IFIS - LITORAL   24734
INSTITUTO DE FISICA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Unoccupied band states and ion induced electron emission
Autor/es:
JULIO FERRÓN; RICARDO VIDAL; RAÚL BARAGIOLA
Lugar:
San Sebastian
Reunión:
Workshop; Quantum 13, Brandt Ritchie Workshop; 2013
Institución organizadora:
Centro de Física de Materiales; Donostia-San Sebatián
Resumen:
The
experimental probing of unoccupied conduction bands near surfaces provides a strong
test of theories, which need to account for the breaking of symmetry and
periodicity but by the finite lifetime of electrons and holes. The latter is of
particular importance in a material like such as carbon, which can be tested in
multiple allotropic forms. In a previous publication we
have reported a study of electron emission from highly-oriented pyrolitic graphite
(HOPG) induced by 1-5 keV He+ and Li+ ions. The energy spectra of emitted
electrons, N(E) obtained over a wide range of polar and azimuthal angles showed
a broad peak at E = 10 ? 20 eV for He+, but not for Li+ projectiles. A
theoretical analysis explained the observations as due to electron promotion in
He-C (but not in Li-C) collisions leading to the formation of a transient
electron-hole pair that decayed into vacuum by autoionization. The results did
not follow usual correlation with structure in the final density of states f-DOS
that helped interpret previous studies of secondary electron emission (SEE) by
electron impact and inverse photoemission.
Other
recent studies on graphene
have returned to the question of whether these peaks in the energy distribution
of secondary electrons can be explained by invoking only structure in the
density of initially empty states in the conduction band. We need to expand the discussion about the
influence of empty DOS in the energy distribution.
For instance works of Hoffmann on electron
induced, Marchand empty states in ups and Masada in MIS. This particular point,
the influence of empty density of states (e-DOS) has been soundly discussed in
the past regarding electron,
photon (UPS),
and metastable-atom electron spectroscopy. We
have now improved and expanded these studies by using an electron energy
analyzer that has a narrow angle of collection around the surface normal of an
HOPG sample. We used as projectiles 2-5 keV He+, 200-1000 eV electrons and 21.2
eV (He-I) and 40.8 eV (He-II) ultraviolet photons incident on either pristine
or ion-damaged surfaces.