Comparative surface dynamics of amorphous and semicrystalline polymer films

Becker, James T.; Brown, Ryan D.; Killelea, Daniel R.; Yuan, Hanqiu; Sibener, S. J.

doi:10.1073/pnas.1008268107

Cited by 24 publications

(21 citation statements)

References 56 publications

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“…The influence of the perpendicular motions was removed from each decay rate, leaving only the parallel contributions, as shown recently for a semicrystalline polymer film. 60 Averaging over the different rates, the parallel mean-square displacements were found to be ͑7.1Ϯ 5.1͒ ϫ 10 −4 Å 2 K −1 for CH 3 -Si͑111͒ and ͑7.2Ϯ 5.3͒ ϫ 10 −4 Å 2 K −1 for CD 3 -Si͑111͒ surfaces, respectively.…”

Section: ͑9͒mentioning

confidence: 99%

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3–Si(111) and CD3–Si(111) surfaces

Becker

Brown

Johansson

et al. 2010

The Journal of Chemical Physics

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The surface structure and vibrational dynamics of CH 3 -Si͑111͒ and CD 3 -Si͑111͒ surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited a lattice constant of 3.82 Å, in accordance with the spacing of the silicon underlayer. The excellent quality of the observed diffraction patterns, along with minimal diffuse background, indicated a high degree of long-range ordering and a low defect density for this interface. The vibrational dynamics were investigated by measurement of the Debye-Waller attenuation of the elastic diffraction peaks as the surface temperature was increased. The angular dependence of the specular ͑ i = f ͒ decay revealed perpendicular mean-square displacements of 1.0ϫ 10 −5 Å 2 K −1 for the CH 3 -Si͑111͒ surface and 1.2ϫ 10 −5 Å 2 K −1 for the CD 3 -Si͑111͒ surface, and a He-surface attractive well depth of ϳ7 meV. The effective surface Debye temperatures were calculated to be 983 K for the CH 3 -Si͑111͒ surface and 824 K for the CD 3 -Si͑111͒ surface. These relatively large Debye temperatures suggest that collisional energy accommodation at the surface occurs primarily through the Si-C local molecular modes. The parallel mean-square displacements were 7.1ϫ 10 −4 and 7.2ϫ 10 −4 Å 2 K −1 for the CH 3 -Si͑111͒ and CD 3 -Si͑111͒ surfaces, respectively. The observed increase in thermal motion is consistent with the interaction between the helium atoms and Si-CH 3 bending modes. These experiments have thus yielded detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces.

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Section: ͑9͒mentioning

confidence: 99%

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3–Si(111) and CD3–Si(111) surfaces

Becker

Brown

Johansson

et al. 2010

The Journal of Chemical Physics

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“…Helium atom scattering is an enormously powerful tool to elucidate the surface structure and surface vibrations of crystalline solids, organic monolayers, and even polymer films. − The diffraction features that make this technique so useful are unfortunately lost for room-temperature liquids because of long-range disorder and extensive thermal motions that promote energy transfer between the He and surface atoms. However, it may still be possible to glean insights into interfacial motions and packing by replacing He atom scattering with He atom evaporation from liquids .…”

Section: Introductionmentioning

confidence: 99%

Probing Gas–Liquid Interfacial Dynamics by Helium Evaporation from Hydrocarbon Liquids and Jet Fuels

