George W. Tyndall

Kinetics and mechanism of laser‐induced photochemical deposition from the group 6 hexacarbonyls

A quartz crystal microbalance has been used to measure the rates of photochemical deposition from Cr(CO)6, Mo(CO)6, and W(CO)6 induced by a focused frequency‐doubled argon ion laser (257 nm). The kinetic data indicate that deposition occurs via single‐photon dissociation of the hexacarbonyl in the gas phase, yielding products that subsequently condense on the substrate surface. This interpretation is supported by the observation of material deposited well outside the area of the substrate that is directly illuminated by the laser beam. A calculation of the deposit thickness versus radial distance from the center of the laser beam, using a simple gas‐phase model of the deposition process, provides an adequate fit to the observed thickness profile of a typical deposit. The presence of ripples in material deposited within the focal spot of the laser beam suggests that secondary photoinitiated dissociation of the gas‐phase photoproducts occurs after they condense on the substrate surface. Adsorption measureme...

Quartz crystal microbalance measurements of absolute laser photodeposition rates: application to 257-nm deposition from W (CO)6

A quartz crystal microbalance has been used to measure absolute rates of laser‐induced photochemical deposition processes in real time. A cw UV laser (257 nm) focused at normal incidence onto the microbalance crystal surface is used to induce deposition by photodecomposition of an organometallic vapor. An equation is derived to obtain the absolute mass of the deposit. The method is demonstrated for photodeposition from W(CO)6.

Excimer laser multiphoton dissociation of Cr(CO)6: Evidence for two distinct dissociation processes

The excimer laser multiphoton dissociation of Cr(CO)6 has been investigated in the gas phase using emission spectroscopy to detect excited state photoproducts. Following laser irradiation at 193 nm (ArF*), 248 nm (KrF*), and 351 nm (XeF*) well‐resolved Cr(I) emission was detected. The photodissociation mechanism was studied by determining the laser fluence dependence, buffer gas pressure dependence, and temporal profiles of the emission intensity for the various Cr(I) excited states. The data suggest that dissociation occurs via two distinct processes, sequential and direct. The sequential process is found to be extremely sensitive to buffer gas pressure, while the direct mechanism is pressure invariant. The Cr(I) excited state distributions formed in the direct process, following irradiation at the three laser wavelengths used, appear to be statistical.

Chemical modification of sputtered amorphous-carbon surfaces

Methods to chemically passivate the surfaces of amorphous-carbon films (a-C) produced by dc magnetron sputtering were studied. The chemical composition of carbon surfaces produced via sputtering are dependent upon the environment to which the carbon is exposed immediately following deposition. When the sputtered film is vented to ambient conditions, free radicals produced at the surface during the deposition process are quenched by reaction with oxygen and/or water to form an oxidized, hydrophilic surface. If the sputtered carbon film is, however, exposed to a reactive gas prior to venting to ambient, the chemical nature of the resulting surface can be modified substantially. Specifically, a less highly oxidized and much more hydrophobic carbon surface is produced when the surface free radicals are quenched via either an addition reaction (demonstrated with a fluorinated olefin) or a hydrogen abstraction reaction (demonstrated with two alkyl amines). Chemical modification of amorphous-carbon films can als...

Lubricant Bonding Effects on Thin Film Disk Tribology

The magnetic recording industry predominantly uses Zdol to lubricate the carbon overcoat of magnetic recording disks. Zdol comprises a perfluoropolyether chain terminated with hydroxyl end groups that are capable of reversibly bonding to the carbon overcoat. Contact start/stop (CSS) tests were done to investigate the effects of Zdol lubricant bonding, thickness, and relative humidity on durability. The durability improved with increasing thickness of fully bonded or mobile Zdol. The durability decreased with increasing initial bonded fraction and with decreasing relative humidity. The bonded fraction increased with time during the tests at elevated temperature and low relative humidity. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

Characterization of a solid fluorocarbon film on magnetic recording media

Fluorocarbon films were deposited on carbon overcoated magnetic recording media from monomers using an ion beam apparatus. The films were characterized using sensitive surface analytical and spectroscopic methods. These include nuclear magnetic resonance spectroscopy, dielectric spectroscopy, infrared spectroscopy, x-ray photoelectron spectroscopy, scanning Kelvin probe, ellipsometry, Rutherford backscattering, Auger electron spectroscopy, secondary ion mass spectroscopy, contact angle, and nanoindentation. The film thickness, chemical composition, hardness, and surface potential were measured across the media surface. The fluorocarbon film was insoluble and no melting or glass transition was observed up to 220 °C. Ambient organic adsorbates are detected on the surface, and the film undergoes a relaxation process that occurs over about 20 days time following deposition. The initial advancing water contact angle is controlled through surface modification by a plasma treatment in the final deposition stage.

