[seminar] IF-ponedjeljak

[Ticijana Ban]

Poštovani,

Obavještavam Vas o održavanju seminara na Institutu za fiziku, Bijenička cesta 46, predavaonica u zgradi Mladena Paića u ponedjeljak 14. srpnja 2008. u 15:00 sati.

Seminar pod naslovom Electronic structure and dynamics of atom and superatom-surface complexes investigated by femtosecond time resolved photoemission and low temperature STM održat će prof. Hrvoje Petek s University of Pittsburgh, Physics & Astronomy Department, Pittsburgh, USA

Sažetak predavanja možete pronaći u nastavku poruke.

Srdačan pozdrav,
Ticijana Ban 
_______________________________________________________________________________________________________________________




Electronic structure and dynamics of atom and superatom-surface complexes investigated by femtosecond time resolved photoemission and low temperature STM

 

 

Hrvoje Petek

 

University of Pittsburgh, Physics & Astronomy Department, Pittsburgh, USA



 

            Nonlinear time-resolved two-photon photoemission and low-temperature STM provide two complementary methods for studying the electronic structure and dynamics of the unoccupied states of atoms and molecules on metal surfaces.  The interaction of alkali atoms with noble metals is the starting point for the development of theories of chemisorption pioneered by Langmuir and Gurney more than 70 years ago. A systematic two-photon photoemission spectroscopic study of Li - Cs on Cu(111) and Ag(111) surface provides the basis for a simple and quantitative theoretical description of the interfacial electronic structure. In addition, photoinduced charge transfer excitation of alkali atoms on Cu and Ag surfaces creates a displacive force driving their photodesorption. By time resolved photoemission measurements, we follow the femtochemistry of alkali atom desorption in competition with the electronic relaxation by the reverse charge transfer. Complementary information on the electronic structure, and adsorbate-adsorbate interactions can be obtained by STM. Spectroscopic images of molecular orbitals of C60 on Cu surfaces taken at bias voltages above 3.5 eV exhibit spherical harmonic shapes centered on the hollow molecular cores that resemble the atomic orbitals of H or alkali atoms. When two C60 molecules are brought together, these superatom molecular orbitals hybridize to form s and p symmetry bonding and antibonding orbitals that resemble those of H2 molecule. Larger aggregates form delocalized quantum wires and quantum wells with free-electron like orbital delocalization. We argue that the superatom orbitals derive from the universal screening property of hollow molecules.


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