Nanoimprint lithography (NIL) is a nonconventional lithographic technique for high‐throughput patterning of polymer nanostructures at great precision and at low costs. Unlike traditional lithographic ...approaches, which achieve pattern definition through the use of photons or electrons to modify the chemical and physical properties of the resist, NIL relies on direct mechanical deformation of the resist material and can therefore achieve resolutions beyond the limitations set by light diffraction or beam scattering that are encountered in conventional techniques. This Review covers the basic principles of nanoimprinting, with an emphasis on the requirements on materials for the imprinting mold, surface properties, and resist materials for successful and reliable nanostructure replication.
Nanoimprint lithography (see figure) is an emerging lithographic technique for high‐throughput patterning of polymer nanostructures at high resolutions and low costs. This Review article considers the basic principles of nanoimprinting, with an emphasis on the requirements placed on materials to allow successful and reliable nanostructure replication.
Abstract
Flexible transparent electrodes are in significant demand in applications including solar cells, light-emitting diodes, and touch panels. The combination of high optical transparency and ...high electrical conductivity, however, sets a stringent requirement on electrodes based on metallic materials. To obtain practical sheet resistances, the visible transmittance of the electrodes in previous studies is typically lower than the transparent substrates the electrode structures are built on, namely, the transmittance relative to the substrate is <100%. Here, we demonstrate a flexible dielectric-metal-dielectric-based electrode with ~88.4% absolute transmittance, even higher than the ~88.1% transmittance of the polymer substrate, which results in a relative transmittance of ~100.3%. This non-trivial performance is achieved by leveraging an optimized dielectric-metal-dielectric structure guided by analytical and quantitative principles described in this work, and is attributed to an ultra-thin and ultra-smooth copper-doped silver film with low optical loss and low sheet resistance.
Droplets provide a well-known transmission media in the COVID-19 epidemic, and the particle size is closely related to the classification of the transmission route. However, the term “aerosol” covers ...most particle sizes of suspended particulates because of information asymmetry in different disciplines, which may lead to misunderstandings in the selection of epidemic prevention and control strategies for the public. In this review, the time when these droplets are exhaled by a patient was taken as the initial time. Then, all available viral loads and numerical distribution of the exhaled droplets was analyzed, and the evaporation model of droplets in the air was combined with the deposition model of droplet nuclei in the respiratory tract. Lastly, the perspective that physical spread affects the transmission risk of different size droplets at different times was summarized for the first time. The results showed that although the distribution of exhaled droplets was dominated by small droplets, droplet volume was proportional to the third power of particle diameter, meaning that the viral load of a 100 μm droplet was approximately 106 times that of a 1 μm droplet at the initial time. Furthermore, the exhaled droplets are affected by heat and mass transfer of evaporation, water fraction, salt concentration, and acid-base balance (the water fraction > 98%), which lead them to change rapidly, and the viral survival condition also deteriorates dramatically. The time required for the initial diameter (do) of a droplet to shrink to the equilibrium diameter (de, about 30% of do) is approximately proportional to the second power of the particle diameter, taking only a few milliseconds for a 1 μm droplet but hundreds of milliseconds for a 10 μm droplet; in other words, the viruses carried by the large droplets can be preserved as much as possible. Finally, the infectious droplet nuclei maybe inhaled by the susceptible population through different and random contact routes, and the droplet nuclei with larger de decompose more easily into tiny particles on account of the accelerated collision in a complex airway, which can be deposited in the higher risk alveolar region. During disease transmission, the infectious droplet particle size varies widely, and the transmission risk varies significantly at different time nodes; therefore, the fuzzy term “aerosol” is not conducive to analyzing disease exposure risk. Recommendations for epidemic prevention and control strategies are: 1) Large droplets are the main conflict in disease transmission; thus, even if they are blocked by a homemade mask initially, it significantly contains the epidemic. 2) The early phase of contact, such as close-contact and short-range transmission, has the highest infection risk; therefore, social distancing can effectively keep the susceptible population from inhaling active viruses. 3) The risk of the fomite route depends on the time in contact with infectious viruses; thus, it is important to promote good health habits (including frequent hand washing, no-eye rubbing, coughing etiquette, normalization of surface cleaning), although blind and excessive disinfection measures are not advisable. 4) Compared with the large droplets, the small droplets have larger numbers but carry fewer viruses and are more prone to die through evaporation.
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•The transmission risk of infectious droplets under varying environments and times.•How the viral load, diameter, evaporation, and deposition are linked to infection risk.•The large droplets dominate initially.•The risk of small droplet nuclei (originally from large droplets) must also be taken seriously.
Pituitary stalk interruption syndrome (PSIS) is a rare congenital defect manifesting with varying degrees of pituitary hormone deficiency. The signs and symptoms of PSIS during the neonatal period ...and infancy are often overlooked and therefore diagnosis is delayed. The typical manifestations of PSIS can be detected by magnetic resonance imaging. Several genes in the Wnt, Notch and Shh signalling pathways related to hypothalamic‐pituitary development, such as PIT1, PROP1, LHX3/LHX4, PROKR2, OTX2, TGIF and HESX1, have been found to be associated with PSIS. Nevertheless, the aetiology in the majority of cases still remains unknown. In the present review, we provide an overview of clinical features of PSIS and summarise our current understanding of the underlying pathogenic mechanisms for this rare syndrome. Furthermore, we propose future research directions that may help our understanding of the aetiology of PSIS.
