Photodissociation and Photoionization Mechanisms in Lanthanide-based Fluorinated β-Diketonate Metal−Organic Chemical-Vapor Deposition Precursors

A detailed photodissociation mechanism for the fluorinated lanthanide (Ln) β-diketonate metal−organic chemical-vapor deposition (MOCVD) precursors Ln(fod) 3, Ln(hfac) 3, and Ln(hfac) 3 diglyme was elucidated using photoionization time-of-flight mass spectrometry. The collisionless environment of the molecular beam source revealed a series of unimolecular steps, starting with dissociation of an intact β-diketonate ligand. Dissociation steps for the second and third ligands are associated with the attachment of a fluoride to the metal ion, leading to one of three ultimate products: Ln, LnF, or LnF 2 . Except in the case of Pr, no LnO is observed. The pattern of ligand fragmentation strongly supports a mechanism for the fluoride-attachment step which is similar to one previously proposed for the thermally activated decomposition of Ce(hfac) 3 glyme. (1) The detailed mechanistic understanding of the step-by-step fluorination will provide a basis for new ligand design, which maintains the advantageous mass-transport properties of the fluorinated precursors while controlling LnF x formation.