Temperature-dependent inner tube growth and electronic structure of nickelocene-filled single-walled carbon nanotubes

Abstract

Abstractauthoren We have filled single‐walled carbon nanotubes (SWCNTs) with nickelocene and transformed them to double‐walled carbon nanotubes by annealing in vacuum. We study the temperature‐dependent inner tube growth by means of Raman spectroscopy and investigate the SWCNTs’ electronic structure by X‐ray photoelectron spectroscopy. It is found that larger diameter inner tubes grow at higher temperatures than smaller diameter tubes. Both electron and hole doping of SWCNTs are achieved as the encapsulated nickelocene molecules are reacted at temperatures in the range from 250 up to 1200° C.

Synthesis and Properties of Single-Walled Carbon Nanotubes Filled with Metal Halogenides and Metallocenes

“…In a typical experiment, the SWCNTs were mixed with the powder of substances, sealed in an ampoule under vacuum, and heated at low temperatures (50-200°C) during several days. This method allowed filling SWCNTs with ferrocene [44,[76][77][78][79][80][81][82][83][84][85][86], cobaltocene [87,88], nickelocene [89][90][91][92], and cerocene [93,94]. It should be noted that ferrocene was also incorporated inside SWCNTs by the liquid phase method using its solution in acetone [95].…”

“…The temperature-dependent inner tube growth inside furnace-or laser-annealed ferrocene- [76,77,79], cobaltocene- [87], and nickelocene-filled SWCNTs [89,90] was investigated by Raman spectroscopy. Authors traced modifications of Raman spectra of the filled SWCNTs that occurred at increasing annealing temperature or laser power at fixed annealing time.…”

“…Authors of Ref. [90] compared the growth temperatures of eight different inner tubes with chiralities of (7,5), (8,4), (7,6), (10,3), (12,3), (11,5), (14,2), (12,6) inside nickelocene-filled SWCNTs. They evaluated the growth temperature as the temperature at which the intensity of the RBM peak of the inner tube reaches the half of its maximum.…”

“…The electronic properties of SWCNTs filled with ferrocene [82], nickelocene [89,90,92], and cerocene [93,94] were studied by XPS and UPS. It was shown that the encapsulated metallocenes cause n-doping of SWCNTs.…”

“…Authors of Refs. [82,89,90,92,93] investigated the modification of the electronic properties of the filled SWCNTs upon annealing. Figure 11(a) shows the UPS spectra of the pristine, nickelocene-filled SWCNTs, and the samples annealed at temperatures between 250 and 1200°C for 2 h [89].…”