Graphene-semiconductor hybrids

Also nanotubes formed by AB semiconductors, and structurally similar to those we have discussed above for carbon, have been considered theoretically. In principle, the existence of the carbon nanotubes can be correlated with the existence of planar graphene sheets that subsequently are rolled up. For carbon, the strong interatomic bonds are formed by sp hybrids, whereas weaker bonds are formed by the p orbitals perpendicular to the sheet. If other materials also can form planar sheets, it may be suggested that nanotubes can exist, too. This is the case, e.g., for BN as well as for BC2N for which a and n orbitals from sp hybrids and p functions, respectively, are responsible for the bonding. For heavier elements the atoms tend to form sp hybrids, which ultimately result in three-dimensional structures and not in sheets. 

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