2024 |
Pollak, E., Roncin, P., Allison, W., & Miret-Artes, S. (2024). Grazing incidence fast atom diffraction: general considerations, semiclassical perturbation theory and experimental implications. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 26.
Résumé: Using semiclassical methods, an analytical approach to describe grazing incidence scattering of fast atoms (GIFAD) from surfaces is described. First, we consider a model with a surface corrugated in the scattering plane, which includes the surface normal and the incidence direction. The treatment uses a realistic, Morse potential, within a perturbation approach, and correctly reproduces the basic GIFAD phenomenology, whereby the scattering is directed primarily in the specular direction. Second, we treat the more general case of scattering from a surface corrugated in two-dimensions. Using time averaging along the direction of fast motion in the incidence direction, we derive a time dependent potential for the GIFAD scattering away from a low index direction. The results correctly describe the observation that diffraction is seen only when the scattering plane is aligned close to a low-index direction in the surface plane. For the case of helium scattering from LiF(001) we demonstrate that the resulting theoretical predictions agree well with experiment and show that the analysis provides new information on the scattering time and the length scale of the interaction. The analysis also gives insights into the validity of the axial surface channeling approximation (ASCA) and shows that within first order perturbation theory, along a low-index direction, the full 3-dimensional problem can be represented accurately by an equivalent 2-dimensional problem with a potential averaged along the third dimension. In contrast, away from low-index directions, the effective 2-dimensional potential in the projectile frame is time-dependent.
|
|
Rousseau, P., & Roncin, P. (2024). Fast ion diffraction of protons on NaCl, the discovery of GIFAD. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 554, 165457.
Résumé: Grazing incidence fast atom diffraction (GIFAD or FAD) has become a technique to track the surface topology of crystal surface at the atomic scale. The paper retraces the events that led to the discovery of unexpected quantum behavior of keV atoms during the thesis of Patrick Rousseau in Orsay and Andreas Schueller in Berlin. In Orsay, it started by diffraction spots whereas in Berlin supernumerary rainbows were first identified at keV. Though the discovery was not anticipated, it did not take place by accident, everything was in place several years before, waiting only for an interest in neutral projectiles with a touch of curiosity.
|
|
2023 |
Buhler, J., Roncin, P., & Brand, C. (2023). Describing the scattering of keV protons through graphene. FRONTIERS IN CHEMISTRY, 11, 1291065.
Résumé: Implementing two-dimensional materials in technological solutions requires fast, economic, and non-destructive tools to ensure efficient characterization. In this context, scattering of keV protons through free-standing graphene was proposed as an analytical tool. Here, we critically evaluate the predicted effects using classical simulations including a description of the lattice's thermal motion and the membrane corrugation via statistical averaging. Our study shows that the zero-point motion of the lattice atoms alone leads to considerable broadening of the signal that is not properly described by thermal averaging of the interaction potential. In combination with the non-negligible probability for introducing defects, it limits the prospect of proton scattering at 5 keV as an analytic tool.
|
|
Debiossac, M., Pan, P., & Roncin, P. (2023). Elastic and inelastic diffraction of fast neon atoms on a LiF surface. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 25(45), 30966–30974.
Résumé: Grazing incidence fast atom diffraction has mainly been investigated with helium atoms, considered as the best possible choice for surface analysis. This article presents experimental diffraction profiles recorded with neon projectile, between 300 eV and 4 keV kinetic energy with incidence angles theta(i) between 0.3 and 1.5 degrees along three different directions of a LiF(001) crystal surface. These correspond to perpendicular energy ranging from a few meV up to almost 1 eV. A careful analysis of the scattering profile allows us to extract the diffracted intensities even when inelastic effects become so large that most quantum signatures have disappeared. The relevance of this approach is discussed in terms of surface topology.
|
|
Pan, P., Kanitz, C., Debiossac, M., Le-Guen, A., Rad, J. N., & Roncin, P. (2023). Lateral line profiles in fast-atom diffraction at surfaces. PHYSICAL REVIEW B, 108(3), 035413.
Résumé: Grazing incidence fast-atom diffraction (GIFAD) uses keV atoms to probe the topmost layer of crystalline surfaces. The atoms are scattered by the potential energy landscape of the surface onto elastic diffraction spots located at the Bragg angles and on the Laue circle. However, atoms transfer a significant momentum to the surface, giving rise to possible phonon excitation. This causes the inelastic intensity to spread above and below the circle along the direction of the surface normal. The relative intensity of the elastic contribution is well fitted by the Debye-Waller model adapted to GIFAD, but the composite azimuthal line profile governing the ability to resolve diffraction spots has not been investigated in detail. The paper reports a series of diffraction measurements of helium on a LiF(001) surface revealing marked differences in the polar (θ) and lateral (ϕ) inelastic profiles but also similarities in the evolution of their line widths σθ and σϕ. We observe two regimes: When elastic diffraction is significant, the Laue circle appears as a reference for inelastic diffraction; the azimuthal inelastic line shape is an exponential decay and its width increases almost linearly as the scattering angle deviates from the specular condition. When elastic diffraction weakens, the inelastic line shape evolves towards a Gaussian and its width is no longer minimum on the Laue circle. As a possible difference with x ray, neutrons, and electrons, the in-plane motion of surface atoms may not be the dominant cause of the broadening of the lateral profile in GIFAD.
|
|
2022 |
Pan, P., Debiossac, M., & Roncin, P. (2022). Temperature dependence in fast-atom diffraction at surfaces. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 24(20), 12319–12328.
Résumé: Grazing incidence fast atom diffraction at crystal surfaces (GIFAD or FAD) has demonstrated coherent diffraction both at effective energies close to one eV (lambda( perpendicular) approximately 14 pm for He) and at elevated surface temperatures offering high topological resolution and real time monitoring of growth processes. This is explained by a favorable Debye-Waller factor specific to the multiple collision regime of grazing incidence. This paper presents the first extensive evaluation of the temperature behavior between 177 and 1017 K on a LiF surface. Similarly to diffraction at thermal energies (TEAS), an exponential attenuation of the elastic intensity is observed but, contrarily to TEAS, the maximum coherence is not directly reduced by the attraction forces that increase the effective impact energy. It is more influenced by the surface stiffness and appears very sensitive to surface defects.
|
|
Pan, P., Rad, J. N., & Roncin, P. (2022). A setup for grazing incidence fast atom diffraction. REVIEW OF SCIENTIFIC INSTRUMENTS, 93(9), 093305.
