Seminars Archive
Luca Petaccia
Abstract
Monday, April 9, 2001, 9:00
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
Low temperature instabilities of the (sqrt3 x sqrt3)R30 tetravalent
adatom structures on Ge(111) and Si(111) surfaces
Luca Petaccia
(Laboratorio TASC-INFM, Trieste)
ABSTRACT
The (sqrt 3 x sqrt 3)R30 structure formed by 1/3 of a monolayer
of tetravalent adsorbates on the (111) surface of Si and Ge has recently
attracted much interest because of the complex and diverse phenomenology
diplayed by systems which, at first glance, look very similar both from
a structural and from an electronic point of view. This has induced to
reconsider the importance of the electron-electron interactions that have
been generally assumed to play a minor role in the determination of the
ground state properties of Si and Ge surfaces.
In order to evaluate the role of many body effects in some of these
controversial systems, we are carrying out experimental studies on 1/3
ML of Sn adsorbed on the (111) surfaces of Ge or Si. The measurements -performed
by using valence band and core level photoemission spectroscopy, photoelectron
diffraction, and tunneling spectroscopy- indicate that both electronic
instabilities and structural distorsions concur to the determination of
the ground state of these systems. By comparing the experimental geometric
and electronic structure with state-of-the-art calculations, we find a
very good agreement between the measured atomic geometry for Sn/Ge(111)
and that calculated in LDA approximation. On the other hand, the experimental
data on the surface electronic structure presents some inconsistency with
the LDA predictions and better agreement with results from extended-Hubbard
model. Experimental methods to disentangle these effects will be also discussed.
