Paper TF-TuA10
Homogeneous Thermal Decomposition of Triethylaluminum: Effect of NH₃

Tuesday, October 19, 2010, 5:00 pm, Room Ruidoso

Thermal decomposition pathways of triethylaluminum ((C₂H₅)₃Al, TEAl) were investigated in a custom, up-flow, cold-wall CVD reactor . The extent of homogeneous decomposition of TEAl in N₂ as well as with added NH₃ was measured using in situ Raman spectroscopy measurement. The results of Density Functional Theory (DFT) calculations were used to assist in assignment of the observed Raman shifts to the decomposition products TEAl:NH₃, DEAlH, TEAl:NH₃ H₂N-AlH-NH-AlH₂, H₂Al-NH₂, MEAlH, MEAlH-AlH₂ and DEAl-AlH₂ as well as the estimating the rates of selected pathways. For the case of thermal decomposition of TEAl with N₂ carrier gas, the species H₂Al–NH₂ was observed . This is believed to result from the reaction of ammonia with the product of β–hydride elimination. This species is a possible reactant for AlN formation. Raman shifts of 600, 1989, 2025, 2580, 2835, 2849, 2900, 2918, 2939, and 3173 cm^-1 were recorded for TEAl in N₂, while shifts of 452, 1462, 1525, 1639, 2580, 2853, 2841, and 2849 cm^-1 were observed for a mixture of TEAl with ammonia in N₂. In addition, four vibrational bands (930, 965, 3230, and 3334 cm^-1) for ammonia were observed with high intensity. The temperature profile along the reactor centerline was measured and this was compared to the simulated results using a custom-FEM Galerkin method. DFT calculations using B3LYP/LanL2DZ level of theory were carried out to find the optimized geometry of each intermediate and transition structure and to calculate activation energy. This methodology, which uses the results from in situ Raman spectroscopy, DFT calculations, and FEM reactor modeling, is a powerful approach to understanding thermal decomposition mechanisms.