Probing oxygen vacancy concentration and homogeneity in solid-oxide fuel-cell cathode materials on the subunit-cell level.

Oxygen vacancy distributions and dynamics directly control the operation of solid-oxide fuel cells and are intrinsically coupled with magnetic, electronic and transport properties of oxides. For understanding the atomistic mechanisms involved during operation of the cell it is highly desirable to know the distribution of vacancies on the unit-cell scale. Here, we develop an approach for direct mapping of oxygen vacancy concentrations based on local lattice parameter measurements by scanning transmission electron microscopy.

Calculations of scattering of N2 molecules from Ru(0001).

Recent experimental measurements of state resolved scattering of nitrogen molecules from a Ru(0001) surface are discussed in comparison with a mixed quantum-classical theory that has given reasonable explanations for similar data on other systems. Acceptable agreement between data and calculations is obtained, but only upon assuming an effective mass of the surface equal to 2.3 times the mass of a single Ru atom.

Translational to rotational energy transfer in molecule-surface collisions.

A theoretical approach that combines classical mechanics for treating translational and rotational degrees of freedom and quantum mechanics for describing the excitation of internal molecular modes is applied to the scattering of diatomic molecules from metal surfaces. Calculations are carried out for determining the extent of energy transfer to the rotational degrees of freedom of the projectile molecule. For the case of observed spectra of intensity versus final rotational energy, quantitative agreement with available experimental data for the scattering of NO and N(2) from close packed metal surfaces is obtained.

Calculations of accommodation coefficients for diatomic molecular gases.

A theoretical study of energy and momentum accommodation coefficients and reduced force coefficients for molecular gases exchanging energy with surfaces has been carried out. The theoretical model uses classical mechanics for describing translational and rotational motions while internal molecular vibrational modes are treated quantum mechanically. Calculations for diatomic molecular gases are compared with recent measurements using hypersonic beams of N2 incident on SiO2 layers deposited on Kapton substrates.

Scattering of O2 from AL111.

Experimental results are presented for the scattering of well-defined beams of molecular oxygen incident on clean Al(111). The data consist of scattered angular distributions measured as a function of incident angle, and for fixed incident angle, the dependence on surface temperature of the angular distributions. The measurements are interpreted in terms of a scattering theory that treats the exchange of energy between the translational and rotational motions of the molecule and the phonons of the surface using classical dynamics.