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ABSTRACT Composite nanowires with typical diameters of 30-100nm, which consisted of Si, P-SiC, amorphous carbon were converted from Si nanowires by ion beam deposition. The Si nanorods were exposed to broad low energy ion beams. The low energy hydrocarbon, argon and hydrogen ions, generated in a Kaufman ion source, reacted with Si nanowires and formed the composite nanowires. It has been assumed that the reaction pathway to form the composite nanowires were driven by both thermal diffusion and kinetic energic of interacting particles.

INTRODUCTION Since the discovery of carbon nanotubes', nanoscale one-dimensional structures have stimulated great interest in the research community because of their exotic electronic and mechanical properties. H. J. Dai et al. 2 first reported an alternative approach to the synthesis of solid carbide nanoscale rods of TiC, NbC, Fe 3C, SiC, and BCx from carbon nanotubes. W. Q. Han et al.3 reported a method to prepare GaN using carbon nanotubes. Recently, another very important nanoscale material, bulk-quantity Si nanowires, have been successfully synthesize from silicon oxide 4. This makes it possible to prepare some other nanoscale materials by using Si nanowires as temp. So far, most work reported on nanoscale materials has focused on the single structure materials. In fact, composite nanoscale materials may have some different properties which every pure material does not have. For instance, J. T. Hu et al.5 reported that the heterojunction of carbon nanotubes and Si nanowires have diode-like I-V characteristics. From the technique point of view, direct deposition by ion beam technique is the most direct method to study the effect of ion bombardment. In fact, low energy species of tens of eV have been used in film deposition in either plasma form or the ion beam technique.6"8 Recently, Chen et al. 9 reported the formation of bulk-buried stoichiomtric SiC layer in the silicon substrates via ion implantation and subsequent annealing treatment. In this letter, we report the synthesis of composite nanowires by the bombardment of a fixed ion beam of CH4 , H 2 and Ar on Si nanowires.

EXPERIMENT A vacuum chamber equipped with a Kaufman ion source (3.0-1500-1000, ION. TECH, INC. USA) was used for the treatment of Si nanowires synthesized by thermal evaporation of a powder mixture of Si and Si0 2 were used as substrate. In order to eliminate contamination, the Si nanowires were put on a mirror-polished Si wafer. The deposition process was carried out in the vacuum chamber with a base pressure of 2x l0-7 Torr. A mixture of methane (>99.90/o), hydrogen (>99.999%) and argon (>99.995%) was introduced into the ion source as the working gas with the ratio of CH 4 :H2:Ar=1:50:173. The total flow rate was 2 sccm and the deposition pressure 235 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society

was kept at about 5x 104 Torr. Ions generated from the ion source were accelerated to bombard the Si nanowires with an accelerating voltage of 200eV. The ion dose measured by a Faraday