Résumé: We describe a UHV setup for grazing incidence fast atom diffraction (GIFAD) experiments. The overall geometry is simply a source of keV atoms facing an imaging detector. Therefore, it is very similar to the geometry of reflection high energy electron diffraction experiments used to monitor growth at surfaces. Several custom instrumental developments are described making GIFAD operation efficient and straightforward. The difficulties associated with accurately measuring the small scattering angle and the related calibration are carefully analyzed.
|
|
2021 |
Debiossac, M., Pan, P., & Roncin, P. (2021). Grazing incidence fast atom diffraction, similarities and differences with thermal energy atom scattering (TEAS). PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 23, 7615–7636.
Résumé: Grazing incidence fast atom diffraction (GIFAD) at surfaces has made rapid progress and has established itself as a surface analysis tool where effective energy E perpendicular of the motion towards the surface is in the same range as that in thermal energy atom scattering (TEAS). To better compare the properties of both techniques, we use the diffraction patterns of helium and neon atoms impinging on a LiF (001) surface as a model system. E-Scan, theta-scan, and phi-scan are presented where the primary beam energy E is varied between a few hundred eV up to five keV, the angle of incidence theta between 0.2 and 2 degrees and the azimuthal angle phi around 360 degrees . The resulting diffraction charts are analyzed in terms of high and low values of effective energy E perpendicular. The former provides high resolution at the positions of the surface atoms and the attached repulsive interaction potentials while the second is sensitive to the attractive forces towards the surface. The recent progress of inelastic diffraction is briefly presented.
|
|
Pan, P., Debiossac, M., & Roncin, P. (2021). Polar inelastic profiles in fast-atom diffraction at surfaces. PHYSICAL REVIEW B, 104, 165415.
Résumé: Elastic diffraction of fast atoms at crystal surfaces under grazing incidence θ ≈ 1° has strong similarities with atomic diffraction at thermal energies discovered almost hundred years ago. Here, we focus on the polar scattering profile, which does not exhibit diffraction features but shows well-defined elastic and inelastic components that are found to be essentially independent of the crystallographic axis. The width σθ of the inelastic component is very sensitive to the weak attractive forces responsible for the physisorption. This effect is visible on an energy range almost ten times larger than the depth D of the physisorption well. Experimental data are analyzed using a binary collision model with a Morse potential where the width σθ of the scattering profile is connected to the classical energy loss and is governed by the surface stiffness, defined as the logarithmic derivative of the interaction potential along the surface normal. The main outcome is that the weak attractive forces make the mean surface potential almost twice harder at low energy.
|
|
2020 |
Debiossac, M., Roncin, P., & Borisov, A. G. (2020). Refraction of Fast Ne Atoms in the Attractive Well of a LiF(001) Surface. J. Phys. Chem. Lett., 11, 4564–4569.
Résumé: Ne atoms with energies of </=3 keV are diffracted under grazing angles of incidence from a LiF(001) surface. For a small momentum component of the incident beam perpendicular to the surface, we observe an increase in the elastic rainbow angle together with a broadening of the inelastic scattering profile. We interpret these two effects as the refraction of the atomic wave in the attractive part of the surface potential. We use a fast, rigorous dynamical diffraction calculation to find a projectile-surface potential model that enables a quantitative reproduction of the experimental data for </=10 diffraction orders. This allows us to extract an attractive potential well depth of 10.4 meV. Our results set a benchmark for more refined surface potential models that include the weak van der Waals region, a long-standing challenge in the study of atom-surface interactions.
|
|
Roncin, P. (2020). Revisiting atomic collisions physics with highly charged ions, a tribute to Michel Barat. Journal of Physics B: Atomic, Molecular and Optical Physics, 53, 202001.
Résumé: Michel Barat passed away in November 2018 at the age of 80 after a rich career in atomic and molecular collisions. He had participated actively in formalizing the electron promotion model, contribuing to low energy reactive collisions at the frontier of chemistry. He investigated electron capture mechanisms by highly charged ions (HCI), switched to collision induced cluster dissociation and finally to UV laser induced fragmentation mechanisms of biological molecules. During this highly active time he created a laboratory, organized ICPEAC and participated actively in the administration of research. This paper covers the 10 years when he mentored my scientific activity in the blossoming field of electron capture by
HCI. In spite of an impressive number of open channels, Michel found a way to capture the important parameters and to simplify the description of several electron capture processes; orientation propensity, electron promotion, true double electron capture, transfer ionisation, transfer excitation, formation of Rydberg states, and electron capture by metastable states. Each time Michel established fruitful collaborations with other groups.
|
|
2019 |
Brand, C., Debiossac, M., Susi, T., Aguillon, F., Kotakoski, J., Roncin P., & Arndt, M. (2019). Coherent diffraction of hydrogen through the 246 pm lattice of graphene. New J. Phys., 21, 033004.
Résumé: We study the diffraction of neutral hydrogen atoms through suspended single-layer graphene using molecular dynamics simulations based on density functional theory. Although the atoms have to overcome a transmission barrier, we find that the de Broglie wave function for H at 80 eV has a high probability to be coherently transmitted through about 18% of the graphene area, contrary to the case of He. We propose an experiment to realize the diffraction of atoms at the natural hexagon lattice period of 246 pm, leading to a more than 400-fold increase in beam separation of the coherently split atomic wave function compared to diffraction experiments at state-of-the art nano-machined masks. We expect this unusual wide coherent beam splitting to give rise to novel applications in atom interferometry.
|
|
Brand, C., Debiossac, M., Susi, T., Aguillon, F., Kotakoski, J., Roncin, P., & Arndt, M. (2019). Coherent diffraction of hydrogen through the 246 pm lattice of graphene. NEW JOURNAL OF PHYSICS, 21(3), 033004.
