Energy Loss Probability Research Articles

Energy loss of fast electrons moving near plane boundaries with dispersive media

The energy loss per unit length experienced by swift electrons in STEM is calculated for trajectories parallel to plane boundaries with dispersive media. Dispersion corrects the logarithmic divergence of the local energy loss probability at the interface given by the local approach. The effect of damping is also studied, and results are related to the spatial resolution in EELS experiments.

Electron Energy Loss Spectrum in Adsorbed Residual Gas on Cooled Arachidic Acid Langmuir-Blodgett Film and Its Adsorbed Gas Amount

The energy-loss spectra of 18 keV electrons in adsorbed residual gas on Langmuir-Blodgett film, made from arachidic acid (C20H40O2) and cooled at temperatures of -10°C, -35°C and -60°C, were measured through use of an electron source that also acted as an adsorbent. In addition, the amount of adsorbed residual gas was estimated from the energy-loss probability.

Surface-plasmon coupling in cylindrical pores.

We have determined the surface-plasmon modes of cylindrical pores in metals and of pairs of coupled cylindrical pores having parallel axes. The eigenfrequencies and the polarization fields are determined in the case of interacting pores of equal radii where the modes are even or odd with respect to the symmetry plane. Numerical application is made for pores in aluminum with inner radii of 20 A\r{} and separation of the axes of 48 A\r{}. The surface-plasmon frequencies and the polarization fields show strong differences with respect to the case of an isolated pore. Frequency shifts up to 2 eV occur, leading in particular to the appearance of two new modes at energies well below the flat-surface-plasmon frequency ${\ensuremath{\omega}}_{p}$/ \ensuremath{\surd}2 . For the one- and two-cylindrical-pore configurations, we have established an expression for the second-quantized interaction Hamiltonian between an electron and the surface-plasmon modes, from which the energy-loss probability for an electron moving parallel to the cylindrical axis is obtained. Application to the scattering of electrons of 10 keV kinetic energy shows, for both configurations, substantial differences in the energy-loss spectra as compared to the flat-surface case. In addition, the loss function for the pair of cylindrical pores is strongly affected by the coupling of the surface-plasmon fields of the two interacting pores.

Spin-polarized electron-energy-loss spectroscopy on Ni.

High-resolution spin-polarized electron-energy-loss data on Ni(110) are presented. Exchange scattering is found to be the dominant loss mechanism. The Stoner excitation spectrum shows a sharp threshold around 65-meV energy loss (Stoner gap). The energy-loss probability for spin-down electrons is up to 3 times larger than for spin-up electrons. An interpretation in terms of the Ni 3d band structure is given.

Analysis of electron energy-loss spectra from electron-beam-damaged amorphous AIF3

Abstract Expressions for the electron energy-loss probability are obtained for electrons travelling parallel to, firstly, one and, secondly, two coaxial cylindrical interfaces between different media. These expressions have been evaluated for Al-vacuum interfaces confirming that the cylindrical modes behave in the manner expected. Experimental spectra are presented for electrons travelling through holes drilled in thin films of amorphous AIF3 (a-A1F3) in a scanning transmission electron microscope. Comparison of these spectra with calculated spectra indicates a discrepancy in the shape which is attributed to a modification of the a-A1F3 surrounding the drilled hole. The presence of a 6 eV peak in some spectra is attributed to the excitation of a surface mode on spheres of aluminium in the a-A1F3 film.

Spectrum of surface-mode contributions to the differential energy-loss probability for electrons passing by a spheroid.

The differential probability of energy loss for a charged-particle beam moving past a spheroid along the direction of a symmetry axis is obtained. Local, frequency-dependent, dielectric functions are used to describe the response of the spheroid and the medium containing the rectilinear trajectory of the beam. While retardation is neglected, all modes are included in the analytical results. Both oblate and prolate spheroids and their counterpart voids are discussed, and numerical results are given for materials of experimental interest.

