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Gellman, Andrew J.; Paserba, Kris R.; Vaidyanathan, Nithya

doi:10.1023/a:1014089701527

Cited by 11 publications

(5 citation statements)

References 6 publications

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“…These values are much higher than k B T/h ≈ 10 13 s -1 . Pre-exponents similar in magnitude have been observed for desorption of n-alkanes [C n H 2n+2 , n ) 5 to 60], 14,17 poly(ethylene glycol) dimethyl ethers [CH 3 (OCH 2 CH 2 ) m OCH 3 , m ) 1 to ∼22] [20], and poly(ethylene glycols) 18 from graphite. These high values of the desorption pre-exponents can been attributed to conformational isomerism in the desorbing species.…”

Section: Energetics Of Lubricant Evaporation From Surfacessupporting

confidence: 53%

“…This is not surprising since the desorption rates of longer chain molecules similar in nature to Zdol also exhibit simple first-order desorption kinetics on graphite. Desorption of n -alkanes, , poly(ethylene glycol) dimethyl ethers, and poly(ethylene glycols) 18 from graphite was found to occur with first-order kinetics. The observation of first-order kinetics for desorption of poly(ethylene glycol) is particularly interesting in the context of the work reported here since the poly(ethylene glycol)s are hydrocarbon analogues of Fomblin Zdol.…”

Section: Discussionmentioning

confidence: 95%

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Desorption Kinetics and Energetics of Monodisperse Fomblin Zdol from Carbon Surfaces

Paserba

Gellman

2001

J. Phys. Chem. B

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Desorption is one of the mechanisms of lubricant loss from the surfaces of data storage media. This work has studied the desorption of monodisperse samples of a typical perfluoropolyalkyl ether lubricant, Fomblin Zdol, from the surface of graphite. Desorption is observed to occur molecularly through a first-order process with an energy barrier to desorption, ∆E des ‡ , that is independent of coverage but is dependent on molecular weight. The ∆E des ‡ of 994 and 1329 g/mole fractions were found to be 128 ( 2 kJ/mol and 155 ( 2 kJ/mol, respectively. The pre-exponents, V, of the first-order desorption rate constant were found to have values of 10 19.6(0.3 s -1 and 10 21.1(0.3 s -1 for the 994 and 1329 g/mole Zdol fractions, respectively. These results clearly reveal the chain length dependence of the ∆E des ‡ , and the high values of the pre-exponents are similar to those observed for desorption of other oligomeric species from graphite.

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Section: Energetics Of Lubricant Evaporation From Surfacessupporting

confidence: 53%

Section: Discussionmentioning

confidence: 95%

Desorption Kinetics and Energetics of Monodisperse Fomblin Zdol from Carbon Surfaces

Paserba

Gellman

2001

J. Phys. Chem. B

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“…Since then further experimental work has examined the desorption kinetics of poly-(ethylene glycol)s [HO(CH 2 CH 2 O) n H] and poly(ethylene glycol) dimethyl ethers [CH 3 O(CH 2 CH 2 O) n CH 3 ] with chain lengths covering a range similar to that used in the study of the alkanes. 22 The chain length dependence of the ∆E des ‡ for poly-(ethylene glycol) dimethyl ethers adsorbed on graphite is almost identical to that observed for the alkanes. The chain length dependence of the ∆E des ‡ for poly(ethylene glycol)s adsorbed on graphite is also nonlinear but appears to reveal the effects of the functional endgroups for short chain lengths.…”

Section: Introductionsupporting

confidence: 52%

“…Empirically it was shown that the desorption barriers could be fit to a power law of the form ( N ) = a + bN γ , with the exponent having a value of γ = 0.50 ± 0.01. Since then further experimental work has examined the desorption kinetics of poly(ethylene glycol)s [HO(CH 2 CH 2 O) n H] and poly(ethylene glycol) dimethyl ethers [CH 3 O(CH 2 CH 2 O) n CH 3 ] with chain lengths covering a range similar to that used in the study of the alkanes . The chain length dependence of the for poly(ethylene glycol) dimethyl ethers adsorbed on graphite is almost identical to that observed for the alkanes.…”

