The Nature of the Chemical Bond Verified by Atomic Force Microscopy

Measuring tiny inter-atomic forces has been an important challenge in the development of atomic force microscopy (AFM). Present force sensitivity achieved by a frequency modulation technique and mechanical stability of AFM allow us to quantify the inter-atomic forces atom-by-atom. We apply the capability to verify the chemical bonding theory established by L. Pauling. First, interaction forces are measured above Si adatoms and H-terminated Si adatoms on the Si(111)-(7×7) surface to compare chemical bonding force and physical force. Chemical bonding force is measured only above Si adatoms that have dangling bonds. We also systematically investigate element dependence of the chemical bonding energy. Covalent bonds are observed above group IV elements on the Si(111)-(7×7) surface while polar covalent bonds are observed above elements with different electronegativity from Si atoms. Chemical bonding energy obtained by various tip apexes can be explained by Pauling’s chemical bonding theory.