Theory of long-range forces in AFM and current versus distance curves in STM on Au(1 1 1)

Tunnelling currents on Au(1 1 1) are evaluated within a theory which regards the tunnelling as an excited state phenomenon. The competition between two effects determines the variations of the tunnelling current with tip–sample distance and leads to a local minimum in the current vs. distance dependence. The theory provides the explanation of various experimental observations in AFM and STM on Au(1 1 1): special features in the current vs. distance curve, the long-range attractive interactions between tip and sample and the anomalously high corrugation amplitudes in STM and AFM.