telecom optical wavelength band.« less
2. Continuous roll-to-roll patterning of three-dimensional periodic nanostructures

   https://doi.org/10.1038/s41378-020-0133-7  

   Chen, I-Te ; Schappell, Elizabeth ; Zhang, Xiaolong ; Chang, Chih-Hao ( April 2020 , Microsystems & Nanoengineering)

   In this work, we introduce a roll-to-roll system that can continuously print three-dimensional (3D) periodic nanostructures over large areas. This approach is based on Langmuir-Blodgett assembly of colloidal nanospheres, which diffract normal incident light to create a complex intensity pattern for near-field nanolithography. The geometry of the 3D nanostructure is defined by the Talbot effect and can be precisely designed by tuning the ratio of the nanosphere diameter to the exposure wavelength. Using this system, we have demonstrated patterning of 3D photonic crystals with a 500 nm period on a 50 × 200 mm²flexible substrate, with a system throughput of 3 mm/s. The patterning yield is quantitatively analyzed by an automated electron beam inspection method, demonstrating long-term repeatability of an up to 88% yield over a 4-month period. The inspection method can also be employed to examine pattern uniformity, achieving an average yield of up to 78.6% over full substrate areas. The proposed patterning method is highly versatile and scalable as a nanomanufacturing platform and can find application in nanophotonics, nanoarchitected materials, and multifunctional nanostructures.
3. (Digital Presentation) Accelerating the Conversion Process of Polysulfides in High Mass Loading Sulfur Cathode for the Longevity Li-S Battery

   https://doi.org/10.1149/MA2022-012383mtgabs  

   Zhang, Yuxuan ; Kivevele, Thomas ; Song, Han Wook ; Lee, Sunghwan ( July 2022 , ECS Meeting Abstracts)

   Conventional lithium-ion batteries are unable to meet the increasing demands for high-energy storage systems, because of their limited theoretical capacity. 1 In recent years, intensive attention has been paid to enhancing battery energy storage capability to satisfy the increasing energy demand in modern society and reduce the average energy capacity cost. Among the candidates for next generation high energy storage systems, the lithium sulfur battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1) and potential cost reduction. In addition, sulfur is a cost effective and environmentally friendly material due to its abundance and low-toxicity. 2 Despite all of these advantages, the practical application of lithium sulfur batteries to date has been hindered by a series of obstacles, including low active material loading, poor cycle life, and sluggish sulfur conversion kinetics. 3 Achieving high mass loading cathode in the traditional 2D planar thick electrode has been challenged. The high distorsion of the traditional planar thick electrodes for ion/electron transfer leads to the limited utilization of active materials and high resistance, which eventually results in restricted energy density and accelerated electrode failure. 4 Furthermore, of the electrolyte to pores in the cathode and utilization ratiomore »of active materials. Catalysts such as MnO 2 and Co dopants were employed to accelerate the sulfur conversion reaction during the charge and discharge process. 5 However, catalysts based on transition metals suffer from poor electronic conductivity. Other catalysts such as transition metal dopants are also limited due to the increased process complexities. . In addition, the severe shuttle effects in Li-S batteries may lead to fast failures of the battery. Constructing a protection layer on the separator for limiting the transmission of soluble polysulfides is considered an effective way to eliminate the shuttle phenomenon. However, the soluble sulfides still can largely dissolve around the cathode side causing the sluggish reaction condition for sulfur conversion. 5 To mitigate the issues above, herein we demonstrate a novel sulfur electrode design strategy enabled by additive manufacturing and oxidative vapor deposition (oCVD). Specifically, the electrode is strategically designed into a hierarchal hollow structure via stereolithography technique to increase sulfur usage. The active material concentration loaded to the battery cathode is controlled precisely during 3D printing by adjusting the number of printed layers. Owing to its freedom in geometry and structure, the suggested design is expected to improve the Li ions and electron transport rate considerably, and hence, the battery power density. The printed cathode is sintered at 700 °C at N 2 atmosphere to achieve carbonization of the cathode during which intrinsic carbon defects (e.g., pentagon carbon) as catalytic defect sites are in-situ generated on the cathode. The intrinsic carbon defects equipped with adequate electronic conductivity. The sintered 3D cathode is then transferred to the oCVD chamber for depositing a thin PEDOT layer as a protection layer to restrict dissolutions of sulfur compounds in the cathode. Density functional theory calculation reveals the electronic state variance between the structures with and without defects, the structure with defects demonstrates the higher kinetic condition for sulfur conversion. To further identify the favorable reaction dynamic process, the in-situ XRD is used to characterize the transformation between soluble and insoluble polysulfides, which is the main barrier in the charge and discharge process of Li-S batteries. The results show the oCVD coated 3D printed sulfur cathode exhibits a much higher kinetic process for sulfur conversion, which benefits from the highly tailored hierarchal hollow structure and the defects engineering on the cathode. Further, the oCVD coated 3D printed sulfur cathode also demonstrates higher stability during long cycling enabled by the oCVD PEDOT protection layer, which is verified by an absorption energy calculation of polysulfides at PEDOT. Such modeling and analysis help to elucidate the fundamental mechanisms that govern cathode performance and degradation in Li-S batteries. The current study also provides design strategies for the sulfur cathode as well as selection approaches to novel battery systems. References: Bhargav, A., (2020). Lithium-Sulfur Batteries: Attaining the Critical Metrics. Joule 4 , 285-291. Chung, S.-H., (2018). Progress on the Critical Parameters for Lithium–Sulfur Batteries to be Practically Viable. Advanced Functional Materials 28 , 1801188. Peng, H.-J.,(2017). Review on High-Loading and High-Energy Lithium–Sulfur Batteries. Advanced Energy Materials 7 , 1700260. Chu, T., (2021). 3D printing‐enabled advanced electrode architecture design. Carbon Energy 3 , 424-439. Shi, Z., (2021). Defect Engineering for Expediting Li–S Chemistry: Strategies, Mechanisms, and Perspectives. Advanced Energy Materials 11 . Figure 1« less
4. Optical nanomanipulation on solid substrates via optothermally-gated photon nudging

