| dc.description.abstract | The orientation and spatial structure at metal electrode can affect the efficiency of charge injection at the molecular/metal interface and thus the performance of OTFTs. In situ scanning tunneling microscopy (STM) was used to reveal the spatial structures of thienothiophene derivatives and rubrene molecules deposited on Au(111) electrode.
First of all, the structures of DFP-DTT(C6F5-DTT-C6F5) adsorbed on Au(111) electrode were examined. For DFP-DTT, it was found that these admolecules could form a long range ordered adlattice characterized as (5 × 4√3) with a coverage of 0.05. Presumably, it will form the attraction between the thienothiophene of the molecular center (electronpositive) and the two perfluorophenyl groups at the two ends of the DFP-DTT (electronegative) to compensate molecular dipole moments. However, the adsorption and desorption of the DTT-based molecules were reversible by potential control.
In addition, the molecular adlayer of FPP-DTT (C6F5-DTT-C6H5) desorbed at -0.2 V, and then switching the potential to +0.3 V for the FPP-DTT molecules readsorbed on Au(111) electrode. After potential modulation rearranged the molecular adlayer, the order adlayer size and potential window were larger than molecular Self-Assembled Monolayer. The size along x-axis measuring of order structures was larger from 15nm to 100nm and the potential window was expanding from 0.05~0.2 V to 0.05~0.7 V.
The molecular center was DTT-based for DP-DTT, FPP-DTT and DFP-DTT, it was mixed with different ratio to form coadsorbed structures. Only DP-DTT and DFP-DTT could coadsorb on Au(111), the structure as (6√3 × 6√3) with a coverage of 0.0556. Presumably, it will form the attraction between the two phenyl groups at the two ends of DP-DTT (electronpositive) and the two perfluorophenyl groups at the two ends of the DFP-DTT (electronegative) to compensate molecular dipole moments.
Lastly, the structures of rubrene adsorbed on Au(111) electrode were examined. The rubrene molecules could form a long range ordered adlattice that characterized as (√3 × 10) and (√3 × 9) with low and high coverage, respectively. Noteworthy, we also could find some bright lines sat on those order arrays due to the special three-dimensional geometry of rubrene moleculars. These moleculars would distort themselves to match the size of gold adatoms and further to generate more stable conformation. However, the adsorption and desorption of rubrene molecules were irreversible by the potential control. | en_US |