Extension of the Electron-Promotion Model to Asymmetric Atomic Collisions

Barat, M.; Lichten, William

doi:10.1103/physreva.6.211

Cited by 813 publications

(152 citation statements)

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“…This atomistic description of ion-surface interactions is adequate because the valence charge is localized at the anion sites in MgO. The binary interaction promotes oxygen-2p electrons along quasi-molecular orbitals (MOs), 24 above a threshold projectile energy which has been determined to be ~50 eV for the analogous case of Na + exciting oxidized Al 17 Electrons in these MOs that correlate to excitons and conduction band states. The population of the final excited levels will decrease with excitation energy ΔE; and therefore will most likely lead to excitonic states.…”

Section: Discussionmentioning

confidence: 99%

Ion-induced electron emission from MgO by exciton decay into vacuum

et al. 2004

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Section: Discussionmentioning

confidence: 99%

Ion-induced electron emission from MgO by exciton decay into vacuum

et al. 2004

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“…Such "richness" in the scattering behavior is intimately linked to local charge exchange phenomena which occur as the atomic orbital ͑AO͒ states of the collision partners quantum mechanically mix into hybrid molecular orbitals ͑MOs͒ during the hard collision step ͑the Fano-Lichten MO mechanism͒. 51 Although many studies have been conducted with Ne + on Mg, Al, and Si at high collision energies, little experimental data exist for the threshold region at low impact energy where local charge exchange processes and inelastic losses begin to occur. We present a brief summary here of our experiments on Ne + collisions with light targets ͑Mg, Si, Al, and P͒ for impact energies Ͻ1400 eV to emphasize why tunable incident energy, as well as mass and energy filtering of scattered products, is necessary.…”

Section: B Charge Exchange Involving Ne + With Light Targetsmentioning

confidence: 99%

Low-energy ion beamline scattering apparatus for surface science investigations

Gordon

Giapis

2005

Review of Scientific Instruments

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We report on the design, construction, and performance of a high current ͑monolayers/ s͒, mass-filtered ion beamline system for surface scattering studies using inert and reactive species at collision energies below 1500 eV. The system combines a high-density inductively coupled plasma ion source, high-voltage floating beam transport line with magnet mass-filter and neutral stripping, decelerator, and broad based detection capabilities ͑ions and neutrals in both mass and energy͒ for products leaving the target surface. The entire system was designed from the ground up to be a robust platform to study ion-surface interactions from a more global perspective, i.e., high fluxes ͑Ͼ100 A/cm 2 ͒ of a single ion species at low, tunable energy ͑50-1400± 5 eV full width half maximum͒ can be delivered to a grounded target under ultrahigh vacuum conditions. The high current at low energy problem is solved using an accel-decel transport scheme where ions are created at the desired collision energy in the plasma source, extracted and accelerated to high transport energy ͑20 keV to fight space charge repulsion͒, and then decelerated back down to their original creation potential right before impacting the grounded target. Scattered species and those originating from the surface are directly analyzed in energy and mass using a triply pumped, hybrid detector composed of an electron impact ionizer, hemispherical electrostatic sector, and rf/dc quadrupole in series. With such a system, the collision kinematics, charge exchange, and chemistry occurring on the target surface can be separated by fully analyzing the scattered product flux. Key design aspects of the plasma source, beamline, and detection system are emphasized here to highlight how to work around physical limitations associated with high beam flux at low energy, pumping requirements, beam focusing, and scattered product analysis. Operational details of the beamline are discussed from the perspective of available beam current, mass resolution, projectile energy spread, and energy tunability. As well, performance of the overall system is demonstrated through three proof-of-concept examples: ͑1͒ elastic binary collisions at low energy, ͑2͒ core-level charge exchange reactions involving 20 Ne + with Mg/ Al/ Si/ P targets, and ͑3͒ reactive scattering of CF 2 + /CF 3 + off Si. These studies clearly demonstrate why low, tunable incident energy, as well as mass and energy filtering of products leaving the target surface is advantageous and often essential for studies of inelastic energy losses, hard-collision charge exchange, and chemical reactions that occur during ion-surface scattering.

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“…In IAES, on the other hand, very large excitation cross sections can occur by promotion of inner shell electrons through crossing of molecular orbitals. Such excitation processes have been described by Barat and Lichten [3] for bi-particle gas phase collisions. In addition to excitation of incident or target atoms, there would also be a substantial momentum transfer from the incident to the target atoms, which may cause the target atom to sputter off leading to the possibility of decay while the atom is either in motion in the solid or is traveling in vacuum after sputtering [e.g.…”

mentioning

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Ion-induced Auger Electron Spectroscopy as a Potential Route to Chemical Focused-Ion Beam Tomography

Parvaneh¹,

Hull²

2014

Microsc Microanal

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In this paper the possible application of ion-induced Auger electron spectroscopy (IAES) for 3D chemical tomography using the focused ion beam (FIB) is discussed. In conventional electron-induced Auger electron spectroscopy (EAES), an electron beam with energy 1-10kV is used to excite inner-shell (core) electrons of the solid. An electron from a higher electron energy state de-excites to this hole and the extra energy is then transferred to another electron, i.e. the Auger electron, which has a characteristic energy and serves to identify the excited atom [e.g. 1, 2]. In IAES, on the other hand, very large excitation cross sections can occur by promotion of inner shell electrons through crossing of molecular orbitals. Such excitation processes have been described by Barat and Lichten [3] for bi-particle gas phase collisions. In addition to excitation of incident or target atoms, there would also be a substantial momentum transfer from the incident to the target atoms, which may cause the target atom to sputter off leading to the possibility of decay while the atom is either in motion in the solid or is traveling in vacuum after sputtering [e.g. 4]. As a result there are differences between spectra induced by electrons and ions. In particular, interpretation of the ion-induced Auger spectra requires separate consideration of both excitation and decay processes.We have successfully integrated a state-of-the-art mass-filtered FIB (Orsay Physics) with a PHI Versaprobe XPS instrument. The concentric hemispherical analyzer (CHA) of the Versaprobe is then utilized to measure the kinetic energy of the Auger electrons induced by the ions from a gold-silicon alloy source. IAE spectra of some of the elements in third-row of the periodic table, namely Na, Mg, Al, Si, and the ones in the fourth-row, namely Ti, V, Cr, Mn, Fe, Co, Ni and Cu acquired using Si ++ and Au + incident ions will be presented and discussed (An example for Cr is shown in Figure 1, left). As a result of energetic collisions between the incident and target atoms, in addition to plasmon excitations, Auger electrons from both colliding particles are generated and detected. The efficiencies of Auger electron generation by ion impact from these elements, acquired under the same conditions, are compared with each other. The elements on the third row of periodic table in particular show narrow peaks emanated mainly from the decay of excited atoms. For heavier elements, however, the increase of fluorescence yield by increasing atomic number results in reduction of atomic contribution to the spectrum. Nevertheless, by using optimized analyzer settings, sharper peaks with higher signal to noise ratio are also achieved for these elements that sets the foundation for chemical tomographic imaging using IAE spectroscopy.

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Extension of the Electron-Promotion Model to Asymmetric Atomic Collisions

Cited by 813 publications

References 81 publications

Ion-induced electron emission from MgO by exciton decay into vacuum

Ion-induced electron emission from MgO by exciton decay into vacuum

Low-energy ion beamline scattering apparatus for surface science investigations

Ion-induced Auger Electron Spectroscopy as a Potential Route to Chemical Focused-Ion Beam Tomography

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