Insulator-protected mechanically controlled break junctions for measuring single-molecule conductance in aqueous environments

摘要

We present a method to fabricate insulated gold mechanically controlled break junctions (MCBJ) by coating the metal with a thin layer of aluminum oxide using plasma enhanced atomic layer deposition. The Al_2O_3 thickness deposited on the MCBJ devices was varied from 2 to 15 nm to test the suppression of leakage currents in deionized water and phosphate buffered saline. Junctions coated with a 15nm thick oxide layer yielded atomically sharp electrodes and negligible conductance counts in the range of 1 to 10~(-4) G_0 (1 G_0 = 77 μS), where single-molecule conductances are commonly observed. The insulated devices were used to measure the conductance of an amphi-philic oligophenylene ethynylene derivative in deionized water.