Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 18: Poster: Towards Molecular Spintronics, Organic Thin Films, Optical Layers, Vibrational Spectroscopy, Tayloring organic interfaces
DS 18.15: Poster
Dienstag, 26. Februar 2008, 14:30–19:30, Poster A
in vivo STM-observation of the growth of 3,4,9,10 perylene tetracarboxylic (PTCDA) crystals on Si(111) 7×7 — •Thorsten Wagner1, Rolf Möller1, Masafumi Sakata2, and Kingo Itaya2 — 1Universität Duisburg-Essen, Fachbereich Physik, Lotharstr. 1-21, 47057 Duisburg — 2Tohoku University, Department of Applied Chemistry, Sendai, Japan
We will show scanning tunnelling microscopy (STM) results on the in vivo observation of the growth of organic nanocrystals. 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA) was thermally evaporated onto a clean Si(111) 7×7 surface held at room temperature. A sequence of images acquired over a period of 24h shows how the unordered structure with no visible molecular resolution evolves to individual crystals which can be well characterized. The size of the crystallites (roughly 10nm by 10nm) is consistent with former thermal desorption experiments (TDS) of PTCDA on Cu(111): The number of crystals increases with the coverage. This can be related to the higher the density of nucleation centres. Between preparation and first imaging had been 12h. In addition, the formation of the crystals took place during the STM obervation. Therefore we propose that the growth of the crystals is not only driven by diffusion. By operating the STM at mean current of 2pA and a bias voltage of +1.5V the tip adsorbat interaction was minimized. Anyway this small force could be enough to push and drag the molecules into the energetically preferred adsorption sites within the crystalline structures. Once the crystalline structures have been formed the images were stable and molecular resolution was possible.