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February 4th, 2007

Linear carbon - the explosive member of the nanocarbon family

Abstract:
The combination of sp3, sp2, and sp hybridized atoms can give rise to a large number of carbon allotropic forms and phases, starting from carbon crystals based on all sp3 (diamond) and sp2 (graphite, fullerene) are well known and characterized. In addition there are innumerable transitional forms of carbon where sp2 and sp3 hybridization bonds coexist in the same solid such as in amorphous carbon, carbon black, soot, cokes, glassy carbon, etc. Solids based on sp hybridization, although subject of intense experimental efforts, seem to be the most elusive of the different carbon families. Such one-dimensional (1D) structures - "real" carbon nanowires - are linear chains of carbon atoms linked by alternating single and triple bonds (polyynes) or only double bonds (polycumulene). They are considered the building blocks for the elusive "carbyne": an ideal crystal constituted by carbon atoms with sp hybridization only. In solid and stable form this would represent a new carbon allotrope whose existence was a matter of great debate in the 1980s. With the immense interest in carbon nanomaterials, sp carbon nanostructures have become objects of renewed interest in recent years since they are considered precursors in the formation of fullerenes and carbon nanotubes; moreover they are interesting in astrophysics since they are considered constituents of interstellar dust. 1D carbon nanowires are expected to show interesting optical, electrical and mechanical properties. Some techniques already permit the synthesis of linear carbon chains in solution. However, their extremely high reactivity against oxygen - they can literally explode - and a strong tendency to interchain crosslinking makes synthesis of pure carbyne solids a major challenge. Researchers in Italy have now presented a simple method to obtain a solid system where polyynes in a silver nanoparticle assembly display long-term stability at ambient conditions.

Source:
nanowerk.com

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