Hybrid nanostructures composed of semiconductor and plasmonic metal components are receiving extensive attention. They display extraordinary optical characteristics that are derived from the simultaneous existence and close conjunction of localized surface plasmon resonance and semiconduction, as well as the synergistic interactions between the two components. They have been widely studied for photocatalysis, plasmon-enhanced spectroscopy, biotechnology, and solar cells. In this review, the developments in the field of (plasmonic metal)/semiconductor hybrid nanostructures are comprehensively described. The preparation of the hybrid nanostructures is first presented according to the semiconductor type, as well as the nanostructure morphology. The plasmonic properties and the enabled applications of the hybrid nanostructures are then elucidated. Lastly, possible future research in this burgeoning field is discussed.

The efficient use of solar energy has received wide interest due to increasing energy and environmental concerns. A potential means in chemistry is sunlight-driven catalytic reactions. We report here on the direct harvesting of visible-to-near-infrared light for chemical reactions by use of plasmonic Au-Pd nanostructures. The intimate integration of plasmonic Au nanorods with catalytic Pd nanoparticles through seeded growth enabled efficient light harvesting for catalytic reactions on the nanostructures. Upon plasmon excitation, catalytic reactions were induced and accelerated through both plasmonic photocatalysis and photothermal conversion. Under the illumination of an 809 nm laser at 1.68 W, the yield of the Suzuki coupling reaction was ~2 times that obtained when the reaction was thermally heated to the same temperature. Moreover, the yield was also ~2 times that obtained from Au-TiOx-Pd nanostructures under the same laser illumination, where a 25-nm-thick TiOx shell was introduced to prevent the photocatalysis process. This is a more direct comparison between the effect of joint plasmonic photocatalysis and photothermal conversion with that of sole photothermal conversion. The contribution of plasmonic photocatalysis became larger when the laser illumination was at the plasmon resonance wavelength. It increased when the power of the incident laser at the plasmon resonance was raised. Differently sized Au-Pd nanostructures were further designed and mixed together to make the mixture light-responsive over the visible to near-infrared region. In the presence of the mixture, the reactions were completed within 2 h under sunlight, while almost no reactions occurred in the dark.

Localized surface plasmon resonance (LSPR)-based sensing has found wide applications in medical diagnosis, food safety regulation and environmental monitoring. Compared with commercial propagating surface plasmon resonance (PSPR)-based sensors, LSPR ones are simple, cost-effective and suitable for measuring local refractive index changes. However, the figure of merit (FOM) values of LSPR sensors are generally 1-2 orders of magnitude smaller than those of PSPR ones, preventing the widespread use of LSPR sensors. Here we describe an array of submicrometer gold mushrooms with a FOM reaching B108, which is comparable to the theoretically predicted upper limit for standard PSPR sensors. Such a high FOM arises from the interference between Wood's anomaly and the LSPRs. We further demonstrate the array as a biosensor for detecting cytochrome c and alpha-fetoprotein, with their detection limits down to 200 pM and 15 ng ml À 1 , respectively, suggesting that the array is a promising candidate for label-free biomedical sensing.

Control over light absorption and emission using plasmonic nanostructures is an enabling technology, which can dramatically enhance the performances of existing optical and optoelectronic devices, such as solar cells, light-emitting devices, biosensors, and high-resolution fluorescence microscopes. This Perspective takes fluorescence as an example, illustrating how plasmonic nanostructures can control the light absorption and emission of nanoscale optical species. The origins of fluorescence intensity enhancements will be first discussed. Different parameters that can largely affect the interactions between plasmonic nanostructures and fluorophore molecules will be examined, including the distance between the fluorophore molecule and the metal nanostructure and the wavelengths of their respective optical responses. The role of plasmonic nanostructures on fluorescence will then be reconsidered from the perspective of optical nanoantennas. We expect that more functionalities of plasmonic nanostructures as optical nanoantennas will further be discovered in analogy with the radio frequency antenna counterparts.

Evolution of the sizes and plasmonic properties of (Au core)−(Ag shell) nanorods is studied. Four plasmon bands are observed on the core−shell nanorods and their properties are investigated. The lowest‐energy one belongs to the longitudinal dipolar plasmon mode, the second‐lowest‐energy one belongs to the transverse dipolar plasmon mode, and the two highest‐energy ones are ascribed to octupolar plasmon modes.