Nickel-chromium interface resolution in Auger depth profiles

Auger depth resolutions for fine-grained crystalline Ni/Cr multilayers have been determined. Resolution is shown to be a function of ion species, ion energy, ion incident angle, and the presence of reactive species. Deterioration of interface resolution with depth is shown to be the result of cumulative surface roughness induced by the ion beam to an extent proportional to the ion velocity normal to the surface. The presence of a reactive species to create an amorphous surface layer is shown to inhibit the development of surface roughness. The best resolution was obtained using low energy Xe ions and large ion beam angles. The ultimate resolution is limited by the fabrication perfection of the standard, and not by the sputtering process or by the Auger mean free path length.     

Relative escape depth of Auger and photoelectrons from a solid surface

A new method of determining the escape depth of electrons in the energy range 0–1000 eV is described. Values obtained were 6.1 Å and 6.8 Å at 234 and 266 eV, respectively, in GeO₂.     

Temperature,roughness and depth resolution in ion sputter profiles

The depth resolutions of evaporated silver layers on polished polycrystalline copper substrates are studied at various temperatures during argon ion sputtemg with AES. A detailed analysis of the profile shape at the interface reveals the nature of contributions to the terms governing interface resolution. The profiles are all accurately described by an error function leading edge followed by an exponential trailing edge. The characteristic of the trailing edge is governed by the development of roughness which depends on the depth, z, sputtered as z^0.875. The roughness is reduced at elevated temperatures by the action of surface diffusion such that the maximum reduction occurs at the highest temperature and the lowest sputtering rate. The characteristic of the leading edge is composed of three terms added in quadrature, (i) defect-enhanced diffusion of copper into the silver film, (ii) roughness as above, and (iii) a constant term due to film nucleation. In the present samples the increased interdiffusion at elevated temperatures and low sputtering rates largely offsets the improvements in topography so that, overall, the depth resolution appears to be a very weak function of temperature. However, in other systems where interdiffusion is small, the resolution could be greatly enhanced.     

Competition between Auger and resonant charge transfer in surface ion neutralization

The present Letter describes a many-electron theory of charge transfer in ion-surface scattering, where the principal charge-transfer processes — Auger and resonance — are both treated on an equal footing. When the participating substrate band is wide, a very simple approximate solution is obtained. For slow ions, the dominating process is the one with the longer range of interaction, whereas, for fast ions, the strength of the interaction is the dominating feature.     

MC model of Auger spectra from highly charged ion beam surface interaction

Abstract

A Monte Carlo code is described which simulates angle resolved Auger electron energy spectra from highly charged ion surface interaction. The combined effect of the Doppler spread of laboratory emission energy and electron scattering by the solid, together with the broad inherent line width, is found to have considerable influence on the spectral lines. As a new feature, low or high energy shoulders can appear. By comparison between simulated and measured spectra information on the kinematic and electronic state of the projectile ions in the moment of electron emission can be extracted. The standard method of spectrum analysis, which is based on the assumption of direct escape of the electrons, is evaluated with respect to the simulated spectra.     

Effect of primary oxygen ion implantation on SIMS depth profiling in glasses

The influence of the primary oxygen ion implantation on SIMS in-depth profiles in halide and chalcogenide glasses was examined. Various behaviours of particular profiles were generally explained in terms of the chemical affinity of analysed reactants and modifications of the glass structure induced by primary ions.     

Dependence of anomalous phosphorus diffusion in silicon on depth position of defects created by ion implantation

Transient enhanced diffusion of phosphorus in silicon has been investigated for implants below and above the threshold for a complete amorphization. Rapid thermal processes (electron beam) and conventional furnaces have been used for the annealing. In the case of implants below amorphization, a strong enhanced diffusion, proportional to the amount of damage produced, has been observed. The extent of the phenomenon is practically independent of the damage depth position. In contrast to this, the formation of extended defects at the original amorphous-crystalline interface makes the diffusivity strongly dependent on depth in the case of post-amorphized samples. No enhanced diffusion effect is observed if the dopant is confined in the amorphous layer, while a remarkable increase in the diffusivity is detected for the dopant located in the crystalline region beyond the amorphous-crystalline interface.Damage distribution after implantation and its evolution during annealing have been determined by double crystal x-ray diffraction and correlated to anomalous P diffusivity. A qualitative distribution of the interstitial excess in solution in the silicon lattice during annealing is proposed for the two different cases. These point defects, released by the dissolution of the interstitial clusters produced by the implanted ions, have been identified as responsible for the observed enhanced P diffusion.     

STM and AES study of the relation between ion sputter induced roughness and depth resolution

Scanning tunneling microscopy has been applied to characterize the enhancement of surface roughness by ion sputtering. A certified Ni/Cr multilayer film was employed as a target. It was found that the roughness induced by ion sputtering increased with the increase of sputtered depth, and that this increase in roughness accounted for most of the reduction in depth resolution in Auger depth profiling.     

Potassium Auger emission by K ion bombardment of the Ni(100) surface

Angle-resolved electron energy spectra induced by bombardment of a Ni(100) monocrystal surface with 0.5–4.5 keV energy K⁺ ions have been measured. In the case when the target is previously implanted by K⁺ ions a peak (discrete structure) in the energy range 15 < E < 17 eV is observed. This phenomenon has been ascribed to deactivation of M₂₃, vacancies of the K atom formed in the symmetrical collisions of projectiles with implanted or adsorbed surface K atoms. The phenomenon of the peak splitting at the higher projectile energies has been discussed within the frame of the Doppler effect in the specific case of symmetrical K-K collisions, where both collision participants can appear as Auger electron emitters.     