Résumé: We study the diffraction of neutral hydrogen atoms through suspended single-layer graphene using molecular dynamics simulations based on density functional theory. Although the atoms have to overcome a transmission barrier, we find that the de Broglie wave function for H at 80 eV has a high probability to be coherently transmitted through about 18% of the graphene area, contrary to the case of He. We propose an experiment to realize the diffraction of atoms at the natural hexagon lattice period of 246 pm, leading to a more than 400-fold increase in beam separation of the coherently split atomic wave function compared to diffraction experiments at state-of-the art nano-machined masks. We expect this unusual wide coherent beam splitting to give rise to novel applications in atom interferometry.
|
|
2018 |
Roncin, P., Debiossac, M., Oueslati, H., & Raouafi, F. (2018). Energy loss and inelastic diffraction of fast atoms at grazing incidence. NIM-B, 427, 100–107.
Résumé: The diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD) was first interpreted only in terms of elastic diffraction from a perfectly periodic rigid surface with atoms fixed at equilibrium positions. Recently, a new approach has been proposed, referred here as the quantum binary collision model (QBCM). The QBCM takes into account both the elastic and inelastic momentum transfers via the Lamb-Dicke probability. It suggests that the shape of the inelastic diffraction profiles are log-normal distributions with a variance proportional to the nuclear energy loss deposited on the surface. For keV Neon atoms impinging on a LiF(001) surface under an incidence angle θ, the predictions of the QBCM in its analytic version are compared with numerical trajectory simulations. Some of the assumptions such as the planar continuous form, the possibility to neglect the role of lithium atoms and the influence of temperature are investigated. A specific energy loss dependence ΔE θ ∝ 7 is identified in the quasi-elastic regime merging progressively to the classical onset ΔE θ ∝ 3. The ratio of these two predictions highlights the role of quantum effects in the energy loss.
|
|
2017 |
Cartry G., Kogut D., Achkasov K., Layet J.M., Farley T., Gicquel A., Achard J., Brinza O., Bieber T., Khemliche H., Roncin P., & Simonin A. (2017). Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H2/D2 plasmas. New J. Phys., 19(2), 025010.
Résumé: This paper deals with a study of H−/D− negative ion surface production on diamond in low pressure
H2/D2 plasmas. A sample placed in the plasma is negatively biased with respect to plasma potential.
Upon positive ion impacts on the sample, some negative ions are formed and detected according to
their mass and energy by a mass spectrometer placed in front of the sample. The experimental
methods developed to study negative ion surface production and obtain negative ion energy and angle
distribution functions are first presented. Different diamond materials ranging from nanocrystalline
to single crystal layers, either doped with boron or intrinsic, are then investigated and compared with
graphite. The negative ion yields obtained are presented as a function of different experimental
parameters such as the exposure time, the sample bias which determines the positive ion impact
energy and the sample surface temperature. It is concluded from these experiments that the electronic
properties of diamond materials, among them the negative electron affinity, seem to be favourable for
negative-ion surface production. However, the negative ion yield decreases with the plasma induced
defect density.
|
|
Debiossac, M., Atkinson, P., Zugarramurdi, A., Eddrief, M., Finocchi, F., Etgens, V. H., Momeni, A., Khemliche, H., Borisov, A. G., & Roncin, P. (2017). Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination. Appl. Surf. Sci., 391, 53–58.
Résumé: brief oveview of the benefit of having a grazing incidence fast atom diffraction (GIFAD) setup inside a molecular beam eppitaxy setup.
|
|
Roncin P., & Debiossac M. (2017). Elastic and inelastic diffraction of fast atoms, Debye-Waller factor, and Mössbauer-Lamb-Dicke regime. Phys. Rev. B., 96, 035415.
Résumé: The diffraction of fast atoms at crystal surfaces is ideal for a detailed investigation of the surface electronic
density. However, instead of sharp diffraction spots, most experiments show elongated streaks characteristic
of inelastic diffraction. This paper describes these inelastic profiles in terms of individual inelastic collisions
with surface atoms taking place along the projectile trajectory and leading to vibrational excitation of the local
Debye oscillator. A quasielastic regime where only one inelastic event contributes is identified as well as a
mixed quantum-classical regime where several inelastic collisions are involved. These regimes describe a smooth
evolution of the scattering profiles from sharp spots to elongated streaks merging progressively into the classical
diffusion regime.
|
|
2016 |
Debiossac, M., & Roncin, P. (2016). Image processing for grazing incidence fast atom diffraction. In NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS (Vol. 382, 36).
Résumé: Grazing incidence fast atom diffraction (GIFAD, or FAD) has developed as a surface sensitive technique.
Compared with thermal energies helium diffraction (TEAS or HAS), GIFAD is less sensitive to thermal
decoherence but also more demanding in terms of surface coherence, the mean distance between defects.
Such high quality surfaces can be obtained from freshly cleaved crystals or in a molecular beam epitaxy
(MBE) chamber where a GIFAD setup has been installed allowing in situ operation. Based on recent pub-
lications by Atkinson et al. (2014) and Debiossac et al. (2014), the paper describes in detail the basic steps
needed to measure the relative intensities of the diffraction spots. Care is taken to outline the underlying
physical assumptions.
|
|
Debiossac, M., Zugarramurdi, A., Mu, Z., Lunca-Popa, P., Mayne, A. J., & Roncin, P. (2016). Helium diffraction on SiC grown graphene: Qualitative and quantitative descriptions with the hard-corrugated-wall model. PHYSICAL REVIEW B, 94(20), 205403.
Résumé: Monolayer epitaxial graphene grown on 6H-SiC(0001) was recently investigated by grazing-incidence fastatom diffraction and analyzed with an ab initio electronic density calculation and with exact atomic diffraction methods. With these results as a reference, the hard-corrugated-wall model (HCW) is used as a complementary analytic approach to link binary potentials to the observed atomic corrugation. The main result is that the HCW model reproduces the macroscopic corrugation of the moir´e pattern on a quantitative level, suggesting that soft-wall corrections may be neglected for macroscopic superstructures, allowing straightforward analysis in terms of a one-dimensional corrugation function.
|
|
Kalashnyk N., Khemliche H., & Roncin P. (2016). Atom beam triangulation of organic layers at 100 meV normal energy:self-assembled perylene on Ag(1 1 0) at room temperature. Appl. Surf. Sci., 364, 235–240.
