Papers by Maria Silvia Gravielle
arXiv (Cornell University), Sep 21, 2022
The effect produced by surface defects on grazing-incidence fast atom diffraction (GIFAD) pattern... more The effect produced by surface defects on grazing-incidence fast atom diffraction (GIFAD) patterns is studied by considering the presence of terraces in a LiF(001) sample. For helium atoms impinging along the 110 direction of the LiF surface, we analyze the influence of a monolayer terrace with its edge oriented parallel or perpendicular to the axial channel. We found that the presence of an outward transverse step introduces a diffuse background above the Laue circle, which displays additional peaked structures. For inward transverse steps, instead, such a background is placed below the Laue circle, showing a much weaker intensity. On the other hand, parallel steps give rise to asymmetric angular distributions, which are completely confined to the Laue circle. Therefore, these theoretical results suggest that GIFAD might be used to characterize terrace defects.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2018
Abstract In this article we address grazing incidence fast atom diffraction (GIFAD) for the He/KC... more Abstract In this article we address grazing incidence fast atom diffraction (GIFAD) for the He/KCl(001) system, for which a systematic experimental study was recently reported [E. Meyer, Ph.D dissertation, Humboldt-Universitat, Berlin, Germany, 2015]. Our theoretical model is built from a projectile-surface interaction obtained from Density Functional Theory (DFT) calculations and the Surface Initial-Value Representation (SIVR), which is a semi-quantum approach to describe the scattering process. For incidence along the 〈 100 〉 and 〈 110 〉 directions, we present and discuss the main features of our interaction potential, the dependence of the rainbow angle with the impact energy normal to the surface, and the simulated GIFAD patterns, which reproduce the main aspects of the reported experimental charts. The features of the diffraction charts for He/KCl(001) are related to the averaged equipotential curves of the system and a comparison is established with the case of He/LiF(001). The marked differences observed for 〈 110 〉 incidence are explained as due to the much larger size of the K+ ion relative to that of Li+.
AIP Conference Proceedings, 2007
The charge-state distribution of 127I ions at the gas stripper of a tandem accelerator was measur... more The charge-state distribution of 127I ions at the gas stripper of a tandem accelerator was measured for a wide range of charge states. When highly-ionized charge states were tuned, it was possible to identify spurious charge states originated in electron-loss collisions of the accelerated ions and the residual gas molecules within the accelerator tube. The rate of these spurious charge states were quantitatively analyzed and compared with calculations which take into account its tuning through the accelerator and cross sections for multiple-electron-loss atomic collisions.
Journal of Physics: Conference Series, 2015
The striking observation of interference structures produced by grazing impact of fast atoms on c... more The striking observation of interference structures produced by grazing impact of fast atoms on crystal surfaces reported a few years ago [1,2] has given rise to the development of a powerful surface analysis technique. This article gives a brief account of the main features of the process, using the Surface Eikonal (SE) approximation as a theoretical tool to analyze the different mechanisms responsible for the quantum interference. The SE approach is a semiclassical method based on the use of the eikonal wave function, which takes into account the coherent superposition of transition amplitudes for different axially channeled trajectories. It has proved to provide a quite good description of experimental diffraction patterns for different collision systems.
Physical Review A, 2000
For ions impinging grazingly on a solid surface, the electron emission from the inner shells of s... more For ions impinging grazingly on a solid surface, the electron emission from the inner shells of solid atoms is investigated by employing a semiclassical formalism. The emission rate is expressed in terms of probabilities of atomic ionization, which are evaluated with the continuum-distorted-wave-eikonal-initial-state approximation, taking into account the full dependency on the impact parameter. The model is applied to the calculation of the differential yield of ejected electrons for fast protons colliding with an aluminum surface. Inner-shell emission is compared with the electron emission from the valence band of the metal, considering different ejection angles. Calculated energy spectra of emitted electrons are in good agreement with the available experimental data.
Physical Review A, 1998
Unfortunately, a mistake was detected in the spelling of one of the author's names. The last name... more Unfortunately, a mistake was detected in the spelling of one of the author's names. The last name of the third author was given as ''Grabielle.'' The correct spelling is ''Gravielle.''
Journal of Physics: Conference Series, 2009
Angular distributions of fast Ne atoms after grazing collisions with a LiF(001) surface under axi... more Angular distributions of fast Ne atoms after grazing collisions with a LiF(001) surface under axial surface channeling conditions are experimentally and theoretically studied. We use the surface eikonal approximation to describe the quantum interference of scattered projectiles, while the atom–surface interaction is represented by means of a pairwise additive potential, including the polarization of the projectile atom. Experimental data serve as a benchmark to investigate the performance of the proposed potential model, analyzing the role played by the projectile polarization.
Physical Review Letters, 2003
The phase ' of the field oscillations with respect to the peak of a laser pulse influences the li... more The phase ' of the field oscillations with respect to the peak of a laser pulse influences the light field evolution as the pulse length becomes comparable to the wave cycle and, hence, affects the interaction of intense few-cycle pulses with matter. We theoretically investigate photoelectron emission induced by an intense, few-cycle laser pulse from a metal surface (jellium) within the framework of timedependent density functional theory and find a pronounced ' dependence of the photocurrent. Our results reveal a promising route to measuring ' of few-cycle light pulses (< 6 fs at 0:8 m) at moderate intensity levels (I p 10 12 W=cm 2) using a solid-state device.
