PTCDA thin films

Tsiper EV, Soos Z, Gao W, Kahn A (2002) Electronic polarization at surfaces and thin films of organic molecular crystals PTCDA. Chem Phys Lett 360 47-52... 

There are, however, a few planar aromatic molecules with different bulk structures which do show the existence of such orientational precursors. One of these exceptions is PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) which has been extensively studied in the past and is commonly considered as a prototype system for organic thin film growth [62, 63]. Especially on Ag(l 11) an epitaxial growth of well-ordered PTCDA films was observed where molecules adopt the same arrangement as in the (102)-plane of the bulk structure of PTCDA [62]. An examination of this (102)-plane reveals that this... 

Comparing the situation for PTCDA with the above discussed cases of pery-lene and pentacene which exhibit a large diffusion already at room temperature (due to their smaller sublimation enthalpy) thus indicates that the film structure of large molecules such as PTCDA prepared at room temperature may not represent the thermodynamic equilibrium structure. Finally, we note that PTCDA reveals only a rather small charge carrier mobility (for thin films values of less than 3 X 10 cmW s were reported [67]), and thus is not well suited for the fabrication of OFETs. 

As a result of the above, and of the direct competition between molecule-substrate and intermolecular interactions, the presence of the metal or insulator can induce interface polymorphs which do not exist in the bulk. Examples for this are the specific thin film phases of pentacene on insulators [16, 74, 75] or metals (e.g., Cu(llO) [16]), the a- and 3-phases of tetraeene on Ag(l 11) [69], or the square phases of PTCDA on Ag(l 11) [30] and Au(l 11) [84]. It is evident that the charge carrier mobilities of organic semiconductors will depend on the crystal phase. 

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