Element-Specific Image and Local Work Function of Fe Submonolayer Film on Au(001) Studied by Scanning Tunneling Microscopy

Spatially resolved maps of the local work function of Fe submonolayer films on an Au(001) surface, together with a topographic image, were obtained using a scanning tunneling microscope with the gap distance modulation technique. A clearer element-specific contrast between Fe and Au was observed compared with that of the topographic image. The observed work function of ultrathin Fe films is larger than that of Au(001) substrate, which is in contrast with the bulk values of each element. The effect of the decay rate of the wave function on the sample surface is discussed. We also observed that the work function of the second Fe layer, which exceeds the bulk value, was larger than that of the first Fe layer.