Combined I(V) and dI(V)/dz scanning tunneling spectroscopy

We present a method to simultaneously record I(V) and dI(V)dz spectra in a scanning tunneling microscopy measurement, where I, V and z refer to the tunnel current, sample bias and tip-substrate separation, respectively. The I(V) spectrum is recorded by ramping the bias voltage, while the feedback loop of the scanning tunneling microscope is disabled. Simultaneously the z-piezo is modulated with a small sinusoidal high frequency signal. The dI(V)dz signal is recorded using a lock-in amplifier. This method allows to simultaneously record the topography, I(V), dI(V)dV and dI(V)dz in a single scanning tunneling microscopy measurement.