INOR 484 |
| Diamondoids are hydrogen-terminated nanosized sp3 bonded diamond fragments, which occur in a large variety of shapes and sizes. The diamaondoids are held by weak van der Waals forces and may have very different thermal properties than diamond which is held together by strong covalent bonds. The study of thermal transport in diamaondoids can offer new insights on the role of interfaces in thermal transport, as well as provide a broader understanding of phonon transmission and scattering in nanostructured materials. Interfaces play a critical role in nanoscale thermal transport, since an interface creates an interruption in the regular crystalline lattice in which phonons propagate. The probability of transmission to either side of the interface depends on the ratio of the density of phonon states. Since diamondoids are nanostructured diamonds, the low frequency part of the phonon spectrum, which is present in diamond, will be non-existent and they will only contain the confined high frequency modes > 10 THz. The van der Waals interactions between diamonddoids are expected to be about 1000 times weaker than sp3 bonded carbon and should lead to resonant frequencies which are 20-50 times lower, i.e. < 1 THz. This mismatch in frequency will make the phonon coupling between diamondoids very weak leading to very low thermal conductance. Hence, while diamond is known to have one of the highest thermal conductivity of any known material above 100K, we expect diamondoids to have one of the lowest thermal conductivity. The experimental results of the measurement of thermal conductivity of diamondoid powder (using the 3-omega method) as a function of temperature, along with a discussion of the thermal transport pathways will be presented. The effect of the size and shape, in the case of isomers of the same diamondoid, on the thermal conductivity will also be discussed. |
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Nanoscience: Characterization
2:00 PM-5:00 PM, Monday, 11 September 2006 Moscone Center -- Room 309, Oral
Division of Inorganic Chemistry |