Molybdenum Selenide Molecular Wires as One-Dimensional Conductors

Scanning tunneling microscopy (STM) has been used to characterize the structure and electronic properties of molybdenum selenide $({\mathrm{Mo}}_{6}{\mathrm{Se}}_{6})$ molecular wires. STM images resolve the 0.45 nm unit cell repeat in isolated molecular wires and bundles of wires. Tunneling spectroscopy measurements exhibit sharp peaks in the local density of states that are consistent with the Van Hove singularities expected for a one-dimensional (1D) system. These data have been compared with previous band structure calculations. Preliminary measurements at 5 K show no evidence of a gap opening at low temperatures. The implications of these results to metal-insulator transitions in 1D systems are discussed.