Calibrating atomic-scale force sensors installed at the tip apex of a scanning tunneling microscope

Scanning tunneling microscopy (STM) tips decorated with either a single carbon monoxide molecule or a single xenon atom are characterized by simultaneous force and conductance measurements using a combined low-temperature noncontact atomic force and scanning tunneling microscope (NC-AFM/STM). It is shown that in both cases the particle decorating the tip simultaneously performs the function of an atomic-scale force sensor and transducer which couples the short-range force acting on the tip to the tunneling conductance of the junction. On the basis of the experimental data, two distinct coupling regimes are identified; in one of them the force sensor-transducer function is calibrated quantitatively.