Gas-phase photofragmentation and multiphoton ionization of transition metal and lanthanide coordination compounds.

摘要

The gas-phase photofragmentation of metal-containing compounds is relevant to photo-assisted chemical vapor deposition (CVD). Understanding and manipulation of photochemical processes that occur during deposition allow for greater control of the overall process. This dissertation reports on the photofragmentation and photoionization of gaseous metal-organic compounds, studied via time-of-flight mass spectrometry, resonance-enhanced multiphoton ionization, and gas-phase luminescence.;Traditional compounds studied are organometallic compounds, including transition metal alkyls and metallocenes. Photoexcitation results in extensive fragmentation: the metal cation is the heaviest and dominant species formed. Photons cleave all metal-ligand bonds before the parent molecule can ionize. The parent ion and smaller metal-containing species are not detected. Intramolecular rearrangements do not occur while ligands remain attached to the metal. This dissertation suggests otherwise: the parent ion can be generated in significant amounts and ligands readily undergo reactions while coordinated.;The dissertation discusses several metal-organic species, including transition metal, main group, and lanthanide compounds. The observed photoproducts are interpreted in terms of the parent molecules' potential as photo-assisted CVD precursors. A series of lanthanide-organic beta-diketonate compounds forms high amounts of Ln+ and LnO+ which can serve as dopants in semiconducting thin metal films. A nickel (II) beta-diketonate compound is found to generate strong yields of both Ni+ and NiF+. Although the presence of metal fluoride discourages the use of this compound as a CVD precursor, a rich amount of photochemistry is observed. NiF+ forms after an intramolecular rearrangement on the ligand, and unprecedented amine to imine formation occurs via multiple photoreaction processes. The rearrangements occur while ligands are still bound to nickel. Metal-amide compounds have the potential to serve as precursors for metal and metal nitride deposition. Excitation of a tin-containing silylamide compound in resonance with known atomic tin transitions cleanly produces Sn +; however, SnN+ is never detected. During UV excitation, Sn+ is a minor ion, as the parent ion and mass peaks containing fragments of coordinated ligand are mostly formed. A mixed-ligand platinum compound never produces Pt+ in a dominant yield. In contrast to the lanthanide series, metal oxide is never formed. However, the compound is yet another example where the photo fragmentation is wavelength-dependent.