Nanowires with a carbon nanotube core and silicon oxide sheath

Content Provider	Semantic Scholar
Author	Hu, Jiangang Wang, Zhenxia Zhang, Wei Xu, Zijian Wu, Yongqing Zhu, Zhiyuan Duan, Xiaoli
Copyright Year	2006
Abstract	Various kinds of core/sheath wire-like structures with different compositions have been studied, using various synthesis methods including the chemical vapor deposition (CVD) [1]. However, to our knowledge, still there are few reports [2,3] on how to encapsulate carbon nanotubes into another sheath structures, although it has been known that carbon nanotube is ideal for fundamental studies of their physical properties and for the fabrication of electronic nanodevices. In addition, the encapsulation of carbon nanotubes within a stable media should serve the dual role of protecting air-sensitive surface of nanotube against degradation [4,5] and reducing the coupling between individual tubes. Here, we report a simple and effective new method, using silicon wafers as a source material and by hydrogen etching and thermal oxidation reaction, to directly deposit silicon oxide on the CVD-multiwalled carbon nanotubes (CVD-MWCNTs) outer surface, thereby forming nanowires with a nanotube core and silicon oxide sheath. As an original material, the purified CVD-MWCNTs were dispersed in ethanol by sonication and deposited onto a silicon wafer surface, then placed into gaseous PECVD reaction chamber. After the samples were heated to a temperature of about 700 C, the hydrogen was introduced into the chamber at a flow rate of 50 sccm. The chamber pressure was kept at 150 Pa and plasma with a power density of 0.5 W/cm was initiated simultaneously. After reaction for about 10 h, the products were cooled down in vacuum to room-temperature. The morphology and structure of the products were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy-loss spectroscopy (EELS). A typical SEM image for the product is shown in Fig. 1(a). The image shows that the product consists of a large quantity of wire-like nanostructures, and the surface is clean without any particle. Fig. 1(b) represents a typical transmission electron microscopy (HR-TEM) image of original carbon nanotubes. These CVD-MWCNTs are of concentric type with well-ordered graphene sheets (lattice fringe spacing d 0.34 nm) of the tube, which must have occurred in the CVD growth process. The structural characterization of an individual nanowire was carried out using TEM. Fig. 1(c) shows a bright-field TEM image revealing the general morphology of segments of the nanowires. Elongated nanotube-like core structures stick out of the nanowire and are marked by arrows. It is noteworthy that some of them have a diameter between 10 and 30 nm, similar to the diameter of the starting (untreated) MWCNTs adopted in our experiment. In addition, the clear light/dark–dark/light contrast variation along the radial direction suggests that the nanowirelike structure appears to be a coaxial tube-sheath structure. In addition, from the cross-sectional TEM image (Fig. 1(e)), the circular cross-sectional shape with contrast
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Language	English
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Subject Keyword	Cardiovascular Diseases Composition Cross-sectional data Diameter (protocol) Diameter (qualifier value) Dual Electron energy loss spectroscopy Elegant degradation Encapsulation (networking) Entity Name Part Qualifier - adopted Ethanol Graphene Hydrogen Mathematical morphology Nanostructured Materials Nanotubes Nanotubes, Carbon Nanowires Oral Wafer Order (action) Physical Phenomenon or Property Physical vapor deposition Plasma Active Plasma-enhanced chemical vapor deposition Radial (radio) Scanning Electron Microscopy Silicon Specimen Source Codes - Tube Thermal oxidation Transmission Electron Microscopy Vacuum deposition Wafer (electronics) Xfig vibrio cholerae CVD 103-HGR strain live antigen 12000000 UNT/ML Oral Suspension
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