This research considers the requirements for molecular electronics to be a realistic complement to silicon electronics. Results of the studies presented here clearly show that simple molecular components can be used for creating complex structures on solid substrates via self-assembly, followed by a series of in-situ reactions. Electrical properties of these systems may be finely tuned by the incorporation of appropriate functional units into their core structures during the synthetic process, or by structural modification of previously self-assembled molecular wires. A variety of such molecular systems were sampled and their specific structural and electronic properties were investigated. Implantation of electron-donating and electron-accepting units into π-conjugated systems resulted in exceptional current rectifying molecular wires.
A rectification ratio of ca. 44 at ± 1 V was obtained for a system with a sequence of two electron-donating elements and two electron-accepting units linked with 1t-conjugated spacers. Much higher rectification, of ca. 200 at ±1 V was observed for a dual-layer organic structure containing densely packed self-assembled cationic molecular wires, coupled with anionic molecules of an ad layer. The technique of in-situ synthesis has also led to the successful formation of a previously designed molecular wire across a ca. 3.6 nm gap of a prefabricated skeleton electrode structure. Electrical measurements on this junction have revealed large molecule-induced currents, relative to the residual
current through the empty device. The current - voltage profiles of this molecular junction matched those from STM studies of self-assembled films on planar substrates and were consistent with theoretical calculations. Moreover, a novel method for a precise and reliable estimation of the current flow asymmetry through STM probed films is presented, and applied to the rectification measurements. This technique was based on a statistical approach to the analysis of the current - voltage characteristics and was registered at various STM tip - molecule separations.