Inelastic Scattering Dynamics of Ar from a Perfluorinated Self-Assembled Monolayer Surface

Abstract

Dynamics of Ar atom collisions with a perfluorinated alkanethiol self-assembled monolayer (F-SAM) surface on gold were investigated by classical trajectory simulations and atomic beam scattering techniques. Both explicit-atom (EA) and united-atom (UA) models were used to represent the F-SAM surface; in the UA model, the CF3 and CF2 units are represented as single pseudoatoms. Additionally the nonbonded interactions in both models are different. The simulations show the three limiting mechanisms expected for collisions of rare gas atoms (or small molecules) with SAMs, that is, direct scattering, physisorption, and penetration. Surface penetration results in a translational energy distribution, P(Ef), that can be approximately fit to the Boltzmann for thermal desorption, suggesting that surface accommodation is attained to a large extent. Fluorination of the alkanethiol monolayer leads to less energy transfer in Ar collisions. This results from a denser and stiffer surface structure in comparison with that of the alkanethiol SAM, which introduces constraints for conformational changes which play a significant role in the energy-transfer process. The trajectory simulations predict P(Ef) distributions in quite good agreement with those observed in the experiments. The results obtained with the EA and UA models are in reasonably good agreement, although there are some differences.

Energy Transfer and Thermal Accommodation in Ozone Scattering from a Perfluorinated Self-Assembled Monolayer

“…9 Figure 6 and Table 3 show the fits of our model to the Ar + F-SAM results. In the limit of high incident energies, 1.8% of the incident energy goes to translation and the remaining 98.2% goes to the surface.…”

“…The first term V surf describes the interactions that take place in the F-SAM surface, 9,10 V O 3 is the ozone potential function, and V O 3 −surf accounts for the interaction between ozone and the surface. The F-SAM surface consists of 48 chains of CF 3 (CF 2 ) 7 S radicals adsorbed on a single layer of 225 Au atoms, which are kept fixed during the dynamics simulations; all atoms are explicitly considered in our model.…”

Dynamics of the Reaction of O(3P) Atoms with Alkylthiol Self-assembled Monolayers

“…[5][6][7] Fairbrother and co-workers have also examined the destruction of alkyl, fluorinated, and X-raymodified SAMs by a thermalized mixture of atomic and molecular oxygen (O( The first such experiment was carried out by Naaman and coworkers 10 using molecular beams of He, Ar, NO, and O 2 from alkyl and fluorinated SAMs and time-of-flight mass spectrometry (TOF-MS) to detect the scattered species. Subsequent work by Siebener and co-workers [11][12][13][14][15] and, most comprehensively, by Morris and co-workers [16][17][18][19][20][21][22][23][24][25][26] has investigated the effects of varying the identity of the impinging gas, impact angle, final angle, initial energy, monolayer temperature, SAM terminal group, alkyl chain length, and metal substrate (hence, surface density). This has led to a wealth of information on factors affecting energy transfer at the gas-SAM interface.…”

Gas–Surface Energy Exchange in Collisions of Helium Atoms with Aligned Single-Walled Carbon Nanotube Arrays

“…[17][18][19][20][21][22][23][24][25][26][27][28] Molecular beam scattering experiments and molecular dynamics (MD) simulations revealed the dominant factors determining the energy exchange efficiency for a variety of gas/SAM surface systems such as the mass of a gas molecule and the terminal group of SAM molecules, [19][20][21][22] attractive forces between gas molecules and the SAM terminal groups, 21,[23][24][25] surface stiffness due to intramonolayer hydrogen bonding, 21,23,26 the chain length of SAM molecules, 26 the deformation of SAM chains, 19,20,27,28 and the penetration of gas molecules into SAM layer. 28 The versatility of functional groups and tail length makes SAMs attractive for surface coatings to control gassurface interactions. Having better thermal stability than SAMs, VA-SWNT films would be another promising option of surface coating material especially for devices operating over a wide range of temperature.…”