Adsorption of CF4 on graphite preplated with a monolayer of CF3Cl

Thomas, Petros; Velázquez, Daniel; Hess, G. B.

doi:10.1063/1.3560655

Cited by 4 publications

(1 citation statement)

References 22 publications

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“…The addition of a second component to such films, as is the case in the following study, adds an entirely new layer of complexity to the problem of simple adsorption on surfaces, as the interplay between adsorbateÀsubstrate interactions for each component, as well as adsorbateÀadsorbate interactions between components, changes the landscape considerably and invites new questions. A recent investigation by Thomas et al 29 into the competition between CF 4 molecules and CF 3 Cl monolayers at a graphite surface highlights this complexity and raises further questions about the precise factors that control this competition for adsorption and how they can be altered.…”

Section: ' Introductionmentioning

confidence: 99%

Characterization of CF₄/CF₃Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Leuty

Tsige

2011

J. Phys. Chem. B

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Molecular dynamics simulations of multilayer adsorption of binary mixtures of two tetrasubstituted halomethanes (CF(4) and CF(3)Br) on two very different substrates (graphite vs hydroxylated SiO(2)) were performed for three different bulk compositions (40%, 50%, and 60% CF(4)) and over a range of temperatures from 80 to 200 K. The goal of these simulations was to investigate in depth how these factors affect film structure, layer composition, lateral arrangement, and molecular orientation in the first adsorbed layer on each substrate. In line with a previous study of single-component adsorption on these surfaces, mixtures adsorbed on the hydroxylated SiO(2) surface show stable number density profiles that are largely independent of temperature, up to 160 K. This level of stability is essentially absent in the case of adsorption on graphite, which show densities and surface populations that are largely dependent on overall film composition, molecular orientation, and adsorbate-substrate interactions, in addition to system temperature. Further, the composition of the first adsorbed layer at each solid surface appears to be influenced by the choice of substrate, with CF(3)Br the majority component at the graphite surface for all compositions and temperatures, while the first adsorbed layer on hydroxylated SiO(2) more clearly mirrors the overall film composition at temperatures below 160 K.

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Section: ' Introductionmentioning

confidence: 99%

Characterization of CF₄/CF₃Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Leuty

Tsige

2011

J. Phys. Chem. B

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Phase diagram of the CF4 monolayer and bilayer on graphite

Thomas

Hess

2014

The Journal of Chemical Physics

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We report an experimental study of physisorbed monolayers and bilayers of CF4 on graphite using infrared reflection absorption spectroscopy supplemented by ellipsometry. The symmetric C-F stretch mode ν3 near 1283 cm(-1) in the gas is strongly blue shifted in the film by dynamic dipole coupling. This blue shift provides a very sensitive measure of the inter-molecular spacing in the monolayer and, less directly, in the bilayer. We find that important corrections are necessary to the volumetric coverage scales used in previous heat capacity and x-ray diffraction studies of this system. This requires quantitative and some qualitative changes to the previously proposed phase diagram. We find evidence for a new phase transition in the middle of the hexagonal incommensurate region and construct new phase diagrams in both the variables coverage-temperature and chemical potential-temperature. We determine the compressibility and thermal expansion in the low-pressure hexagonal incommensurate phase and values for the entropy change in several phase transitions. Below about 55 K there is evidence of solution of up to 7% of an impurity, most likely CO, in our monolayer but not the bilayer film.

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Solution and displacement in monolayer and multilayer binary films of SF6 and CF4 on graphite

Thomas

Grogan

Hess

2015

The Journal of Chemical Physics

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Infrared reflection absorption spectroscopy is used to study the evolution of binary physisorbed films on graphite. A predeposited monolayer of SF6 is exposed to slowly increasing pressure of CF4 at constant temperature between 80 and 113 K. Shifts in the frequencies of the dominant vibrational mode of each species due to resonant dipole-dipole coupling serve as proxies for the areal density of each species in the monolayer. If the initial SF6 film is far below saturation (coexistence with bulk solid), the SF6 can be largely displaced by continuous solution of CF4. However, if the initial SF6 layer is at or near saturation, a layer of CF4 condenses on top at a well defined CF4 pressure after only 2%-3% dilution of the SF6 layer. Simultaneously, most of the dissolved CF4 is withdrawn from the SF6 layer. With further increase in CF4 pressure, the CF4 layer is compressed and additional layers condense, while the SF6 layer is again diluted. Still, the SF6 layer retains about 90% concentration until the CF4 pressure is very close to saturation, at which point the SF6 is rapidly displaced, apparently going into dilute solution in the rapidly growing CF4 multilayer. Monte Carlo simulations are used to quantitatively relate measured frequency shifts to concentrations in the binary monolayer.

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Adsorption of CF4 on graphite preplated with a monolayer of CF3Cl

Cited by 4 publications

References 22 publications

Characterization of CF₄/CF₃Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Characterization of CF₄/CF₃Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Phase diagram of the CF4 monolayer and bilayer on graphite

Solution and displacement in monolayer and multilayer binary films of SF6 and CF4 on graphite

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Adsorption of CF4 on graphite preplated with a monolayer of CF3Cl

Cited by 4 publications

References 22 publications

Characterization of CF4/CF3Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Characterization of CF4/CF3Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Phase diagram of the CF4 monolayer and bilayer on graphite

Solution and displacement in monolayer and multilayer binary films of SF6 and CF4 on graphite

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Product

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Characterization of CF₄/CF₃Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation

Characterization of CF₄/CF₃Br Binary Mixture Adsorption on Hydrophobic/Hydrophilic Surfaces via Atomistic MD Simulation