Regensburg 2004 – wissenschaftliches Programm

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SYOH: Organic and Hybrid Systems for Future Electronics

SYOH 3: Electronic Structure and Transport Properties

SYOH 3.2: Vortrag

Donnerstag, 11. März 2004, 16:15–16:30, H37

Dynamics of Hot Electrons in PTCDA Thin Films — •Steffen Berger, Alexander Mönnich, Jens Wüsten, Martin Aeschlimann, and Christiane Ziegler — University of Kaiserslautern, Department of Physics,

Charge carrier dynamics are of importance for many applications of organic semiconductors. We therefore studied the electron dynamics in 100 nm thin 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) films without and with dopants by means of time-resolved two-photon photoelectron spectroscopy (TR-2PPE) on a femtosecond scale.

As light source a titanium-sapphire laser system with a repetition rate of 80 MHz and a pulse length of 20 fs was used. Frequency doubling gives a photon energy of 3.1 eV, which allows to examine the life time of electrons in PTCDA with energies of 1.3-3.0 eV above the Fermi level.

By deposition of alkali-metals such as Na the conductivity of the n-type organic semiconductor 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) can be increased by several orders of magnitude. In TR-2PPE we observed an increase in the life time of electrons with energies >1.2 eV above E_F after Na reaction. This can be explained by results from inverse photoemission spectroscopy which reveals that the density of states at 1.2 eV above E_F is reduced by the same process, i.e. there are less unoccupied states in which the hot electrons can relax.