Highly efficient synthesis of small-diameter single-walled carbon nanowires through transformation of polyyne molecules into long linear carbon chains inside single-walled carbon nanotubes

Single-walled carbon nanowires (SWCNWs)—long linear carbon chains (LLCCs) or carbynes confined inside single-walled carbon nanotubes (SWCNTs)—are synthesized by inserting polyynes (C_2nH₂) as a carbon source into SWCNTs, followed by annealing under high vacuum. By optimizing the polyyne solution concentration, high-yield SWCNWs (diameters <0.8 nm) were efficiently prepared. The I_L/I_G ratio in Raman spectrum reached 3.6, and it was much higher than the reported values for such small-diameter SWCNWs. Thus, high-density LLCCs were encapsulated inside small-diameter SWCNTs. I_L/I_G was markedly enhanced under the resonance condition of the host SWCNTs, where the energy was effectively transferred from the host SWCNTs to LLCCs.