Effect of adsorbed water on perfluoropolyether-lubricated magnetic recording disks

The impact of water on the hydroxyl-terminated perfluoropolyether, Zdol, and the amorphous carbon overcoats commonly used on magnetic recording disks was investigated via computer modeling, kinetic experiments, and surface energy measurements. Water is shown to interact via hydrogen bonding with the hydroxyl end groups of Zdol and the polar, carbon–oxygen functionalities on the carbon overcoat. The interaction between water and the hydrophobic perfluorinated backbone is, however, repulsive. The corrosion susceptibility of Zdol lubricated magnetic recording disks was also studied. Reduced levels of corrosion were observed when the total Zdol thickness, and/or the bonded thickness, were increased. The results are consistent with a heterogeneous corrosion mechanism in which electron transfer from the polar functionalities on the carbon overcoat to the surface adsorbed water is the rate limiting step. The disk lubricant inhibits the electrochemical conductivity of the disk surface by; (a) a screening of the e...

Plasma induced copolymerization of hexafluoropropylene and octafluoropropane

Ultrathin fluoropolymer films were deposited by a plasma-enhanced chemical vapor deposition process, from mixtures of hexafluoropropylene (C3F6) and octafluoropropane (C3F8) precursors. Different monomer feed compositions result in different rates of deposition. The C3F6 is the primary polymerizing species and C3F8 acts to reduce the deposition rate. The structure and composition of these films were characterized using Fourier transform infrared and angle-resolved x-ray photoelectron spectroscopy. The bulk F:C ratio is 1.1 for the homopolymer film (deposited from C3F6 only) and 1.4 for the copolymer film (deposited from C3F6+C3F8 monomer feed). The copolymer film has more –CF3 groups and has a more highly branched structure. The surface F:C ratio is 1.5 for the homopolymer and 1.7 for the copolymer film. The water contact angle increased with film thickness and with addition of C3F8 to the monomer feed. A mechanism is presented to describe how the addition of C3F8 modifies the polymerization process, caus...

Photodissociation of Cr(CO)6 in a molecular beam at 248 nm: observation of primary and secondary photoproducts by mass spectrometry

Photodissociation of Cr(CO)6 induced by a KrF* excimer laser (248 nm) was examined under molecular beam conditions, using a quadrupole mass spectrometer with electron impact ionization (11–19 eV) to detect the products as their respective ions. The ions of all Cr(CO)x products (x=0–5) were produced upon photodissociation of Cr(CO)6 at laser fluences from 1 to 10 mJ cm−2. The quantitative behavior of the Cr(CO)+x product ion yields vs laser fluence as well as statistical rate calculations indicate that Cr(CO)4 is the major product formed upon single‐photon dissociation of Cr(CO)6 under collisionless conditions at 248 nm. The additional Cr(CO)+x (x<4) product ions observed at low fluences are formed primarily by electron‐impact fragmentation of Cr(CO)4 in the mass spectrometer ionizer. At laser fluences ≳5 mJ cm−2, secondary photodissociation of Cr(CO)4 becomes important. Cr(CO)2 is assigned as the major photoproduct formed via secondary photodissociation of Cr(CO)4.

CW and pulsed UV laser-induced deposition from Cr(CO)6, Mo(CO)6, and W(CO)6

Abstract Photochemical deposition from Cr(CO) 6 , Mo(CO) 6 , and W(CO) 6 is described for processes induced by a CW frequency-doubled argon ion laser (257 nm) and a pulsed KrF ∗ excimer laser (248 mm). Kinetic data on the deposition process induced by the frequency-doubled argon ion laser indicate that deposition is initiated by single-photon dissociation of the hexacarbonyl in the gas phase. A more qualitative study of projection deposition from W(CO) 6 induced by the KrF ∗ laser indicates that gas-phase photodissociation of the hexacarbonyl is also important in the pulsed laser deposition process.