Colloidal Gold Nanorings and Their Plasmon Coupling with Gold Nanospheres

Abstract

Gold nanorings are attractive as plasmonic metal nanocrystals because they have a hollow inner cavity. Their enhanced electric field inside the ring cavity is accessible, which is highly desirable for assembling with other optical components and studying their plasmon‐coupling behaviors. However, the lack of robust methods for synthesizing size‐controllable and uniform Au nanorings severely impedes the study of their attractive plasmonic properties and plasmon‐driven applications. Herein, an improved wet‐chemistry method is reported for the synthesis of monodisperse colloidal Au nanorings. Using circular Au nanodisks with different thicknesses and diameters as templates, Au nanorings are synthesized with thicknesses varied from ≈30 to ≈50 nm and cavity sizes varied from ≈90 to ≈40 nm. The produced Au nanorings are assembled with colloidal Au nanospheres to yield Au nanoring–nanosphere heterodimers in sphere‐in‐ring and sphere‐on‐ring configurations on substrates. The sphere‐in‐ring heterodimers exhibit the interesting feature of plasmonic Fano resonance upon the excitation of the dark quadrupolar plasmon mode of the Au nanorings. The open cavity in a nanoring holds a great promise for studying plasmon‐coupled systems, which will facilitate the construction of advanced metamaterials and high‐performance Fano‐based devices.

Substrate‐Modulated Electromagnetic Resonances in Colloidal Cu2O Nanospheres

“…As one of the most commonly employed plasmonic nanoparticles, Au nanospheres have been intensively investigated owning to their highly symmetric spherical shape and facile preparation methods. [52][53][54][55] The electromagnetic behaviors of Au nanospheres can be examined analytically using the Mie theory due to their isotropic spherical geometry. [56] The diameters of Au nanospheres can be adjusted in a wide range through many different synthetic approaches.…”

Gold nanomaterials for optical biosensing and bioimaging

“…By engineering the shape and size of AuNPs, one can tune many optical properties of AuNPs including localized surface plasmon resonance (LSPR), ratio between light absorption and scattering coefficients, surface enhanced Raman scattering (SERS), uorescence, etc. To date, researchers have fabricated dozens of Au nanostructures, including nanospheres (AuNS), 1 nanorods (AuNR), [2][3][4] nanoshells (AuNSh), [5][6][7][8][9][10][11][12] nanoprisms (AuNPr), [13][14][15] nanopyramids (AuNPy), 16 nanobipyramids (AuNBP), [17][18][19] nanocages (AuNC), [20][21][22][23][24][25] nanorings (AuNRg), [26][27][28][29] nanodisks (AuND), 22,30 nanostars (AuNSt), 31,32 nanorice, 33 nanobowls, 34 nanocrescents (AuNCr), 35,36 etc. (Fig.…”

Large-Area Fabrication of Vertical Silicon Nanotube Arrays via Toroidal Micelle Self-Assembly

“…Block copolymer (BCP) self-assembly provides an avenue for the formation of a myriad of nano-scale morphologies, with applications such as optoelectronics, biosensing, filtration, bioactive surfaces, surface coatings, and magnetic applications, among others. − More usual microphase separated self-assembled architectures include lamellar, cylindrical, spherical, and gyroidal structures as well as various micellar-based morphologies such as helices, tubes, disks, and toroids. − Micelle formation is defined as the self-assembly of an amphiphilic BCP in a solvent medium to form a structure typically with a core and corona. , Of the myriad of available micellar structures, toroidal micelles, in particular, have garnered interest owing to their proven applicability in synthesizing unique nanostructured materials with unique plasmonic and magnetic properties. , Such structures are typically fabricated via incorporating various metals and metal oxides, which upon removal of the polymer matrix produce metallic toroidal or nanoring structures . These metal/metal oxide structures have also been utilized as hard masks for patterning underlying silicon substrates, yielding high aspect ratio nanotube arrays. , Nonetheless, one notable drawback of toroidal micelles obtained via BCP or triblock copolymer self-assembly is that the size distributions of the structure are often too small for optoelectronic applications …”