Résumé: The controlled growth of organic layers on surfaces is still waiting for an in-situ reliable technique thatwould allow their quality to be monitored and improved. Here we show that the growth of a perylene monolayer deposited on Ag(110) at room temperature can be tracked with low energy atoms in a regime where the energy perpendicular to the layer is less than 0.1 eV and below the organic film damage threshold. The image processing required for this atom triangulation technique is described in detail.
|
|
Sereno, M., Lupone, S., Debiossac, M., Kalashnyk, N., & Roncin, P. (2016). Active correction of the tilt angle of the surface plane with respect to the rotation axis during azimuthal scan. In NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS (Vol. 382, 123).
Résumé: A procedure to measure the residual tilt angle ττ between a flat surface and the azimuthal rotation axis of the sample holder is described. When the incidence angle θ and readout of the azimuthal angle ϕ are controlled by motors, an active compensation mechanism can be implemented to reduce the effect of the tilt angle during azimuthal motion. After this correction, the effective angle of incidence is kept fixed, and only a small residual oscillation of the scattering plane remains.
|
|
2015 |
Lupone, S., Damoy, S., Husseen, A., Briand, N., Debiossac, M., Tall, S., & Roncin, P. (2015). A large open ratio, time and position sensitive detector for time of ight measurements in UHV. RSI, 86, 126115.
Résumé: We report on the construction of an UHV compatible 40 mm active diameter detector based on micro channel plates and assembled directly on the feed-throughs of a DN63CF flange. It is based on the charge division technique and uses a standard 2 inch Si wafer as a collector. The front end electronic is placed directly on the air side of the flange allowing excellent immunity to noise and a very good timing signal with reduced ringing. The important aberrations are corrected empirically
providing an absolute positioning accuracy of 500 μm while a 150 μm resolution is measured in the center.
|
|
Zugarramurdi, A., Momeni, A., Debiossac, M., Lunca-Popa, P., Mayne, A.J., Borisov, A.G., Mu, Z., Roncin, P. & Khemliche, H. (2015). Determination of the geometric corrugation of graphene on SiC(0001) by grazing incidence fast atom diffraction. Appl. Phys. Lett., 106(10), 101902.
Résumé: We present a grazing incidence fast atom diffraction (GIFAD) study of monolayer graphene on 6H-SiC(0001). This system shows a Moiré-like 13x13 superlattice above the reconstructed carbon buffer layer. The averaging property of GIFAD results in electronic and geometric corrugations that are well decoupled; the graphene honeycomb corrugation is only observed with the incident beam parallel to the zigzag direction while the geometric corrugation arising from the superlattice is revealed along the armchair direction. Full-quantum calculations of the diffraction patterns show the very high GIFAD sensitivity to the amplitude of the surface corrugation. The best agreement between the calculated and measured diffraction intensities yields a corrugation height of 0.27 +- 0.3A° .
|
|
2014 |
Atkinson, P., Eddrief, M., Etgens, V. H., Khemliche, H., Debiossac, M., Momeni, A., Mulier, M., Lalmi, B., & Roncin, P. (2014). Dynamic grazing incidence fast atom diffraction during molecular beam epitaxial growth of GaAs. Appl. Phys. Lett., 105(2).
Résumé: A Grazing Incidence Fast Atom Diffraction (GIFAD) system has been mounted on a commercial molecular beam epitaxy chamber and used to monitor GaAs growth in real-time. In contrast to the conventionally used Reflection High Energy Electron Diffraction, all the GIFAD diffraction orders oscillate in phase, with the change in intensity related to diffuse scattering at step edges. We show that the scattered intensity integrated over the Laue circle is a robust method to monitor the periodic change in surface roughness during layer-by-layer growth, with oscillation phase and amplitude independent of incidence angle and crystal orientation. When there is a change in surface reconstruction at the start of growth, GIFAD intensity oscillations show that there is a corresponding delay in the onset of layer-by-layer growth. In addition, changes in the relative intensity of different diffraction orders have been observed during growth showing that GIFAD has the potential to provide insight into the preferential adatom attachment sites on the surface reconstruction during growth. (C) 2014 AIP Publishing LLC.
|
|
Debiossac M. and Roncin P. (2014). Atomic diffraction under oblique incidence: An analytical expression. Phys. Rev. A., 90, 054701.
Résumé: The semiclassical perturbation method developed by Henkel et al. [J. Phys. II 4, 1955 (1994)] to model
cold-atom diffraction by optical standing waves, is applied to the diffraction of fast atoms on crystal surfaces at
grazing incidence (GIFAD or FAD).We first show that the interaction time and interaction length embedded in the
obliquity factor is well suited to explain the transition from three-dimensional to two-dimensional (2D) diffraction.
The situation of a slightly misaligned primary beam, corresponding to oblique incidence in the effective 2Dsystem,
is addressed pointing out discrepancies such as the absence of net deflection of the atomic beam. Guided by
time-reversal considerations, we propose an arbitrarily symmetrized form significantly improving the agreement
with experimental data recorded in oblique incidence.
|
|
Debiossac, M., Zugarramurdi, A., Lunca-Popa, P., Momeni, A., Khemliche, H., Borisov, A. G., & Roncin, P. (2014). Transient Quantum Trapping of Fast Atoms at Surfaces. Phys. Rev. Lett., 112(2).
Résumé: We report on the experimental observation and theoretical study of the bound state resonances in fast atom diffraction at surfaces. In our studies, the He-4 atom beam has been scattered from a high-quality LiF(001) surface at very small grazing incidence angles. In this regime, the reciprocal lattice vector exchange with the surface allows transient trapping of the 0.3-0.5 keV projectiles into the quasistationary states bound by the attractive atom-surface potential well which is only 10 meV deep. Analysis of the linewidths of the calculated and measured resonances reveals that prior to their release, the trapped projectiles preserve their coherence over travel distances along the surface as large as 0.2 μm, while being in average only at some angstroms in front of the last atomic plane.
|
|
Debiossac, M. and Z., A. and Khemliche, H. and Roncin, P. and Borisov, A. G. and Momeni, A. and Atkinson, P. and Eddrief, M. and Finocchi, F. and Etgens, V. H. (2014). Combined experimental and theoretical study of fast atom diffraction on the β2(2×4) reconstructed GaAs(001) surface. Phys. Rev. B, 90(15), 155308.
