Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.
Plasmonic photocatalysis has received much attention owing to attractive plasmonic enhancement effects in improving the solar-to-chemical conversion efficiency. However, the photocatalytic efficiencies have remained low mainly due to the short carrier lifetime caused by the rapid recombination of plasmon-generated hot charge carriers. Although plasmonic metal-semiconductor heterostructures can improve the separation of hot charge carriers, a large portion of the hot charge carriers are lost when they cross the Schottky barrier. Herein, a Schottky-barrier-free plasmonic semiconductor photocatalyst, MoO 3−x , which allows for efficient N 2 photofixation in a "one-stone-two-birds" manner, is demonstrated. The oxygen vacancies in MoO 3−x serve as the "stone." They "kill two birds" by functioning as the active sites for the chemisorption of N 2 molecules and inducing localized surface plasmon resonance for the generation of hot charge carriers. Benefiting from this unique strategy, plasmonic MoO 3−x exhibits a remarkable photoreactivity for NH 3 production up to the wavelength of 1064 nm with apparent quantum efficiencies over 1%, and a solar-to-ammonia conversion efficiency of 0.057% without any hole scavenger. This work shows the great potential of plasmonic semiconductors to be directly used for photocatalysis. The concept of the Schottkybarrier-free design will pave a new path for the rational design of efficient photocatalysts.
and breakthroughs by use of dielectric nanoparticles as building blocks, such as structural coloring, [6][7][8] directional light scattering, [9][10][11][12][13] optical chirality, [14] surfaceenhanced spectroscopies, [15,16] light-matter strong coupling, [17][18][19] and multifunctional metasurfaces. [20][21][22] The most common dielectric materials include semiconductors with high refractive indexes above 3.5 (Si, Ge, GaAs) and metal oxides with moderate refractive indexes around 2-3 (TiO 2 , ZrO 2 , ZnO, Cu 2 O). High-refractive-index nanoparticles tend to exhibit well-separated electric and magnetic resonance peaks in their extinction/scattering spectra. On the contrary, the electric and magnetic modes supported by moderate-refractive-index nanoparticles tend to largely overlap with each other. Such different spectral features lead to distinct optical properties. [23] The dielectric nanostructures in previous works have dominantly been fabricated by physical methods, such as femtosecond laser ablation and electron-beam lithography. [4][5][6][7][8][9]11,14,[20][21][22][23] In particular, the fabrication of patterns of dielectric nanomaterials by electron-beam lithography is more complicated than that of plasmonic nanomaterials, since the deposition of thin films of dielectric materials on substrates usually requires chemical vapor deposition, atomic layer deposition and other techniques. Only a few studies have so far demonstrated the chemical synthesis of monodisperse dielectric nanoparticles, including silicon, [24] titania, [25][26][27][28] and cuprous oxide. [10,29] In addition, chemical vapor deposition and aerosol spray have also been developed for the preparation of dielectric sub-micrometer spheres with broad size distributions. [30][31][32] In general, the chemical methods are more facile, cost-efficient and therefore more desirable for large-scale production than the physical methods. Among the aforementioned methods, the aerosol spray method is the most general and powerful one for synthesizing different types of dielectric nanoparticles, including various monometallic metal oxide and complex metal oxide nanoparticles. [33][34][35][36] However, a majority of the previous studies on aerosol spray have focused on the production of mesoporous or hollow metal oxides for catalysis and gas sensing. [35][36][37][38][39] Little attention has been paid to its ability in producing solid and dense metal oxides with high or moderate refractive indexes.In the family of metal oxides, TiO 2 has been recognized as a low-loss and high-performance material for all-dielectric nanophotonics governed by Mie resonances, [40,41] in additionMetal oxide nanostructures represent a large class of dielectric nanomaterials with high or moderate refractive indexes. Dielectric nanomaterials have recently attracted much attention in the field of all-dielectric nanophotonics. They can support both electric and magnetic resonances without suffering from high losses or heating as their plasmonic counterparts. Although various intrig...
Surface-enhanced Raman scattering (SERS) spectroscopy has found a wide range of applications in biomedicine, food safety and environmental monitoring. However, to date, it is difficult for most SERS substrates to provide an extremely sensitive and highly uniform Raman response simultaneously. Here, we developed a sensitive and uniform SERS sensing strategy based on grating-integrated gold nanograsses (GIGNs), which can amplify the SERS signal up to 10-fold compared to the nanograss without grating (namely on the flat substrate) experimentally. Numerical simulation results show that such an improvement of SERS sensitivity arises from the enhanced hotspots relying on the strong coupling between the localized surface plasmon resonances of individual stripe-regulated gold nanorod assemblies and Wood's anomalies in air and dielectric grating. Importantly, these hotspots on the substrate can be flexibly tailored by adjusting the height and periodicity of the loaded grating. The SERS performances of the GIGNs have further been successfully demonstrated with the label-free detection of adenine and cytosine (DNA bases) molecules at the nanomolar level.Moreover, the GIGNs also presented the uniform spot-to-spot and sample-to-sample SERS signals of the analyte molecules (relative standard deviations down to B11% and 13%, respectively). These advantages suggest that our GIGN substrates are of great potential for SERS-related sensing.
Light–matter interaction involving magnetic resonance at optical frequencies has recently been extensively investigated for the development of optical metamaterials. Nevertheless, effective manipulation of magnetic dipole transitions at optical frequencies is rarely demonstrated. Herein is reported on an aerosol‐spray method for the gram‐scale production of all‐dielectric europium‐doped sub‐micrometer zirconia spheres, which support strong magnetic Mie resonances. In contrast to previous structures where magnetic dipole emitters are positioned outside dielectric nanoresonators, this structure offers an unprecedented opportunity for the light emitters to access the strong magnetic field within the dielectric nanoresonator. This unique architecture allows the magnetic emission from the doped europium ions to be effectively manipulated. Moreover, in gold nanosphere–europium‐doped zirconia sphere heterostructures, the electric dipole emissions of the europium ions are enhanced strongly by the plasmon resonance of the gold nanospheres, while the magnetic dipole emission is weakly affected, suggesting much weaker interaction between the magnetic dipole transition and the electric resonance. This work demonstrates the feasibility of using all‐dielectric nanoresonators for selectively manipulating the magnetic dipole emissions from embedded quantum emitters. In addition, this cost‐effective and productive synthesis method opens up many possibilities for the wide use of lanthanide‐doped dielectric nanoresonators in the field of nanophotonics.
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