Regensburg 2010 – scientific programme
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O: Fachverband Oberflächenphysik
O 13: Semiconductor substrates: Adsorption
O 13.7: Talk
Monday, March 22, 2010, 16:30–16:45, H34
Adsorption of PTCDA on GaN(0001) surfaces — •Christian Schulz1, Cherno Jaye2, Christian Tessarek1, Stephan Figge1, Jan Ingo Flege1, Thomas Schmidt1, Detlef Hommel1, Daniel A. Fischer2, and Jens Falta1 — 1Institute of Solid State Physics, University of Bremen, 28359 Bremen — 2Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
Ordered growth of thin PTCDA layers is mainly observed on metals but recent reports (S. Yim et al. J. Phys.: Condens. Matter 15, (2003)) have shown that some molecules also show ordered layers on unpassivated III-V semiconductor surfaces. In this work we investigate the adsorption of PTCDA on gallium-polar GaN(0001) with different methods.
X-ray photoelectron spectroscopy (XPS) shows that the molecules are not dissociating after deposition, because the peak area ratios (including the shake-up’s) for the perylene to carboxylic C1s feature is near the expected ratio for the intact molecule.
Scanning tunneling microscopy (STM) and spot profile analyzing low energy electron diffraction (SPA-LEED) measurements reveal an island growth mode. For monolayer equivalent deposits, the near edge X-ray absorption fine structure (NEAFS) data of the C K-edge exhibit no polarization dependence indicating a disordered mixture of molecules in upstanding and down-lying geometry.
However, for multilayer equivalent deposits a polarization dependence is observed which suggests a flat-lying geometry of the molecules. These findings are in good agreement with high-resolution STM and SPA-LEED data which reveal lateral ordering, compatible with a bulk-like configuration, within the islands.