One-dimensional silicon-carbon nanotubes and nanowires of various shapes and structures were synthesized via the reaction of silicon (produced by disproportionation reaction of SiO) with multiwalled carbon nanotubes (as templates) at different temperatures. A new type of multiwalled silicon carbide nanotube (SiCNT), with 3.5-4.5 A interlayer spacings, was observed in addition to the previously known beta-SiC (cubic zinc blende structure) nanowires and the biaxial SiC-SiO(x) nanowires. The SiCNT was identified by high-resolution transmission microscopy (HRTEM), elemental mapping, and electron energy loss spectroscopy (EELS). The multiwalled SiCNT was found to transform to a beta-SiC crystalline structure by electron beam annealing under TEM.

Silicon nanowires (SiNWs) have attracted intense interest in recent years [1] because they are not only important for fundamental studies on various size-dependent phenomena, but they are also potential building blocks for nanoscale electronic and optoelectronic devices. [1±2] Various growth methods, including laser ablation, [3±6] thermal evaporation, [6±9] and chemical vapor deposition, [10±11] have been used to synthesize SiNWs. One important target of the synthetic approaches is to achieve a high degree of control of the diameter, growth orientation, and morphology of the SiNWs. A good understanding of the growth mechanism is obviously the key to obtaining SiNWs with desired properties required for various novel applications. While recent efforts have substantially advanced our understanding on the growth mechanisms of SiNWs, [6] many fundamental issues remain unclear. [3] Although SiO 2 -clad SiNWs appear generally circular in crosssection as shown by transmission electron microscopy (TEM) images, the cross-section of the Si crystalline core has been neither observed nor investigated. The cross-sectional study of SiNWs is expected to provide structural information about the boundary between the crystalline core and the oxide sheath, which, in turn, may shed light on the growth mechanism.In the present work, we have developed a unique samplepreparation technique to prepare the cross-sectional samples of SiNWs for TEM examinations. Using this technique, we successfully prepared and studied the cross-sections of SiNWs, which revealed that the Si core is bounded by well-defined facets of low-index crystallographic planes. We also obtained statistical data to elucidate the growth directions of the SiNWs synthesized by the OAG approach. We point out that the developed technique should be generally applicable to preparing the cross-sectional TEM samples of one-dimensional nanomaterials including nanowires and nanotubes.The as-grown SiNWs are randomly oriented with a length of more than 10 lm and a typical diameter of about 20 nm, as shown in Figure 1a. It is clearly revealed that SiNWs have different shapes. Some have a uniform size along the length of COMMUNICATIONS

A new type of well-structured, hydrocarbon nanomaterial including nanotubes and onions, with interlayer spacing ranging from 3.4 to 5.8 A, was discovered by reacting SiNWs with common organic solvents in a laboratory sonicator under ambient conditions (room temperature and atmospheric pressure).