   https://doi.org/10.1038/s41467-019-13676-3  

   Li, Jingang ; Liu, Yaoran ; Lin, Linhan ; Wang, Mingsong ; Jiang, Taizhi ; Guo, Jianhe ; Ding, Hongru ; Kollipara, Pavana Siddhartha ; Inoue, Yuji ; Fan, Donglei ; et al ( December 2019 , Nature Communications)

   Constructing colloidal particles into functional nanostructures, materials, and devices is a promising yet challenging direction. Many optical techniques have been developed to trap, manipulate, assemble, and print colloidal particles from aqueous solutions into desired configurations on solid substrates. However, these techniques operated in liquid environments generally suffer from pattern collapses, Brownian motion, and challenges that come with reconfigurable assembly. Here, we develop an all-optical technique, termed optothermally-gated photon nudging (OPN), for the versatile manipulation and dynamic patterning of a variety of colloidal particles on a solid substrate at nanoscale accuracy. OPN takes advantage of a thin surfactant layer to optothermally modulate the particle-substrate interaction, which enables the manipulation of colloidal particles on solid substrates with optical scattering force. Along with in situ optical spectroscopy, our non-invasive and contactless nanomanipulation technique will find various applications in nanofabrication, nanophotonics, nanoelectronics, and colloidal sciences.
5. Tape nanolithography: a rapid and simple method for fabricating flexible, wearable nanophotonic devices

   https://doi.org/10.1038/s41378-018-0031-4  

   Wang, Qiugu ; Han, Weikun ; Wang, Yifei ; Lu, Meng ; Dong, Liang ( October 2018 , Microsystems & Nanoengineering)

   This paper describes a tape nanolithography method for the rapid and economical manufacturing of flexible, wearable nanophotonic devices. This method involves the soft lithography of a donor substrate with air-void nanopatterns, subsequent deposition of materials onto the substrate surface, followed by direct taping and peeling of the deposited materials by an adhesive tape. Without using any sophisticated techniques, the nanopatterns, which are preformed on the surface of the donor substrate, automatically emerge in the deposited materials. The nanopatterns can then be transferred to the tape surface. By leveraging the works of adhesion at the interfaces of the donor substrate-deposited material-tape assembly, this method not only demonstrates sub-hundred-nanometer resolution in the transferred nanopatterns on an area of multiple square inches but also exhibits high versatility and flexibility for configuring the shapes, dimensions, and material compositions of tape-supported nanopatterns to tune their optical properties. After the tape transfer, the materials that remain at the bottom of the air-void nanopatterns on the donor substrate exhibit shapes complementary to the transferred nanopatterns on the tape surface but maintain the same composition, thus also acting as functional nanophotonic structures. Using tape nanolithography, we demonstrate several tape-supported plasmonic, dielectric, and metallo-dielectric nanostructures, as well asmore »several devices such as refractive index sensors, conformable plasmonic surfaces, and Fabry-Perot cavity resonators. Further, we demonstrate tape nanolithography-assisted manufacturing of a standalone plasmonic nanohole film and its transfer to unconventional substrates such as a cleaved facet and the curved side of an optical fiber.

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