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Two-Photon Photoemission Investigation of Electronic and Dynamical Properties of Alkali Atoms Adsorbed on Noble Metal Surfaces

Sametoglu, Vahit (2009) Two-Photon Photoemission Investigation of Electronic and Dynamical Properties of Alkali Atoms Adsorbed on Noble Metal Surfaces. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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We present a systematic time-resolved two-photon photoemission study of the electronic and dynamical properties of Li through Cs adsorbed on Cu(111) and Ag(111) surfaces. A fundamental problem in surface science is how to describe the electronic structure of a chemisorption interface based on the intrinsic properties of the interacting materials. Because of their simple s-electron structure, elements of the alkali atom group comprise paradigmatic adsorbates in many theories of chemisorption, whereas the complementary experimental studies are sparse and incomplete. Through a combination of spectroscopic and femtosecond time-resolved surface measurements, we are able to probe systematically the binding energies, symmetries, and electron and nuclear relaxation dynamics of the initially unoccupied alkali atom resonances. As a prelude, we study the two-photon photoemission process occurring at the bare Ag(111) surface. We develop a quantitative model for two-photon photoemission process, where the nonresonant and k-dependent two-photon absorption between the lower and upper sp-bands is modeled by the optical Bloch equations, and the angle-dependent intensities are described by the Fresnel equations. Our two-photon photoemission spectra of Li through Cs chemisorbed Cu(111) and Ag(111) surfaces reveal two resonances with the m=0 and m=+-1 symmetry ('m' is the projection of the orbital angular momentum ‘l’ onto the surface plane). For the m=0 resonance, which is derived from the hybridization of the ns and npz orbitals of alkali atoms, we find a binding energy of 1.84-1.99 eV below the vacuum level, which is independent of the alkali atom period, and tunes with coverage in a universal manner. At 0.3-0.7 eV higher energy, we discover and identify the m=+-1 resonance by its characteristic angular intensity distribution, which derives from the antisymmetry of the npx and npy orbitals. We implement a quantitative model for the alkali atom chemisorption based on the dominant Coulomb interactions invoked by Langmuir and Gurney. Moreover, the time-resolved photoemission measurements on Cs/Ag(111) surface reveal an unprecedented nonexponential electronic population decay, which is indicative of the bond rupture; we follow the femtochemistry, i.e., the dissociative wave packet motion, on nearly the picosecond time scale.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Sametoglu, Vahitvas6@pitt.eduVAS6
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairPetek, Hrvojepetek@pitt.eduPETEK
Committee MemberSnoke, Davidsnoke@pitt.eduSNOKE
Committee MemberWaldeck, Daviddave@pitt.eduDAVE
Committee MemberDutt, Gurudevgdutt@pitt.eduGDUTT
Committee MemberKim, Hong-Kookim@engr.pitt.eduHKK
Date: 24 June 2009
Date Type: Completion
Defense Date: 2 March 2009
Approval Date: 24 June 2009
Submission Date: 2 April 2009
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: adsorption; alkali atoms; angle-resolved photoemission; chemisorption; femtochemistry; femtosecond lasers; frustrated desorption; molecular electronics; noble metals; photoemission; time-resolved two-photon photoemission; two-photon photoemission; ultrafast lasers
Other ID:, etd-04022009-195031
Date Deposited: 10 Nov 2011 19:33
Last Modified: 15 Nov 2016 13:38


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