Chemical Identification of the Foremost Tip Atom in Atomic Force Microscopy.

Chemical identification of individual surface atoms has been achieved by measuring the chemical bonds between tip and surface atoms using atomic force microscopy. On the other hand, the discrimination of chemical species at the tip apex is still a challenging task, even though the differences of the species have significant effects on atomic-scale contrast and atom manipulation. Here, we perform the chemical identification of a foremost tip atom using bond energies measured on precharacterized atomic species on a Si surface. We find that chemically different tips show different trends in the chemical bond energy on the sites and that Pauling's equation for polar covalent bonds well describes those trends. On the basis of this knowledge, in situ chemical identification becomes possible. Using the chemically identified (here, Si and Al) tips, we determine the electronegativity of locally formed silicon oxide solely by experiments. Previously such determination was difficult without the help of theoretical calculations. These successful results confirm the validity and versatility of Pauling's equation for application to atomic-scale objects.