Zao Yi

Nanoparticle attachment on Ag nanorings and nanoantenna for large increases of surface-enhanced Raman scattering

A simple and inexpensive approach based on the heat-treatment of Ag+/PVA/PVP composite film on quartz glass has been developed for fabricating large-area Ag nanorings attached small nanoparticles. The explosive decomposition of AgNO3, PVA and PVP by calcination could explain their formation. A maximum enhancement factor of 1.9 × 1010 can be obtained with the self-organized Ag nanorings attached small nanoparticles. Moreover, using the three-dimensional finite-difference time-domain (3D-FDTD) simulations, we stipulate that the EF can be obviously improved via some small Ag particle attachment on these nanorings because of the strong coupling between the discrete plasmon states of the small nanoparticles and the term of propagating plasmons of the Ag nanorings. Understanding and realization of the enhancing mechanism of nanostructured surface attachment small nanoparticles could have potential to effectively improve the SERS property of the SERS substrates.

Self-Organized Ag Nanorings Antenna Substrates for Surface-Enhanced Raman Spectroscopy

We investigate the surface-enhanced Raman spectroscopy of Ag nanorings antenna in both experiment and simulation. Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. The three-dimensional finite-difference time-domain simulation calculations indicate that the electric field enhancement of Ag nanoring antenna is strongly dependent on the gap distance. A very strong surface plasmon coupling in the gap region of Ag nanoring antenna is observed, whose field intensity is enhanced four times compared to that for Ag nanodomes antenna with the same gap distance. Surface-enhanced Raman scattering (SERS) measurements have shown that the SERS intensity acquired from the Ag nanoring antenna is about 16 times stronger than that obtained from Ag nanodomes antenna. These results pave the way to design plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.

Study of strong dipole and quadrupole plasmon resonance in Ag nanorings antenna

Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. By using absorption measurements and three-dimensional finite-difference time-domain (3D-FDTD) calculations, the dipole and quadrupole plasmon resonances of Ag nanorings antenna were investigated experimentally and theoretically. Calculations have shown that large electric fields are confined at the quadrupole of the Ag nanoring, leading to quadrupole plasmon resonances. Compared the electric enhancement factor of the exterior surfaces of Ag nanoring, the electric enhancement factor of the interior surface is about six times excited by an incident light with 514.5 nm wavelength. Furthermore, the highest electric-field intensity of Ag nanorings is around four times larger than that for Ag nanodome with the same condition. These results pave the way to design plasmonic nanostructures for practical applications that require metallic nanoparticles with enhanced electric fields.

Synthesis and characterization of aligned ZnO/BeO core/shell nanocable arrays on glass substrate

By sequential hydrothermal growth of ZnO nanowire arrays and thermal evaporation of Be, large-scale vertically aligned ZnO/BeO core/shell nanocable arrays on glass substrate have been successfully synthesized without further heat treatment. Detailed characterizations on the sample morphologies, compositions, and microstructures were systematically carried out, which results disclose the growth behaviors of the ZnO/BeO nanocable. Furthermore, incorporation of BeO shell onto ZnO core resulted in distinct improvement of optical properties of ZnO nanowire, i.e., significant enhancement of near band edge (NBE) emission as well as effective suppression of defects emission in ZnO. In particular, the NBE emission of nanocable sample shows a noticeable blue-shift compared with that of pristine ZnO nanowire, which characteristics most likely originate from Be alloying into ZnO. Consequently, the integration of ZnO and BeO into nanoscale heterostructure could bring up new opportunities in developing ZnO-based device for application in deep ultraviolet region.PACS61.46.K; 78.67.Uh; 81.07.Gf.

Experimental and simulative study on surface enhanced Raman scattering of rhodamine 6G adsorbed on big bulk-nanocrystalline metal substrates

Big bulk-nanocrystalline metal materials of silver (Ag) and aluminum (Al) for surface-enhanced Raman scattering (SERS) spectroscopy have been synthesized in a mold under different pressures using vacuum-warm-compaction technology. It was discovered that pressure could control the SERS activity of the bulk-nanocrystalline material. SERS properties of the bulk-nanocrystalline material in the presence of adsorbed rhodamine (R6G) could be obtained through selecting a proper pressure. Compared with the Ag nanoparticles (Al nanoparticles), the SERS peak intensity of R6G adsorbed on the bulk-nanocrystalline material is about 1000 times (100 times) stronger. The electric field enhancement of the bulk-nanocrystalline material has been described to be a systematic investigation by using three-dimensional finite-difference time-domain (3D-FDTD) simulation. The FDTD calculations have shown that the electric field enhancement of the bulk-nanocrystalline material is strongly dependent on the gap distance. In summary, SERS active bulk-nanocrystalline materials have been synthesized simply, greenly and cost effectively by the method reported here, and this method is expected to be utilized in the development of SERS-based analytical devices.

Nanoscale Energy Confinement and Hybridization of Surface Plasmons Based on Skin Depth in Au/Ag Core-Shell Nanostructures

The electric field tends to become distributed within a conductor due to skin effect such that the field density is largest near the surface of the conductor and decreases with greater depths in the conductor. The electric field mainly distributes at the skin of the conductor, between the outer surface and a level called the skin depth. For a plasmonic nanosystem smaller than the skin depth, oscillations of the metal electrons will be driven by the optical electric field penetrating the entire system. This effect will induce confinement of optical energy inside the whole systems and influence the performance of surface plasmon. A theoretical model that a gold core is embedded within Ag nanoshell is constructed to simulate hybridization of surface plasmon and energy confinement in Au/Ag core/shell nanostructures based on the skin depth. Indeed, nanoshells in the core/shell system greatly influence the surface plasmon resonance, and the shell frequency is tuned efficiently through hybridization of surface plasmon. The plasmon resonances in core/shell particles can be understood in terms of hybridization between the plasmon modes of the surfaces and interfaces supported by cavity of the metallic shells. The hybridized plasmons induced by interaction of these plasmon modes can result in energy alteration over a wide range in wavelength. Combining with extinction spectra and field distributions, it can be seen that skin depth plays an important role in energy confinement and hybridization of surface plasmom.