Highly sensitive and stable SERS probes of alternately deposited Ag and Au layers on 3D SiO_2 nanogrids for detection of trace mercury ions

The hazard of Hg ion pollution triggers the motivation to explore a fast, sensitive, and reliable detection method.Here, we design and fabricate novel 36-nm-thick Ag–Au composite layers alternately deposited on three-dimensional(3D)periodic SiO_2 nanogrids as surface-enhanced Raman scattering(SERS) probes. The SERS effects of the probes depend mainly on the positions and intensities of their localized surface plasmon resonance(LSPR) peaks, which is confirmed by the absorption spectra from finite-difference time-domain(FDTD) calculations. By optimizing the structure and material to maximize the intrinsic electric field enhancement based on the design method of 3D periodic SERS probes proposed,high performance of the Ag–Au/SiO_2 nanogrid probes is achieved with the stability further enhanced by annealing. The optimized probes show the outstanding stability with only 4.0% SERS intensity change during 10-day storage, the excellent detection uniformity of 5.78%(RSD), the detection limit of 5.0×10~(-12) M(1 ppt), and superior selectivity for Hg ions. The present study renders it possible to realize the rapid and reliable detection of trace heavy metal ions by developing highperformance 3D periodic structure SERS probes by designing novel 3D structure and optimizing plasmonic material.     

Direct transition of potential of water droplets to electric energy using aligned single-walled carbon nanotubes

In this paper,we report that an electromotive force (EMF) can be induced in a rope of aligned single-walled carbon nanotubes (SWNTs) when water droplets fall on this rope.The magnitude of this EMF depends sensitively on the slant angle of the SWNTs.Most interestingly,both the magnitude and the direction of the induced EFM can be modulated by applying a current to the SWNTs.The concepts of electrical slip and no-slip are proposed and can be quantitatively described by "electrical slip resistance".This kind of generator does not need any magnet,rotor,etc and shows quite a different operating mechanism and design compared with a conventional large scale hydroelectric power generator.     

An electrically tunable metasurface integrated with graphene for mid-infrared light modulation

We propose a low-cost plasmonic metasurface integrated with single-layer graphene for dynamic modulation of midinfrared light. The plasmonic metasurface is composed of an array of split magnetic resonators(MRs) where a nano slit is included. Extraordinary optical transmission(EOT) through the deep subwavelength slit is observed by excitation of magnetic plasmons in the split MRs. Furthermore, the introduction of the slit provides strongly enhanced fields around the graphene layer, leading to a large tuning effect on the EOT by changing the Fermi energy of the graphene. The proposed metasurface can be utilized as an optical modulator with a broad modulation width(15 μm) or an optical switch with a high on/off ratio( 100). Meanwhile, the overall thickness of the metasurface is 430 nm, which is tens of times smaller than the operating wavelength. This work may have potential applications in mid-infrared optoelectrical devices and give insights into reconfigurable flat optics and optoelectronics.     

Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is -4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γn=4.51 mJmol^-1K^2 and the Debye temperature θD=419 K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/γnTc = 2.84 exp（-1.21Tc/T）. This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.     

Synthesis of high-TC ferromagnetic Mn-doped ZnO nanorods by thermal evaporation

This paper reports that a large amount of Mn-doped ZnO nanorods have been synthesized through thermal evaporation. The morphologies and properties are studied with x-ray diffraction, a scanning electron microscope, transmission electron microscope and Raman spectroscope. The results indicate that the manganese atoms occupy the zinc vacancies in the wurtzite lattice of ZnO without forming secondary phases. The exact manganese content has been studied by the x-ray fluorescence spectrum. Meanwhile, the magnetic moment versus temperature result proves that the as-prepared Mn-doped ZnO nanorods show ferromagnetic properties at temperatures as high as 400 K. These studies provide a good understanding of the origin of magnetic properties in diluted magnetic semiconductors.     

与富勒烯C_(36)直径(0.5nm)相等的碳纳米管及其制备

在电弧放电方法制备碳纳米管中 ,通过用碳纳米管填充阳极进行放电实验 ,成功地得到了小直径单层碳纳米管 .同时在多层管的最内层得到了直径 0 5nm的碳纳米管 .这个结果表明直径小于C60 (直径 0 7nm)的碳纳米管是存在的 .     

Giant magnetic moment at open ends of multiwalled carbon nanotubes

The attractions of cantilevers made of multiwalled carbon nanotubes(MWNTs)and secured on one end are studied in the non-uniform magnetic field of a permanent magnet.Under an optical microscope,the positions and the corresponding deflections of the original cantilevers(with iron catalytic nanoparticles at the free end)and corresponding cut-off cantilevers(the free ends consisting of open ends of MWNTs)are studied.Both kinds of CNT cantilevers are found to be attracted by the magnet,and the point of application of force is proven to be at the tip of the cantilever.By measuring and comparing deflections between these two kinds of cantilevers,the magnetic moment at the open ends of the CNTs can be quantified.Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes,it is called giant magnetic moment,and its possible mechanisms are proposed and discussed.     

Growth of aligned single-walled carbon nanotubes under ac electric fields through floating catalyst chemical vapour deposition

Through floating catalyst chemical vapour deposition(CVD) method,well-aligned isolated single-walled carbon nanotubes (SWCNTs) and their bundles were deposited on the metal electrodes patterned on the SiO₂/Si surface under ac electric fields at relatively low temperature(280℃). It was indicated that SWCNTs were effectively aligned under ac electric fields after they had just grown in the furnace.The time for a SWCNT to be aligned in the electric field and the effect of gas flow were estimated. Polarized Raman scattering was performed to characterize the aligned structure of SWCNTs. This method would be very useful for the controlled fabrication and preparation of SWCNTs in practical applications.     

与富勒烯C36直径(0.5nm)相等的碳纳米管及其制备

在电弧放电方法制备纳米管中,通过用碳纳米管填充阳极进行放电实验,成功地得到了小直径单层碳纳米管。同时在多层管的最内层得到了直径0.5nm的碳纳米管。这个结果表明直径小于C60（直径0.7nm）的碳纳米管是存在的。     

Direct growth of graphene on gallium nitride by using chemical vapor deposition without extra catalyst

Graphene on gallium nitride(GaN) will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graphene on GaN without an extra catalyst by chemical vapor deposition. Raman spectra indicate that the graphene films are uniform and about 5–6 layers in thickness. Meanwhile, the effects of growth temperatures on the growth of graphene films are systematically studied, of which 950℃ is found to be the optimum growth temperature. The sheet resistance of the grown graphene is 41.1Ω/square,which is close to the lowest sheet resistance of transferred graphene reported. The mechanism of graphene growth on GaN is proposed and discussed in detail. XRD spectra and photoluminescence spectra indicate that the quality of GaN epi-layers will not be affected after the growth of graphene.