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Direct Imaging of Thermodynamic Process in Atom Migration by Using Scanning Tunneling Microscopy

We report novel imaging of surface adatom migration that allowed us to probe the impurity atoms buried in a semiconductor, by scanning tunneling microscopy (STM). We adsorbed Ga atoms onto a chemically inactive H-terminated Si(100) surface, and directly observed thermal Ga-atomic motion near 100 K. By exploiting the fact that the STM image reveals the thermodynamic distribution function of atomic trajectories, we achieved high-sensitivity detection of a positional variation in the surface potential. The position of subsurface P dopants was thereby obtained, in combination with first principles calculations of electronic states.