Advanced ion energy loss models: Applications to subnanometric resolution elemental depth profiling

In principle, the depth distribution of the different chemical elements near the surface of solids can be determined quantitatively and absolutely with subnanometric depth resolution using medium energy ion scattering (MEIS), which is a refined version of Rutherford backscattering spectrometry (RBS). The energy resolution of current MEIS analyzers reveals spectral features that cannot be resolved using conventional RBS detectors. Thus, the usual data analysis framework based on a standard Gaussian approximation for the ion energy distribution in the target is applicable to regular RBS, but not generally to MEIS, in particular if one aims at subnanometric depth resolution. The observed asymmetry in the ion energy loss distributions is a direct consequence of the asymmetric character of inelastic energy transfers during individual atomic collisions and of the stochastic character of the resulting energy losses. We propose a model that accounts for the proper statistics of the small energy loss events and for an approximate electronic energy loss distribution during the backscattering event. The validity of this model is discussed and applied to the determination of HfO₂ and TiO₂ film thicknesses as well as to detect Al₂O₃ and HfO₂ intermixing. This final application case also illustrates the potentialities as well as some inherent limitations of MEIS. The model developed here has been made available to the public in the form of a software for MEIS data analysis.     

Binary collision model for neon Auger spectra from neon ion bombardment of the aluminum surface

A model is developed to account for the angle-resolved Auger spectra from neon ion bombardment of the aluminum surface recently obtained by Pepper and Aron. The neon is assumed to be excited in a single asymmetric neon-aluminum collision and scattered back into the vacuum where it emits an Auger electron. The velocity of the Auger electron acquires a Doppler shift by virtue of the emission from a moving source. The dependence of the Auger peak shape and energy on the incident ion energy, angle of incidence and on the angle of Auger electron emission with respect to the surface is presented. Satisfactory agreement with the angle resolved experimental observations is obtained. The dependence of the angle-integrated Auger yield on the incident ion energy and angle of incidence is also obtained and shown to be in satisfactory agreement with available experimental evidence.     

Mobility and surface recombination processes of primary electrons in dielectric systems during Auger electron spectroscopy

The time evolution of the surface electric field in a dielectric system during Auger electron spectroscopy is calculated. It is shown that steady electric fields are very quickly attained. Their steady value is connected to primary electron mobility.     

High resolution Auger electron spectroscopy of metallic copper

Part of the LMM Auger spectrum from metallic copper has been studied in a high resolution X-ray photoelectron spectrometer. Fine structure not earlier reported has been observed. The main L₃M_4,5M_4,5 peak is very narrow, 1.0 eV, although the valence band is involved in the transition. The agreement between experimental and calculated Auger electron energies is very good. Since fine structure is found to be an intrinsic property in Auger spectra the interpretation of “satellite” peaks as due to electron—plasmon interactions should be used with care. The L₃M_4,5M_4,5 peak is very sensitive to the copper surface conditions. Surface oxygen affects the peak in a characteristic way.     

Auger electron spectroscopy and ion sputter profiles of oxides on aluminum

To check the validity of those assumptions needed to relate the Auger peak to peak height (APPH) to quantitative elemental concentrations in oxide films, oxide films on aluminum were monitored by AES during ion-sputter-etching. Before and after film profiling with AES, contour maps of film thickness were obtained with ellipsometry. Ion-sputter-AES profiles are entirely misleading if interpreted as quantitative concentration profiles, but are very informative as to qualitative analysis and when properly understood reveal physical and chemical non-isotropy within the films.     

Molecular secondary ion emission from adenine overlayers in dependence on the primary ion species and substrate material

The influence of the primary ion species (He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺ and SF₅⁺) and substrate material (graphite, Al, Cu, Ag and Pb) on the secondary ion emission from molecular overlayers of the purine base adenine was investigated in dependence on the layer thickness. The measurements showed an increasing yield with increasing mass of the primary ions and its number of constituents. The yield enhancement, defined as the ratio between the maximum yield obtained from approximately a monolayer coverage of adenine to the yield obtained from a multilayer coverage, was shown to depend on the substrate material. However, a clear dependence on the primary ion species was not found.     

Fabrication of durable hydrophobic surfaces through surface texturing

Low surface energy polymer thin-films can be applied to surfaces to increase hydrophobicity and reduce friction for a variety of applications. However, wear of these thin films, resulting from repetitive rubbing against another surface, is of great concern. In this study, we show that highly hydrophobic surfaces with persistent abrasion resistance can be fabricated by depositing fluorinated carbon thin films on sandblasted glass surfaces. In our study, fluorinated carbon thin films were deposited on sandblasted and as-received smooth glass using deep reactive ion etching equipment by only activating the passivation step. The surfaces of the samples were then rubbed with FibrMet abrasive papers in a reciprocating motion using an automatic friction abrasion analyzer. During the rubbing, the static and kinetic friction forces were also measured. The surface wetting properties were then characterized using a video-based contact angle measuring system to determine the changes in water contact angle as a result of rubbing. Assessment of the wear properties of the thin films was based on the changes in the water contact angles of the coated surfaces after repetitive rubbing. It was found that, for sandblasted glass coated with fluorinated carbon film, the water contact angle remained constant throughout the entire rubbing process, contrary to the smooth glass coated with fluorinated carbon film which showed a drastic decrease in water contact angle with the increasing number of rubbing cycles. In addition, the static and kinetic friction coefficients of the sandblasted glass were also much lower than those of the smooth glass.     

High resolution resonant Auger spectroscopy of free atoms and molecules

Recent progress in high resolution resonant Auger spectroscopy in the VUV/soft X-ray region is discussed in some detail both from the experimental and theoretical points of view. Some illustrative examples are presented in order to show the progress in the field, emphasized by recent high resolution measurements at “the Finnish beamline”, bl 51, at the MAX I synchrotron radiation facility.