Journal of Physics: Conference Series, 2017
Pairwise additive potentials for multielectronic atoms interacting with a LiF(001) surface are re... more Pairwise additive potentials for multielectronic atoms interacting with a LiF(001) surface are revisited by including an improved description of the electron density associated with the different lattice sites, as well as non-local electron density contributions. Within this model, the electron distribution around each ionic site of the crystal is described by means of an onion approach that accounts for the influence of the Madelung potential. From such densities, binary interatomic potentials are then derived by using well-known non-local functionals for the kinetic, exchange and correlation terms. Rumpling and long-range contributions due to projectile polarization and van der Waals forces are also included in an analogous fashion. We apply this pairwise additive approximation to evaluate the interaction potential between closed-shell - He, Ne, Ar, Kr, and Xe - and open-shell - N, S, and Cl - atoms and the LiF surface, analyzing the relative importance of the different contributi...
Synopsis: Ionization of atomic targets produced by ultra-short laser pulses is studied within a d... more Synopsis: Ionization of atomic targets produced by ultra-short laser pulses is studied within a distorted-wave formalism. We introduce the Impulse Coulomb-Volkov (ICV) approximation, which makes use of the Volkov phase to describe the action of the electromagnetic field on both the initial and final channels. Here photoelectron emission from hydrogen is used as a benchmark for the theory, comparing the results to values derived from the numerical solution of the time-dependent Schrödinger equation (TDSE). We found the ICV method represents an improvement over the CV approach for laser frequencies lower than the initial electronic energy.
Synopsis Pairwise additive potentials for closedand openshell atoms interacting with a LiF(001) s... more Synopsis Pairwise additive potentials for closedand openshell atoms interacting with a LiF(001) surface are revisited by including an improved description of the crystal electron density, as well as non-local electron density contributions. The electron distribution around each ionic site of the crystal is described with an onion model that takes into account the influence of the Madelung potential. From such densities, binary interatomic potentials are then derived by using well-known non-local functionals. Rumpling and contributions due to projectile polarization and van der Waals forces are also included. The potential model is assessed by contrasting angular positions of rainbow and supernumerary rainbow maxima produced by fast grazing incidence of He, N, Ne, S, Cl, Ar, and Kr with available experimental data.
Synopsis We study the influence of thermal lattice vibrations on the visibilty of the interferenc... more Synopsis We study the influence of thermal lattice vibrations on the visibilty of the interference structures present in the projectile distributions produced by grazing fast atom diffraction (GIFAD). For a LiF(001) surface in thermal equilibrium, GIFAD spectra are evaluated within the PhononSurface Initial Value Representation (PSIVR) approach, which takes into account the vibrational modes of the crystal lattice. It is found that, even at room temperature, the relative intensities of the Bragg peaks are affected by the phonon contribution, this fact being relevant for surface analysis.
Physical Review B, 2021
In this work we address, both experimentally and theoretically, the very grazing scattering of He... more In this work 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 vdW interactions in the potential improves the theoretical accord with experiments for both the corrugation and the rainbow angle.
Journal of Physics: Conference Series, 2020
Synopsis We address the effect of lattice vibrations of the crystal on grazing incidence fast ato... more Synopsis We address the effect of lattice vibrations of the crystal on grazing incidence fast atom diffraction (GIFAD) from insulator surfaces. To describe the phonon contribution to GIFAD we introduce a semi-quantum method, named Phonon-Surface Initial Value Representation (P-SIVR), which represents the surface with a harmonic crystal model, while the scattering process is given by the Surface Initial Value Representation approach including phonon excitations. P-SIVR results for Ne/LiF(001) are compared with other theoretical methods and available experiments.
Diffraction patterns produced by grazing scattering of fast atoms from insulator surfaces are use... more Diffraction patterns produced by grazing scattering of fast atoms from insulator surfaces are used to examine the atom-surface interaction. The method is applied to He atoms colliding with a LiF(001) surface along axial crystallographic channels. The projectile-surface potential is obtained from an accurate DFT calculation, which includes polarization and surface relaxation. For the description of the collision process we employ
Physical Review A, 1988
Electron capture from the K shell by protons is calculated by using the exact an-shell impulse an... more Electron capture from the K shell by protons is calculated by using the exact an-shell impulse and eikonal wave functions in the final and initial channels, respectively. Both wave functions have the proper normalization and asymptotic conditions. A good agreement with available experiments is found.
Physical Review A, 2014
The energy lost by helium atoms axially scattered from a Ag(110) surface is studied in order to i... more The energy lost by helium atoms axially scattered from a Ag(110) surface is studied in order to investigate the influence of dissipative processes on fast atom diffraction spectra. In this work inelastic projectile distributions are evaluated within a semiclassical formalism that includes dissipative effects due to electron-hole excitations through a friction force. For incidence along the [112] and [110] directions the model predicts the presence of multiple peaks in the energy-loss spectrum for a given impact energy. But these structures are completely washed out when the experimental dispersion of the incident beam is taken into account, giving rise to a smooth energy-loss distribution. Simulations including the experimental energy spread are in fairly good agreement with available experimental data for the [112] channel. In addition, our results suggest that inelastic processes produce an almost constant background in the transverse momentum distribution, except in the extremes of the momentum range where classical rainbow maxima appear. By adding elastic and inelastic contributions, experimental diffraction patterns are well reproduced.
Physical Review A, 2008
ions by impact of protons with energies ranging from 25 to 1000 keV. Cross sections of singly cha... more ions by impact of protons with energies ranging from 25 to 1000 keV. Cross sections of singly charged ions are relevant to the calculation of electron yields in collisions with insulator surfaces. Calculations were performed within the continuum distorted wave-eikonal initial state method using an angular expansion in spherical harmonics and a numerical evaluation of the radial functions corresponding to both the initial ͑bound͒ and the final ͑continuum͒ states. The first Born approximation was used on an equal footing. We find that this first-order theory holds for proton energies larger than 300 keV. For comparison, we also calculate the shellwise local plasma approximation. Our results show that it gives a good account of the cross sections for neutral targets.
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Papers by Maria Silvia Gravielle