Highly resolved non-contact atomic force microscopy images of the Sn/Si(111)-(2√3 x 2√3) surface

The Sn/Si(111)-(2 root 3 x 2 root 3) surface is observed by using non-contact atomic force microscopy (NC-AFM) at room temperature. The images at relatively far tip - surface distances show four protrusions in each (2 root 3 x 2 root 3) unit cell, which are similar to previously reported scanning tunnelling microscopy (STM) images. On the other hand, it is found that, at closer tip - surface distances, eight protrusions are clearly resolved, which indicates that the spatial resolution of NC-AFM is higher than that of STM as far as imaging this surface is concerned. Our high-resolution NC-AFM images are in good agreement with a recently proposed model based on 13 Sn atoms per unit cell.