Abstract: We present a combined experimental and theoretical study on carbon nanodiamonds (NDs) using Raman and DAC experimentation and ab initio calculations. Our calculations confirm the surface reconstruction to a fullerene-like structure, and indicate compression of the diamond core, producing an estimated internal pressure of 50 GPa. Quantum molecular dynamics simulations of hypervelocity collisions of NDs show that upon collision, shock-induced amorphization first occurs, followed by complete disruption of the ND surface and ejection of reactive particles into the vacuum. Raman spectra of oxidized ND samples at increasing pressures showed a subtle increase in the vibrational intensity of the Raman feature centered near 1335 cm-1 near 18 GPa and continued under subsequent pressure increases. The intensification of this vibrational feature is consistent with a thinning of the amorphous carbon outer shell, which results in greater exposure to the diamond core with increasing pressure and may be a precursor to Structural Bond Energy Release (SBER) initiation. Additionally, a nearly twofold increase in the vibrational intensity of the sp2 graphite peak centered near 1630 cm-1 in the spectra of the oxidized nanodiamond sample suggests the possibility of a sluggish partial phase transition from sp3 hybridized diamond to sp2 hybridized graphite.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Pages: |
20 |
| Report Date: |
Apr-2009 |
| Report Number: |
A764794 |
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