Magnetic reconnection is a fundamental plasma process that plays a critical role not only in energy release in the solar atmosphere, but also in fusion, astrophysics, and other space plasma ...environments. One of the challenges in explaining solar observations in which reconnection is thought to play a critical role is to account for the transition of the dynamics from a slow quasi-continuous phase to a fast and impulsive energetic burst of much shorter duration. Despite the theoretical progress in identifying mechanisms that might lead to rapid onset, a lack of observations of this transition has left models poorly constrained. High-resolution spectroscopic observations from NASA's Interface Region Imaging Spectrograph now reveal tell-tale signatures of the abrupt transition of reconnection from a slow phase to a fast, impulsive phase during UV bursts or explosive events in the Sun's atmosphere. Our observations are consistent with numerical simulations of the plasmoid instability, and provide evidence for the onset of fast reconnection mediated by plasmoids and new opportunities for remote-sensing diagnostics of reconnection mechanisms on the Sun.
A continuous roll-to-roll nanoimprint lithography (R2RNIL) technique can provide a solution for high-speed large-area nanoscale patterning with greatly improved throughput; furthermore, it can ...overcome the challenges faced by conventional NIL in maintaining pressure uniformity and successful demolding in large-area imprinting. In this work, we demonstrate large-area (4 in. wide) continuous imprinting of nanogratings by using a newly developed apparatus capable of roll-to-roll imprinting (R2RNIL) on flexible web and roll-to-plate imprinting (R2PNIL) on rigid substrate. The 300 nm line width grating patterns are continuously transferred on either glass substrate (roll-to-plate mode) or flexible plastic substrate (roll-to-roll mode) with greatly enhanced throughput. In addition, the film thickness after the imprinting process, which is critical in optical applications, as a function of several imprinting parameters such as roller pressure and speed, is thoroughly investigated, and an analytical model has been developed to predict the residual layer thickness in dynamic R2RNIL process.
ABSTRACT Our understanding of the process of fast reconnection has undergone a dramatic change in the last 10 years driven, in part, by the availability of high-resolution numerical simulations that ...have consistently demonstrated the break-up of current sheets into magnetic islands, with reconnection rates that become independent of Lundquist number, challenging the belief that fast magnetic reconnection in flares proceeds via the Petschek mechanism which invokes pairs of slow-mode shocks connected to a compact diffusion region. The reconnection sites are too small to be resolved with images, but these reconnection mechanisms, Petschek and the plasmoid instability, have reconnection sites with very different density and velocity structures and so can be distinguished by high-resolution line-profile observations. Using IRIS spectroscopic observations we obtain a survey of typical line profiles produced by small-scale events thought to be reconnection sites on the Sun. Slit-jaw images are used to investigate the plasma heating and re-configuration at the sites. A sample of 15 events from 2 active regions is presented. The line profiles are complex with bright cores and broad wings extending to over 300 km s−1. The profiles can be reproduced with the multiple magnetic islands and acceleration sites that characterize the plasmoid instability but not by bi-directional jets that characterize the Petschek mechanism. This result suggests that if these small-scale events are reconnection sites, then fast reconnection proceeds via the plasmoid instability, rather than the Petschek mechanism during small-scale reconnection on the Sun.
It is experimentally shown that bianisotropic metasurfaces allow for extreme polarization control of light with high performance. A metasurface providing asymmetric transmission (i.e., polarization ...conversion) of circularly polarized light is reported at a wavelength of 1.5 μm. The experimental transmittance and extinction ratio are 50% and 20:1, which represents an order of magnitude improvement over previous optical structures exhibiting asymmetric transmission. The metasurface consists of patterned gold sheets that are spaced at a subwavelength distance from each other. The same design and fabrication processes can be used in the future to completely control the phase, amplitude, and polarization of light.
In this study, we report nonmetal plasmonic MoS2@TiO2 heterostructures for highly efficient photocatalytic H2 generation. Large area laminated MoS2 in conjunction with TiO2 nanocavity arrays is ...achieved via carefully controlled anodization, physical vapor deposition, and chemical vapor deposition processes. The broad spectral response ranging from ultraviolet-visible (UV-vis) to near-infrared (NIR) wavelengths and finite element frequency-domain simulations suggest that this MoS2@TiO2 heterostructure enhances photocatalytic activity for H+ reduction. A high H2 yield rate of 181 μmol h−1 cm−2 (equal to 580 mmol h−1 g−1 based on the loading mass of MoS2) is achieved using a low catalyst loading mass. The spatially uniform heterostructure, correlated with plasmon-resonance through the conformal MoS2 coating that effectively regulates charge transfer pathways, is proven to be vitally important for the unique solar energy harvesting and photocatalytic H2 production. As an innovative exploration, our study demonstrates that the photocatalytic activities of nonmetal, earth-abundant materials can be enhanced with plasmonic effects, which may serve as an excellent catalytic agent for solar energy conversion to chemical fuels.
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