K. D. Gibson

Experimental and simulation study of neon collision dynamics with a 1-decanethiol monolayer

A study of the energy accommodation of neon colliding with a crystalline self-assembled 1-decanethiol monolayer adsorbed on Au(111) is presented. The intensity and velocity dependencies of the scattered neon as a function of incident angle and energy were experimentally measured. Scattering calculations show good agreement with these results, which allows us to examine the detailed dynamics of the energy and momentum exchange at the surface. Simulation results show that interaction times are, at most, a few picoseconds. Even for these short times, energy exchange with the surface, both normal and in-plane, is very rapid. An important factor in determining the efficiency of energy exchange is the location at which the neon collides with the highly corrugated and structurally dynamic unit cell. Moreover, our combined experimental and theoretical results confirm that these are truly surface collisions in that neon penetration into the organic boundary layer does not occur, even for the highest incident energies explored, 560 meV.

Experiments and simulations of Ar scattering from an ordered 1-decanethiol–Au(111) monolayer

A study of the scattering of Ar from a well-ordered standing-up phase of 1-decanethiol adsorbed on Au(111) at surface temperatures from 110 to 185 K is presented. The final energies and intensities were measured as a function of incident polar and azimuthal angles using incident energies from 65 to 600 meV. These experimental results are compared to classical trajectory calculations. Scattering shows two distinct exit channels. The higher energies are due to direct inelastic scattering and have the greatest intensities at glancing incident and final angles. The lower energy channel is due to trapping-desorption; it has a Maxwell–Boltzmann energy distribution at the surface temperature and a cosine angular intensity profile. The simulations show that the timescale for normal momentum accommodation is very fast. The parallel momentum accommodation takes slightly longer, dependent on the initial conditions, but is still complete within only a few picoseconds. The result is that much of the Ar undergoes trapp...

Lattice Dynamics of Rare Gas Multilayers on the Ag(111) Surface. Theory and Experiment.

We discuss the lattice dynamics of argon, krypton, and xenon overlayers on the Ag(111) surface. We consider monolayer, bilayer, trilayer and 25 layer films of each of these adsorbates. Data are also presented on the dispersion relations of selected branches of the phonon spectra of these overlayers. The data have been obtained by the method of angle‐resolved inelastic He scattering. Several models of the lattice dynamics are compared with the data. It is concluded that the gas phase potentials proposed by Barker and co‐workers prove suitable for a description of lateral interactions between the adsorbates, within the accuracy of the available data, provided that the phonon spectra are calculated for a lattice with the experimentally determined lattice constants.

The pulmonary histopathologic manifestations of the anti-Jo-1 tRNA synthetase syndrome.

Of the idiopathic inflammatory myopathies, the anti-aminoacyl tRNA synthetase syndrome has the greatest association with interstitial lung disease (ILD). We reviewed 13 open surgical lung biopsies, four autopsies, and three native lungs resected at transplantation, for pulmonary ILD associated with the presence of anti-histidyl tRNA synthetase (anti-Jo-1) autoantibodies. Fifty percent (N=10) of patients presented with an acute decompensation of pulmonary function manifested as diffuse alveolar damage, although in five patients (25%) this marked diminution in function was superimposed on an underlying chronic interstitial pneumonia (usual interstitial pneumonia (three); nonspecific interstitial pneumonia(two)). Seven (35%) patients had usual interstitial pneumonia and two (10%) had nonspecific interstitial pneumonia exclusively, whereas one patient presented with an organizing pneumonia (5%). This study is the first to highlight the high biopsy incidence of diffuse alveolar damage in this patient population both de novo and superimposed on underlying chronic ILD, and also shows that usual interstitial pneumonia remains a significant pattern of interstitial injury in this autoimmune group. On the basis of coexisting patterns of lung injury, this study also suggests that nonspecific interstitial pneumonia in connective tissue disorders may progress over time to a usual interstitial pneumonia pattern of fibrosis, an observation that could be better assessed with future inclusion of autopsy and transplanted native lungs in study groups.

The adsorption of water on clean and oxygen predosed Rh(111): Surface templating via (1×1)-O/Rh(111) induces formation of a novel high-density interfacial ice structure

Water adsorbed on clean Rh(111) forms an ordered structure with a (∛×∛)R30° diffraction pattern. This is facilitated by the close match of surface lattice constants for Rh(111) and the (0001) face of hexagonal ice, Ih. The preadsorption of small quantities of disordered oxygen improves the long-range ordering of the water overlayer. When a well-ordered half-monolayer of oxygen is grown on the Rh(111) prior to H2O exposure, there is no evidence of any long-range ordering of the water. However, when H2O is adsorbed on a (1×1)-O/Rh(111) surface, where there is a well-ordered monolayer of adsorbed oxygen, the adsorbed H2O forms a new high-density structure exhibiting a (1×1) diffraction pattern. The adsorbed H2O structure is epitaxial with respect to the underlying oxygen and rhodium. This structure persists for many layers of adsorbed water. On the clean Rh(111) surface, water molecules are adsorbed through the oxygen lone pair orbital. When the surface is fully covered with oxygen, the first layer of water ...

