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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.

We analyze quantum correlations in four-wave mixing in three-level ⌳ and V atomic systems by using dressed atomic states and squeeze-transformed cavity modes. Two dissipation channels are identified, through which the dressed atoms simultaneously absorb in the excitations from the pair of squeeze-transformed modes. It is in the presence of two channels that the entanglement is greatly enhanced and the best achievable state approaches the original Einstein-Podolsky-Rosen entangled state. This scheme is applicable in the optical regime where atomic spontaneous emission has to be taken into account, unlike the two-step atomic reservoir engineering scheme, which is limited to the microwave regime.