Measurement of I-V characteristic of organic molecules using step junction

We investigate devices fabricated using a step junction technique, which is a simple fabrication method to build electrodes with average gap width of 10∼20 nm using only micro-fabrication. 1,4-benzenedimethane-thiols(xylyl-dithiol; XYL) are self-assembled onto this nanoscale junction (sacrificial step junction) and connected in series by 20 nm gold clusters (GC). Since the gap size in some devices is believed to be locally as small as a single molecule dimension due to variations in the step junction fabrication, another sample (titanium step junction) was prepared using only XYL molecules to bridge the gap. The current-voltage characteristic of XYL was measured using these structures, and compared with the tunneling current before molecular deposition. The conductance of sacrificial step junction devices increased with a yield of 30% after forming a molecule/cluster/molecule bridge, while a lower yield (∼5%) was observed for the molecule-only devices. Temperature dependent measurement performed on titanium step junction devices, indicate that the molecular conduction is via tunneling.