Special attention has been paid to nanotubes and nanowires due to their interesting properties and potential applications. Since the discovery of carbon nanotubes [1] various nanotubes such as WS 2 , MoS 2 , BN, BC 2 N, and semiconductor nanowires such as CdTe and ZnCdSe have been synthesized. [2±7] The template technique is an important method of nanowire fabrication. Usually, there are two types of template: ªtrack-etchº polymer membranes, such as the polycarbonate membrane with 60 nm diameter pores, and the porous aluminum oxide membrane, with a pore diameter of 70 nm. [8,9] However, the challenges of fabricating semiconductor nanowires with a quantum confinement effect are great because technically useful quantum wires will require lateral dimensions less than 10 nm, and it is difficult to fabricate quantum wires on a scale lower than 10 nm. [10] Nanocables with a wire/sheath structure are another kind of potentially useful one-dimensional nanostructure. There have been a few reports on the preparation of semiconductor/insulator nanocables. For example, Si/SiO 2 nanocable has been prepared by combining laser-ablation cluster formation with vapor±liquid±solid (VLS) growth, [11] and b-SiC/SiO 2 nanocable has been obtained by the carbothermal reduction of sol±gel derived silica xerogels containing carbon nanoparticles at 1650 C. [12] In both cases, the outer layers of SiO 2 in nanocables are induced by the reaction atmosphere.In this communication, we design a new strategy for synthesizing a semiconductor/polymer nanocable in a heterogeneous solution system. In this system, an organic monomer with polar groups can self-organize into amphiphilic supramolecules, utilizing the difference in solubility of different fragments in the monomer molecule. Such supramolecules can polymerize to a pre-organized polymer tubule with a hydrophilic core and a hydrophobic sheath. Then the polymer tubule acts as both template and nanoreactor for the following growth of inorganic semiconductor nanowires in the hydrophilic cores from various water-soluble sources. Thus, a nanocable with semiconductor wire in a polymer sheath can be obtained. In this approach, g-irradiation offers an ideal means by which the supramolecules can be polymerized and the tubular structure can be solidified with the desired diameter at room temperature under ambient pressure.Based on the above strategy, a CdSe/poly(vinyl acetate) (PVAc) nanocable with a 6 nm core and an 80 nm diameter sheath was successfully synthesized from a heterogeneous system of vinyl acetate (VAc) monomer, cadmium sulfate (CdSO 4 ×8/3H 2 O), and sodium selenosulfate (Na 2 Se-SO 3 ) under g-irradiation at room temperature and ambient pressure. Appropriate amounts of analytically pure CdSO 4 [8/3H 2 O, Na 2 SeSO 3 , and isopropanol were dissolved in distilled water in a ground-glass stoppered flask, then mixed with VAc. Sodium selenosulfate can be synthesized by refluxing selenium powders in a sodium sulfite (Na 2 SO 3 ) solution according to the literature. [13] Isopropanol was used...
We demonstrate a microcantilever array with an in-plane photonic transduction method for simultaneous readout of each microcantilever. The array is fabricated on a silicon-on-insulator substrate. Rib waveguides in conjunction with a compact waveguide splitter network comprised of trench-based splitters and trench-based bends route light from a single optical input to each microcantilever on the chip. Light propagates down a rib waveguide integrated into the microcantilever and, at the free end of the microcantilever, crosses a small gap. Light is captured in static asymmetric multimode waveguides that terminate in Y-branches, the outputs of which are imaged onto an InGaAs line scan camera. A differential signal for each microcantilever is simultaneously formed from the two outputs of the corresponding Y-branch. We demonstrate that reasonable signal uniformity is obtained with a scaled differential signal for seven out of nine surviving microcantilevers in an array.
A compact and low loss silicon-on-insulator rib waveguide 90 degrees bend is designed and demonstrated. An interface realized by a trench filled with SU8 at the corner of a waveguide bend effectively reflects incoming light through total internal reflection (TIR). In order to accurately position the SU8-filled trench relative to the waveguide and reduce sidewall roughness of the interface, electron beam lithography (EBL) is employed while inductively coupled plasma reactive ion etching (ICP RIE) is used to achieve a vertical sidewall. The measured loss for TE polarization is 0.32 dB +/- 0.02 dB/bend at a wavelength of 1.55 microm.
Compact silicon-on-insulator (SOI) rib waveguide 90 degrees splitters based on narrow, high-aspect ratio (~10:1) trenches are designed and experimentally demonstrated. The splitter area is only 11 mum x 11 mum. Splitter optical performance is investigated as a function of both trench width and refractive index of the trench fill material. We examine three trench fill materials, air (n=1.0), SU8 (n=1.57), and index matching fluid (n=1.733), and find good agreement between experimental measurement and three dimensional (3D) finite difference time domain (FDTD) simulation. A splitting ratio of 49/51 (reflection/transmission) is measured for an index fluid-filled trench 82nm wide.
We demonstrate compact waveguide splitter networks in siliconon- insulator (SOI) rib waveguides using trench-based splitters (TBSs) and bends (TBBs). Rather than a 90 degrees geometry, we use 105 degrees TBSs to facilitate reliable fabrication of high aspect ratio trenches suitable for 50/50 splitting when filled with SU8. Three dimensional (3D) finite difference time domain (FDTD) simulation is used for splitter and bend design. Measured TBB and TBS optical efficiencies are 84% and 68%, respectively. Compact 105 degrees 1 x 4, 1 x 8, and 1 x 32 trench-based splitter networks (TBSNs) are demonstrated. The measured total optical loss of the 1 x 32 TBSN is 9.15 dB. Its size is only 700 microm x 1600 microm for an output waveguide spacing of 50 microm.
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