Nanometric Studies of the Structure and Tribology of Carbon Nitride Materials
Final technical rept. 15 Jun 95-14 Jun 98
HARVARD UNIV CAMBRIDGE MA DEPT OF CHEMISTRY AND CHEMICAL BIOLOGY
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Significant effort has been placed on several areas. First, we have carried out systematic studies of the growth of carbon nitride materials as a function of carbon reactant energetics, nitrogen flux and growth temperature and have quantitatively analyzed the structure and local bonding in these materials. The emphasis of these studies has been to determine unambiguously conditions that can produce sp3-bonding since this is required for a superhard coating. Significantly, we have show recently that there is a nitrogen-driven sp3 to sp2 structural transformation in the carbon nitride materials as nitrogen content is increased about 15 atomic percent. With these limits worked out we have also prepared films with optimal C-N ratios for hardness, and investigated their nanotribological properties by force microscopy. In addition, we have carried out theoretical cluster calculations to understand the origin of this sp3 to sp2 transition. Significantly, these calculations demonstrate that the transition is an intrinsic property of carbon nitride system since 1 the sp2 bonded structure becomes thermodynamically favored for 15 nitrogen and 2 the barrier between sp3 and sp2 structures also reduces significantly for 15 nitrogen.
- Inorganic Chemistry