The use of gas-phase electron-impact activation of metalorganic complexes to facilitate atomic layer depositions (ALD) was tested for the case of (methylcyclopentadienyl)Pt(IV) trimethyl (MeCpPtMe) on silicon oxide films. Uptake enhancements of more than 1 order of magnitude were calculated from X-ray photoelectron spectroscopy (XPS) data. On the basis of the measured C:Pt ratios, the surface species were estimated to mainly consist of MeCpPt moieties, likely because of the prevalent formation of [MeCpPtMe - nH] ions after gas-phase ionization (as determined by mass spectrometry). Counterintuitively, more extensive adsorption was observed on thick SiO films than on the native thin SiO film that forms on Si(100) wafers, despite the former having virtually no surface OH groups. The adsorption of MeCpPt fragments on silicon oxide surfaces was determined by density functional theory (DFT) calculations to be highly exothermic and to favor attachment to Si-O-Si bridge sites.
The thermal chemistry of several metal organic compounds
with amidinate,
diketonate, or cyclopentadienyl (Cp) ligands on oxide surfaces, mainly
on silicon dioxide but also on aluminum oxide, was studied by using
surface sensitive techniques, including temperature-programmed desorption
(TPD), X-ray photoelectron spectroscopy (XPS), reflection–absorption
infrared spectroscopy (RAIRS), and static secondary ion mass spectrometry
(SSIMS), and those studies were complemented with quantum mechanics
calculations. With the amidinates, TPD experiments revealed complex
decomposition pathways, starting with a ligand-exchange step with
OH surface groups. That is followed by migration of the remaining
ligands from the metal center to the surface, where decomposition
occurs mainly via bond scission at the terminal alkyl groups and β-hydride
elimination steps to produce the corresponding olefins. At that stage,
XPS data show that the metal is partially, but not completely, reduced,
indicating a partially ionic metal–oxygen surface bond. The
diketonates display only limited reactivity on silica, again via an
initial ligand exchange step, but much higher reactivity is seen on
alumina, where subsequent decomposition and olefin production are
observed. The Cp ligands proved to be the most stable, hindering in
fact the effective adsorption of these metal organic compounds unless
prior activation in the gas phase via electron-impact excitation is
carried out. After adsorption, the Cp proved to be quite sturdy, surviving
long exposures to outside atmospheres (as shown by SSIMS). They can,
however, be protonated (deuterated) upon high-temperature exposure
to H2O (D2O). All this chemistry is discussed
in general terms and contrasted with known reactivity in solution.
The chemistry of trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPt(CH 3 ) 3 ), a platinum organometallic compound often used for the chemical deposition of Pt films, on nickel oxide surfaces was investigated. Particular emphasis was placed on following the coordination of the initial ligands, methylcyclopentadienyl (MeCp) and methyl moieties, by using time-of-flight secondary ion mass spectrometry (ToF-SIMS) in combination with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) computations. It is shown that the MeCp fragment is stable and, upon reacting with NiO surface, remains attached to the Pt center. The methyl groups, on the other hand, can migrate to the nickel surface or remain bonded to the Pt, but on NiO surfaces they prefer to interact with the nickel centers rather than with the oxygen atoms. In addition to these findings, ToF-SIMS data confirmed that gasphase electron-impact activation can truly enhance the activity of the MeCpPt-(CH 3 ) 3 precursor.
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