Growth of π-conjugated nanorods and application to organic fight emitting diodes

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Attaching functional organic layers to semiconductor surfaces may have applications in a number of areas, including molecular and biomolecular electronics, sensors and lithography. In this study, we have developed a novel, two-step strategy for the covalent bond formation between aromatic molecules and silicon surfaces. In the first step, a H-terminated Si (III)surface reacts with amino radicals to give a NH_2-terminated Si (III) surface at room temperature. The amino radicals were generated by the thermal decomposition of ammonia gas with Tungsten filament heated at 1000-1200℃. The formation of NH_2-terminated surface and the monolayer was confirmed by X-ray photoelectron spectroscopy (XPS) and Multi Internal Reflection Fourier Transfer Infrared Spectroscopy (MIR FT-IR). In the second step, the reaction of amino-terminated Si surface with an aromatic dialdehydes (1,4-bis (4-formylstyryl)benzene) (BFSB) was carried out by vacuum deposition of BFSB on the substrate heated at 130℃ under high vacuum. The reaction of amino-terminated surface between BFSB and the monolayer formation was confirmed by XPS and MIR FT-IR. Distinct images such as an island structure with the diameter of around 5 nm can be seen in non-contact atomic force microscopy (nc-AFM) images. The islands consist of several dots with the height of each dot was about 2.3 nm. According to the molecular orbital calculation (MOPAC), the length of BFSB molecule is about 2.2 nm. These results suggest that the each dot corresponds to the vertically aligned BFSB molecules. On the other hand, no photoluminescence from BFSB was observed on silicon surface, due to an energy transfer. Next, we have investigated the formation of organic monolayer on indium-tin-oxide (ITO) electrode and the effect to device performance of OLEDs. We have found that the carrier injection efficiency was enhanced by modification of ITO by organic monolayers depending on their chemical structure.