Modeling of evaporation rates of cerium beta-diketonate

The effect of sublimation rate from the surface of solid precursor was included in our model for predicting the evaporation rates of cerium beta-diketonate (Ce(thd)(4)). This model suggested that when the rate of mass transfer was comparable to that of sublimation from surface, the organometallic (OM) concentration at the solid surface would become lower than its saturation pressure. On the other hand, when the sublimation rate was fast, such as in the case of Cu(thd)(2), the OM surface concentration would reach its saturated value. In addition, Ce(thd)(4) also exhibited solid-state decomposition whose contribution to weight losses should also be included for better fitting of the evaporation results. This was especially important when the evaporation rates were slow at low temperatures and high pressures. When the measured fluxes were plotted versus 1/T under different operating pressures, we obtained different ''apparent'' activation energies ranging from 26.7 to 34.5 kcal mol(-1) for Ce(thd)(4). Nevertheless, this activation energy remained constant for Cu(thd)(2) at 29.4 kcal mol(-1) regardless of operating pressures. The above difference was successfully simulated with our proposed model.