Initial Steps of Rubicene Film Growth on Silicon Dioxide

Abstract

The film growth of the conjugated organic molecule rubicene on silicon dioxide was studied in detail. Since no structural data of the condensed material were available, we first produced high quality single crystals from solution and determined the crystal structure. This high purity material was used to prepare ultrathin films under ultrahigh vacuum conditions, by physical vapor deposition. Thermal desorption spectroscopy (TDS) was applied to delineate the adsorption and desorption kinetics. It could be shown that the initial sticking coefficient is only 0.2 ± 0.05, but the sticking coefficient increases with increasing coverage. TDS further revealed that first a closed, weakly bound bilayer develops (wetting layer), which dewets after further deposition of rubicene, leading to an island-like layer. These islands are crystalline and exhibit the same structure as the solution grown crystals. The orientation of the crystallites is with the (001) plane parallel to the substrate. A dewetting of the closed bilayer was also observed when the film was exposed to air. Furthermore, Ostwald ripening of the island-like film takes place under ambient conditions, leading to films composed of few, large crystallites. From TDS, we determined the heat of evaporation from the multilayer islands to be 1.47 eV, whereas the desorption energy from the first layer is only 1.25 eV.

Structural Polymorphism and Thin Film Transistor Behavior in the Fullerene Framework Molecule 5,6;11,12‐di‐o‐Phenylenetetracene

“…Thepreferred growth of the polymorphic orientation of 2 on Si/SiO 2 might be due to as ubstrate induced epitaxial reorientation as found for rubicene and has been nicely shown by Winkler et al [14] Crystalline 2 obtained from solution as well as from the gas phase indeed reveals strong anisotropic Figure 2. ORTEP plot of 2 with ellipsoidsd rawn at 50 %probability level.…”

“…In contrast to the P 2 1 /n phase obtained when 2 is sublimed onto aglass surface (calcd: 11.05, 16.24, 25.508 8 2q), the major reflections at 8.10/16.358 8 2q in GIXRD experiments give distinct evidence for the full staggered packing mode (calcd: 8.18, 16.40, 24.418 8 2q;exp:8.08, 16.308 8 2q)of2 in C 2/c. Thepreferred growth of the polymorphic orientation of 2 on Si/SiO 2 might be due to as ubstrate induced epitaxial reorientation as found for rubicene and has been nicely shown by Winkler et al [14] Crystalline 2 obtained from solution as well as from the gas phase indeed reveals strong anisotropic Figure 2. ORTEP plot of 2 with ellipsoidsd rawn at 50 %probability level.…”

“…Due to the observed film morphology the growth mechanism of 2 is in full accordance with observations on film growth of closely related rubicene on Si/ SiO 2 substrate. [14] Thus,m ainly Ostwald ripening of the initially adsorbed molecules leads to an anisotropic island growth of crystals of 2 preventing the development of ah omogeneous thin film. Furthermore,w ea nalyzed all thin films of 2 by UV/Vis transmission mode in order to correlate the absorption spectra to the varying film thickness (5,10,20, and 40 nm) ( Figure 6) and to validate evidence of the so far observed structural ordering what has also an effect on the electronic behavior.…”

Controlling the growth mode of para-sexiphenyl (6P) on ZnO by partial fluorination

“…The arrangement of 6P-F 4 in this wetting layer is not known, however, the thickness implies that it is either composed of more than one layer of flat lying molecules as for instance in the case of Rubicene on SiO 2 (ref. 28) or the molecules are tilted. It should be noted that we did not find evidence for the existence of a wetting layer at the 6P/ZnO(10 % 10) interface though it has been observed, for example, when depositing 6P on mica (001) or amorphous mica.…”

Idiosyncrasies of Physical Vapor Deposition Processes from Various Knudsen Cells for Quinacridone Thin Film Growth on Silicon Dioxide

“… 19 − 22 Despite recent reports of air-stable quinacridone field-effect transistors with relatively high carrier mobilities of 0.2 cm 2 /(V s), 23 there is still a lack of knowledge concerning the kinetics of vacuum deposition and film formation on industrially relevant silicon dioxide substrates. Comparable investigations on the kinetics of adsorption, layer growth and desorption exist for a number of organic molecules (e.g., pentacene on SiO 2 24 and rubicene on SiO 2 25 ), while the focus has only recently shifted to H-bonded semiconductors. 26 − 29 …”