J. Ferrón

The effect of surface roughness on XPS and AES

Abstract By using a Monte Carlo method of electron trajectory simulation we have evaluated the effect of surface roughness on electron emission for electron energies of interest in X-ray photoelectron and Auger electron spectroscopy. We have calculated the angular distributions and total yields for 500, 1000 and 1396 eV electrons emitted from a cone shaped aluminum surface. We found that normalized electron yields depend strongly on the surface roughness magnitude, and are nearly independent of the electron energy.

Escape depth of auger electrons; the elastic scattering effect

Abstract We have performed Monte Carlo calculations of the contribution to KLL (1396 eV) and LVV (68 eV) aluminum Auger electrons peaks from the surface atomic layers. These allowed us to calculate the escape depth of Auger electrons considering the effects of elastic scattering among electrons and ion cores. We found some disagreement with the calculation based on an exponential attenuation law.

Surface concentration changes in Cu-Zn alloys under ion bombardment

Abstract We have measured the depth profile of a Cu-48.2at%Zn alloy by means of Auger Electron Spectroscopy combined with Ar + ion bombardment. We have also measured the steady state surface concentration for different ion energies, and the transient variation of surface concentration when ion energies were changed from 0.5 to 5 keV and vice versa. We found that the effect of altered layer thickness and the Auger electron escape depth can produce an incorrect measurement of the preferential sputtering energy dependence. We also found that the presence of a strong preferential sputtering can shadow AES measurement of concentration variations along a depth profile.

Early stages of bump formation on the surface of ion-bombarded graphite

Abstract We investigate possible mechanisms for the formation of bumps, of atomic dimensions, in the surface layer of graphite under low-energy, single ion bombardment. We perform a Molecular Dynamics simulation and analyse the results in view of recent experimental data obtained with the Scanning Tunnelling Microscope. Only the early stages of bump formation are described. The depth profile of momentum deposited in the cascade is evaluated and used, in conjunction with the atomic density profile, to characterise interlayer distortions. The surface bumps appear under the presence of stresses developed in the near-surface layers of the target, due to defects created by the collision cascade. The bump originates around the positions of vacancies and interstitials, and is stabilised by the presence of interlayer interstitials. We have also produced a video film that helps in the visualisation of the time evolution of topographical features.

The elastic scattering factor in Auger electron spectroscopy

Abstract We have calculated the contribution of elastic scattering of primary electrons to the Auger yield for Al, Si and Cu. We found an important contribution of the forward scattered electrons. We have also measured the primary energy dependence of the Auger yield for pure Al, Si and Cu. We found differences among calculations and measurements as great as 40%, which are attributed to uncertainties in escape depth and Auger transition rates rather than to the scattering effect.

Extended Hückel cluster calculations of the L2,3VV auger transition in silicon

We report an independent-electron model calculation of the L2,3VV Auger lineshape for an ideal Si(100) surface. Valence states were calculated for a cluster of Si atoms using the extended Huckel approximation. Atomic Auger matrix elements were evaluated using the Clementi wave functions for the Si atoms and a Coulombian wave for the continuum wave function. Fairly good agreement between theoretical results and experimental data is found when the presence of the free surface is taken into account.

Information depth of auger electron and appearance potential spectroscopies : a Monte Carlo study

Abstract We have studied, through Monte Carlo simulations, the effect of elastic scattering, the initial angular distribution and the presence of the surface on the in-depth contribution and information depth in appearance potential spectroscopy (APS). We compared these results with previous one in Auger electron spectroscopy (AES). We found that although the mechanisms involved in the generation of the APS and AES in-depth contributions are qualitatively different, the practical results, i.e. the information depths related to both techniques are similar.

Comments on “pseudo first principle” calculations of Auger sensitivity factors

Des corrections deffet de matrice sont necessaires quand on utilise la methode du facteur de sensibilite en analyse AES quantitative. Mais il reste beaucoup a faire pour que lon puisse accorder confiance aux facteurs de correction numeriques

Backscattering correction to depth profiling of interfaces

Abstract We have performed Monte Carlo calculations of Auger yields of thin overlayers as a function of their thicknesses. This problem resembles an ideal depth profiling with no ion beam effects present. We found that in addition to the escape depth broadening, the backscattering effect must be considered in order to reproduce the analyzed depth profile. We propose a very simplified deconvolution formula which takes account of the backscattering effect, improving the in-depth resolution of the depth profile.

The First Stages of Oxidation of Polycrystalline Cobalt Studied with Electron Spectroscopies

Many studies of oxygen adsorption on cobalt, have been performed [1–3]. They include adsorption on crystalline and polycrystalline surfaces. In general, these studies show the same sequence of events: oxide formation is preceded by the chemisorption of oxygen.