Carbon monoxide oxidation on Rh(111): Velocity and angular distributions of the CO2 product

The velocity and angular distributions of CO2 produced by CO oxidation on Rh(111) have been measured as a function of surface temperature and oxygen coverage. Both the velocity and angular distributions are bimodal. The velocities of one component are well fit by a Maxwell–Boltzmann distribution at the surface temperature, and the angular distribution of its intensity is cosine. The second component is non‐Boltzmann, and the angular distribution is sharply peaked toward normal. The average energy of this feature is a very strong function of the surface temperature, increasing with a slope of 8.7kb, where kb is the Boltzmann constant, between 475 K and 700 K. Surprisal analysis proves useful in condensing and interpreting these data.

Inelastic helium scattering studies of ordered Ar, Kr, and Xe monolayers physisorbed on Ag(111): dispersion curves, scattering cross sections, and excitation line shapes

This paper is the first in a series covering our experiments examining the physical properties of ordered overlayers of Ar, Kr, and Xe physisorbed on Ag(111). In this paper, we examine the desorption kinetics of the Xe monolayer/Ag(111) system. Desorption is zeroth order until ∼90% of the monolayer has desorbed, then becomes first order. We also measured the inelastic scattering of an 18 meV He beam from unconstrained monolayers of (111) oriented Ar, Kr, and Xe. The transitions are mapped across the entire surface Brillouin zone from Γ to M. The data are dispersionless, indicating that for the measured mode the adatoms are behaving as independent Einstein oscillators. Parametrized physisorption potentials for RG–Ag(111) [RG=Ar, Kr, Xe] are constructed using these results. Inelastic scattering probabilities and linewidths are also presented. The inelastic scattering probabilities vary by at most a factor of 3 across the entire surface Brillouin zone, and are reported as a function of incident angle, fina...

High density adsorbed oxygen on Rh(111) and enhanced routes to metallic oxidation using atomic oxygen

Exposure of Rh(111) to atomic oxygen leads to the facile formation of a full-coverage and ordered (1×1)-O monolayer which is stable at room temperature. This result differs markedly from the half-coverage (2×1)-O overlayer which forms at saturation when using molecular oxygen. This demonstrates that kinetic rather than thermodynamic constraints inhibit the formation of dense oxygen overlayers when O2 is the oxidant. We also report that O absorption into the bulk proceeds much more readily when using O rather than O2, a finding with direct implications for enhanced methods of low-temperature metallic oxidation. These results demonstrate that there are important fundamental differences in the way in which low-energy beams of atomic and molecular oxygen interact with metals.

Determination of the sticking coefficient and scattering dynamics of water on ice using molecular beam techniques

The sticking coefficient for D(2)O impinging on crystalline D(2)O ice was determined for incident translational energies between 0.3 and 0.7 eV and for H(2)O on crystalline H(2)O ice at 0.3 eV. These experiments were done using directed molecular beams, allowing for precise control of the incident angle and energy. Experiments were also performed to measure the intensity and energy of the scattered molecules as a function of scattering angle. These results show that the sticking coefficient was near unity, slightly increasing with decreasing incident energy. However, even at the lowest incident energy, some D(2)O did not stick and was scattered from the ice surface. We observe under these conditions that the sticking probability asymptotically approaches but does not reach unity for water sticking on water ice. We also present evidence that the scattered fraction is consistent with a binary collision; the molecules are scattered promptly. These results are especially relevant for condensation processes occurring under nonequilibrium conditions, such as those found in astrophysical systems.

Elastic helium scattering studies of ordered overlayers of Ar, Kr, and Xe physisorbed on Ag(111)

We describe experiments that measured the angle resolved intensity of He (Ei=18 and 66 meV) elastically scattering from the surfaces of rare gas overlayers physisorbed on Ag(111). These studies were done on a layer‐by‐layer basis for 1, 2, 3, and ∼25 ordered overlayers of Ar, Kr, and Xe. Two types of experiments are described. The first is diffraction, where the scattered He intensity was measured as a function of the detector angle, with the incident polar and azimuthal angles held constant. In the second type of experiment, selective adsorption, we measured the specular intensity as a function of incident angle. The purpose of these experiments was to examine the He–surface potential, to assess the relative contributions that various He–rare gas pair potentials, nonadditive multibody terms, and He–substrate interactions make to the systems studied. The experiments are compared with the results of accurate close‐coupling calculations, in order to quantitatively perform these assessments. The comparisons ...