Résumé: A grazing incidence fast atom diffraction (GIFAD or FAD) setup, installed on a molecular beam epitaxy chamber, has been used to characterize the β2(2×4) reconstruction of a GaAs(001) surface at 530∘C under an As4 overpressure. Using a 400-eV 4He beam, high-resolution diffraction patterns with up to eighty well-resolved diffraction orders are observed simultaneously, providing a detailed fingerprint of the surface structure. Experimental diffraction data are in good agreement with results from quantum scattering calculations based on an ab initio projectile-surface interaction potential. Along with exact calculations, we show that a straightforward semiclassical analysis allows the features of the diffraction chart to be linked to the main characteristics of the surface reconstruction topography. Our results demonstrate that GIFAD is a technique suitable for measuring in situ the subtle details of complex surface reconstructions. We have performed measurements at very small incidence angles, where the kinetic energy of the projectile motion perpendicular to the surface can be reduced to less than 1 meV. This allowed the depth of the attractive van der Waals potential well to be estimated as −8.7 meV in very good agreement with results reported in literature.
|
|
2013 |
Rios Rubiano, C. A., Bocan, G. A., Gravielle, M. S., Bundaleski, N., Khemliche, H., & Roncin, P. (2013). Ab initio potential for the He-Ag(110) interaction investigated using grazing-incidence fast-atom diffraction. Phys. Rev. B, 87(1), 012903.
Résumé: Experimental diffraction patterns produced by grazing scattering of fast helium atoms from a Ag(110) surface are used as a sensitive tool to test an ab initio potential model derived from accurate density-functional theory (DFT) calculations. The scattering process is described by means of the surface eikonal approximation, which is a distorted-wave method that includes the quantum interference between contributions coming from different projectile paths, taking into account the complete corrugation of the three-dimensional projectile-surface potential. A fairly good agreement between the theoretical and experimental momentum distributions is found for incidence along different low-indexed crystallographic directions. This agreement is indicative of the quality of the DFT potential. The effective corrugation of the interaction potential across the incidence channel is also investigated. DOI: 10.1103/PhysRevA.87.012903
|
|
Zugarramurdi, A., Debiossac, M., Lunca-Popa, P., Alarcon, L. S., Momeni, A., Khemliche, H., Roncin, P., & Borisov, A. G. (2013). Surface-grating deflection of fast atom beams. Phys. Rev. A, 88(1), 0129074.
Résumé: For energetic atomic beams grazingly incident at the surface along the low index directions, fast motion parallel to the surface and slow motion perpendicular to the surface lead to the quantum diffraction pattern in the scattered beam. In this experimental and theoretical joint study we show that when the incident beam is misaligned with respect to an axial channel, the characteristic deformation of the diffraction pattern reflects an overall deflection of the scattered beam from the specular direction. The deflection is maximum for the azimuthal misalignment angles close to the rainbow angle and we show how this effect can be explained with the detailed balance principle relating diffraction of misaligned and perfectly aligned beams. We also demonstrate that using the detailed balance principle the diffraction charts for the incident beams aligned along the axial channel can be reconstructed from the azimuthal incidence angle dependence of the data obtained with misaligned beams.
|
|
2012 |
Cassimi, A., Ikeda, T., Maunoury, L., Zhou, C. L., Guillous, S., Mery, A., Lebius, H., Benyagoub, A., Grygiel, C., Khemliche, H., Roncin, P., Merabet, H., & Tanis, J. A. (2012). Dynamics of charge evolution in glass capillaries for 230-keV Xe23+ ions. Phys. Rev. A, 86(6), 062902.
Résumé: We have measured the transmission of 230-keV (10-keV/q) Xe23+ ions through insulating tapered glass capillaries of microscopic dimensions. The dynamics of charging and discharging processes have been investigated, evidencing an unexpected slow alignment of the beam along the capillary axis. Oscillations of the exiting beam position have been observed during the charging process associated to the formation of charge patches on the capillary inner walls. The emerging ions are guided with a characteristic guiding angle falling on a universal curve proposed for PET polymer nanocapillaries. This result, very similar to the channeling process, is somewhat surprising in view of the significant differences between the straight nanocapillary polymer foils and the tapered microscopic single glass capillary used here. The transmitted ions show no evidence of energy loss or charge changing except for the production of a small neutral fraction that was determined to be due to ions that had become neutralized to form atoms rather than due to photon emission. These results thus test and confirm the validity of transmission and guiding and provide insight into the dynamics of higher-energy ions than have been previously studied in this regard, allowing a determination of the maximum energy for which the guiding process might occur.
|
|
Hocine Khemliche, P. R., Patrick Rousseau. (2012). Device and method for characterizing surfaces.
Résumé: A method of characterizing surfaces comprises the steps of:
directing a beam (2) of neutral atoms or molecules on a surface (3) for characterizing; and
detecting in position-sensitive manner the neutral atoms or molecules of said beam that have been diffused forwards by said surface (3) for characterizing;
the properties of said beam (2) being selected in such a manner that at least some of said neutral atoms or molecules that are diffused forwards are diffractive by said surface for characterizing.
A device for implementing such a method comprises means (1) for generating such a beam (2) of neutral atoms or molecules and position-sensitive detector means (4) for detecting the neutral atoms or molecules that are diffused forwards by said surface (3) for characterizing.
date de priorité: 7 juil. 2006
EP2044423A2, US20090250600, WO2008003865A2, WO2008003865A3
|
|
Lalmi, B., Khemliche, H., Momeni, A., Soulisse, P., & Roncin, P. (2012). High resolution imaging of superficial mosaicity in single crystals using grazing incidence fast atom diffraction. J. Phys. Condens. Matter., 24(44), 442002.
