Ordered and heterostructured NiSi2/Si nanowire arrays have been successfully fabricated by reacting nickel thin films on silica-coated ordered Si NW arrays. The coating of thin silica shell on Si NW arrays has the effects of limiting the diffusion of nickel during silicidation process to achieve the single crystalline NiSi2 NWs and maintain the straightness of the nanowire. The work function of Si NWs with NiSi2 tip (4.88 eV) was lower than the original Si NW arrays (5.01 eV). Excellent field emission properties were found for NiSi2/Si NW arrays. The excellent field emission characteristics are attributed to the well-aligned and highly ordered arrangement of the heterostructured NiSi2/Si field emitters. The characteristic of the Schottky junction were also verified by the I-V measurement. The weak ferromagnetic properties were also determined by the SQUIDs.
The heterostructured CoSi2/Si and PtSi/Si NW arrays have been also fabricated by silicidation of Si NW with a Co and Pt film, respectively. The CoSi2 is of platelet shape and forms endotaxial structure in Si NWs. The results indicate that the thin SiOx coated on Si NW arrays will be effective to obstruct the diffusion of the Co atoms and form platelet-shaped CoSi2.

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