2023 |
Michoulier, E., Lemoine, D., Spiegelman, F., Nave, S., & Rapacioli, M. (2023). Dissipative friction dynamics within the density-functional based tight-binding scheme. EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS, 232(12), 1975–1983.
Résumé: The accurate description of an atom or molecule colliding with a metal surface remains challenging. Several strategies have been performed over the past decades to include in a Langevin dynamics the energy transfer related to electron–hole pair excitations in a phenomenological way through a friction contribution. We report the adaptation of two schemes previously developed in the literature to couple the electronic friction dynamics with the density-functional based tight-binding (DFTB) approach. The first scheme relies on an electronic isotropic friction coefficient determined from the local electronic density (local density friction approximation or LDFA). In the second one, a tensorial friction is generated from the non-adiabatic couplings of the ground electronic state with the single electron–hole excitations (electron tensor friction approximation or ETFA). New DFTB parameterization provides potential energy curves in good agreement with first-principle density-functional theory (DFT) energy calculations for selected pathways of hydrogen atom adsorbing onto the (100) silver surface or penetrating subsurface. Preliminary DFTB/Langevin dynamics simulations are presented for hydrogen atom scattering from the (100) silver surface and energy loss timescales are characterized.
|
|
Mukherjee, A., Momeni, A., Allouche, A. R., Staicu Casagrande, E. M., Minea, T., & Khemliche, H. (2023). Grazing incidence fast atom diffraction in high-pressure conditions. Surf. Interfaces, 37, 102754.
Résumé: Grazing Incidence Fast Atom Diffraction (GIFAD) is a recent technique for characterizing surface structures and real-time monitoring of thin film growth. Up to now, GIFAD has only been used in Ultra-High-Vacuum conditions, typically in the range of 10−10 to 10−8 mbar, and has therefore only been considered for high vacuum deposition methods like Molecular Beam Epitaxy or very low-pressure Chemical Vapor Deposition (CVD). At pressures exceeding 10−6 mbar, gas phase collisions along the atom beam trajectory not only reduce the mean free path but also degrade the beam coherence length and thus potentially suppress the diffraction signal. In addition, pressures lower than 10−5 mbar are required to maintain a low noise level on the scattered particle detector. In a new configuration, we demonstrate that GIFAD can operate at pressure as high as 10−2 mbar of argon with well-contrasted diffraction patterns. This opens wide avenues for the study of surface reactivity, thin film growth in Magnetron Sputtering Deposition, where electron diffraction is inevitably perturbed by the electromagnetic fields. This High-Pressure version of GIFAD could also be extended to Reactive Pulsed Laser Deposition and many CVD variants.
|
|
2022 |
Bobrov, K., Kalashnyk, N., & Guillemot, L. (2022). Two-dimensional dynamic perylene ordering on Ag(110). AIP ADVANCES, 12(11), 115223.
Résumé: We present a room temperature STM study of dynamics of the quasi-liquid perylene monolayer formed on Ag(110) under thermal equilibrium. We observe that the thermodynamic balance of the molecule–molecule and molecule–substrate interactions generates a compact two-dimensional (2D) quasi-liquid state established by mobile perylene molecules dynamically distributed into three distinct motion modes. Monitoring of the quasi-liquid monolayer indicates that each motion mode is triggered by spontaneous recognition of specific locations of the substrate lattice into which transient locking occurs. Analysis of the STM topographies shows that the substrate lattice guides the whole molecule ensemble and provides each of the modes with a distinct register. In each mode, the substrate registry forces the transiently immobile molecules to alternate with the transiently mobile ones. The dynamic interminglement of the modes prevents segregation of the dynamically active and inactive molecules. The substrate provides memory to the intermingled molecules and eliminates ergodicity of the quasi-liquid state. Fourier transform of the topographies unravels the long-range spatial correlations and epitaxial character of the quasi-liquid state. Analysis of the short-range mode coupling allows us to understand the mechanism of the long-range mode coupling. The substrate force field induces the dynamical ergodic–non-ergodic phase transition giving rise to the stationary long-range ordered quasi-liquid state.
|
|
2021 |
Bocan, G. A., Breiss, H., Szilasi, S., Momeni, A., Staicu Casagrande, E. M., Sánchez, E. A., Gravielle, M. S., & Khemliche, H. (2021). Dynamical effects as a window into van der Waals interactions in grazing-incidence fast He-atom diffraction from KCl(001). Phys. Rev. B, 104, 235401.
Résumé: In this paper we address, both experimentally and theoretically, the very grazing scattering of He atoms off KCl(001) with incidence along the ⟨100⟩ channel. Our theoretical model combines a semiquantum description of the scattering dynamics and a high-precision interaction potential. By means of a thorough analysis of the quantum phase for in-plane scattering and rainbow trajectories, we are able to connect the presence of the physisorption well with the significant enhancements of the corrugation and rainbow angle, relative to the hard corrugated wall predictions. We trace this connection to dynamical effects on the incident and scattered beams due to their traversing of the physisorption well. Finally, we show that the inclusion of van der Waals interactions in the potential improves the theoretical accord with experiments for both the corrugation and the rainbow angle.
|
|
2020 |
Bocan, G. A., Breiss, H., Szilasi, S., Momeni, A., Staicu Casagrande, E. M., Gravielle, M. S., Sánchez, E. A., & Khemliche, H. (2020). Anomalous KCl(001) Surface Corrugation from Fast He Diffraction at Very Grazing Incidence. Phys. Rev. Lett., 125, 096101.
Résumé: We present theoretical and experimental evidence of an anomalous surface corrugation behavior in He-KCl(001) for incidence along ⟨110⟩. When the He normal energy decreases below 100 meV, i.e., He-surface distances Z>2 Å, the corrugation unexpectedly increases up to an impressive ≳85%. This is not due to van der Waals interactions but to the combination of soft potential effects and the evolution of He-cation and He-anion interactions with Z. This feature, not previously analyzed on alkali-halide surfaces, may favor the alignment properties of weakly interacting overlayers.
|
|
|
Staicu Casagrande, E. M., Momeni, A., & Khemliche, H. (2020). Fast atom interaction with surfaces at grazing incidence: classical and quantum scattering applied to thin film growth. In Journal of Physics: Conference Series (Vol. 1412, 202010). IOP.
|
|
2018 |
Momeni, A., Staicu Casagrande, E. M., Dechaux, A., & Khemliche, H. (2018). Ultrafast Crystallization Dynamics at an Organic-Inorganic Interface Revealed in Real Time by Grazing Incidence Fast Atom Diffraction. J. Phys. Chem. Lett., 9(4), 908–913.
Résumé: The poor structural properties of organic-inorganic interfaces and their variability represent the main cause of device under-performance. Understanding and controlling the development of these properties in real time has been a difficult experimental challenge. Using a recent technique based on grazing incidence fast atom diffraction (GIFAD), we were able to directly observe during deposition structural transitions in a perylene monolayer on Ag(110). Crystallization from the liquid phase occurs into two distinct structures with drastically different dynamics. Transition to the most compact packing occurs by self-organization only after a second layer has started to build up; subsequent incorporation of molecules from second to first layer triggers an ultrafast crystallization on a macroscopic sale. The final compact crystalline structure shows a long-range order and superior stability, which opens good perspectives for producing in a controlled manner highly ordered hybrid interfaces for photovoltaics and molecular electronics.
|
|
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.
|
|
2016 |
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.
|
|
2015 |
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., 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.
|
|
