Theoretical Study of Extraction of a Single Al Atom from Al(111) Surface by Scanning Tunneling Microscopy W Tip

Based on the discrete variational method with the local-density-functional approximation, the cluster models were chosen to simulate the extraction of a single Al atom from Al(111) sample surface by a scanning tunneling microscopy W tip with and without external bias voltages. The calculated results show that the tip-sample effects of W tip on the extraction of an Al atom are very important. The Al atom can be extracted from the Al(111) surface by the pure W tip without external bias, as the tip approaches the sample within 10 a.u. (5.3Å). When the separation between the tip and the sample is larger than 10 a.u., a positive bias must be applied to the sample. The extracted Al atom is expected to have net positive charge when it escapes from the Al(111) sample surface. The corresponding critical field is about 0.6V/Å. This value is in good agreement with experimental results.