Nitrogen Doping of Confined Carbyne

Abstract

Low-dimensional carbon allotropes belong to the most revolutionary materials of the most recent decades. Confined carbyne, a linear chain of sp¹-hybridized carbon encapsulated inside a small-diameter carbon nanotube host, is one extraordinary nanoengineering example. Inspired by these hybrid structures, we demonstrate the feasibility to synthesize nitrogen-doped confined carbyne by using azafullerenes (C₅₉N) encapsulated in nanotubes ("peapods") as precursors for the growth of confined carbyne. Resonance Raman spectroscopy as a site selective local probe has served to identify the changes in the spectra of nitrogen-doped versus pristine carbon peapods and confined carbyne. We are able to disentangle frequency changes due to charge transfer from changes due to the difference in mass for both the nanotube and the carbyne, where different effects dominate. This study demonstrates a suitable pathway to achieve controlled doping of carbyne chains via the use of specifically doped precursors.

1

Synthesis of undoped (left) and nitrogen-doped (right) confined carbyne: (a) C₆₀ inside a SWCNT; (b) C₅₉N inside a SWCNT; (c) undoped DWCNT; (d) nitrogen-doped DWCNT; (e) undoped CC@DWCNT; (f) nitrogen-doped CC@DWCNT.

2

(a) Raman spectra of C₆₀ (dark blue) and C₅₉N (teal) peapods, measured with a 488 nm laser (in resonance with the fullerene A_g(2) mode). The shift of the A_g(2) mode is highlighted. (b) Raman spectra of doped/undoped CC@DWCNTs, measured with a 568 nm laser (in resonance with the CC).

3

Raman spectra of DWCNTs grown from C₆₀ (dark blue) and C₅₉N (teal) peapods: (a) line-shape analysis of the G mode of doped DWCNTs; (b) line-shape analysis of the 2D mode of doped DWCNTs; (c) line-shape analysis of the G mode of undoped DWCNTs; (d) line-shape analysis of the 2D mode of undoped DWCNTs.

4

Analysis of CC grown from nitrogen-doped fullerenes (teal) and undoped fullerenes (dark blue): (a) line-shape analysis of the CC mode of the undoped sample compared to the doped sample; (b) average frequency shifts of components of the doped sample (10 different spots measured) compared to the undoped sample (4 different spots measured).