Scalable manufacturing of high-index atomic layer-polymer hybrid metasurfaces for metaphotonics in the visible.

Metalenses are attractive alternatives to conventional bulky refractive lenses owing to their superior light-modulating performance and sub-micrometre-scale thicknesses; however, limitations in existing fabrication techniques, including high cost, low throughput and small patterning area, have hindered their mass production. Here we demonstrate low-cost and high-throughput mass production of large-aperture visible metalenses using deep-ultraviolet argon fluoride immersion lithography and wafer-scale nanoimprint lithography. Once a 12″ master stamp is imprinted, hundreds of centimetre-scale metalenses can be fabricated using a thinly coated high-index film to enhance light confinement, resulting in a substantial increase in conversion efficiency. As a proof of concept, an ultrathin virtual reality device created with the printed metalens demonstrates its potential towards the scalable manufacturing of metaphotonic devices.

Surface urban heat island in South Korea's new towns with different urban planning.

A new town is strategically built within a short period compared to naturally developed cities. It is considered an appropriate study area for analyzing the urban climate problems such as surface urban heat islands (SUHIs) that is differently generated according to urban planning and development. In this study, we suggest comprehensive method for determining and comparing changes in surface UHI distribution during 1989-2048 in two new towns with different urban planning. First, a substantial increase in built-up areas was observed from 1989 (< 5%) to 2018 (> 40%) in both new towns. However, SUHI phenomenon-increasing patterns were different of about 12.25% depending on urban planning and urban morphology. Results also showed the importance of vertical and horizontal structures which can have a great influence on SUHI intensity and accordingly, the difference in SUHI distribution between two new towns was confirmed. Moreover, without effective mitigation, the built-up area in both new towns is estimated to increase to approximately 60%, and the SUHI intensity in most areas to increase by 4 °C in 2048. In addition, the spread and intensification of the SUHI phenomenon are predicted to be greater due to the characteristics of the building structure and the active urban expansion. Thus, these results combined with architectural assessment models can improve the understanding of thermal environmental impacts of urbanization and provide directions for sustainable urban development and renovation.

Structure of single-wall carbon nanotubes: a graphene helix.

Evidence is presented in this paper that certain single-wall carbon nanotubes are not seamless tubes, but rather adopt a graphene helix resulting from the spiral growth of a nano-graphene ribbon. The residual traces of the helices are confirmed by high-resolution transmission electron microscopy and atomic force microscopy. The analysis also shows that the tubular graphene material may exhibit a unique armchair structure and the chirality is not a necessary condition for the growth of carbon nanotubes. The description of the structure of the helical carbon nanomaterials is generalized using the plane indices of hexagonal space groups instead of using chiral vectors. It is also proposed that the growth model, via a graphene helix, results in a ubiquitous structure of single-wall carbon nanotubes.

Integrated metasurfaces for re-envisioning a near-future disruptive optical platform.

Metasurfaces have been continuously garnering attention in both scientific and industrial fields, owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures. To date, research has mainly focused on the full control of electromagnetic characteristics, including polarization, phase, amplitude, and even frequencies. Consequently, versatile possibilities of electromagnetic wave control have been achieved, yielding practical optical components such as metalenses, beam-steerers, metaholograms, and sensors. Current research is now focused on integrating the aforementioned metasurfaces with other standard optical components (e.g., light-emitting diodes, charged-coupled devices, micro-electro-mechanical systems, liquid crystals, heaters, refractive optical elements, planar waveguides, optical fibers, etc.) for commercialization with miniaturization trends of optical devices. Herein, this review describes and classifies metasurface-integrated optical components, and subsequently discusses their promising applications with metasurface-integrated optical platforms including those of augmented/virtual reality, light detection and ranging, and sensors. In conclusion, this review presents several challenges and prospects that are prevalent in the field in order to accelerate the commercialization of metasurfaces-integrated optical platforms.

The seeded growth of graphene.

In this paper, we demonstrate the seeded growth of graphene under a plasma chemical vapor deposition condition. First, we fabricate graphene nanopowders (~5 nm) by ball-milling commercial multi-wall carbon nanotubes. The graphene nanoparticles were subsequently subject to a direct current plasma generated in a 100 Torr 10%CH4 - 90%H2 gas mixture. The plasma growth enlarged, over one hour, the nuclei to graphene sheets larger than one hundred nm(2) in area. Characterization by electron and X-ray diffraction, high-resolution transmission electron microscopy images provide evidence for the presence of monolayer graphene sheets.