Batch Fabrication of Broadband Metallic Planar Microlenses and Their Arrays Combining Nanosphere Self-Assembly with Conventional Photolithography

Morphology-Controlled Fabrication of Large-Scale Dendritic Silver Nanostructures for Catalysis and SERS Applications

Highly branched metallic nanostructures, which possess a large amount of catalyst active sites and surface-enhanced Raman scattering (SERS) hot spots owing to their large surface areas, multi-level branches, corners, and edges, have shown potential in various applications including catalysis and SERS. In this study, well-defined dendritic silver (Ag) nanostructures were prepared by a facile and controllable electrochemical deposition strategy. The morphology of Ag nanostructures is controlled by regulating electrodeposition time and concentration of AgNO₃ in the electrolyte solution. Compared to conventional Ag nanoparticle films, dendritic Ag nanostructures exhibited larger SERS enhancement ascribed to the numerous hot spots exist in the nanogaps of parallel and vertically stacked multilayer Ag dendrites. In addition, the prepared dendritic Ag nanostructures show 3.2-fold higher catalytic activity towards the reduction of 4-nitrophenol (4-NP) by NaBH₄ than the Ag nanoparticle films. The results indicate that the dendritic Ag nanostructures represent a unique bifunctional nanostructure that serves as both efficient catalysts and excellent SERS substrates, which may be further employed as a nanoreactor for in situ investigation and real-time monitoring of catalytic reactions by SERS technique.

An Investigation of Influencing Factors on Practical Sub-Diffraction-Limit Focusing of Planar Super-Oscillation Lenses

Planar super-oscillation lenses (SOLs) can fulfill super-resolution focusing and nanoscopic imaging in the far field without the contribution of evanescent waves. Nevertheless, the existing deviations between the design and experimental results have been seldomly investigated, leaving the practical applications of SOLs unpredictable and uncontrollable. In this paper, some application-oriented issues are taken into consideration, such as the inevitable fabrication errors and the size effect of the designed SOLs, with the aim of providing an engineering reference to elaborately customize the demanded focusing light field. It turned out that a thicker structural film makes the focal spots enlarged, while the sloped sidewalls just weaken the intensity of the focal hotspot. Furthermore, the focal lengths are diminished with the decrease of device size, while the focal spots are enlarged. This research will promote the wide-spread applications of SOLs for sub-diffraction-limit far-field focusing in the areas of nanoscopy and high-density optical storage.

TE-polarized design for metallic slit lenses: a way to deep-subwavelength focusing over a broad wavelength range

Slit arrays based on noble metals have been widely proposed as planar transverse-magnetic (TM)-lenses, illuminated by a linearly polarized light with the polarization perpendicular to slits and implementing the focusing capability beyond the diffraction limit. However, due to intrinsic plasmonic losses, these TM-lenses cannot work efficiently in the ultraviolet wavelengths. In this Letter, taking advantage of the unique transmission through metallic slits not involving plasmonic losses, a metallic slit array with transverse-electric (TE)-polarized design is proposed, showing for the first time, to the best of our knowledge, the realization of sub-diffraction-limit focusing for ultraviolet light. Additionally, in contrast to the situations of TM-lenses, a wider slit leads to a greater phase delay and much larger slits can be arranged to construct the TE-lenses, which is quite beneficial for practical fabrication. Furthermore, deep-subwavelength focusing can be achieved by utilizing the immersing technology.