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) beta-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 beta-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.