Analytical applications of elastic electron backscattering from surfaces

Measurements of probability of elastic electron backscattering from surfaces can provide information on physical properties of the surface region with thickness comparable to the inelastic mean free path (IMFP) of electrons. The analytical technique, based on such measurements, is known as elastic peak electron spectroscopy (EPES). The most frequent application of EPES is the determination of the IMFP in solids. However, this technique can also be used to measure overlayer thickness, or to determine surface composition.

Quantitative applications of EPES, addressed here, require a reliable theoretical model describing the elastic backscattering probability from surfaces with a given structure and composition. Unfortunately, there is no simple analytical model which describes the elastic backscattering probability with an acceptable accuracy. Values of the elastic backscattering probability are usually estimated from Monte Carlo (MC) simulations of elastic backscattering events, since the theoretical model implemented in the MC scheme seems closest to reality, as compared with models leading to different analytical expressions. It is shown that the reliability of the theory is associated with accuracy of the parameters needed in the calculations. The most important parameters are the differential elastic scattering cross-sections which are presently known, especially in some angular regions, with limited accuracy. The IMFP values, determined in different laboratories via EPES, exhibit a considerable scatter, which may be due to the fact that different experimental geometries are used in measurements. Other sources of errors are briefly discussed.     

Monte Carlo simulation of full energy spectrum of electrons emitted from silicon in Auger electron spectroscopy

A Monte Carlo simulation including surface excitation, Auger electron‐ and secondary electron production has been performed to calculate the energy spectrum of electrons emitted from silicon in Auger electron spectroscopy (AES), covering the full energy range from the elastic peak down to the true‐secondary‐electron peak. The work aims to provide a more comprehensive understanding of the experimental AES spectrum by integrating the up‐to‐date knowledge of electron scattering and electronic excitation near the solid surface region. The Monte Carlo simulation model of beam–sample interaction includes the atomic ionization and relaxation for Auger electron production with Casnati's ionization cross section, surface plasmon excitation and bulk plasmon excitation as well as other bulk electronic excitation for inelastic scattering of electrons (including primary electrons, Auger electrons and secondary electrons) through a dielectric functional approach, cascade secondary electron production in electron inelastic scattering events, and electron elastic scattering with use of Mott's cross section. The simulated energy spectrum for Si sample describes very well the experimental AES EN(E) spectrum measured with a cylindrical mirror analyzer for primary energies ranging from 500 eV to 3000 eV. Surface excitation is found to affect strongly the loss peak shape and the intensities of the elastic peak and Auger peak, and weakly the low energy backscattering background, but it has less effect to high energy backscattering background and the Auger electron peak shape. Copyright © 2014 John Wiley & Sons, Ltd.     

Direct X‐Ray Scattering Evidence for Metal–Metal Interactions in Solution at the Molecular Level

The study of the aggregation of small molecules in solution induced by metallophilic interactions has been traditionally performed by spectroscopic methods through identification of chemical changes in the system. Herein we demonstrate the use of SAXS (small‐angle X‐ray scattering) to identify structures in solution, taking advantage of the excellent scattering intensity of heavy metals which have undergone association by metallophilic interactions. An analysis of the close relationship between solid‐state and solution arrangements of a dynamic [Ag₂(bisNHC)₂]²⁺ (NHC=N‐heterocyclic carbene) system, and how they are complementary to each other, is reported.     

Macromolecules at surfaces: Research challenges and opportunities from tribology to biology

A comprehensive review of ongoing and recommended research directions concerning the structure, dynamics, and interfacial activity of synthetic and naturally occurring macromolecules at the solid–liquid interface is presented. Many new developments stem from the ability to target new size regimes of 1–100 nm. These rapid developments are reviewed critically with respect to chemical synthesis, processing, structural characterization, dynamic processes, and theoretical and computational analysis. The common problems shared by flat and particulate surfaces are emphasized. A broad spectrum of material properties are discussed, from the control of interfacial friction between surfaces in moving contact, to the mechanical strength and durability of the interfaces in hybrid materials, to optical and electronic properties. Future research opportunities are identified that involve (1) the emergence of nanoscale material properties, (2) polymer‐assisted nanostructures, and (3) the crossroads between interfacial science and biological and bioinspired applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2755–2793, 2003