Breaking through the Thermodynamics “Wilds” of Metal–Organic Chemical Vapor Deposition Precursors: Metal tris-Acetylacetonates

Abstract

Metal acetylacetonates belong to the β-diketonate family and are considered as classics among precursors for metal–organic chemical vapor deposition (MOCVD). The success of film preparation is crucially dependent on the volatilization thermodynamics of the precursors used. Data on the volatilization thermodynamics of metal acetylacetonates are in huge disarray. We amassed and analyzed experimental data on the vapor pressures and on the enthalpies and entropies of fusion, vaporization, and sublimation of acetylacetonate tris-complexes of metals(III) (Al, Sc, Cr, Mn, Fe, Co, Ru, Rh, In, and Ir) available in the literary sources. In addition, saturated vapor pressures over crystalline Al(III), Cr(III), and In(III) acetylacetonates and corresponding thermodynamic sublimation properties were determined. New findings enabled us to arbitrate the conflict among literature data. The enthalpies and entropies of sublimation, vaporization, and fusion were adjusted to the reference temperature for a correct comparison using the empirically estimated differences in heat capacities. The heat capacity of the crystalline phase was shown to depend weakly on the metal atom. As a result, a reliable set of enthalpies and entropies of the mentioned processes of fundamental importance was derived for ten metal complexes. Relationships between volatility and structure were established depending on the central metal. The suggested algorithm can be fairly easily transferred to the acetylacetonate or other β-diketonate isoligand complexes with metals of different valence.