Résumé: A new table top technique is used to simultaneously analyze the local morphology of crystalline surfaces as well as the misalignment of large scale domains at the topmost surface layer. The approach is based on fast atom diffraction at grazing incidence (GIFAD); the diffraction pattern yields the structural characteristics and the topology of the surface electronic density with atomic resolution. If superficial mosaicity is present, diffraction patterns arising from each mosaic domain can be distinguished, providing high sensitivity to the properties of each of the domains. Taking NaCl(001) as an example, we observe a discrete tilt angle distribution of the mosaic domains following an arithmetic progression with a 0.025 degrees +/- 0.005 degrees difference; a twist mosaic angle of 0.09 degrees +/- 0.01 degrees is also observed.
|
|
2011 |
Bundaleski, N., Soulisse, P., Momeni, A., Khemliche, H., & Roncin, P. (2011). Decoherence in fast atom diffraction from surfaces. Nucl. Instrum. Methods Phys. Res., B, 269(11), 1216–1220.
Résumé: Diffraction of fast atoms from crystal surfaces at grazing incidence (GIFAD) has now been observed on all types of materials, from wide band gap insulators to metals, including semiconductors. Since mainly the (slow) motion normal to the surface is important diffraction patterns are comparable to those obtained in thermal energies atomic diffraction (TEAS), however, the specific scattering geometry of GIFAD has a strong influence on decoherence phenomena. The contribution of atomic vibrations is much less pronounced than in TEAS but other sources of decoherence such as electronic excitations, clearly observed on metals, can participate due to the comparatively large projectile velocity parallel to the surface. We present here simple models that describe these decoherence effects. The results are in good agreement with the experimental results. (C) 2010 Elsevier B.V. All rights reserved.
|
|
2010 |
Anouchah Momeni, P. S., Patrick Rousseau, Hocine Khemliche, and Philippe Roncin. (2010). Grazing Incidence Fast Atom Diffraction (GIFAD): Doing RHEED with Atoms. e-J. Surf. Sci. Nanotech, 8, 101–104.
Résumé: We describe a new diffraction technique to investigate the surface of single crystal surfaces. Its geometry is the
same as that of the RHEED technique. In GIFAD, instead of 10-30 keV electrons, the projectiles are neutral atoms
(mainly helium) with energies in the keV range. We present few results obtained with GIFAD highlighting the
simplicity of interpretation.
|
|
2009 |
Bundaleski, N., Khemliche, H., Rousseau, P., Cassimi, A., Maunoury, L., & Roncin, P. (2009). Discharging dynamics of insulator surfaces irradiated by highly charged ions. In 14TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF HIGHLY CHARGED IONS (HCI 2008) (Vol. 163, 012091).
Résumé: Guiding and focusing of keV to MeV ions by insulator micro-capillaries offer exciting perspectives for the production of low divergence micro-sized beams and the spatial control over the irradiated zone. These effects result from the local charging of the capillary inner wall and depend strongly on the charging/discharging dynamics of the insulating material. This dynamics has been studied on various glass insulator surfaces (borosilicate, fused silica and quartz) by grazing incidence highly charged ion beams. We propose simple experimental methods to derive the relevant time constant and study the influence of temperature and different material properties to the charging process.
|
|
Cassimi, A., Maunoury, L., Muranaka, T., Huber, B., Dey, K. R., Lebius, H., Lelievre, D., Ramillon, J. M., Been, T., Ikeda, T., Kanai, Y., Kojima, T. M., Iwai, Y., Yamazaki, Y., Khemliche, H., Bundaleski, N., & Roncin, P. (2009). Imaging dynamics of charge-auto-organisation in glass capillaries. In NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS (Vol. 267, pp. 674–677).
Résumé: Multiply charged ion beam transmission through insulating capillaries is today a very active field of research. Thanks to the work of several groups during the last five years, several features of this unexpected process have been evidenced. The open challenge is to understand and control the self-organized charging-up of the capillary walls, which leads finally to the ion transmission. Up to now, the specific charge distribution on the inner surface, as well as the dynamics of the build-up, are still to be understood. While capillaries usually studied are microscopic pore networks etched in different materials, our concern is in macroscopic single capillaries made of glass. With a length of several centimeters and a diameter of a few micrometers at the exit, these capillaries have nevertheless the same aspect ratio as the etched pores (length/diameter approximate to 100). One of the leading goals of this research on single capillaries is to produce multi-charged ion beams with diameters smaller than a micrometer (nano-beams). These glass capillaries offer the opportunity to be used as an ion funnel due to their amazing proper-ties of guiding and focusing highly charged ion beams without altering neither their initial charge state nor the beam emittance (<10(-3) pi mm mrad). However, the understanding of the underlying process is not complete and relies on models assuming charge patches distributed along the capillary and which still need to be tested. We present the first observation imaging the dynamics of the charging-up process in single glass capillaries. During the build-up of the self-organized charge deposition on the capillary walls, the 230 keV Xe(23+) transmitted beam is deflected back and forth several times as the outgoing current increases. This is in agreement with the picture of charge patches created sequentially along the capillary and thus deflecting the beam until a stationary state is reached. (C) 2008 Elsevier B.V. All rights reserved.
|
|
Khemliche, H., Rousseau, P., Roncin, P., Etgens, V. H., & Finocchi, F. (2009). Grazing incidence fast atom diffraction: An innovative approach to surface structure analysis. Appl. Phys. Lett., 95(15), 151901.
Résumé: An alternative diffraction technique, based on grazing incidence scattering of high energy atoms, is applied to surface structure determination of crystalline surfaces. This technique, named GIFAD for grazing incidence fast atom diffraction, uses the same geometry as reflection high energy electron diffraction but is less invasive, more surface sensitive, and readily interpretable quantitatively. We present here a demonstration of this approach on a prototypical II-VI compound, ZnSe(001). Besides providing lattice parameter with high accuracy, we show that GIFAD gives straightforward access to the surface valence electron density profile, allowing clear identification of an electron transfer from Zn to Se. (C) 2009 American Institute of Physics. [doi:10.1063/1.3246162]
|
|
2008 |
|
Bundaleski, N., Khemliche, H., Rousseau, P., Cassimi, A., Soulisse, P., & Roncin, P. (2008). COLLISIONS OF IONS WITH INSULATOR SURFACES: CHARGING AND DISCHARGING DYNAMICS. In 24TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (Vol. 133, 012016).
|
|
Bundaleski, N., Khemliche, H., Soulisse, P., & Roncin, P. (2008). Grazing incidence diffraction of keV helium atoms on a Ag(110) surface. Phys. Rev. Lett., 101(17), 177601.
