Fei Mei

Efficiency enhancements in Ag nanoparticles-SiO2-TiO2 sandwiched structure via plasmonic effect-enhanced light capturing

TiO2-SiO2-Ag composites are fabricated by depositing TiO2 films on silica substrates embedded with Ag nanoparticles. Enhancement of light absorption of the nanostructural composites is observed. The light absorption enhancement of the synthesized structure in comparison to TiO2 originated from the near-field enhancement caused by the plasmonic effect of Ag nanoparticles, which can be demonstrated by the optical absorption spectra, Raman scattering investigation, and the increase of the photocatalytic activity. The embedded Ag nanoparticles are formed by ion implantation, which effectively prevents Ag to be oxidized through direct contact with TiO2. The suggested incorporation of plasmonic nanostructures shows a great potential application in a highly efficient photocatalyst and ultra-thin solar cell.

Monolayer graphene on nanostructured Ag for enhancement of surface-enhanced Raman scattering stable platform

We have reported that the Ag nanostructure-based substrate is particularly suitable for surface-enhanced Raman scattering when it is coated with monolayer graphene, an optically transparent and chemistry-inertness material in the visible range. Ag bowtie nanoantenna arrays and Ag nanogrids were fabricated using plasma-assisted nanosphere lithography. Our measurements show that atmospheric sulfur containing compounds are powerless to break in the monolayer graphene to vulcanize the surfaces of the Ag bowtie nanoantenna arrays and Ag nanogrids by various means, including scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). Furthermore, the Ag nanostructure substrate coated with the monolayer graphene film shows a larger enhancement of Raman activity and the electromagnetic field than the uncoated substrate. Compared with those of bare Ag nanostructures, the averaged EFs of graphene-film-coated Ag nanostructures were estimated to be about 21 and 5 for Ag bowtie nanoantenna arrays and nanogrids after one month later in air, respectively. These observations are further supported by theoretical calculations.

Enhanced and polarization dependence of surface-enhanced Raman scattering in silver nanoparticle array-nanowire systems

We report a surface-enhanced Raman scattering (SERS) platform composed of a single Ag nanowire (NW) and nanoparticle array (NW-array). There are three different fundamental combination patterns of NW-array systems. Optical excitation of sandwich nanostructure provides a stronger SERS hot array at the gap between the NW and array. We also have studied the polarization dependence of SERS in the coupled NW-array system for three kinds of pattern. We find SERS are strongly enhanced when the incident light is polarized across the junction between the particle of array and NW, the enhancement is amazingly insensitive to the detailed geometrical structure of coupled pattern.

Side-to-side alignment of gold nanorods with polarization-free characteristic for highly reproducible surface enhanced Raman scattering

A large-batch method for fabricating large-area, low-cost, and flexible surface enhanced Raman scattering (SERS) arrays with Au nanorods (NRs) using an inkjet printing technique was presented. The Raman mapping results of 441 points reveal clearly that the Au NRs arrays are a well reproducible SERS substrate for the detection of various chemicals. The neighbouring Au NRs aligned side-to-side nanoclusters were formed on printer paper as a highly reproducible SERS platform due to its polarization-free properties which were further confirmed by theoretical calculations of the electric field enhancement change about only two. Therefore, the SERS signals can be more evenly enhanced.

Synthesis and optical properties of gold nanorods with controllable morphology.

Searching for architectural building blocks with tunable morphology and peculiarity is a prominent challenge for novel diagnostic and therapeutic applications. Here, the aqueous-based seed-mediated methods for preparing highly mono-dispersed Au nanorods with a different aspect ratio are systematically studied by controlling the amounts of Ag ions and seeds. We also explore the effect of pH on the synthesis of gold nanorods. The realization of the overlap of longitudinal plasmon band and excitation source with different degrees is made by changing the aspect ratio of nanorod in order to determine its effect on the overall surface enhancement. In addition, the gold octahedra are prepared by overgrowth on Au nanorods. The SERS effects of Au nanorods are researched and the FDTD simulations are performed to reveal the morphology induced plasmon modes.

Influence of annealing temperature on structure and photocatalytic activity of TiO2 thin films prepared by DC reactive magnetron sputtering method

Transparent TiO2 thin films were successfully prepared on high purity silica substrates by DC reactive magnetron sputtering method and annealed at different temperatures. The effects of the annealing temperature (300–600 °C) on crystalline structure, morphology, and photocatalytic activity of the TiO2 thin films were discussed. The photocatalytic activity of the films was evaluated by photodegradation of methylene blue solution. With increasing annealing temperature, the photocatalytic activity of the TiO2 thin films gradually increased because of the improvement of crystallization of anatase TiO2 thin films. At 500 °C, the TiO2 thin film shows the highest photocatalytic activity due to the improvement of crystallization of anatase TiO2 thin films. When the annealing temperature increases to 600 °C, the photocatalytic activity of thin film decreases owing to the formation of rutile phase and the decrease of surface area.

Fabrication of highly homogeneous surface-enhanced Raman scattering substrates using Ag ion implantation

In recent times, surface-enhanced Raman scattering (SERS) has attracted attention for its excellent potential application in chemical and biological detection. In this work, we demonstrate that a highly homogeneous SERS substrate can be realized by Ag ion implantation and the subsequent annealing process. Both the implantation and annealing parameters have been optimized for a high sensitivity SERS substrate. The SERS measurement indicates that a sample implanted by 20u2009kV Ag ions with a dosage of 3u2009u2009×u2009u200910(16) ions cm(-2) exhibits the highest SERS activity. In addition, the SERS activity of the Ag-implanted substrates depends highly on the annealing temperature and time. Since none of the fabrication processes contain chemical reactions, our substrate is a clean system without any chemical residues.