Multipole surface excitations on small oxide-covered metal particles by fast electrons

Inelastic scattering of fast electrons by small oxide-covered metal particles is studied within the hydrodynamic model. The oxide layer is described by a static dielectric function ɛ0. The surface plasmon frequency and the energy loss probability for multipole surface modes are calculated. Results forrs=2 jellium and ɛ0=3.7 are reported. Many higher multipole contributions are suppressed by the presence of the oxide layer. However, the surface modesl=2 can still be seen clearly in the excitation probability.

Plasmon Excitation in Metal Surface Layers by Fast Electrons

AbstractThe interaction of fast electrons with metal overlayers on metal substrates is studied within the hydrodynamic model. Retardation effects and damping are included. The energy loss probability of surface and interface plasmons is calculated for external electron beam travelling parallel to the metal surface. Numerical calculations are carried out for potassium layer on aluminium substrate.

Energy-loss probability in electron microscopy.

New general results on the self-energy of fast electrons interacting with metal surfaces are presented with emphasis on the energy-loss problem in electron microscopy. Some applications to both spherical and planar targets are considered. Our results are relevant to the understanding of inelastic electron scattering near small structures, at the nanometer scale.

Plasmon Excitation in the Interaction of Fast Electrons with Metal Surfaces

AbstractThe interaction of fast electrons with semi‐infinite metals is studied within the hydrodynamic model. Retardation effects, damping, and diffuseness of the electron density at the surface are included. The energy loss probability of surface plasmons is calculated for external electron beam travelling parallel to the metal surface. Numerical calculations are carried out for rs = 2 jellium.

Surface Excitations on Small Metal Particles by Fast Electrons

AbstractInelastic scattering of fast electrons by isolated small metal particles is studied within the hydro‐dynamic model. The energy loss probability for multipole surface modes is calculated. Numerical calculations for rs = 2 jellium are carried out for different parameters: fast electron energy, electron impact parameter, radius of the partide, and energy loss.

Generation of surface excitations on dielectric spheres by an external electron beam.

The energy loss and differential probability of energy losses is calculated to all multipole orders for a charged particle moved uniformly past a sphere. The sphere's response is characterized by use of a local dielectric function.

Plasmon excitation in metallic spheres.

A detailed study is presented of the influence of several parameters on the energy-loss probability of fast electrons (\ensuremath{\sim}100 keV) incident on small metallic spherical particles. We consider the collective modes of the sphere, including bulk-type modes which do not appear to have been considered previously in the literature. A Gaussian distribution is used to describe the electron in the plane transverse to the trajectory. We discuss the effects of the variation of several parameters---incident beam size, probe velocity, radius of the sphere, impact parameter, and the excited mode---and conclude that the absorption spectra depend critically on the geometry of the probe as the experimental data of Batson and Treacy suggest.

Analysis of the induction of chlorophyll fluorescence in leaves and isolated thylakoids: contributions of photochemical and non-photochemical quenching

Quantitative analysis of the changes in the reduction-oxidation state of photosystem 2 electron acceptors and excitation energy distribution between photosystems 1 and 2 during the induction of chlorophyll fluorescence at 685 nm from a minimal to a maximal level in dark-adapted leaves and isolated thylakoids from Pisum sativum are presented. The data show that changes in the fluorescence yield during the induction phase are attributable not only to changes in the probability of trapped excitation energy being used for photosystem 2 photochemistry, as previously predicted, but also to large changes in the probability of energy loss through non-photochemical processes. A significant and variable amount of fluorescence quenching by non-photochemical processes in both leaves and thylakoids is demonstrated. The non-photochemical quenching of fluorescence during induction in isolated thylakoids was not modified by addition of a range of ionophores, which effectively destroyed delocalized electrical and cation concentration gradients across the membranes. Significant quenching of fluorescence by non-photochemical processes was also observed in both leaves and thylakoids treated with 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea.

