ZnO-nanotaper array sacrificial templated synthesis of noble-metal building-block assembled nanotube arrays as 3D SERS-substrates

This paper describes a ZnO-nanotaper array sacrificial templated synthetic approach for the fabrication of the arrays of nanotubes with tube-walls assembled by building-blocks of Ag-nanoplates, Au-nanorods, Pt-nanothorns or Pd-nanopyramids, thus possessing high-density 3D ＂hot spots＂ in sub-10-nm gaps of neighboring building blocks with nano-tips, -corners or -edges. Additionally, these hierarchical nanostructure arrays possess high surface area with rich surface chemistry, being beneficial to capturing the analyte. The Ag-nanoplate- assembled nanotube arrays can be used as sensitive surface-enhanced Raman scattering （SERS） substrates with good signal uniformity and reproducibility. Using such Ag hierarchical nanostructure arrays as SERS-substrates, not only has 10-14 M rhodamine 6G been identified, but also 10-7 M polychlorinated biphenyls （PCBs, a notorious class of persistent organic pollutants） are recognized, and even two congeners of PCBs can be identified in a mixture, showing the potential applications of the materials in SERS-based rapid detection of environmental organic pollutants.

Analysis of coupling between nanotaper SiGe-SOI waveguide and fiber

Based on a submicrometer-sized SiGe-SOI waveguide, the coupling loss mechanism is analyzed between the submicrometer-sized SiGe-SOI waveguide and the fiber. The main sources of coupling loss are analyzed, and the mismatch loss of the mode field is the mainly lost during connection between the submicrometer-sized waveguide and the fiber. In order to reduce the mismatch loss of the mode field, the structure ofa nanotaper SiGeSOI waveguide with a nanometer-sized tip is adopted. By reducing the waveguide dimensions to increase the mode field size, coupling loss could be reduced between the waveguide and the fiber. Different mode field dimensions ofnanotaper SiGe-SOI waveguides and fiber are quantitatively analyzed, and the quantitative relationship between nanotaper SiGe-SOI waveguide dimensions and mode field dimensions are obtained. Finally, nanotaper SiGe-SOI waveguides are made, and the test and analysis have been done. The final experimental results accord well with the theoretical analysis. When the waveguide width is 0.5 μm, the minimum coupling loss of the SiGe-SOI waveguide is 0.56 dB/facet, and also the correctness of the design method and theoretical analysis are verified.

A novel way to synthesize Pb nanotapes in liquid ammonia

Lead nanotapes were synthesized in liquid ammonia solvent in the presence of sodium metal at low temperature.The process was template free.Transmission electron microscopy（TEM） observations and X-ray diffraction（XRD） characterizations revealed that the as-prepared Pb nanotapes have average diameters in the range of 40-50 nm.and lengths up to several hundred nanometers, and exhibit cubic crystal structures.