Well-defined sub-nanometer graphene ribbons synthesized inside carbon nanotubes

Abstract

Graphene nanoribbons with sub-nanometer widths are extremely interesting for nanoscale electronics and devices as they combine the unusual transport properties of graphene with the opening of a band gap due to quantum confinement in the lateral dimension. Strong research efforts are presently paid to grow such nanoribbons. Here we show the synthesis of 6-and 7-armchair graphene nanoribbons, with widths of 0.61 and 0.74 nm, and excitonic gaps of 1.83 and 2.18 eV, by high-temperature vacuum annealing of ferrocene molecules inside single-walled carbon nanotubes. The growth of the so-obtained graphene nanoribbons is evidenced from atomic resolution electron microscopy, while their welldefined structure is identified by a combination of an extensive wavelength-dependent Raman scattering characterization and quantum-chemical calculations. These findings enable a facile and scalable approach leading to the controlled growth and detailed analysis of well-defined sub-nanometer graphene nanoribbons.

Magnetic nanoribbons with embedded cobalt grown inside single-walled carbon nanotubes

“…In previous works, hydrogen-terminated GNRs formed inside of the SWCNTs were successfully imaged by HR-TEM, despite the electron beam damage. 29 In the case of sulfur terminated or chlorine terminated NRs, the edges of the encapsulated structures are more stable and can be resolved clearly in a zigzag configuration. 32,33 However, even when the exact atomic structure of the nanoribbon edge is not possible to be resolved by HR-TEM, the key structural characteristic is the helical twist, a result of nanoribbon confinement inside the nanotube, that allows distinguishing NRs from the encapsu-lated molecules or internal nanotubes.…”

“…In addition to the bottom-up approach 26,27 that is limited to the onsurface synthesis and to only specific precursors that can be used, GNRs can be specifically formed inside the nanotubes. Growth inside the nanotube channels is advantageous since various molecules can be used including fullerenes, 28 PAH, 17 and ferrocenes, 29 resulting in the formation of long and narrow GNRs with various geometries. Recent experiments combining transmission electron microscopy and multi-wavelength Raman spectroscopy unambiguously prove the formation of highly uniform GNRs with identical properties inside the nanotubes.…”

“…Recent experiments combining transmission electron microscopy and multi-wavelength Raman spectroscopy unambiguously prove the formation of highly uniform GNRs with identical properties inside the nanotubes. 29 However, magnetic NRs formed inside the nanotubes, a material that can be perspective for quantum technologies, were not demonstrated so far. While the bottom-up approach can result in the formation of GNRs with nontrivial magnetic ground states, 30 a complicated precursor synthesis route provides limited amounts of samples and hampers the near-term implementation of the material.…”

Nanotube‐Based 1D Heterostructures Coupled by van der Waals Forces

“…Recently, it was demonstrated that by carefully controlling the starting SWCNT diameters and the exact annealing temperature, 6-and 7 armchair graphene nanoribbons (6-and 7-AGNRs) with well-defined structure were grown inside SWCNTs, and their electronic and vibrational properties were characterized in detail by wavelength-dependent Raman scattering spectroscopy (Figure 6d). [108] The Raman spectra show the features of the surrounding SWCNTs (RBMs, D and G-bands), those of newly synthesized inner tubes in the RBM region (highlighted by the circle in Figure 6d) and the distinctive radial-breathing-like-modes (RBLM) and higher-frequency modes of the encapsulated armchair graphene nanoribbons (AGNRs) (highlighted by the squared boxes in Figure 6d). Interestingly, the synthesis of GNRs inside SWCNTs can be achieved both from functionalized fullerenes, polycyclic aromatic hydrocarbons, and ferrocene, thus showing that mainly carbonrich precursors are needed combined with other atoms (H, O, N, S, …) to terminate the edges.…”

“…The right panels present a selection of the electronic resonance profiles for the D-modes of the AGNRs, plotting Raman intensity as a function of excitation energy, directly yielding information on the electronic structure of the AGNRs. Adapted with permission [108]. Copyright 2021, Elsevier.…”