1. H. F. Hess, R. B. Robinson and J. V. Waszczak, PhysicaB169, 422 (1991).
2. Oxford Instruments, model Kelvinox-300.
3. The STM head with our special design was manufactured by Omicron Vakuumphysik GMBH based on their commercial model MICRO-STM.
4. T. Kumakura, H. Tan, T. Handa, M. Morishita and H. Fukuyama, this proceedings.