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.     

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.     

Life-time and surface effects on the L23 VV Auger spectra of aluminum

Electronic life-time and surface effects on the L₂₃ VV Auger spectrum of Al have been calculated. The resulting spectrum predicts a low energy secondary peak due to plasmon excitation and shows good agreement with experiment at the main peak region.     

Auger electron emission by ion bombardment of light metals

The energy distribution of secondary electrons ejected from a metallic target upon ion bombardment (Ar⁺, 10 keV) is studied with a 180° magnetic analyser, particularly in the vicinity of the Auger peaks that appear in the electron spectra of the light metals (Li, Be; Na, Mg, Al, Si). A qualitative explanation based on the correlation diagrams which described the evolution of the electronic levels during the collision of two atoms inside the target is proposed to interpret the variation of the Auger peak intensity with the atomic number of the target.     

Spatially nonlocal model of surface erosion by ion bombardment

A model of solid surface erosion under ion bombardment is proposed. This model takes into account the dependence of the local sputtering yield on the nanoscale relief at a given point and the point of incidence of a primary ion. Such an approach leads to spatially nonlocal erosion model, which predicts the formation of a wavelike relief in the presence of nanoscale inhomogeneities on the surface.     

Auger spectra of aluminium and magnesium induced by caesium-ion bombardment

A caesium ion beam has been used to excite electron emission from Mg, Al, AlAs and GaAs. The portions of the electron emission spectra that result from Auger transitions are compared with previously reported spectra generated with different primary ion beams. It is observed that 10 keV Cs⁺-ion bombardment produces very few excited ions with two 2p vacancies. Evidence for two atomic-like peaks discussed by previous authors, but not unambiguously identified, is also presented.     

Variational treatment of continuum orbitals for Auger electrons emitted from neon

A variational method is applied to obtain the wave function of the continuum Auger electron emitted from an ionized neon atom. The trial function is taken to depend on several adjustable parameters, and the wave function of the electrons in different orbitals, such that all possible virtual states of the quantum mechanical system composed of the Auger electron and the ion are represented. The continuum wave function is improved iteratively by increasing the number of terms.Auger transition rates are then calculated applying the angular momentum average scheme, and are compared with other theoretical and experimental results. Agreement with the latest experiment is achieved.     

Study of theK α satellites and hypersatellites in the x-ray and Auger spectra of neon

We report in this paper our calculations of the energies of the satellite and hypersatellite lines in the x-ray and Auger spectra of neon, using screened hydrogenic wavefunctions. Our calculations have enabled us to draw an energy level diagram for the neon atom in various defect-electron configurations. It is possible to show the transitions giving rise to the various x-ray and Auger satellites and hypersatellites using this diagram. The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion     

Multiatomic clusters emerging from a metal surface under ion bombardment

[Ag _n ]^? ions emerging from a silver target under bombardment with energetic krypton ions have been measured forn ranging up to 60. The relative intensities of ions with odd numbers are strikingly favoured. The numbersn=8 and 20 mark minima in the abundance of ions with even numbers. The observations are briefly discussed.     

The KLL Auger spectrum of neon from the EC-decay of Na

The low energy KLL Auger electrons of neon emitted after EC-decay of ²²Na have been investigated with a 4 eV instrumental resolution using an electrostatic spectrometer and a solid state radioactive source. This is the first experimental investigation of the KLL Auger spectrum of neon from the solid state. Relative intensities and energies of all resolved spectrum components were determined. Measured absolute energy of the dominant KL₂L₃(¹D) transition was found to be 824.5(19) eV, i.e. about 20 eV higher than that obtained in experiments with free Ne atoms. Within the experimental uncertainties, no influence of solid state effects on relative intensities of the KLL transitions was found.     

