Regensburg 2004 – wissenschaftliches Programm

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SYOH: Organic and Hybrid Systems for Future Electronics

SYOH 5: Poster

SYOH 5.20: Poster

Donnerstag, 11. März 2004, 18:00–21:00, B

Structural investigation of the low temperature order-disorder phase transition of NTCDA on Ag(111) using NIXSW — •C. Stadler, J. Stanzel, M. Scheuermann, S. Hansen, C. Kumpf und E. Umbach — Exp. Physik II, Uni Würzburg

The properties of organic thin films largely depend on their interaction with the underlying substrate. For NTCDA on Ag(111) the bonding is regarded as chemisorption as revealed e. g., by photoemission or thermal desorption spectroscopy. Recently an unusual phase transition upon cooling of NTCDA (sub)monolayers on Ag(111) has been observed by electron diffraction studies and other techniques. Upon cooling the long range order disappears below 180 K. Normal Incident X-Ray Standing Waves (NIXSW) measurements were performed using the wiggler beamline ID32 at the ESRF. We report on detailed structural results of different room temperature and low temperature phases, especially on the precise bonding distance between the NTCDA molecules and the Ag substrate. A comparison of the NIXSW results obtained from photoemission- and Auger-yield measurements enables a reasonable correction for non-dipolar contributions to the photoeletron yield as well as for electron induced Auger processes. Both effects cannot be neglected for small atomic species.