“Graphene helix”的意思、由来-开放百科全书

The graphene helix has been suggested as a structural model for single-wall carbon nanotubes (SWNTs). In the model, the one-dimensional materials are resulted from spiral growth of a graphene ribbon, like an ivy growing on a tree in nature, resulting in a helically opened, tube-like structure.

Lee et. al. suggested unique "nodal morphology" as evidence for the helix model for SWNTs,^[1] which prevails in high-resolution transmission electron microscopy (HRTEM) and scanning tunneling microscopy (STM) images reported since 1993. The helix model for SWNTs is supported by strain energy calculation. The strain energy of the helical growth of a zigzag or armchair graphene ribbon is just about a quarter that of seamless cylindrical SWNTs. This calculation suggests that the growth of seamless SWNTs may be energetically prohibitive and uncompetitive with the structure proposed here under the conditions of conventional chemical vapor deposition processes.

The model addresses previous experimental evidence in the literature, diverse electron diffraction patterns, HRTEM and STM morphologies as well as inconsistencies in the measured mechanical and electrical properties of SWNTs. Electrical property of SWNTs can be regarded as a (zigzag) graphene nanoribbon which is a conductor. In the mode, the chirality is not a necessary condition for the growth of SWNTs and the observation of chirality (or semiconducting properties) in the literature may be the result of an erroneous interpretation of the distortion of the graphene helix.

Based on spiral growth model, further works were carried out to investigate the mechanical properties (evaluation of tensile process by stress distribution) ^[2].

Recently, Park et al. reinterpreted SWNTs to be a graphene helix via Raman spectroscopy, showing that the typical Raman spectrum for SWNTs is the signature of their helical structure with density functional theory simulation and structure analysis for hydrogenated and dehydrogenated SWNTs samples. They demonstrated that the G- mode at ~1570 cm-1 is unique to opened tubular graphene structures (i.e., graphene helix) of ~2 nm in diameter. They also demonstrate that D mode of ~1350 cm-1 is originated from edge defects of opened SWNTs revealing strong Eigenvectors, which is absent in concentric tubes. They also showed that the analysis for the Raman spectra of SWNTs is consistent with general understanding on Raman analysis of carbon materials

References

1. ^{{cite journal|last1=Lee|first1=J.-K.|last2=Lee|first2=S.|last3=Kim|first3=J.G.|last4=Min|first4=B.K.|last5=Kim|first5=Y.I.|last6=Lee|first6=K.I.|last7=An|first7=K.H.|last8=John|first8=P.|title=Structure of Single-Wall Carbon Nanotubes: A Graphene Helix|journal=Small |date=2014|volume=10|page=3283–3290|doi=10.1002/smll.201400884}}
2. ^{{cite journal|last1=Jhon|first1=Y.I.|last2=Kim|first2=C.|last3=Seo|first3=M.|last4=Cho|first4=W.J.|last5=Lee|first5=S.|last6=John|first6=Y.M.|title=Tensile Characterization of Single-Walled Carbon Nanotubes with Helical Structural Defects|journal=Scientific Reports |date=2016|volume=6|doi=10.1038/srep20324|bibcode=2016NatSR...620324J}}
3. ^{{cite journal|last1=Park|first1=Y.|last2=Hembram|first2=K.P.S.S.|last3=Yoo|first3=R.|last4=Jang|first4=B.|last5=Lee|first5=W.|last6=Lee|first6=S.-G.|last7=Kim|first7=J.-G.|last8=Kim|first8=Y.I.|last9=Moon|first9=D.J.|last10=Lee|first10=J.-K.|last11=Lee|first11=J.-K.|title= Reinterpretation of Single-Wall Carbon Nanotubes by Raman Spectroscopy|journal=C |date=2019|volume=xx|doi= 10.1021/acs.jpcc.9b02174}}