L.H. Jenkins

Auger and other characteristic energies in secondary electron spectra from Al surfaces

The energy spectra of secondary electrons back-scattered from clean, oxygen covered, and Cu covered Al surfaces have been determined. The data support the previous suggestion that Auger electrons can experience both characteristic energy loss and absorption phenomena. From the experimental results it was not possible to determine whether densities of states of electrons in the valence band affected the Al L2,3 VV Auger spectrum. This portion of the spectrum was greatly changed by oxygen absorption on the Al surface, but little affected by less than a monolayer of Cu. Conversely, characteristic loss spectra were less sensitive to oxygen on the surface, but were highly sensitive to the presence of copper at even less than monolayer coverage. A correlation between characteristic loss and “true” secondary spectra from clean surfaces was established and possible reasons for the correlation are discussed.

The energy spectrum of back-scattered electrons and characteristic loss and gain phenomena of the Cu(111)☆

Abstract The energy spectrum of electrons back-scattered from the Cu(111) has been determined. Approximately ten characteristic loss values were detected in the range immediately below elastic peak energies. Satellite peaks were observed on both sides of the ≈ 60 eV Cu Auger doublet. The relative positions of these satellites suggest that Auger electrons experienced characteristic gains, as well as losses. Analysis of the spectrum at near zero kinetic energy showed many structural details just above the inelastic peak. Energies of discrete events relative to the inelastic peak correlated well with the loss spectrum. It appeared that electrons with energies within the spectrum of the inelastic peak could undergo characteristic energy gains analogous to the characteristic losses by primary electrons. It was concluded that the experimental evidence gave support to the concept of a characteristic gain phenomenon.

LEED and Auger investigations of Cu (111) surface

Abstract After ultrahigh vacuum bake-out, electropolished Cu (111) surfaces were shown by Auger analysis to be contaminated by C, N, O, S and Cl. Other than C and S, which were contained in the bulk, the impurities were introduced by surface preparation; but all were easily removed by light Ar ion bombardment. Heating to ≈ 750°C caused diffusion of C and S from the bulk to the extent that a clear diffraction pattern corresponding to a √7 × √7 structure was produced by S on the surface. At ≈ b 900°C evaporation of Cu occurred to an observable degree, and S and C could no longer be detected on the surface. Auger analysis of clean Cu surfaces showed many details of the LMM and MMM types of transitions. Kinetic energies of all observed Auger electrons were in excellent agreement with calculated values. Also, the ≈ 62 eV MMM peak was resolved into two components related to the small differences in the M2 and M3 energy levels. The LMM transitions were classified according to their intensities, which could be rationalized on the basis of Coster-Kronig transitions and transition probabilities, as L3MM > L2MM > L1MM.

Characteristic energies in secondary electron spectra from Si(111) surfaces

Abstract The entire energy spectra of back-scattered electrons from clean, oxygen and Cu covered Si(111) surfaces were carefully investigated, and evidence of plasmon absorption by Auger electrons was obtained. Correlations between the Si Auger and characteristic loss spectra led to the conclusion that much of the Si Auger spectrum resulted from characteristic losses by 91 eV Auger electrons. Thin film Cu, ≲ 5 monolayers thick, deposited on Si showed no characteristics of a Cu single crystal. However, the Cu overlayer suppressed the higher order Si plasma loss peaks, presumably by reducing the penetration depth of the primary beam electrons into the substrate lattice.

Determination of a Cu(110) surface contraction by leed intensity analysis

Abstract Normal incidence LEED intensity spectra from six symmetrically inequivalent diffraction beams from a clean Cu(110) surface are presented and analyzed. The analysis has employed the results of two distinct sets of dynamical LEED calculations, which differ only in the choice of the electron scattering potential. It is indicated by the analysis that the Cu(110) surface region is in lateral registry with the truncated bulk, the first atomic layer is contracted toward the second by 10.0 ± 2.5% relative to the bulk spacing, and the second to third layer spacing is within 2.5% of the bulk value. A discrepancy of unknown origin has been found between the experimental and calculated I – V proflies for three beams in the 60 eV region; however, this discrepancy does not appear to affect the crystallographic conclusions of the analysis.

The Auger satellite and other characteristic events in Mg secondary electron spectra

Abstract Peaks in the very low energy, “true secondary”, portions of Mg secondary electron spectra are correlated with characteristic processes such as plasmon decay, etc. The satellite peak at an energy slightly greater than the main peak in the Auger spectrum is shown not to be due solely to double ionization in the L 23 level, and it is suggested that perhaps both plasmon absorption and double ionization processes contribute to the formation of the satellite peak. It is shown that it is not necessary to apply correction factors to values for ground state electron shell binding energies in free-electron-gas-like solids to achieve agreement between estimated and observed values of kinetic energies of Auger electrons ejected from valence bands.

Angular effects in Auger electron emission from Cu (110)

Abstract Angular variations in the emission intensities of M 2, 3 VV (62 eV) Auger electrons from a Cu (110) surface have been measured. Large changes are observed as a function of both polar and azimuthal angles. Effects of the incident beam energy and angle of incidence have been determined, and interpretations of the the data are proposed.

Characteristic energy gain and loss, double ionization, and ionization loss events in Be and BeO secondary electron spectra

Abstract Two satellite peaks have been observed on the high energy side of the Be KVV Auger peak. The lower energy satellite is attributed to coupling of energy from bulk plasmon de-excitations with Auger electrons, and the higher energy event to Auger electrons ejected from Be atoms with doubly ionized K levels. Following oxidation, the ionization loss spectra of BeO were observed to have structure which is interpreted as being related to the density of unfilled electron states above the BeO valence band. In addition, the characteristic loss and the low energy (“true secondary”) spectra of Be and BeO were determined. Peaks in these spectra are discussed in terms of characteristic energies related to excited electron states in the solids.

Auger and ionization loss spectra from Be surfaces

Abstract Auger and ionization loss spectra have been obtained from clean and Si-contaminated Be surfaces both before and after oxidation. The Auger spectrum from the clean Be surface exhibits only one major minimum at 105 eV in the d N ( E )d E versus E spectrum. Si-contaminated Be surfaces produced corresponding spectra with two major minima at 92 and 105 eV. Partial oxidation of clean Be surfaces resulted in Auger spectra which resemble in kind those obtained from Be-Si surfaces. Following extensive oxidation, Auger spectra from both types of surfaces were indistinguishable, and Si L 23 level ionization losses could no longer be detected.

Angular resolved L3VV Auger emission spectra from Cu(100)

Abstract The angular intensity distribution of electron induced L 3 VV Auger electron emission from a Cu(100) crystal has been measured. Angular positions of relative maxima in the distribution are aligned with prominent crystallographic directions suggesting strong diffraction effects.