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Light manipulation has been widely employed in lighting, display, and energy storage, becoming an inseparable part of human lives. However, the conventional optical devices suffer from the diffraction limit of electromagnetic waves. To overcome the limitation, plasmonic and dielectric nanoantennas are introduced for the control of light direction at nanoscale. The directionality of the nanoantennas stems from their electromagnetic resonance properties or the interference between different resonance modes. The near‐field interaction between the nanoantennas and fluorescent emitters or Raman molecules will generate directional light emission. The directional nanoantennas are widely applied in various fields. Although light manipulation at nanoscale is briefly discussed in several review articles, they are not specifically devoted to directional nanoantennas. A more selective, focused and up‐to‐date review article about light manipulation by directional nanoantennas is deemed necessary because of the rapid development in this field. In this article, the properties and mechanisms of various types of nanoantennas made of plasmonic or dielectric nanostructures are introduced, the current developments of the nanoantennas are summarized, and an outlook for future investigation on directional nanoantennas is offered. It is believed that the directional light control with the nanoantennas will be a flourishing and promising research field in the future. [ABSTRACT FROM AUTHOR]

Abstract: Surface‐enhanced infrared absorption (SEIRA) spectroscopy, the enhancement of molecular vibrational signals using resonant metal nanostructures, has recently attracted much attention owing to its potential use in molecular detection in chemistry, biology, and medicine. This study reports on the growth of high‐aspect‐ratio metal nanocrystals and their application for SEIRA. Highly uniform Ag nanorods are synthesized through Au nanobipyramid‐directed Ag overgrowth, and Au nanotubes are further prepared through the galvanic replacement reaction from the Ag nanorods. Both Ag nanorods and Au nanotubes possess narrow distributions in diameter and length and exhibit highly tunable plasmon wavelengths in the near and mid‐infrared regions. The Ag nanorods are employed as plasmonic nanoantennas to enhance the molecular vibration signals of cetyltrimethylammonium bromide molecules that are embedded in a mesostructured silica layer coated on the Ag nanorods. The dimension‐dependent SEIRA performances are carefully investigated both experimentally and numerically. The experimental and simulated SEIRA enhancement factors are in good agreement and both determined to be of the order ≈103. The results point out a promising route to the utilization of chemically synthesized, colloidal metal nanostructures as SEIRA platforms. The synthesis method also provides high‐quality metal nanostructures for exploring various plasmon‐based optical and sensing applications in the infrared region. [ABSTRACT FROM AUTHOR]

Directional light control at nanoscale shows great potential in applications such as holograms, optical neural networks, and ultracompact photonic circuits. Plasmonic nanostructures with designed geometrical shapes or complex architectures have been employed to manipulate light directionally. The interaction among the electric dipole and multipole resonances in plasmonic nanostructures enables the wavefront reshaping of light, leading to directional light scattering behaviors. However, traditional methods for directional light control suffer from complicated fabrication procedures and large footprints. In this work, heterodimers are constructed out of chemically grown Au nanodisks and Au nanorods, with the nanorod sitting vertically on the nanodisk, and their directional light scattering behaviors are studied. When the nanorod is located off the center of the nanodisk, the incident light is scattered asymmetrically by the heterodimer, producing a crescent‐shaped far‐field scattering pattern. The light scattering directionality of the heterodimers is further proved to be highly dependent on the aspect ratio of the nanorod, the relative position of the two nanocrystals, and the orientation of the nanorod. The study provides a solid and useful foundation for the directional light manipulation in ultracompact nanophotonic systems. [ABSTRACT FROM AUTHOR]

Electroluminescence efficiency and operating stability of solution‐processed perovskite light‐emitting diodes (PeLEDs) are limited by luminescence quenching induced by indium or tin released from indium tin oxide (ITO) electrode upon deposition of highly acidic conventional hole injection layer (HIL) (i.e., poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)) and inefficient hole injection into perovskite emitting layer. Here, a synergistic molecular strategy to develop a neutralized gradient HIL, which possesses low acidity and high work function (WF) simultaneously, is proposed. First, it is shown that aniline with relatively low basicity and dipole moment efficiently neutralizes HIL while maintaining its original confirmation and high WF. Both acidity‐neutralizing aniline and WF‐modifying agent (perfluorinated ionomer) are incorporated into PEDOT:PSS to achieve high pH ≈ 6 and WF > 5.8 eV, which suppresses etching of underlying ITO and luminescence quenching while maintaining efficient hole injection into perovskite emitting layer. With this synergetic molecular engineering, high current efficiency = 52.55 cd A−1 with extended operating lifetime is achieved in PeLEDs that use colloidal formamidinium lead bromide nanoparticle films. This result provides a simple and efficient way to develop efficient and stable PeLEDs in industrial displays and solid‐state lighting. [ABSTRACT FROM AUTHOR]