Single-Electron and Oxide-Impurity Effects in Junctions Formed by a CryogenicScanning Tunneling Microscope

摘要

We show that the I-V characteristics measured at 4 K of single tunnel junctionsbetween the tip of a scanning tunneling microscope and a metallic sample are sensitive to the materials used. The superconducting energy gap of lead is observed for tips without surface oxides, but eliminated for tips with thick oxides. Probing bulk etched tungsten, observation of the Coulomb staircase suggests capacitive effects due to a small metallic-oxide impurity.