Properties of two classes of carbon systems containing mixed sp2-sp3 atomic hybridizations were characterized using molecular simulation. The first class of system is composed of fullerene nanotubes chemically bonded to diamond structures. The motivation for studying these systems comes from experimental evidence for the formation of fullerene-like structures attached to diamond clusters formed during high temperature annealing,  and preliminary electronic structure calculations suggesting that these systems could have important applications as diodes, novel quantum dots, and robust field emitters. Generalized rules for producing defect-free and stable bonding configurations have been derived for these structures from geometrical considerations combined with energies and stresses estimated from an atomic analytic potential function. The analysis demonstrates that a variety of nanotubes can form chemically and mechanically stable interfaces with diamond, including zigzag nanotubes with diamond (111) and (100) surfaces, and small-radii armchair tubules bonded to diamond pentaparticles.
The second class of system is comprised of methyl radical molecules chemically bonded to random positions on fullerene nanotubes of various radii and helical structures. These studies are motivated by the potential use of nanotubes in composites for mechanical and thermal management applications, where chemical functionalization could lead to enhanced mechanical and thermal coupling between nanotube fibers and polymer matrices. Atomic simulations predict that functionalization can significantly reduce the tensile modulus of zigzag nanotubes, but has little influence on the modulus of armchair nanotubes. The effect of chemical functionalization on the thermal conductivity, bending modulus, and critical load for plastic deformation predicted by atomic simulation for tubules of various radii and helical structures will be presented.
V.L. Kuznetsov et.al., Chem. Phys. Lett. 289, 353(1998)
This work is funded by the Office of Naval Research and by NASA.