摘要
Cl-functionalized scanning tunneling microscopy （STM） tips are fabricated by modifying a tungsten STM tip in situ on islands of ultrathin NaCI（100） films on Au（111） surfaces. The functionalized tips are used to achieve clear atomic- resolution imaging of NaCI（100） islands. In comparison with bare metal tips, the chemically modified tips yield drastically enhanced spatial resolution as well as contrast reversal in STM topographs, implying that Na atoms, rather than C1 atoms, are imaged as protrusions. STM simulations based on a Green＇s function formalism reveal that the experimentally observed contrast reversal in the STM topographs is due to the highly localized character of the Cl-pz states at the tip apex. An additional remarkable characteristic of the modified tips is that in dI/dV maps, a Na atom appears as a ring with a diameter that depends crucially on the tip-sample distance.
