Surface Physics Research at the Centro Atómico Bariloche (since 1987 to 2001)

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)










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)










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










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.










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)










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










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

Surface Physics Research at the Centro Atómico Bariloche (since 1987 to 2001)

Documents

ion bombardmentatom

inelastic processes

hard amorphous carbon

interaction of electrons

surface physics research

valence band photoemission

grizzi collaboration

molecule adsorption