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O: Fachverband Oberflächenphysik

O 77: Organic Molecules on Inorganic Substrates V: Solid-Liquid Interfaces, Self-Organization, Ordering

O 77.11: Vortrag

Donnerstag, 4. April 2019, 13:00–13:15, H9

Phase diagram and order-disorder phase transitions of NTCDA/Ag(111) — •Sebastian Thussing, Martin Grünebohm, and Peter Jakob — Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany

A chopped-heating setup has been employed to derive the phase diagram and to follow order-disorder phase transitions of (sub-)monolayer NTCDA on Ag(111). This well-known model system has been chosen to optimize parameters in the experimental setup and to minimize detrimental effects associated with sample heating (direct current heating). We examined 2D SPA-LEED images taken at elevated temperatures as well as 1D line scans obtained during annealing of the molecular layers. NTCDA molecules on Ag(111) experience attractive lateral interactions, leading to island growth already at 150 - 200K for submonolayer coverages. Upon annealing the average NTCDA island size increases steadily (Ostwald ripening) as indicated by an increase of the correlation length of the relaxed monolayer NTCDA LEED reflexes. Further annealing eventually leads to a dissolution of NTCDA islands into the 2D gas phase. The temperature of this transformation depends strongly on the amount of deposited NTCDA. Moreover, this order-disorder transition is preceded by thermal desorption for coverages above 0.55 ML. By analyzing the coverage dependency of the order-disorder phase transition in conjunction with thermal desorption spectroscopy the phase diagram for this system has been derived.