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Electron loss and electron emission for grazing impact of noble gas atoms with energies in the keV domain are investigated via time-of-flight spectra recorded in coincidence with the number of emitted electrons. The data is analyzed in terms of computer simulations concerning the interaction of the fast atoms with the electron gas in the selvedge of the Al(1 1 1) surface. The interaction is approximated by binary collisions of the fast atoms with Fermi electrons of the conduction band and differential cross sections obtained for electron scattering from free atoms. For an effective number of collisions of about 50 the energy loss spectra are fairly well reproduced by our calculations. We show that for our conditions the shift of the energy spectra for the emission of an additional electron from the surface is close to the work function of the target.

Kinetic electron emission (KE) for grazing scattering of H, He, Ne, and Ar ground state atoms with keV/amu impact energies on clean monocrystalline atomically flat Al and Cu surfaces has been studied in coincidence with projectile energy loss. Measured KE yields are subject to a clear impact energy threshold, in agreement with a free electron gas model description for the target electron momentum distribution (“classical” KE threshold). For smaller projectile scattering angles corresponding to larger distances of closest approach to the surface, this classical KE threshold is shifted to higher impact energies. By measuring KE threshold energies for different projectile scattering angles, we have probed the effective electron surface potential. For scattering of Ne and Ar atoms, a very weak electron emission is observed below the classical KE threshold, which within a more realistic description of the electron momentum distribution for the target surface can be ascribed to higher electron momenta. Grazing projectile scattering also permits a practically non-destructive surface structure determination, because a considerably larger number of electrons is emitted when changing from planar to axial surface scattering “surface triangulation”.

The energy loss of hydrogen atoms with energies of 400 eV and 1 keV is studied in coincidence with the number of emitted electrons during grazing scattering from atomically clean and flat KI(001) and LiF(001) surfaces. The energy loss spectra for specific numbers of emitted electrons are analyzed in terms of a binary interaction model based on the formation of transient negative ions via local capture of valence band electrons from anion sites. Based on computer simulations we derive for this interaction scenario probabilities for the production of surface excitons, for electron loss to the conduction band of KI, for emission of electrons, and for formation of negative hydrogen ions. The pronounced differences of data obtained for the two surfaces are attributed to the different electronic structures of KI and LiF.

Kinetic emission (KE) of electrons near its threshold is studied for grazing impact of keV He atoms on flat and clean Al(111), Al(110), and Cu(111) surfaces. We observe a defined dependence of the KE threshold behaviour on the scattering conditions. The data are analyzed in the framework of a classical model for electron emission based on momentum transfer in binary encounters between atomic projectiles and conduction electrons of the metal target. From the impact velocity dependence of KE yields near threshold we obtain information on momenta of Fermi electrons as a function of distance from the surface and on the corresponding electronic surface potential.

The energy loss of He atoms with energies E ⩽ 28 keV scattered from Al(1 1 1) under a grazing angle of incidence is recorded in coincidence with the number of electrons emitted in the collision. From our data we deduce the mean energies for emission of a specific number of electrons during impact of the atomic projectiles. We observe that only a fraction of some percent of the energy transferred to metal electrons results in their emission. The mean energy for emission of electrons in head-on binary collisions of He atoms with conduction electrons is estimated from a simple classical model which describes the data fairly well. For higher energies of the projectile motion with respect to the surface normal, i.e. collisions with surface atoms under smaller impact parameters, the mean energy transfer to emitted electrons is enhanced which is attributed to an electron promotion mechanism.

In grazing collisions of atoms and ions with monocrystalline surfaces, projectiles are scattered along defined trajectories, and electron emission therefore proceeds under well characterised conditions compared to large-angle impact on polycrystalline target surfaces. Total electron yields can be measured in coincidence with energy loss of scattered projectiles, down to 10-4 electrons per projectile near the threshold for kinetic electron emission. In the present comment we demonstrate the recent experimental progress for grazing scattering of slow (>100 eV up to some keV per amu) atoms and multiply charged ions on metal (Au, Al) and insulator (LiF) surfaces. Observed kinetic and potential electron emission processes can be quantitatively explained in terms of simple model assumptions. These experiments are carried out in a practically non-destructive manner with intriguing aspects for novel surface-analytical applications.

We present an analysis of data obtained in coincident studies on projectile energy loss and number distributions of emitted electrons for scattering of hydrogen atoms from an atomically clean and flat LiF(0 0 1) surface. The emission of electrons, production of surface excitons and formation of negative ions is explained by a model of electron capture by projectiles at fluorine lattice sites where the formation of negative hydrogen ions is the common precursor for the electronic processes of relevance here. We describe the interactions in terms of concepts for gas phase collisions and derive probabilities for the detachment of negative ions during the collision with the insulator surface.