et al. 2015

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We have monitored the speeds of evaporating helium atoms dissolved in liquid octane, isooctane, 1-methylnaphthalene, dodecane, squalane, ethylene glycol, and two jet fuels. In all cases, the average kinetic energies of the evaporating He atoms exceed the Maxwellian value of 2RT. The energies roughly track solvent surface tensions; this correlation may reflect the tighter packing and attractions of interfacial solvent molecules that restrict the gaps through which He atoms escape. Mixtures of dodecane, squalane, and 1-methylnaphthalene generate He evaporation energies that lie between the pure liquid values. We find, however, that He atoms evaporate from pure 1-methylnaphthalene with kinetic energies lower than expected based on its high surface tension, perhaps because the sideways packing of the aromatic rings provides more direct channels for the escaping He atoms. Additionally, He evaporates from two complex fuel mixtures, Jet A and JP-8, with nearly identical energies, implying that the extra additives in JP-8 do not segregate to the surface in ways that alter the dynamics of evaporation. ■ INTRODUCTIONHelium atom scattering is an enormously powerful tool to elucidate the surface structure and surface vibrations of crystalline solids, organic monolayers, and even polymer films. 1−5 The diffraction features that make this technique so useful are unfortunately lost for room-temperature liquids because of long-range disorder and extensive thermal motions that promote energy transfer between the He and surface atoms. However, it may still be possible to glean insights into interfacial motions and packing by replacing He atom scattering with He atom evaporation from liquids. 6 We continue our studies here by measuring the energy distributions of He atoms evaporating from a wide range of linear and branched hydrocarbon liquids, including mixtures, jet fuels, and ethylene glycol (as a model for a deicing additive). The experiments are performed by dissolving He atoms into each liquid, injecting the liquids into a vacuum as microjets, 7,8 and monitoring the velocities of the evaporating He atoms.The evaporation of He atoms dissolved in hydrocarbons, alcohols, and salty water appears to be special: these small and weakly attractive atoms evaporate at speeds that are faster than predicted by a Maxwell−Boltzmann (MB) distribution. This behavior stands in contrast to larger and more polarizable species such as Ar, N 2 , O 2 , H 2 O, CO 2 , HCl, and HNO 3 , which evaporate with flux-weighted average energies of 2RT liq consistent with a MB energy distribution for a liquid at temperature T liq . 6,9 We recently found that the He speed distributions depend on the nature of the solvent molecules, with average kinetic energies ranging from 1.14 × 2RT liq for He evaporation from dodecane to 1.7 × 2RT liq from a 7.5 M LiBr/ H 2 O solution. 6 Detailed balancing of the incoming and outgoing fluxes implies that He atoms must preferentially dissolve at higher kinetic energies as well. 10 In this timereversed picture, the attractive...

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“…Helium atom scattering provides known sensitivity to organic adsorbates, ,, and here we determine the benzene–substrate energy landscape from helium spin–echo (HeSE) measurements of the thermal motion of adsorbed benzene. The principle of the technique is illustrated in Figure a, while a detailed description has been given elsewhere. , In brief, helium atoms scatter from mobile adsorbates on the surface, providing a measurement of the correlation in their positions with time.…”

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Mass Transport in Surface Diffusion of van der Waals Bonded Systems: Boosted by Rotations?

Hedgeland

Sacchi

Singh

et al. 2016

J. Phys. Chem. Lett.

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Mass transport at a surface is a key factor in heterogeneous catalysis. The rate is determined by excitation across a translational barrier and depends on the energy landscape and the coupling to the thermal bath of the surface. Here we use helium spin− echo spectroscopy to track the microscopic motion of benzene adsorbed on Cu(001) at low coverage (θ ∼ 0.07 ML). Specifically, our combined experimental and computational data determine both the absolute rate and mechanism of the molecular motion. The observed rate is significantly higher by a factor of 3.0 ± 0.1 than is possible in a conventional, point-particle model and can be understood only by including additional molecular (rotational) coordinates. We argue that the effect can be described as an entropic contribution that enhances the population of molecules in the transition state. The process is generally relevant to molecular systems and illustrates the importance of the pre-exponential factor alongside the activation barrier in studies of surface kinetics.

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Comparative surface dynamics of amorphous and semicrystalline polymer films

Cited by 24 publications

References 56 publications

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3–Si(111) and CD3–Si(111) surfaces

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3–Si(111) and CD3–Si(111) surfaces

Probing Gas–Liquid Interfacial Dynamics by Helium Evaporation from Hydrocarbon Liquids and Jet Fuels

Mass Transport in Surface Diffusion of van der Waals Bonded Systems: Boosted by Rotations?

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