FROM CHEMISORPTION TO MECHANISM ON SURFACES - AN EXPLORATION OF THE PYROLYSIS OF TRIISOBUTYLALUMINUM IN THE CHEMICAL VAPOR-DEPOSITION OF ALUMINUM THIN-FILMS

The chemisorption of H, CH3, C2H5, and C2H4 is examined on Al(111) and Al(100) surfaces by the extended Huckel method, using a tight-binding formalism. A local chemical viewpoint is sought through fragment analyses, decompositions of the density of states and overlap populations. Various adsorption sites have been studied. On both surfaces, the first three species prefer to bind in the on-top site by a sigma-type interaction with the coordinated Al atom. Ethylene, on the other hand, favor the twofold bridging site by a di-sigma bonded interaction with its highest occupied molecular orbital and lowest unoccupied molecular orbital. In addition, the mobility of all these species on surfaces is investigated. Finally, the mechanism for the thermal decompositions of the triisobutylaluminum is studied. A beta-hydride elimination rate-determining step is established, in which the activation barrier of the reaction in Al(111) is lower than Al(100). This result is in agreement with the experimental findings.