Long-Lived Gold Single-Atom Junctions Formed by a Flexible Probe for Scanning Tunneling Microscopy Applications

Flexible probes have shown promise in improving resolution and sensitivity in various scanning probe microscopy based imaging and spectroscopy techniques. However, it has not been utilized in scanning tunneling microscopy (STM) based break-junction (BJ) and fixed-junction (FJ) techniques. In this report, flexible STM tips are facilely fabricated by using gold-coated quartz nanopipettes. The feasibility of using conductive nanopipettes as STM tips is demonstrated by using the STM BJ technique to repeatedly form stable gold quantum point contacts and reliably measure their conductance at an ambient condition. These nanopipette tips are surprisingly durable in the measurements. The junction formation rate and the lifetime of the formed gold atomic junctions are found to be greatly improved using flexible tips. In addition, the most probable lifetime of single-atom junctions formed by the STM FJ method reaches the natural bond lifetime. Thermally activated gold atom relaxations near the banks of the long-lived single-atom contacts are clearly revealed, permitting the insightful study of the mechanical and electrical properties of single gold atoms or atomic-chain structures. In contrast to the conventional solid metal probes, the flexible probes show significant advantages in creating and stabilizing the single-atom junctions, providing exciting opportunities for STM based techniques, molecular electronics, and biosensors.