Mean Escape Depth Research Articles

Attenuation length and escape depth of excited electrons in solids

Escape probability and mean escape depth λ e of emitted electrons are determined as a function of attenuation length λ a of excited electrons, their initial energy E n , and the height of the surface barrier χ. A variable energy loss parameter permits to apply the proposed model to different kinds of electron emission, including the energy loss free Auger and ESCA electrons. An analytical expression was found correlating the internal energy distribution of excited electrons and the external energy distribution of emitted electrons. By means of this excitation energies of secondary electrons and exoelectrons were determined.

ChemInform Abstract: ON THE COMPOSITION OF THE PASSIVATING FILMS FORMED ON ALUMINUM IN CHROMATE SOLUTIONS

AbstractDie chemische Zusammensetzung der sich beim Eintauchen von Al in Chromatund Chromat/Chlorid‐Lösungen bei offenem Stromkreis und bei anodischer Polarisation bildenden Passivfilme wird mit Hilfe der Röntgen‐Photoelektronenspektroskopie untersucht.

ESCA Investigations of Ion Beam Effects on Surfaces

The sampling depth of ESCA is about two to three times the mean escape depth of the photoelectrons; thus, in general, a surface layer with a thickness of about 100 Å contributes to the signal. Within this range, information concerning the depth distribution of elements and compounds can be obtained non-destructively. ESCA can therefore be used to reveal the nature of the artefacts that are inevitably formed during the removal of surface layers by ion bombardment. Examples are given of the following effects: selective sputtering (accumulation of Cu on brass, depletion of Cr in the removal of oxide layers on steels), implantation of primary ions and surface atoms, and ion-induced reactions (destruction and formation of compounds). Particular attention is paid to the processes occurring in the bombardment of the oxide-metal interface.

On the Composition of the Passivating Films Formed on Aluminum in Chromate Solutions

The chemical constitution of the passive oxide films formed on aluminum in chromate and chromate/chloride solutions under simple immersion (at open‐circuit potential) and under anodic polarization has been investigated by means of x‐ray photoelectron spectroscopy. It has been shown that these films, whose thickness is comparable with the mean escape depth of photoelectrons, are composed of a mixture of hydrated chromium (III) oxide, aluminum (III) oxide, and chromium (VI) species. A considerable amount of chloride species has been detected in the films formed in chromate/chloride solutions, independently whether chlorides were initially present in the solution or were added only after 18 hr immersion of the sample in chromates. The extent of chloride incorporation within the oxide film from solution was not modified by the anodic polarization of aluminum from open‐circuit potential up to critical pitting potential. This situation is quite different from that observed in chloride solutions, in the absence of chromates, where the amount of chlorides in the oxide film increases appreciably between and. The nature of the inhibiting effect of chromate ions on the pitting corrosion of aluminum is discussed on the basis of these results.

Abstract: Stoichiometry of SiO2/Si interfacial regions. I. Ultrathin oxide films

Nonstoichiometric interfacial transition regions located between thermally grown silicon oxide films and silicon substrates have been identified by variation in silicon and oxygen x‐ray photoelectron spectral data.1 Changes in Si 2p binding energies, and line intensities and linewidths of both Si 2p and O 1s photoelectron lines are detected in spectra of oxide films less than 25‐A thick and are each consistent with a silicon‐rich transition region. The composition and width of the nonhomogeneous oxide transition regions in ultrathin, thermally grown silicon oxide films are quantitatively evaluated in the present study using Si 2p binding energy and intensity data.Homogeneous reference films are used to relate Si 2p binding energies with oxygen content of the films. The determination of a mean escape depth for Si 2p photoelectrons from oxide films provides a relationship between Si 2p line intensities and oxide film thickness. Changes in Si 2p binding energies and intensity data are used to identify change...

Electron mean escape depths from x−ray photoelectron spectra of thermally oxidized silicon dioxide films on silicon

The mean escape depths of Si 1s, Si 2p, and O 1s photoelectrons from silicon−silicon dioxide structures were determined over a wide kinetic−energy range with magnesium, aluminum, and chromium x−ray sources. Variations in photoelectron line intensity were measured as a function of oxide film thickness. Film thicknesses were determined from ellipsometric data assuming an index of refraction of 1.47 for the oxide. Discrepancies in fitting intensity data to an escape−depth curve for films <20−Å thick are associated with nonstoichiometry of the oxide film near the interface. The incompletely oxidized interfacial region is identified by variations in linewidth and in binding energies of the spectral lines as well as by the deviations from predicted intensity data.

Simultaneous observations of partially oxidized surfaces by AES and SIMS for Al, Si, Ti, V, and Cr

The advantage of performing simultaneous SIMS and AES analysis together with measurements of sputtering rates is demonstrated by studies of oxidized Al on Si. As the OKLL Auger peak increases, due to increased oxygen coverage, there is enhanced emission of metal ions. Normalized SIMS and Auger signals for Al, Si, Ti, V, and Cr are intrinsic to each metal−oxygen system. From estimates of the escape depth of OKLL Auger electrons, the mean escape depths of metal ions from oxide were estimated. A step−like decrease in sputtering rate is observed and correlated with the thickness of the oxide layer. The Ag−O system was also studied and found to give an anomalous effect.

A theoretical model for the energy dependence of electron channelling patterns in scanning electron microscopy

Equations given by Hirsch and Humphreys (1970) and by Spencer et al (1972) for describing the contrast in electron-channelling patterns (ECP) are generalized by taking into account the energy losses which the fast electrons experience in the specimen. In this way a theory is established which considers diffraction, backscattering and energy losses. This theory is used and calculations are made of the dependence of the contrast in ECP on the energy of the backscattered electrons. Unlike earlier theories for ECP the present work gives the correct behaviour of the backscattering coefficient for large foil thicknesses. It is shown that the visibility can be strongly enhanced by using an energy-analysing detector, in agreement with experimental results. The signal-to-noise ratio is evaluated to find the energy window which gives optimum contrast. For Si, Cu and Au these windows are approximately E0 > E > E0 − 700eV, E0 > E > E0 − 250 eV and E0 > E > E0 − 400 eV respectively. Calculations of the mean escape depth as a function of energy show that the electrons are emitted from a thin surface layer for small energy losses. The resolution can therefore be significantly improved in the backscattered mode by using an energy-analysing detector.

Auger Electron Spectroscopy of fcc Metal Surfaces

The energy spectra of Auger electrons from clean Au, Ag, Cu, Pd, and Ni surfaces have been determined. Uniform deposition of a second metal onto clean metal surfaces has made it possible to assess the depth of the surface region which contributes to the Auger peaks in the secondary electron energy distribution characteristic. These results indicate that the mean escape depth for Auger electrons in Ag (without significant loss of energy) varies between 4 and 8 Å for energies of 72 and 362 eV, respectively. It has been shown (using Auger electron spectroscopy for detection of surface imuprities and low-energy electron diffraction for determining surface structure) that a clean Au (100) surface is reconstructed into a (1×5) structure, while clean Ag (100), Cu (100), and Pd (100) surfaces are characterized by bulk atomic arrangement. The combination of these two techniques has also been effectively applied to the interpretation of the structure and composition of CuAu surface alloys.