Surface Physics Research at the Centro Atómico Bariloche (since 1987 to 2001)
Post on 10-Jan-2016
16 Views
Preview:
DESCRIPTION
Transcript
Surface Physics Research at the Centro Atómico Bariloche(since 1987 to 2001)
People
Dr. Hugo AscolaniDr. Oscar GrizziDr. Esteban A. SánchezDr. Guillermo Zampieri
Dra. María L. MartiarenaDr. Víctor H. Ponce
Dr. Julio E. Gayone (postdoc)Lic. Silvina Bengió (PhD student)Lic. L. De Ferrariis (PhD student)Gonzalo Otero (student)
Publications: 60 in international journals (since 1996)Invited talks: 10 (since 1996)PhD thesis: 8 (since 1987)Budget: $250,000 (since 1996)
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Surface Characterization by TOF-ISSG. Otero, J.E. Gayone, E.A. Sánchez, O. Grizzi
Collaboration with Surface Physics Group of Santa Fe (INTEC) - Argentina
• Surface Reconstruction
• Adsorption Kinetics
• Adsorption sites
• Thin film growth
• Charge exchange
H
(d)
0 10 200
H:GaAs
CleanGaAs
1
c2
c
1
c
Ne
I BS(A
s)
(arb
.un
its)
INCIDENT ANGLE (deg)
6 70
CO
UN
TS
(a)
TIME OF FLIGHT (s)
[100]
[110] 5.65 Å
= -64.7o
AsGa
(b)
Hydrogen adsorption on GaAs(110)
After H adsorption, the substrate atoms move backto bulk positions and the As atoms become shadowedby their Ga neighbours.
(c)
Charge Fractions in Cs/GaAs
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0
20
40
60
80
100
Charge fractions in Cs/GaAs(110)
5 keV Kr+ -> Cs / GaAs
As-
As+
Ga+
Cs+
DR
Ion
Fra
ctio
ns (%
)
Cs Coverage (ML)
Growth of AlF3 on GaAs(110)
4 8 12 16
FS Ga
FS As
DR AsDR Ga
MC
AlF
Substratetemperature
cleansurface
RT
250oC
400oC
Cou
nts (a
rb. u
nits)
Time of flight (s)30 60 640 680
250oC
FAl0GaAl+3As
dN(E
) / d
E (a
rb. u
nits)
Substratetemperature
400oC
RT
cleansurface
Auger energy (eV)
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Atom and molecule adsorption on semiconductor surfacesSilvina Bengió and Hugo Ascolani
Collaboration: M.C. Asensio, spanish-french beam-line at LURE, Orsay, France.
Photoemission and syncrhotron radiation
•Estructural properties: Photoelectron diffraction
•Chemical and electronic properties: XPS and ARUPS
•Adsorption site of the OH radicals in the H2O/Si(100) system.
•Electronic Structure of Ga/Si(111).
•Order-disorder phase transition of the Sn/Ge(111) system.
Photoelectron diffraction
Adsorption of H2O on Si(100)
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Electronic Structure of Transition-Metal Perovskites. G. Zampieri, J.E. Gayone.
Collaboration: Dr M. Abbate, Laboratorio Nacional de Luz Sincrotron, Campinas, (Brazil) CAB-Bariloche, Argentina
Studied Systems: Sr2FeMoO6,LaNiO3-x (0<x<0.5), CaMnO3-x (0<x<0.5),LaMnO3+y (0<y<0.15), SrFe1-xCoxO3.
Study of occupied and unoccupied electron densities of states with XPS, UPS and XAS
526 527 528 529 530 531 532 533 534
Sr2FeMoO
6
O 1s Absorption edge.
Photon Energy (eV)
-2 -1 0 1 2 3 4 5 6
- F (eV)
down spin
up spinMo e
g
Fe eg
Mo t2g
Fe-Mo t2g
C'B'
A'
-10-50
0.0
0.2
0.4
0.6
0.8
1.0XPS
h=1486.6 eV
+2 +3Fe-2p3/2
Relative B.E. (eV)
Sr2FeMoO6
Fe2O3
Fe
Norm
alized Intensity
-15 -10 -5 0 5
0.0
0.2
0.4
0.6
0.8
1.0 XPS +5+6
Mo-3d3/2,5/2
Sr2FeMoO
6
MoO3
Mo
Relative B.E. (eV)
XPS: Valences of Fe and Mo in Sr2FeMoO6
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Excitation of Phonons in Medium-Energy Electron Spectroscopies.
H. Ascolani, G. Zampieri, J.E. Gayone.Collaboration: Dr. Ph. Hofmann, Institute for Storage Ring Facilities, University of
Aarhus, Aarhus, Denmark
Experimental and theoretical study of the excitation/absorption of phonons in:• LEED-MEED• Valence-band photoemission.
Valence Band Photoemission from Al(100)
-40 -20 0 20 40 60 80 100 120
1
2
3b) [011][101]
Inte
nsid
ad (
unid
. arb
.)
Angulo Azimutal
1
2
3a) [011][101]
LEED
MEED
LEED-MEED Transition
The angular pattern changes as the wave vector conservation rules are gradually relaxed by the excitation/absorption of phonons.
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Electron emission in grazing ion-surface collisionsE.A. Sánchez, O. Grizzi and G. Otero
Collaboration with LCAM-Orsay, France
Effect of surface induced- and track- potentialsInelastic processes:
Convoy electronsAuger electron emissionProjectile autoionization Plasmon excitation and decay.
0 10 20 30 40 50 60 70 800
5
10
15
20
25
30
35
AlF3
Ar+
Al(111)
H+ de 60 keV, ==1
o
dN(E
)/dE
(u.
a.)
Electron Energy (eV)
Effect of the surface topography
20 25 30
5 keV Ne+- Al(111)
()
()
(III)(II)
(I)
dN(E
)dE
(a.
u.)
Electron energy (eV)
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Theoretical studies of electron emission in grazing ion-
surface collisions M.L. Martiarena and V.H.Ponce.
•Surface ionization by ion impact
•Binary - electron production
•Convoy electron emission
Continuum wave of an hydrogen atom in front of metallic surfaces
-2 .00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50
Y
-1.00
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
Z
(y,z)2
k,m=0
Intrinsic properties of materials
•Characterization of surfaces by ion scattering
•Characterization of surfaces by photoemission
•Electronic properties of perovskites
•Characterization of hard amorphous carbon films.
Interaction of electrons and ions with surfaces.
•Excitation of phonons in medium-energy electron spectroscopies.
•Inelastic processes in ion-surface collisions
•Modifications of surfaces by ion bombardment
Modification of surfaces by ion bombardmentE.A. Sánchez and G. Otero
Collaboration with CAB-Bariloche, Argentina
Roughening of flat semiconductor
surfaces by Blistering and Sputtering
Swelling
Flattening of rough metal
surfaces by Sputtering
Phase transformation in alloys
0 10 20 30 40 50 60-800
-400
0
400
800
Sur
face
hei
ght (
A)
Ion dose (1016 ions/cm2)
0 10 20 30 40 50 600
40
80
120
160
200
Ro
ug
hn
ess
(Å
)
Ion dose (1016
ions/cm2)
6.5 dpa (3 x 1015 ions/cm2), 30 keV Ar
Cu-Zn-Al(100)
Mechanically polished
After grazing bombardment
top related