Attachment of pi-conjugated molecules on silicon(001) surfaces and its application in molecular/organic electronics

We have developed a new strategy for forming oriented arrays of pi-conjugated organic molecules on silicon surfaces. The Si=Si dimers of the reconstructed Si(001) surface can selectivity react with the dicarbonyl group of 9,10-phenanthrenequinone, leading to cyclic molecular structure between the attached molecule and underlying Si substrate. This reaction is formally analogous to a heteroatomic Diels-Alder reaction. This binding chemistry not only avoids disrupting the pi-conjugated system of the attached molecule, but also helps to retain the orientation of the molecules along a specific crystalline direction, which might be very important when a group of molecules have to work cooperatively as molecular electronic devices.; Additionally, we demonstrated that using proper methods, the structure of pi-conjugated molecules could be modified either by organic synthesis before the surface attachment or by photo-illumination after the surface attachment, which gives us more options of the desired molecular structures that might bring unique optical/electric properties. We also discovered that organic monolayers produced by this Diels-Alder reaction could be used as a substrate to grow high quality pentacene thin films, an important component in the organic thin film field-effect transistors.