Regulation of hot spots exhibits excellent potential in many applications including nanolasers, energy harvesting, sensing, and subwavelength imaging. Here, hat-shaped hierarchical nanostructures with different space curvatures have been proposed to enhance hot spots for facilitating surface-enhanced Raman scattering (SERS) and plasmon-driven catalysis applications. These novel nanostructures comprise two layers of metal nanoparticles separated by hat-shaped MoS2 films. The fabrication of this hybrid structure is based on the thermal annealing and thermal evaporation of self-assembled polystyrene spheres, which are convenient to control the metal particle size and the curvature of hat-shaped nanostructures. Based on the narrow gaps produced by the MoS2 films and the curvature of space, the constructed platform exhibits superior SERS capability and achieves ultrasensitive detection for toxic molecules. Furthermore, the surface catalytic conversion of p-nitrothiophenol (PNTP) to p, p′-dimercaptobenzene (DMAB) was in situ monitored by the SERS substrate. The mechanism governing this regulation of hot spots is also investigated via theoretical simulations.
We report in this work that quantum efficiency can be significantly enhanced in an ultra-thin silicon solar cell coated by a fractal-like pattern of silver nano cuboids. When sunlight shines this solar cell, multiple antireflection bands are achieved mainly due to the self-similarity in the fractal-like structure. Actually, several kinds of optical modes exist in the structure. One is cavity modes, which come from Fabry-Perot resonances at the longitudinal and transverse cavities, respectively; the other is surface plasmon (SP) modes, which propagate along the silicon-silver interface. Due to the fact that several feature sizes distribute in a fractal-like structure, both low-index and high-index SP modes are simultaneously excited. As a whole effect, broadband absorption is achieved in this solar cell. Further by considering the ideal process that the lifetime of carriers is infinite and the recombination loss is ignored, we demonstrate that external quantum efficiency of the solar cell under this ideal condition is significantly enhanced. This theoretical finding contributes to high-performance plasmonic solar cells and can be applied to designing miniaturized compact photovoltaic devices.
The combination of metallic nanoparticles (NPs) with semiconductors used as surface-enhanced Raman scattering (SERS) substrates have been widely reported. However, the additional enhancements provided by the semiconductors are impressively small and have little effect on the SERS signal compared with that from the metallic NPs alone. Herein, thermoelectric semiconductor material gallium nitride (GaN) and silver nanoparticles (Ag NPs) are combined to create an electric-field-induced SERS (E-SERS) substrate, which further improves the SERS signal intensity by an order of magnitude compared to that without electric field induction. Based on the chemical enhancement induced by the thermoelectric potential, the presented E-SERS substrate realizes the detection over a broad kind of molecules, even with small Raman scattering cross sections.We show that the thermoelectric potential could regulate the charge exchange between GaN and Ag NPs and then shift the Fermi level of the Ag NPs over a wide-ranging distribution, which could increase the resonant electron transition probabilities with the detected molecules. Furthermore, the E-SERS substrate is also realized to monitor and manipulate the plasmon-activated redox reactions. Based on the finite element calculations, a detailed and comprehensive theoretical analysis is conducted to deepen the understanding of the chemical SERS and plasmon-activated photocatalyst mechanism.
The simultaneous output of highly sensitive and reproducible signals for surface-enhanced Raman spectroscopy (SERS) technology remains difficult. Here, we propose a two-dimensional (2D) composite structure using the repeated annealing method with MoS2 film as the molecular adsorbent. This method provides enlarged Au nanoparticle (NP) density with much smaller gap spacing, and thus dramatically increases the density and intensity of hot spots. The MoS2 films distribute among the hot spots, which is beneficial for uniform molecular adsorption, and further increases the sensitivity of the SERS substrate. Three kinds of molecules were used to evaluate the SERS substrate. Ultra-sensitive, highly repetitive, and stable SERS signals were obtained, which would promote the application process of SERS technology in quantitative analysis and detection.
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