F. Pellerin

An important step in quantitative auger analysis: The use of peak to background ratio

Abstract If the Auger ratio is defined as being the ratio of the Auger peak to the background at the same energy, this Auger ratio can be considered as an intrinsic measurement, characteristic of the sample, and in a very large degree independent of the instrumental parameters adjustment: intensity of the primary electron beam, modulation voltage, Wehnelt voltage, focusing, deflection, sample positioning, electron multiplier gain and further amplification. However, this Auger ratio depends on the primary electron energy. In a specimen homogeneous in depth, the Auger ratio of an element X normalized to that obtained on a pure X sample yields a direct measurement of the volume fraction occupied by that element in the sample. It is no longer necessary to normalize an Auger peak to the sum of all the other peaks, or to resort to the ratio of the peaks on a given spectrum. Providing that the respective mean free paths of the Auger electrons are sufficiently different, it is even possible to acquire a valuable information on the depth distribution of the elements.

Comparison of the secondary‐electron spectrum with the electron‐loss spectrum on pure Al by low‐energy electron‐reflection spectroscopy

The secondary‐electron (SE) spectrum, energy‐loss (EL) spectrum, and Auger electron spectrum (AES) for pure Al were measured by low‐energy electron‐reflection spectroscopy. The SE spectrum taken at primary energies higher than 50 eV is compared to the spectrum at 30 eV when excitation of surface and bulk plasmons is negligible. Both spectra do not change in the peak position and shape. Therefore the contribution of secondary electrons emitted by plasmon decay is negligibly small compared to the contribution of those emitted by the single‐electron excitations. Some additional peaks are observed in EL and SE when O2 is sorbed on the surface.

The use of peak to background ratio in quantitative Auger analysis

Abstract The Auger signal is defined as being the ratio, in the direct mode, of the height of the Auger peak to the background at the same energy. This Auger signal is shown to be an intrinsic measurement, proportional to the volume fraction of a given element in the sample. It is in a very large degree independent of the instrumental parameters adjustment, except for the primary beam energy. Provided the respective mean free paths of the Auger electrons are sufficiently different, it is even possible to acquire a precise information on the depth distribution of the elements.

Characteristic energy losses on carbon contaminated layers correlated with secondary electron, auger electron emission and contrasts in scanning microscope

Abstract The secondary electron (SE) spectrum (0 E ∗ ) as already proposed in the transmission ELS. The few eV change of the loss peak energy of various carbon compounds may correspond to slightly different carbon-carbon distances. The 20 eV secondary electrons could be produced by the relaxation of the excited state (σ ∗ → σ transition) via an Auger process. The cross section for molecular electronic excitation is higher than that of atomic ionization for inner level. The loss peak is as intense as the SE peak and higher by more than two orders of magnitude than the C KLL Auger peak. The modification of secondary emission under carbon contamination has been observed on a silicon sample by Scanning Electron Microscopy (SEM) in the Secondary Electron Image (SEI) mode.

An electron energy loss spectroscopy study of hydrogen physisorption on aluminum and alumina surfaces at room temperature

Abstract This paper deals with electron energy loss spectra (EELS) of hydrogen adsorbed at room temperature on Al and Al 2 O 3 surfaces. It is shown that while hydrogen physisorption on Al 2 O 3 is detected under H 2 pressures in the 10 -4 Torr range, no hydrogen physisorption is observed on clean Al under the samw experimental conditions. These observations are consistent with calculations of the potential well depth of interaction between the H 2 molecule and the aluminum and alumina surfaces.

Hydrogen detection by electron energy loss spectroscopy

Abstract Hydrogen adsorbed at room temperature on tantalum, platinum, and silicon surfaces was analyzed by means of reflexion Energy Loss Spectroscopy (ELS). When a molecular hydrogen pressure higher than 10−4Torr was introduced in the apparatus, an ELS peak located at 13 eV below the elastic peak appeared on all samples. This peak was attributed to the excitation of the molecular hydrogen bond. Furthermore, on silicon, a second peak corresponding to the adsorption of atomic hydrogen was observed. This technique could be applied to the detection of hydrogen trapped in the wall of nuclear fusion devices.

Depth information in Auger electron spectroscopy

Two different methods giving non destructive depth information in Auger Electron Spectroscopy (AES) are described, (i) The first one is based on the Auger ratio PB (ratio of the Auger peak to the background at the same energy). In the case of a binary alloy XY, and as soon as the Auger electron mean free paths of the two elements are sufficiently different, it is possible to obtain a depth information by plotting (PB)x versus (PB)y (ii) The second one is more general and uses the ratio of the Auger tail height (T) to the Auger peak height (P). This ratio (TP) is independent of the concentration of the element. It is only dependent on its depth distribution. Both methods are applied to the experimental example of a silver deposit on a Si(111) surface.

Variation of relative intensities between surface and bulk plasmon losses due to crystal orientations for aluminium in low energy electron reflection loss spectroscopy

Abstract The contrast change of secondary electron images due to the crystal orientations is observed by the ultra high vacuum scanning electron microscope (UHV-SEM) for crystal grains of clean surface of polycrystalline Al in the primary energy E p of 200 eV to 5 KeV. The low energy electron loss spectra are measured by the cylindrical mirror analyzer. The relative intensity ratio between surface and bulk plasmon loss spectra was dependent on the crystal orientations. The SEM images taken by the surface and bulk plasmon signals at E p = 230 eV show the inverse contrast depending on the grains. The inversion of the relative intensities between the surface and bulk plasmon losses is explained qualitatively by taking into account of variation of the penetration depth of the incident beam caused by the electron channeling.

Diffraction effects in the low energy electronic excitations of a clean Al(111) surface

The low energy electronic excitations of an Al(111) surface have been studied by means of Electron Energy Loss Spectroscopy (EELS) in the incident electron energy range 20 < Ep < 100 eV. Apart from the well known plasmon lines, two EELS peaks are observed A (1.5–2 eV) and B (4–5 eV). Diffraction effects are observed in the variation of the intensity of these peaks versus primary energy. They are interpreted in the frame of Dukes two-step model. Peak A is attributed to a bulk interband transition at the W point of the bulk Brillouin zone, while peak B is interpreted in terms of a transition involving surface states.