Section: Introductionmentioning

confidence: 89%

Kinetics and Mechanism of Oligomer Desorption from Surfaces: n-Alkanes on Graphite

Gellman

Paserba

2002

J. Phys. Chem. B

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A previous study of the desorption of straight-chain alkanes [H(CH 2 ) N H, N ) 5-60] from the surface of graphite has revealed that the measured desorption barriers, ∆E des ‡ , have a nonlinear dependence on the chain length (Paserba, K. R.; Gellman, A. J. Phys. ReV. Lett. 2001, 86 (19), 4338). A model is proposed for the mechanism of oligomer desorption that accounts for the chain length dependence of the ∆E des ‡ through consideration of both the energy and entropy of oligomers interacting with a surface. The segments of the oligomer are identified with individual backbone bonds such that an alkane with N carbon atoms has I ) N -1 segments. The oligomer segments are rapidly attaching to and detaching from the surface such that the various partially detached oligomers are in equilibrium with one another and can be classified by the number of detached segments i. Equilibrium among the partially detached oligomers is dictated by their relative free energies ∆A i , which are dependent on the numbers of detached segments. The energy E i of an oligomer is simply linear in the number of detached segments. The entropy, S i , is given by the statistics for detachment of i of I segments from the surface and by the number of trans-gauche conformations about each detached C-C bond. Finally, desorption is irreversible and occurs via a transition state with all segments detached from the surface. This model has been used to derive an expression for the measured ∆E des ‡ which accounts for the contributions of both segment-surface detachment and trans-gauche conformational isomerism. The theory accurately reproduces the nonlinear dependence of the ∆E des ‡ on chain length for alkane desorption from graphite.

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“…The DLC overcoats used in this work were supplied from a commercial manufacturer and not fully characterized; however, past experience in studies of fluoroether lubricant adsorption on similar films provided by various commercial manufacturers has shown that there is a great deal of consistency among them, independent of their source of origin. [13][14][15][16][17][18][19][20][21][22][23] A 1 cm 2 square sample with the DLC film deposited on one side was mounted inside the UHV chamber on a Ta support plate. The plate could be heated resistively and cooled with liquid nitrogen through thermal contact with a liquid nitrogen cold finger.…”

Section: Methodsmentioning

confidence: 99%

Controlling the work function of a diamond-like carbon surface by fluorination with XeF2

Tarditi

Kondratyuk

Wong³

et al. 2010

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Thin diamond-like carbon films were subjected to fluorination with gaseous XeF 2 under ultrahigh vacuum conditions in order to increase the work function of the diamond-like carbon surface. Changes in the work function and surface composition were monitored with UV photoemission spectroscopy and x-ray photoemission spectroscopy, respectively. Successive XeF 2 exposures raised the work function by as much as 1.55 eV. Surprisingly, approximately half of the increase in the work function occurred while the coverage of fluorine remained below 0.02 monolayers ͑ML͒. This suggests that initial doses of XeF 2 remove extrinsic adsorbates from the diamond-like carbon film and that fluorine desorbs with the reaction products. Increasing the exposure of the diamond-like carbon to XeF 2 leads to the expected covalent fluorination of the surface, which saturates at fluorine coverages of 6 F atoms/ nm 2 ͑ϳ0.3 ML͒. Annealing of the diamond-like carbon to temperatures above 850 K was required to reduce the surface fluorine concentration to undetectable levels. This did not, however, cause the work function to return to its original, prefluorination value.

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Untitled

Cited by 11 publications

References 6 publications

Desorption Kinetics and Energetics of Monodisperse Fomblin Zdol from Carbon Surfaces

Desorption Kinetics and Energetics of Monodisperse Fomblin Zdol from Carbon Surfaces

Kinetics and Mechanism of Oligomer Desorption from Surfaces: n-Alkanes on Graphite

Controlling the work function of a diamond-like carbon surface by fluorination with XeF2

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