In situ mass spectrometry during thermal CVD of the tris-acetylacetonates of 3-d transition metals

Abstract
The processes of thermal decomposition of 3-d metal acetylacetonates (ScL₃, VL₃, CrL₃, MnL₃, FeL₃, CoL₃) and HL were investigated within the 370-870 K temperature range using a high-temperature molecular beam source with mass spectrometric sampling of the gas phase composition directly at the outlet from the reaction zone. A scheme of thermal decomposition of complexes vapour is suggested. According to the scheme, at the first reaction stage the β-diketone HL_gas and [LM(L - H)_ads and [L₄M₂(L - H)]_ads intermediate species are formed on the surface in the "low-temperature" stage of decomposition processes. In the next "high-temperature" stage these intermediate species are decomposed to produce ML₂, ML and (C₅H₆O), (C₅H₆O)₂ gas species and metal oxides on the surface. The effective values of kinetic parameters in Arrhenius equation are calculated from temperature curves of ML₃ complexes for the first order reaction. The saturated vapour pressure of these chelates was determined as a function of temperatures according to the Knudsen effusion method. From temperature dependence of vapour pressure the thermodynamic parameters of the chelate sublimation processes are calculated. It is shown that the volatility of complexes decreases in the row from Sc to Co compounds. The mechanisms of thermal decomposition of complexes in vapour phase and their conversion into the metal oxide on surface are discussed.