Résumé: Diffraction of fast atoms at grazing incidence has been recently demonstrated on the surface of alkali halides and wide band gap semiconductors, opening applications for the online monitoring of surface processes such as growth of ultrathin layers. This Letter reports energy resolved diffraction of helium on Ag(110) metal surface showing that a band gap is not mandatory to restrict the decoherence due to electron-hole pair excitations by the keV projectile. Measurement of the energy loss, which is in the eV range, sheds light on the scattering process.
|
|
Khemliche, H., Soulisse, P., Bundaleski, N., & Roncin, P. (2008). SURFACE AND THIN FILM ANALYSIS USING GRAZING INCIDENCE FAST ATOM DIFFRACTION (GIFAD). In Publications of the Astronomical Observatory of Belgrade (Vol. 84, p. 142).
Résumé: Grazing collisions at surfaces offer rather contrasted conditions. For well ordered flat surfaces, the scattering is spread among several lattice sites, each of which produces only a tiny elementary deflection. If, in addition, the atomic projectile is aligned along a crystallographic direction, the surface appears as made of parallel furrows which act as a diffraction grating for the atomic wave. We will show that the analysis of characteristic diffraction pattern recorded on the position sensitive detector located downstream allow a sensitive measure of the shape of the surface electronic density. At variance, if a terrace edge or an ad-atom is sitting on the surface along the trajectory, a quasi-binary collision will follow in which energy and momentum conservation allow identification of the mass of the collision partner.
|
|
Manson, J. R., Khemliche, H., & Roncin, P. (2008). Theory of grazing incidence diffraction of fast atoms and molecules from surfaces. Phys. Rev. B, 78(15), 155408.
Résumé: Prompted by recent experimental developments, a theory of surface scattering of fast atoms at grazing incidence is developed. The theory gives rise to a quantum-mechanical limit for ordered surfaces that describes coherent diffraction peaks whose thermal attenuation is governed by a Debye-Waller factor, however, this Debye-Waller factor has values much larger than would be calculated using simple models. A classical limit for incoherent scattering is obtained for high energies and temperatures. Between these limiting classical and quantum cases is another regime in which diffraction features appear that are broadened by the motion in the fast direction of the scattered beam but whose intensity is not governed by a Debye-Waller factor. All of these limits appear to be accessible within the range of currently available experimental conditions.
|
|
Rousseau, P., Khemliche, H., Bundaleski, N., Soulisse, P., Momeni, A., & Roncin, P. (2008). Surface analysis with grazing incidence fast atom diffraction (GIFAD). In 24TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (Vol. 133, 012013).
Résumé: Grazing collisions at surfaces offer rather contrasted conditions. For well ordered flat surfaces, the scattering is spread among several lattice sites, each of which produces only a tiny elementary deflection. If, in addition, the atomic projectile is aligned along a crystallographic direction, the surface appears as made of parallel furrows or as a washboard which act as a diffraction grating for the atomic wave. We will show that the analysis of characteristic diffraction pattern recorded on a position sensitive detector located downstream allows a sensitive measure of the shape of the surface electronic density. A modified Debye Waller factor is proposed to explain the observed diffraction signal.
|
|
2007 |
Rousseau, P., Khemliche, H., Borisov, A. G., & Roncin, P. (2007). Quantum scattering of fast atoms and molecules on surfaces. PHYSICAL REVIEW LETTERS, 98(1), 016104.
Résumé: We present evidence for the diffraction of light keV atoms and molecules grazingly scattered on LiF(001) and NaCl(001) surfaces. At such energies, the de Broglie wavelength is 2 orders of magnitude smaller that the mean thermal atomic displacement in the crystal. Thus, no coherent scattering was expected and interaction of keV atoms with surfaces is routinely treated with classical mechanics. We show here that well-defined diffraction patterns can be observed indicating that, for grazing scattering, the pertinent wavelength is that associated with the slow motion perpendicular to the surface. The experimental data are well reproduced by an ab initio calculation.
|
|
Rousseau, P., Khemliche, H., & Roncin, P. (2007). Auger rates on NaCl(001), effect of the final state and modeling via an effective length. In NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS (Vol. 258, pp. 13–17).
Résumé: Neutralization of keV He+, Ne+ and F+ ions colliding on NaCl(001) at grazing incidence is studied by energy loss in coincidence with emitted electrons. Three closely related Auger-like mechanisms are identified. In all processes, two electrons are removed from the valence band, one is captured on the ground state of the neutral projectile whereas the remaining electron is found either in the electron continuum, in the conduction band or in a surface excited state. To help comparing the three different processes, a procedure is proposed that allows a first order correction of so-called trajectory effect's on the observed neutralization fraction without a priori knowledge of the detailed trajectory. (C) 2006 Elsevier B.V. All rights reserved.
|
|
2005 |
Rousseau, P., Gugiu, M., Khemliche, H., & Roncin, P. (2005). Neutralization of noble gas ions on ionic insulators: Auger neutralization or double-electron capture. In NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS (Vol. 230, pp. 361–368).
Résumé: The neutralization of noble gas singly charged ions on large band gap ionic insulators may take place through two distinct mechanisms involving two valence band electrons. One is a kinetically assisted Auger neutralization, and the other a simultaneous double electron capture. Both lead to the same final states, that is at grazing incidence angles a scattered neutral projectile connected to a surface excited state (trion) or an ejected electron. So it is virtually impossible to experimentally identify the neutralization process. From comparison to systems whose neutralization mechanism is clearly identified, the incidence angle dependence of the trion population relative to the total neutral fraction appears as a robust parameter for distinguishing the primary capture process. (c) 2004 Elsevier B.V. All rights reserved.
|
|
2003 |
Borisov, A. G., Sidis, V., Roncin, P., Momeni, A., Khemliche, H., Mertens, A., & Winter, H. (2003). F- formation via simultaneous two-electron capture during grazing scattering of F+ ions from a LiF(001) surface. PHYSICAL REVIEW B, 67(11), 115403.