Multiple scattering features in neon ion scattering spectra (ISS) from polycrystalline materials

A systematic investigation of multiple scattering from polycrystalline materials in ion scattering spectrometry was carried out using Ne⁺ at a scattering angle of 90° over the energy range of 100 to 2500 eV. It was found that the intensity of multi scattering shoulders increased with ion beam energy. The intensity at a given energy could be predicted on the basis of interatomic distances of the target. The larger the interatomic distance, the more intense the multi scattering shoulder. The separation of the double scattering shoulder from the binary peak decreased linearly with increasing mass, and the maximum of the shoulder to higher energies from the binary peak could be calculated by the relationship $\text{ΔE}\text{E}{}_0\text{= 0.166 ?(0.00064)M}$, where M is the mass of the target atom.     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明:自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

Theoretical energy distributions of atoms sputtered from elastic collision spikes by monomer and dimer ion bombardment

The energy spectra of atoms sputtered from metal targets by bombardment with heavy monomer and dimer ions have been investigated on the basis of a standard model for elastic collision spikes. In particular we calculated the energy distributions for a Au sample bombarded by 4 keV I⁺ and 8 keV I ₂ ⁺ ions. The results were compared with the recent time of flight measurements performed by de Vries and coworkers. It was shown that the model described accurately most of the experimental observations: the count rates and the relative cascade to spike ratios for both I⁺ and I ₂ ⁺ projectiles, and the energy spectrum for dimer sputtering. The spectrum for monomer bombardment, however, was shifted towards lower energies in comparison to the experimental one. The possible source of this discrepancy is discussed.This work was supported by the Central Research Program CPBP 01.09     

The energy spectra of secondary ions emitted during ion bombardment

Secondary ion energy spectra have been measured for singly charged ions emitted from targets irradiated with 43 keV A⁺ ions. Targets studied include the 3d transition metals (Sc, Ti, V, Cr, Fe, Ni) Cu and Zn, Zr, Al and Si and the compounds SiO₂, Al₂O₃, NaCl, KCl. Energy spectra were measured in the energy range 1–600 eV. In several cases a peak in the energy spectrum in the region around 200 eV has been found. This is in addition to the usual low energy peaks in the region of 5–10 eV. In many cases the low energy peak was observed to decay steadily with irradiation time or to increase with oxygen pressure. In the case of the cleanest Zn spectrum, only the high energy peak can be detected. The data are discussed in relation to current models of secondary ion emission. We conclude that, in general, elemental metal targets which are clean are characterised by the high energy peak in the secondary ion energy spectrum. The slower ions emitted have been neutralised by electron exchange processes. The low energy peaks in unclean, partially clean, oxide coated or compound targets (NaCl, KCl) arise because the neutralisation of the slower ions is either not as efficient or is not possible. The secondary ion emission model of Blaise and Slodzian could account for the emission of ions from most targets.     

脉冲离子束作用下靶面次级电子的抑制

论述了离子束作用下固体表面次级电子产生的机制,介绍了特种真空器件中次级电子抑制的各种方法及其优缺点,提出了脉冲离子束作用下靶面次级电子抑制的自偏势法和曲面靶法等设计思路,并在实验上进行了初步验证。实验结果表明,自偏势电压大于80 V后,次级电子得到很好的抑制。在相同束流情况下,曲面靶较平面靶的次级电子产额少。利用实验结果进行估算得到了近似的次级电子产额约为0.67,比文献中的结果(0.58)偏大。对实验中自偏势法抑制反峰电子电流的效果进行了分析和讨论,结果表明：自偏势法不但能够有效抑制离子打靶产生的次级电子,还能抑制由功率源不稳定带来的入射反峰电子流。     

Modification of the lunar surface by solar wind ion bombardment

Trivalent osmium ions are substitutionally incorporated into aqueous precipitates and melt-grown single crystals of AgBr and AgC1. The ions are distributed between three structurally inequivalent lattice sites in both salts. From epr studies, we have inferred that these sites are distinguished by the arrangement of charge-compensating silver ion vacancies in the two closest cation subshells. The most reasonable dopant-vacancy configurations have been deduced from the epr data. These configurations persist up to at least 300 K, and are compared with those observed in other trivalent metal ion doped systems.     

A model for the impregnated cathode emission behaviour under ion bombardment

The electron current emitted by a cathode in the saturation region decrease if the cathode is exposed to ion bombardment. The change in surface coverage with barium (oxide) is used in the model to describe the current behaviour. The steady state current reached (equilibrium current) depends on the gas pressure. The experimental results can be explained in terms of the model and the parameters are determined. The temperature dependence of the barium supply rate for an S-and M-type impregnated cathode are determined.