Luminescent Photofragments of (1,1,1,5,5,5-Hexafluoro-2,4-pentanedionato) Metal Complexes in the Gas Phase

Abstract

The luminescence that is observed under gas phase photolytic deposition conditions is studied for Cr(hfac)3, Ni(hfac)2, and Pt(hfac)2. This luminescence is analyzed under a variety of conditions, including the relatively high pressures of an evacuated gas cell and the collision-free conditions of a molecular beam. The effects of inert buffer gas are also studied. Features in these spectra indicate that, in general, multiple photolysis processes occur. Some simple fragments that are produced from these compounds are identified, including bare metal atoms (Ni, Cr), metal monofluorides (NiF, CrF), CH (in the case of Ni(hfac)2), and metal carbide from Pt(hfac)2. It is postulated that the difference in the observed photofragmentation pathway in the case of platinum is due to σ bonding to the β carbon of the hfac moiety as opposed to the bidentate bonding of the other two metals. Possible mechanisms are presented. Detailed analysis of the spectra allows characterization of the internal energy of the platinum carbide photofragment.

Wavelength Dependence of Photooxidation vs Photofragmentation of Chromocene

“…In our studies of chromium metal deposition using tris(hexafluoroacetylacetonate)chromium, Cr(hfac) 3 , as the precursor, we discovered that chromium atoms are readily formed by photolysis but that significant amounts of the undesired diatomic photofragment CrF were also produced intramolecularly. 14,15 To avoid fluorine contamination of the deposit, we investigated other chromium precursors including chromocene, bis(cyclopentadienyl)chromium, Cr(Cp) 2 .…”

“…The gas phase photochemical reactions of metal compounds, and especially the primary photochemical processes such as photodissociation and photofragmentation, are attracting interest because of their importance in understanding laser assisted chemical vapor deposition. − Identification and quantification of the photofragments use luminescence spectroscopy and mass spectroscopy as the primary analytical methods. − Our interest in the photochemistry was sparked by our observations that both desired photofragments (i.e., those having the stoichiometry of the desired deposit) and undesired species (i.e., those that lead to contamination of the desired deposit) are produced by intramolecular processes in the gas phase. − The amounts of the photofragments that are produced depend on both the wavelength and the fluence of the exciting light. In our studies of chromium metal deposition using tris(hexafluoroacetylacetonate)chromium, Cr(hfac) 3 , as the precursor, we discovered that chromium atoms are readily formed by photolysis but that significant amounts of the undesired diatomic photofragment CrF were also produced intramolecularly. , To avoid fluorine contamination of the deposit, we investigated other chromium precursors including chromocene, bis(cyclopentadienyl)chromium, Cr(Cp) 2 .…”

Sensitive Wavelength Dependence of PdC And Pd Formation from Photolysis of Bis(hexafluoroacetylacetonato)palladium(II)

“…Gas-phase photolysis of metal-containing molecules readily causes photofragmentation to produce metal atoms and ions. − More recently it has been shown by luminescence spectroscopy that photolysis of these molecules also readily produces diatomic metal-containing molecules in the gas phase. − These discoveries have assisted in the elucidation of the photolytic decomposition pathways relevant to laser-assisted chemical vapor deposition (LCVD). Both desired fragments (e.g., TiN in the LCVD of TiN films) 11 and undesirable fragments containing heteroatoms that contaminate the final films (e.g., CuF, CrF, NiF, and PtC in the laser CVD of the respective metal films) 6-10 have been identified.…”

Gas Phase Photoproduction of Diatomic Metal Nitrides During Metal Nitride Laser Chemical Vapor Deposition

“…Recent spectroscopic studies of luminescent fragments produced during gas-phase photolysis of metal-containing precursors for laser-assisted chemical vapor deposition (LCVD) have shown that atoms or small molecules having the elemental compositions of the final deposits are produced in the gas phase. − For example, luminescence from both atoms and diatomics of metals are observed during the deposition of gold, and both metal and chalcogen are observed during the deposition of II/VI semiconductors. , It has also been found that diatomic molecules are formed containing the desired metal combined with an undesired heteroatomic impurity that contaminates the final film. For example, when metal hexafluoroacetylacetonates are used as the precursor molecules, diatomic metal fluorides are observed during LCVD of Cr, Ni, and Cu, , and diatomic metal carbide is observed during the LCVD of Pt . These studies demonstrate that both desired and undesired species are produced in the purely gas-phase component of the CVD process.…”