Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 77: Electronic structure I
O 77.4: Vortrag
Donnerstag, 29. März 2012, 16:45–17:00, MA 043
Energy level alignment and ultrafast electron dynamics at pristine and pyridine-covered ZnO(1010) — •Jan-Christoph Deinert, Daniel Wegkamp, Julia Stähler, and Martin Wolf — Fritz-Haber-Institut der MPG, Abt. Physikalische Chemie, Faradayweg 4-6, 14195 Berlin
Organic adlayers on semiconductor surfaces are promising candidates for highly functional molecular electronics devices, e. g. organic LEDs. Such hybrid systems may exhibit electronic and excitonic properties that go beyond the linear combination of the two material classes’ stand-alone properties. An example is the formation of new interface states through hybridization of molecular and semiconductor states. Efficient functionalization requires sound knowledge of both occupied and unoccupied electronic structure at the hybrid interface. In our experiment we can directly access these states and examine their ultrafast dynamics upon excitation using femtosecond time-resolved two-photon photoemission (2PPE). Characterization of the pristine ZnO(1010) surface yields the valence and conduction band (CB) edge energies. Besides a time-dependent down shift of the sample work function by few 10 meV, our spectra show the hydrogen-induced downward shift of the CB minimum below EF. Furthermore, we directly monitor the hot electron relaxation in the ZnO CB on femtosecond timescales and subsequent formation of a long-lived state. Adsorption of pyridine leads to a massive reduction of the work function of the sample up to ΔΦ=−2.7 eV, which makes this system a good candidate for further studies of energy level alignment.