In coincident studies on projectile energy loss and number distributions of emitted electrons for scattering of hydrogen atoms from an atomically clean and flat LiF(0 0 1) surface we derive probabilities for emission of electrons and production of surface excitons near their respective kinematic thresholds. We analyze our data in terms of electron transfer in binary atomic collisions with one collision partner being embedded at the anion site of an ionic crystal and derive information on the energy defects in these collisions.

The energy loss of kilo-electronvolt hydrogen atoms for scattering from a LiF(001) surface under a grazing angle of incidence is measured in coincidence with the number of emitted electrons. The combined time-of-flight and electron number distributions show discrete features which are attributed to specific numbers for emitted electrons and production of surface excitons. The distributions are fairly well reproduced in terms of binomial distributions. The corresponding probabilities for electron and exciton production can consistently be related to a model where the formation of negative hydrogen atoms via local electron capture from halogen lattice sites is considered as a precursor for both processes.

Neutral hydrogen atoms with energies ranging from 300 eV to 1.5 keV are scattered from a clean and flat LiF(0 0 1) surface under grazing angles of incidence. By detection of time-of-flight spectra in coincidence with the number of emitted electrons, we study electron emission and excitation phenomena near their respective thresholds. We find in this energy regime population of surface excitons as dominant inelastic interaction channel. The data are consistently interpreted in the framework of a binary collision model where the formation of negative hydrogen ions is the common precursor of electronic excitation of the target and electron emission.

Neutral hydrogen atoms with energies ranging from about 1 to 20 keV are scattered from a clean and flat LiF(0 0 1) surface under grazing angles of incidence. By detection of time-of-flight (TOF) spectra in coincidence with the signal of an electron number detector, we study electron emission and excitation phenomena. We present recent progress in an on-line processing of spectra by means of a double coincidence unit.

Electron emission from LiF, KCl, and KI crystal surfaces during grazing collisions of swift protons is studied using a first-order distorted-wave formalism. Owing to the localized character of the electronic structure of these surfaces, we propose a model that allows us to describe the process as a sequence of atomic transitions from different target ions. Experimental results are presented for electron emission from LiF and KI and energy loss from KI surfaces. Calculations show reasonable agreement with these experimental data. The role played by the charge of the incident particle is also investigated.

The energy loss of $100\text{\ensuremath{-}}\mathrm{keV}$ hydrogen atoms scattered under a grazing angle of incidence from a clean and flat Cu(111) surface is studied in coincidence with the number of emitted electrons. From the dependence of the energy loss on the angle of incidence we deduce the position dependent stopping power which shows the same functional dependence but a factor of about 2 higher values than recent calculations. From the number of emitted electrons related to a specific energy loss we reveal processes related to electron emission as dominant channel for energy dissipation of scattered projectiles.

The number of electrons emitted during grazing scattering of Ne atoms with kilo-electron-volt energies from an Al(111) surface is recorded in coincidence with the energy loss of scattered projectiles. Irrespective of the total projectile energies used, we observe a pronounced increase of total electron emission yields when the energy for motion normal to the surface exceeds about 25 eV. Based on energy loss spectra and classical computer simulations of projectile trajectories we attribute electron emission under these scattering conditions to a promotion mechanism in binary collisions between Ne and Al target atoms resulting in single and double excitations of projectiles.

The coincident measurement of projectile time-of-flight spectra and number of emitted electrons for grazing scattering of fast ${\mathrm{H}}^{0}$ atoms from a LiF(001) surface allows us to investigate electronic excitation and emission processes, including those without emission of electrons. Using this method, we are able to study very small electron emission yields and thus kinetic threshold behavior for projectile induced electronic processes. We observe different onsets for electron emission and electronic excitation of the target, providing important conclusions on the relevant interaction mechanisms. Near the kinetic thresholds, inelastic processes are found to be dominated by production of surface excitons.

Fast He + ions and He° atoms are scattered under grazing incidence from a clean and flat Al(111) surface. The target current recorded as function of azimuthal angle with respect to the surface orientation is enhanced for scattering along low-index crystallographic directions. Coincident studies on the number of electrons emitted per ion impact allow us to explore this effect. We find that the increase of the total electron yield for surface channeling along low-index directions stems primarily from projectiles with trajectories in the subsurface region and the consequent emission of a substantially larger number of electrons.