The adsorption of oxygen on the steps of a copper (410) surface has been studied with Low Energy Ion Scattering. The adsorption kinetics suggest that oxygen adsorbs dissociatively. The linear decrease of the logarithm of the scattering signal from oxygen with the bombarding dose indicates that there is only one type of adsorption site. The cross section for desorption with 5 keV Ne+ is 4.5 × 10−15 cm2. From the angular distributions of the projectiles scattered from the copper atoms and the adsorbed oxygen atoms, it is found that the oxygen atoms are adsorbed at the hollow sites of the steps between 0.2 Å below and 0.7 Å above the terrace plane and protruding 0.2–0.7 Å from the edges. A computer simulation study gives qualitative support for these findings, but fails in giving a more precise oxygen position because of a lack of knowledge of the vibrational motion and the interaction potential of the atoms involved. At the saturation level of adsorption the coverage is 0.25 of a monolayer, corresponding to an occupation of all available step sites.

The ion fractions of lithium, sodium and potassium scattered from a copper (100) surface have been measured as a function of several experimental parameters. The ion fraction appears to be almost independent of the final energy, i.e. independent of the type of scattering trajectory at or below the surface. This means that the alkali ions can be used very well in several cases when experimental data are to be compared with theoretical scattering models. Typical values of the ion fraction are: 63% for lithium, 76% for sodium and 99% for potassium (values are given for a primary energy of 5 keV). A comparison of the results has been made with a theory based on ideas developed for the adsorption and scattering of very low energy alkali particles. A qualitative agreement has been found for the dependence of the ion fraction on the ionization energy of the alkali atoms and the (slight) variation with the primary energy.

Multiple scattering effects in low energy ion scattering (LEIS) can be related to the structure of the bombarded solid surface. Some examples of the use of multiple scattering phenomena for structure analysis of copper (100) and (410) surfaces are discussed.

A comparison was made of ion scattering and neutralization results obtained by two time-of-flight systems, one neutral-stripping system, and two electrostatic analyzers, using 5 keV H + , He + , Ne + , N 2 + and Ar + beams on polycrystalline gold targets with a scattering angle of 90°. Data presented include energy distributions of ions plus neutrals, ions only, and ion fractions. Computer simulations of the ion plus neutral spectra are also included.

The average relaxation of the (100) terraces of the stepped copper (410) surface has been studied with Ion Scattering Spectroscopy, using 10 keV He, and appears to be very small: <0.03 A toward, corresponding to less than 1.7% of the (100) interlayer spacing. Also the average edge atom depression with respect to the sub-edge atoms has been measured, using 21 keV H+, and is 10.3%. The results suggest the (410) surface to be somewhat “smoothed” by a depression of particularly the protruding edge atoms and a lift of the corresponding sub-edge atoms (both by about 10% maximum) in such a way that the average relaxation of all surface atoms is very small.

The ratio R of the intensities of the single and double scattering peaks observed in Ion Scattering Spectroscopy has been determined as a function of several experimental parameters. If all particles scattered through a certain scattering angle are detected with a time of flight spectrometer or when alkali ions are used as primary particles then the absolute value of R as well as the dependence on the experimental parameters correspond with the results of several theoretical models. A simple two atom model, using the Thomas-Fermi-Molière potential, yields very satisfying results. For low index directions on the surface R is a straightforward measure for the interatomic distance of neighbour surface atoms. For high index directions surface zig-zag collisions complicate the interpretation, but the shape of the energy spectra can be understood reasonably well. When noble gas ions are used as primary particles and only the scattered ions are detected, R+ is influenced by charge exchange and neutralization processes, which complicate the interpretation, and the dependence of R+ on the experimental parameters does not agree with theoretical expectations for R.

The ion fractions η+ of low energy (5–10 keV) neon particles scattered from a Cu(100) surface are measured with a time of flight spectrometer. These fractions are obtained for neutral as well as charged projectiles and for different crystal directions. The scattering angle θ was 30°. For a primary energy E0 of 5 keV neutral projectiles have a value for η+ which is 30 times lower than for charged projectiles; these values are 0.15 and 4.5% respectively. For E0 = 10 keV the values of η+ are about the same (~22%). Energy differences up to 22 eV, depending on E0, are observed between the single scattering peaks in the ion spectra of charged and neutral projectiles but also between the single scattering peak in the spectra of all scattered particles and of ions, with ions as projectiles. A qualitative discussion of these data is given, involving charge transfer processes of noble gas particle and target atom. The data suggest that these neutralization processes can be described more adequately with interatomic neutralization processes along the trajectory than with Auger neutralization by conduction electrons.

The position of the edge atoms of a stepped Cu(410) surface has been measured by Ion Scattering Spectroscopy using 21 keV H+. The edge atoms are depressed 5.0±1.5% of the copper lattice spacing, corresponding to 0.18±0.05 Å.

A projectile which is scattered through an angle theta by an atom with smaller mass can have two different energies after scattering. This phenomenon is treated and demonstrated by the scattering of 9 keV 84Kr+ ions from a stepped (410) copper surface. The measured energy and intensity distributions agree very well with theoretical expectations.

