No abstract

The increasing prevalence of infectious diseases in recent decades has posed a serious threat to public health. Routes of transmission differ, but the respiratory droplet or airborne route has the greatest potential to disrupt social intercourse, while being amenable to prevention by the humble face mask. Different types of masks give different levels of protection to the user. The ongoing COVID-19 pandemic has even resulted in a global shortage of face masks and the raw materials that go into them, driving individuals to self-produce masks from household items. At the same time, research has been accelerated towards improving the quality and performance of face masks, e.g., by introducing properties such as antimicrobial activity and superhydrophobicity. This review will cover mask-wearing from the public health perspective, the technical details of commercial and home-made masks, and recent advances in mask engineering, disinfection, and materials and discuss the sustainability of mask-wearing and mask production into the future.

Fabrication and synthesis of plasmonic structures is rapidly moving towards sub-nanometer accuracy in control over shape and inter-particle distance. This holds the promise for developing device components based on novel, non-classical electro-optical effects. Monochromated electron energy-loss spectroscopy (EELS) has in recent years demonstrated its value as a qualitative experimental technique in nano-optics and plasmonic due to its unprecedented spatial resolution. Here, we demonstrate that EELS can also be used quantitatively, to probe surface plasmon kinetics and damping in single nanostructures. Using this approach, we present from a large (>50) series of individual gold nanoparticles the plasmon Quality factors and the plasmon Dephasing times, as a function of energy/frequency. It is shown that the measured general trend applies to regular particle shapes (rods, spheres) as well as irregular shapes (dendritic, branched morphologies). The combination of direct sub-nanometer imaging with EELS-based plasmon damping analysis launches quantitative nanoplasmonics research into the sub-nanometer realm.

No abstract

Cu 2 ZnSnS 4 (CZTS), a quarternary chalcogenide p-type semiconductor, is currently receiving considerable attention as absorber materials for low-cost photovoltaics due to its high absorption coefficient, optimal band gap, and naturally abundant and nontoxic elemental components.[1] The growing technological interest in this material has motivated the study of the nature of its crystal structures.[2] The groundstate crystal structure of CZTS is the kesterite form (space group I4 ), which is a tetragonal superstructure derived from the binary II-VI cubic zinc-blende (ZB) lattice. Several other ZB-related structural modifications of CZTS have been considered, and these include the stannite structure (space group I4 2m). This structure type differs from the kesterite form only in the ordering of Cu + and Zn 2 + ions. In a recent theoretical study, Chen et al. have shown that there are two low-energy structural configurations of CZTS that are not based on the ZB unit cell.[2f] Instead, these two predicted structures are derivatives of the binary II-VI hexagonal wurtzite (WZ) structure and are conveniently referred to as WZ-kesterite and WZ-stannite, owing to their structural relationship with the ZB-derived kesterite and stannite polytypes, respectively. The WZ-kesterite form is a monoclinic (pseudo-orthorhombic) superstructure of the WZ unit cell and has the space group Pc. The WZ-stannite phase, on the other hand, is described by an orthorhombic supercell with space group Pmn2 1 . In bulk form, WZ-type superstructures have long been reported for a number of quarternary chalcogenides such as Cu 2 MGeS 4 (in which M = Mn, Zn, Cd).[3] Bulk CZTS with a WZ-derived phase, however, has yet to be synthesized.In nanocrystalline form, CZTS materials have been colloidally prepared by means of the hot-injection synthetic strategy involving the reaction of the Cu, Zn, and Sn precursors with elemental sulfur in oleylamine at high-temperature conditions.[4] The nanocrystals produced by this method are quite polydisperse in shape and size, and adopt the thermodynamically more stable ZB-derived tetragonal phase. Very recently, Lu et al. have employed the hot-injection technique and used dodecanethiol as the sulfur source in preparing CZTS nanoprisms and nanoplates that are 20-50 nm in size.[5] X-ray diffraction (XRD) measurements revealed that these nanocrystals possess a WZ-related crystal structure. Their proposed structure is based on the hexagonal WZZnS unit cell described by the space group P6 3 mc, in which the metal cations are randomly distributed in the cation sites (i.e., cation-disordered). However, the possibility that their WZ-type CZTS exhibits the theoretically predicted lower-energy cation-ordered WZ-kesterite and WZ-stannite structures has not been considered.Herein, we provide a facile noninjection synthetic route to preparing monodisperse anisotropic CZTS nanocrystals that adopt a WZ-type crystal structure. The noninjection or "heating up" approach to colloidal nanocrystals is better in terms of synthetic reprodu...

We report a facile chemical synthesis of well-defined gold nanocrosses through anisotropic growth along both <110> and <001>, whereas gold nanorods grow only along either <110> or <001>. The multiple branching was achieved by breaking the face-centered-cubic lattice symmetry of gold through copper-induced formation of single or double twins, and the resulting gold nanocrosses exhibited pronounced near-IR absorption with a great extension to the mid-IR region. As studied by discrete dipole approximation (DDA) simulations, the entire nanocross gets excited even when one of the branches is exposed to incident light. The above properties make them useful as octopus antennas for capturing near-IR light for effective photothermal destruction of cells. The cell damage process was analyzed using the Arrhenius model, and its intrinsic thermodynamic characteristics were determined quantitatively. Besides effective photothermal treatment and two-photon luminescence imaging, the near- and mid-IR-absorbing gold nanocrosses may also find applications in IR sensing, thermal imaging, telecommunications, and the like.

The coating makes the wire bundle: High-quality free-standing copper nanowires have been successfully produced by disproportionation of Cu(+) in oleylamine. This provides an effective way to prepare high-quality copper nanowires, but also enriches synthetic routes to other nanostructures. These copper nanowires can self-assemble by surface ligand exchange of oleylamine with trioctylphosphine.

In fabricating materials at the nanometer scale, nanotechnologists typically employ two general strategies: bottom-up and top-down. While the bottom-up approach constructs nanomaterials from basic building blocks like atoms or molecules, the top-down approach produces nanostructures by deconstructing larger materials with the use of lithographic tools (i.e., physical top-down) or through chemical-based processes (i.e., chemical top-down). This tutorial review summarizes the various top-down nanofabrication methods, with great emphasis on the chemical routes that can generate nanoporous materials and ordered arrays of nanostructures with three-dimensional features. The chemical top-down routes that are discussed in detail include (1) templated etching, (2) selective dealloying, (3) anisotropic dissolution, and (4) thermal decomposition. These emerging nanofabrication tools open up new avenues in the creation of functional nanostructures with a wide array of promising applications.