Francesc Salvat-Pujol

Surface excitations in electron spectroscopy. Part I: dielectric formalism and Monte Carlo algorithm.

The theory describing energy losses of charged non-relativistic projectiles crossing a planar interface is derived on the basis of the Maxwell equations, outlining the physical assumptions of the model in great detail. The employed approach is very general in that various common models for surface excitations (such as the specular reflection model) can be obtained by an appropriate choice of parameter values. The dynamics of charged projectiles near surfaces is examined by calculations of the induced surface charge and the depth- and direction-dependent differential inelastic inverse mean free path (DIIMFP) and stopping power. The effect of several simplifications frequently encountered in the literature is investigated: differences of up to 100% are found in heights, widths, and positions of peaks in the DIIMFP. The presented model is implemented in a Monte Carlo algorithm for the simulation of the electron transport relevant for surface electron spectroscopy. Simulated reflection electron energy loss spectra are in good agreement with experiment on an absolute scale. Copyright

First-principles determination of Heisenberg Hamiltonian parameters for the spin-12kagome antiferromagnet ZnCu3(OH)6Cl2

Herbertsmithite (ZnCu3(OH)6Cl2) is often discussed as the best realization of the highly frustrated antiferromagnetic kagome lattice known so far. We employ density functional theory calculations to determine eight exchange coupling constants of the underlying Heisenberg Hamiltonian. We find the nearest neighbour coupling J1 to exceed all other couplings by far. However, next-nearest neighbour kagome layer couplings of 0.019 J1 and interlayer couplings of up to -0.035 J1 slightly modify the perfect antiferromagnetic kagome Hamiltonian. Interestingly, the largest interlayer coupling is ferromagnetic even without Cu impurities in the Zn layer. In addition, we validate our DFT approach by applying it to kapellasite, a polymorph of herbertsmithite which is known experimentally to exhibit competing exchange interactions.

Contribution of surface plasmon decay to secondary electron emission from an Al surface

Spectra of secondary electrons (SE) emitted from a polycrystalline Al surface have been measured in coincidence with 500 eV‐electrons for energy losses between 10 and 155 eV. The spectra for a given energy loss are qualitatively similar, consisting of surface and volume plasmon decay and a contribution attributable to direct electron–electron scattering. The similarity of the contribution of surface and volume plasmon decay in the SE spectra proves directly that electron multiple scattering is governed by a Markov‐type process. The average value of the surface plasmon decay contribution to the SE spectrum amounts to ∼25%.

Physics-based simulation models for EBSD: advances and challenges

EBSD has evolved into an effective tool for microstructure investigations in the scanning electron microscope. The purpose of this contribution is to give an overview of various simulation approaches for EBSD Kikuchi patterns and to discuss some of the underlying physical mechanisms.

Angular dependence of electron induced surface plasmon excitation

The angular dependence of the probability for electron induced surface plasmon excitation has been measured on semi-infinite planar polycrystalline Al and Au surfaces for energies between 500 and 4000 eV. The results agree accurately with the simple model in which the surface excitation probability is proportional to the surface penetration time. However, the penetration time differs from the rectilinear motion model due to deflections during elastic collisions within the surface scattering zone. A simple formula to account for the effect of elastic scattering in the surface scattering zone is given.

Contribution of Surface Plasmon Decay to Secondary Electron Emission from an Al Surface

Secondary electron spectra emitted from polycrystalline Al have been measured in coincidence with 500 eV electrons reflected after undergoing a given energy loss. Contributions from bulk- and surface-plasmon decay have been observed, as well as contributions from LVV Auger electrons and electron-electron scattering.