The ion fractions η+ of low energy (5–10 keV) argon particles scattered from a Cu(100) surface, are measured with a time of flight spectrometer. Neutral as well as charged projectiles are used. The scattering angle θ is 30°. The results for different angles of incidence ψ and crystal directions are reported. For scattering in the 〈100〉 direction, with a ψ-value of 15° and a primary energy E0 of 5 and 10 keV, the ion fractions for the quasi single scattering peak, η+QS, are 1.5 and 6.1% respectively. When E0 is between 5 and 10 keV a reionization process with a constant reionization probability occurs during the violent interaction. This process, but also neutralization along the outgoing trajectory, determines η+QS. With ions as projectiles, an energy difference of about 16 eV is observed between the quasi single scattering peaks in the spectra of all scattered particles and of ions only. The ion fraction for the quasi double scattering peak, η+QD. depends largely upon E0, indicating that the efficiency of the reionization process increases with E0. A qualitative discussion of the data is given, using the reionization process and the interatomic neutralization processes along the trajectory of the scattered particles.

The ion fractions, η+, of 10 keV argon particles, scattered from a damaged copper surface, are measured with a time of flight spectrometer. The damage was introduced by bombardment with argon ions. The scattering angle was 30°. The results for different angles of incidence, ψ, are reported. For Ψ < 10° the ion fraction is relatively high (∼27% for Ψ = 4°) and decreases as Ψ increases. For Ψ = 15° the value of η+ is 7%, whereas for 21° < Ψ < 27° the value of η+ appears to be constant (∼14%). An explanation is given by assuming interatomic ionization as well as neutralization processes along the trajectory of the scattered particles. The number of step-atoms, induced by ion bombardment, is estimated to be about 2 × 1014/cm2.

Angle Resolved ion-Electron Spectroscopy (ARIES), combined with Low Energy Ion Scattering (LEIS), is presented as a new technique with a wide applicability to study solid surfaces. Energy and angular distribution of secondary electrons emitted due to the ionization of (ad)-sorbates on a Cu (001) surface upon bombardment with 10 keV He+ are examined. When sulphur atoms—diffused from the bulk to the surface upon a 600°C anneal—are involved in the emission process, a strongly anisotropical emission is found. The anisotropy is related only to the incoming beam direction and appears to be fully independent of the copper target orientation. Some points of importance for a theoretical description are discussed. The anisotropy effect can effectively be used to determine the relative position of contaminant and substrate atoms in the uppermost surface layers. Thus, it is found that (1) sulphur atoms diffused to positions just below the surface occupy substitutional sites and (2)in this situation surface relaxation for the copper atoms in the first layer is negligible.

In low-energy noble gas ion scattering (LEIS) neutralisation plays an important role. Comparison of energy spectra of neutral scattered particles with ion spectra, and ion fractions derived from these data, provides information on neutralisation. To measure the energy of neutrals in the energy range (2-10 keV) a time-of-flight (TOF) spectrometer was used as well as a stripping cell in front of the electrostatic analyser. The results of both methods were compared for argon and neon neutrals of 5-10 keV with helium, nitrogen and argon as stripping gas. To investigate the properties of the cell neutral particles were used, obtained by scattering from a Cu(100) surface.

Ion Scattering Spectroscopy applied in the multiple scattering mode is used to determine the structure of a stepped Cu(410) surface. The energy of singly scattered ions is influenced by the presence of neighbour surface atoms. This effect can be used to determine interatomic distances up to about 10Å, as is shown by the results of 8 keV Ar+ and 11 keV Ne+ scattered through θ = 50°. The edge-edge distance of the stepped copper surface appears to be in accordance with the results of LEED experiments obtained by other investigators. The experiments show a good agreement with the results of the analytical 3-atom model of Poelsema. The energy of the so-called “plateau collision” appears to depend on the effective plateau length l as measured in the plane of incidence. Lengths l between 15 and 60 Å can be determined with an accuracy of 5 Å. Results are shown for 8 and 12 keV Ar+, θ = 40° and 60°, and 8 keV Kr+ θ = 40°. The experimental dependence of the energy on lis described correctly by a phenomenological model.

An apparatus is described for low energy (0.1–10 keV) ion scattering (LEIS) experiments. A time of flight (TOF) spectrometer is incorporated in the system to be able to measure the energy of particles in the neutral state after scattering. The energy resolution ΔE/E of the TOF spectrometer is discussed and found to be 0.5% (FWHM). This is sufficient for our scattering experiments. An electrostatic analyzer (ESA) is used to measure the energy of scattered ions [ΔE/E=0.5% (FWHM)]. Experiments show that in general the ion dose needed to obtain a TOF spectrum (2×1010 ions/cm2) is much smaller than the dose needed for an ESA-spectrum (6×1013 ions/cm2). The ion spectra measured with the TOF spectrometer, by subtracting the neutral yield from the total yield, as well as with the ESA are found to agree quite well. This provides a way to calibrate the TOF spectrometer. The determination of the ion fraction of scattered particles is discussed [10 keV40Ar+ on Cu(100), scattering angle 30°]. It is shown that the TOF spectrometer is able to measure light recoil particles (e.g. hydrogen) from a heavy substrate. In the analysing system is, in addition to the TOF spectrometer, also incorporated a stripping cell to measure the energy of neutral scattered particles. An energy spectrum of neutral scattered particles measured with both methods is shown.

Measurements of the ion fraction using the time of flight (TOF) technique, of low energy Ne (5–10 keV) scattered from a Cu (100) face are reported. The scattering angle θ is 30°. The scattering plane is in the 〈100〉, 〈110〉, 〈210〉 and 〈310〉 directions respectively. The ion fraction as a function of the final energy of the scattered particles has about the same shape as the ion spectrum: single and double collisions can be distinguished. Also there is a small difference between the energies of the scattered ions and neutrals in the single collision peak. The ion fractions indicate an increasing re-ionization during the scattering process as function of E0.

By temperature dependent Mössbauer measurements the magnetic hyperfine fields at different iron sites are determined. The Curie temperatures are also determined. These results are interpreted in terms of a modified Zener-Vonsovskii model.

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