Nanofabrication of self-assembled molecular-scale electronics

Single electron tunneling devices were made by combining standard electron beam lithography and the self-assembly of chemically synthesized gold clusters. These clusters, with diameters from 2 to 5 nm, were captured in a 5-10 nm gap between two gold electrodes. The gold particles as well as the electrodes were covered with self-assembled monolayers(SAM) of organic molecules which served as tunnel barriers. Operating devices show a suppressed current due to the Coulomb blockade of tunneling at room temperature. When cooled to 4.2 K, a Coulomb staircase was observed. By applying a voltage to an oxidized aluminum gate beneath the electrodes and the trapped gold cluster the current voltage characteristics were modulated. Anomalous effects are observed such as constant current plateaus whose positions are gate-voltage dependent. An electrodeposition method for gold has been used to fabricate gaps between electrodes smaller than 2 nm. A self-assembled monolayer was used successfully on the electrodes in order to prevent the gold atoms from migrating on the surface between the electrodes and thereby short-circuiting the junction. The conductance of such a tunnel junction has been measured and compared to the theory with good agreement. From this comparison the capacitance of Me junction was estimated, and we could use that value to calculate a rough estimation of the distance between the electrodes.