Sticking probability on metal surfaces: Temperature dependence of the electron-hole pair mechanism

We have studied how the sticking coefficient on metal surfaces depends on the substrate temperature ${T}_{s}$ when the energy exchange is due to electron-hole pairs. A previously derived exact result for the energy-loss (-gain) probability in one round trip is generalized to finite substrate temperatures. This serves as the input for the stochastic equation which is used to describe the adparticle motion in the adsorption well. The solution of this equation shows that two competing effects can lead to a very weak dependence of the sticking probability on the substrate temperature.

Energy bands of the cadmium halides from electron energy loss spectroscopy

The wavevector and frequency dependent dielectric function epsilon (q, omega ) was determined from electron energy loss spectroscopy for the layered solids CdI2, CdBr2 and CdCl2. Electron energy loss measurements were carried out in the energy range 0-90 eV and at wavevector magnitudes up to the Brillouin zone dimension. For each value of the wavevector, epsilon (q, omega ) was determined from the energy loss probability using Kramers-Kronig analysis. The data analysis which includes a method for removing the effect of multiply scattered electrons from the raw data is described. Thin polycrystalline films were used and these were found to be highly oriented with the basal planes of the crystallites parallel to the substrate. The energy loss experiments were performed with the electron beam direction perpendicular to the basal planes. Based on the dielectric function obtained for these materials an electron energy band scheme is proposed. It was found that on going from CdI2 to CdBr2 to CdCl2 the upper valence band narrowed and the conduction bands became more separated. In general, with increasing q, both epsilon 1 and epsilon 2 become broader and decrease in peak height. At the same time the main weight of epsilon 2 moves to higher energies and the negative portion of epsilon 1 diminishes and tends to remain positive for all omega . This behaviour is expected to be similar for all semiconductors.

Energy losses of fast electrons in multi-layer systems

Starting from Maxwell's equations a formula for the energy loss probability of fast electrons in systems of a given number of thin layers is derived for normal incidence. Retardation effects are neglected. For three layers of arbitrary thickness the equations are fully solved. As examples, a two-metallic-layer system with energy-dependent dielectric functions is discussed. Furthermore, the tarnish of metals e.g. Al−Al2O3, Be−BeO, Ag−Ag2S is considered as three-layer systems. The energy loss spectrum of the system Al2O3−Al−Al2O3 is calculated in agreement with the experiment. It turns out that the bulk longitudinal optical mode of the covering layer is excited in the infra-red. In the case of the oxidation of a dielectric film the transversal mode of the oxide is expected to prevail in the energy loss spectrum.

Reaction probabilities and threshold energy in the abstraction reaction between hydrogen atoms and neopentane

The reactions of photochemically generated deuterium atoms of selected translational energies with neopentane have been investigated. The variation with energy of the relative probability of reaction or energy loss on collision with neopentane was followed, and the phenomenological threshold energy measured as 45±5 kJ mol–1. The threshold values for molecules containing only primary or secondary C—H bonds and molecules with both bond types are discussed. The probabilities of reaction per bond for different bond types are compared and a simple model for reaction probability assessed.

Apparent Higher-OrderZ1Effects Due to Asymmetric Energy Straggling

Recently published data for the stopping power of fully stripped channeled ions are interpreted in terms of the Vavilov theory of energy straggling. The qualitative dependence of $\frac{{(\frac{\mathrm{dE}}{\mathrm{dx}})}_{p}}{{{Z}_{1}}^{2}}$ on charge and velocity can be explained by the dependence of the asymmetry of the energy-loss probability density on these variables through the parameter $\frac{\ensuremath{\xi}}{{\ensuremath{\epsilon}}_{max}}$.

Energieverlustmessungen an III–V-Verbindungen

Energy loss measurements with 55 keV electrons were made on the III–V compounds GaP, GaAs, GaSb, InAs and InSb. Retardation effects become important, because for these substances the condition for Cerenkov radiation is fulfilled. These produce an additional peak in the energy loss spectrum; its angular distribution and its dependance on the foil thickness were measured. The experimental results are in good agreement with the energy loss probability calculated by Kroger taking into account the retardation.