Résumé: For slow F+ ions (v<0.05 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence, large fractions of negative F- ions have recently been observed in the reflected beam, while for neutral F-0 projectiles no negative F- ions are produced in the same velocity range [P. Roncin , Phys. Rev. Lett. 89, 043201 (2002)]. From detailed studies on projectile energy loss and charge fractions, the conclusion was drawn that the F- ions are formed from F+ via a simultaneous capture of two electrons from adjacent F- sites at the surface. We present a theoretical description of the double-electron-capture process leading to F- formation from F+ projectiles grazingly scattered from the LiF(001) surface. We use quantum chemistry calculations to determine the relevant Hamiltonian matrix and close-coupling solution of the time-dependent Schrodinger equation. The theoretical results are in good agreement with experimental observations.
|
|
2002 |
Khemliche, H., Borisov, A. G., Momeni, A., & Roncin, P. (2002). Exciton and trion formation during neutralization of Ne+ at a LiF(001) surface. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 191, 221–225.
Résumé: The grazing angle interaction of 2 keV Ne+ projectiles with a LiF(0 0 1) surface is studied with the combination, in coincidence, of projectile and electron time-of-flight spectroscopy. The measurements reveal that besides the standard Auger neutralization process that leads to electron ejection, there is another neutralization mechanism that does not result in electron emission. The latter process has been identified as the formation of an electron-bihole complex termed trion. We report here the detailed study of the scattering angle dependence of these two neutralization channels, with comparison with the process leading to population of surface excitons. (C) 2002 Published by Elsevier Science B.V.
|
|
Roncin, P., Borisov, A. G., Khemliche, H., Momeni, A., Mertens, A., & Winter, H. (2002). Evidence for F- formation by simultaneous double-electron capture during scattering of F+ from a LiF(001) surface. PHYSICAL REVIEW LETTERS, 89(4), 043201.
Résumé: Slow F+ ions (v<0.1 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence exhibit a high probability for forming F- ions in the reflected beam, whereas no negative ions are found for neutral F-0 projectiles. From detailed studies of projectile energy loss and charge transfer, we find evidence for a correlated double-electron capture process in the formation of the F- ions.
|
|
2001 |
Khemliche, H., Villette, J., Borisov, A. G., Momeni, A., & Roncin, P. (2001). Electron bihole complex formation in neutralization of Ne+ on LiF(001). PHYSICAL REVIEW LETTERS, 86(25), 5699–5702.
Résumé: Neutralization of low keV Ne+ ions at a LiF(001) surface is studied in a grazing incidence geometry. The combination of energy loss and electron spectroscopy in coincidence reveals two neutralization channels of comparable importance. Besides the Anger process, the Nef neutralization can proceed via peculiar target excitation, corresponding to the formation of an electron bihole complex termed trion.
|
|
Roncin, P., Khemliche, H., Momeni, A., & Borisov, A. G. (2001). Translational spectroscopy in grazing collisions on insulators. The importance of the transient negative ion and of target excitations. In PHOTONIC (pp. 571–579).
Résumé: Energy loss spectroscopy is applied to grazing collisions of keV ions on insulator surfaces. For W projectiles, analyzing in coincidence the energy loss, the final charge state and the secondary electrons, the role of the intermediate negative ions formed on the surface is outlined. The study is extended to other projectiles to probe the influence of the projectile affinity level.
|
|
2000 |
Khemliche, H., Villette, J., Roncin, P., & Barat, M. (2000). Surface exciton population in proton impact with LiF(100). NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 164, 608–613.
Résumé: We have recently shown that the large energy loss experienced by slow protons interacting with a LiF surface is primarily caused by the population of surface excitons [11]. These states are most probably populated by electron transfer from H- ions formed at halogen sites, whereas secondary electron emission results from direct detachment of the negative ions in collisions with halogen sites. We report here on the impact energy dependence of the charge-state of the scattered projectile, its energy loss and the associated electron yield. From these complete measurements, the transfer probability to the surface excitons and its dependence upon impact energy is derived in the range 0.6-10 keV. (C) 2000 Elsevier Science B.V. All rights reserved.
|
|
Villette, J., Borisov, A. G., Khemliche, H., Momeni, A., & Roncin, P. (2000). Subsurface-channeling-like energy loss structure of the skipping motion on an ionic crystal. PHYSICAL REVIEW LETTERS, 85(15), 3137–3140.
Résumé: The skipping motion of Ne+ ions in grazing scattering from the LiF(001) surface is studied for velocity below 0.1 a.u. with a time-of-flight technique. It is demonstrated that suppression of electronic excitation and dominance of optical phonon excitation in the projectile stopping results in an odd 1,3, 5,... progression of the energy loss peaks, a feature usually ascribed to subsurface channeling. The experimental findings are well reproduced by parameter-free model calculations where thermal vibrations are the dominant cause for the ion trapping and detrapping.
|
|
1999 |
Roncin, P., Villette, J., Atanas, J. P., & Khemliche, H. (1999). Energy loss of low energy protons on LiF(100): Surface excitation and H- mediated electron emission. PHYSICAL REVIEW LETTERS, 83(4), 864–867.
Résumé: Impact of 600 eV protons at grazing incidence on LiF(100) is studied with a new coincidence technique combining energy loss and electron spectroscopy. Correlation between the secondary electrons and the charge state of the scattered projectiles demonstrates the role of the H- ions formed on the surface as precursors for electron emission. However, the main channel for energy loss is not associated with electron emission but is interpreted as the population of surface excitons.
|
|
Villette, J., Atanas, J. P., Khemliche, H., Barat, M., Morosov, V., & Roncin, P. (1999). Grazing collision of keV protons on LiF correlation between energy loss and electron emission. In NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS (Vol. 157, pp. 92–97).
Résumé: Grazing interaction of low energy protons with LiF(1 0 0) is studied using a new coincidence technique combining energy loss, charge state analysis and electron spectroscopy. Correlation between the scattered projectile energy loss and the number of emitted electrons points to an energy loss mechanism not leading to electron emission. Detailed analysis of the energy loss spectra, which show well-resolved structures, suggests that this mechanism corresponds to the population of surface excitons. Moreover the correlation between the projectile final charge stare and the number of emitted electrons sheds new light on the major role played by the negative ion at the surface. Electron removal from the valence band proceeds mainly through formation of H- at halogen sites, whereas electron emission results from the detachment of these negative ions at subsequent F- sites. (C) 1999 Elsevier Science B.V. All rights reserved.
|
|
