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O: Fachverband Oberflächenphysik

O 42: Organic/bio Molecules on Metal Surfaces IV

O 42.7: Vortrag

Mittwoch, 13. März 2013, 12:00–12:15, H38

Initial growth of quinacridone on Ag(111) — •Thorsten Wagner, Michael Györök, Daniel Huber, and Peter Zeppenfeld — Johannes Kepler University, Institute of Experimental Physics, Linz, Austria

The organic dye pigment quinacridone (QAC) may play a role as an outsider in view of record breaking organic semiconductors like rubrene, but its dominant H-bonds might be a key to innovative device structures. Therefore, this work focusses on the initial growth of quinacridone on Ag(111) surfaces at room temperature. During deposition, the local electron yield was monitored in a photoelectron emission microscope (PEEM) showing no spatial inhomogeneities on a scale between 100 nm and 100 µm for up to 5 monolayers. This could be either due to a smooth layer-by-layer growth or the formation of extraordinary small 3D crystallites. The initial increase of the yield can be attributed to a lowering of the work function upon formation of the first monolayer. As the ionization potential of QAC (5.4 eV [1]) is actually higher than the photon energy (4.9 eV), a continuous decrease even below the emission of the bare Ag(111) substrate was observed afterwards. Scanning tunneling microcopy images of the initial layer exhibit a simple, raw-like stacking of parallel molecules which can be explained by hydrogen bonding between adjacent, flat-lying molecules. After annealing to a temperature of T=550-570 K, which is close to the desorption temperature of the multilayer, the structure changes to a stacking of dimers. Additional LEED data support the STM findings.

[1] Glowacki et al. in Applied Physics Letters 101, 023305 (2012)