  The qPlus sensor allows simultaneous measurements of scanning tunneling
microscopy (STM) and atomic force microscopy (AFM). Its design for use in
frequency modulation AFM (FM-AFM) involves separate electrodes, applied on an
oscillating quartz cantilever, for the detection of an electronic tunneling
current and the deflection signal. Cable resistance and capacities in the
electronic setup can induce cross talk phenomena. We report a tunneling
current-induced cross coupling observed in a combined STM/AFM setup which uses
the qPlus sensor. This cross coupling can induce a positive or negative change
of the amplitude excitation signal, thus acting as an apparent dissipation or
drive. The experimental data is explained well by tunneling current-induced
fluctuations of the electric potential on the sensor electrodes.
