INVESTIGADORES
BOCAN Gisela Anahi
congresos y reuniones científicas
Título:
FAST ATOM DIFFRACTION FROM METALS
Autor/es:
M.S. GRAVIELLE; C.A. RÍOS RUBIANO; G.A. BOCAN; J.I. JUARISTI; N. BUNDALESKI; H. KHEMLICHE; P. RONCIN
Lugar:
Wirrina Cove
Reunión:
Workshop; 20th International Workshop on Inelastic Ion-Surface Collisions; 2014
Institución organizadora:
IISC
Resumen:
Since the unexpected observation of grazing incidence
diffraction of fast atoms (GIFAD) on crystal surfaces [1,2],
extensive experimental and theoretical research has been devoted
to the subject [3,4]. The first experimental
evidences of this phenomenon were reported at insulator
materials [1,2], where the presence of a wide band-gap helps
to suppress inelastic processes. In these insulator surfaces
the minimum electronic excitation amount to ~10 eV,
corresponding to an exciton. When this exciton is populated,
it has been shown that the coherence is strongly destroyed
[5]. The situation is different for metals, where much weaker
electronic excitations are possible. However, experiments for
metal surfaces have shown diffraction effects [6,7], with a
comparable total energy loss. The aim of this work is to
investigate the diffraction patterns produced by fast He
atoms grazingly impinging on a Ag(110) surface, focusing
on the contribution of inelastic processes. This collision
system corresponds to the first and simplest metallic case for
which GIFAD effects were experimentally observed [6], in
conjunction with considerable energy losses.
To describe the elastic process we employ a distorted wave
theory ? the surface eikonal (SE) approximation ? that
makes use of the eikonal wave function to represent the
quantum scattering with the surface, while the projectile
motion is classically described using different initial
conditions [8]. The SE approach has been applied to evaluate
GIFAD distributions from insulator surfaces, providing
results in good agreement with the experimental data [9].
Concerning the projectile-surface interaction, we use a
precise description of the potential energy surface (PES)
obtained from an accurate density functional theory
calculation, where the PBE functional is used to approximate
the exchange-correlation energy. This PES takes into
account the projectile's three degrees of freedom and it is
built from a dense grid of ab-initio energies by means of a
sophisticated interpolation technique. Projectile momentum
distributions obtained with the SE approach are compared
with the experimental spectra considering different incidence
directions [10].
The contribution coming from inelastic processes, originated
by electron-hole pair excitations, is evaluated by introducing
a friction force in the calculation of the classical projectile
trajectories. This dissipative force is expressed in terms of
the transport cross section at the Fermi level by considering
the scattering with an electron gas, whose density is
evaluated from density functional theory calculations [11].
[1] A. Schüller et al., Phys. Rev. Lett. 98, 016103 (2007).
[2] P. Rousseau et al., Phys. Rev. Lett. 98, 016104 (2007).
[3] H. Khemliche et al., Appl. Phys. Lett. 95, 151901 (2009).
[4] H. Winter et al., Prog. Surf. Sci. 86, 169 (2011).
[5] M. Busch et al., Vacuum, 86, 1618 (2012).
[6] N. Bundaleski et al., Phys.Rev. Lett. 101, 177601 (2008).
[7] M. Busch et al., Surf. Sci. 603, L23 (2009).
[8] M.S. Gravielle et al., Phys. Rev. A 78, 022901 (2008).
[9] A. Schüller et al., Phys Rev. A 80, 062903 (2009).
[10]C. Ríos Rubiano et al., Phys. Rev. A 87, 012903 (2013).
[11] J. I. Juaristi et al., Phys. Rev. Lett. 100, 116102 (2008).