Novel ion-molecular surface reaction to result in CH3 adsorbates on (111) surface of chemical vapor deposition diamond from ethane and surface anionic sites

The existence of CH3 adsorbates on (111) surface of chemical vapor deposited diamond, which was observed by scanning tunneling microscopy, was explained by the following SN2 (bimolecular, substitutional, and nucleophilic) type surface reaction; C(s)-+C2H6->C(s)-CH3+CH3-, where C(s) denotes a surface carbon atom. The activation energy was estimated to be 36.78 kcal/mol and the reaction proved to be exothermic with the enthalpy change of -9.250 kcal/mol, according to ab initio molecular orbital calculations at MP2/3-21+G*//RHF/3-21G* level; this result is consistent with typical substrate temperatures, namely about 900 degree C, for chemical vapor deposition of diamond. Charge transfer from the highest occupied molecular orbital of the surface anionic site to the lowest unoccupied molecular orbital of ethane, that is antibonding at the CH3 - CH3 bond, has been clearly visualized. A characteristic configuration of an ethane molecule which is associated with an anionic vacant site C(s)- on hydrogenated (111) surface of diamond was also found. [copyright] 2001 American Institute of Physics