Data scattering in scanning tunneling spectroscopy

We investigated the scattering of current–voltage data obtained with scanning tunneling spectroscopy (STS) at room temperature at a solid–liquid interface on highly oriented pyrolytic graphite (HOPG) and in ultrahigh vacuum on HOPG and Au(1 1 1). For both experimental conditions, the data scattering can be described by a lognormal function for a moderate number of subsequent measurements. The lognormal distribution of the current can be explained by a normal distribution of the tip–surface distance. We give a simple empirical rule for STS data sorting.