Dependence of STM Images οn Bias Polarity for Sm Layers οn Mo(110) and Mo(211) Surfaces

Thin Sm layers adsorbed on Mo(110) and (211) surfaces were studied with scanning tunneling microscope. It was found that obtained images of these adsorption systems significantly depend on the polarity of the scanning tunneling microscope bias voltage. This dependence is more pronounced for the Sm on Mo(110) than on Mo(211). For Sm/Mo(110), at low Sm coverages the change of bias polarity results in significant difference in the measured height of the adsorbed Sm layer, while the heights of substrate terraces remain the same for both signs of the applied bias voltage. In the coverage range 0.65<θ<1, scanning tunneling microscope images, obtained with negative bias, show the gaps in Sm layers, which are invisible for positive bias.