Multi-walled carbon nanotubes (MWCNTs), 7-70 nm thick and up to 30 μm long, were efficiently grown by room-temperature continuous-wave laser vaporization of a graphite target containing B4C in an ambient Ar gas. Adjusting the boron content in the target and Ar gas pressure resulted in a maximum fraction of ～60 of MWCNTs in the deposits. The straightness of the MWCNTs and graphene layers with an interlayer spacing of ～0.35 nm indicated that the degree of graphitization was fairly high in the grown MWCNTs. However, the features of D, G, and 2D bands in the Raman spectrum of a deposit suggested boron doping in the MWCNTs. An apparent Young's modulus of a grown MWCNTwas measured to be 0.68 TPa and comparable to those of heat-treated vapor grown carbon nanofibers. MWCNTs are thought to grow on molten boron carbide particles acting as seeds at high temperatures of up to ～2400 °C.
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