Real-Time Observation of the Dynamics of Single Pb Atoms onSi(111)−(7×7)by Scanning Tunneling Microscopy

The very early stages of Pb deposition on $\mathrm{Si}\left(111\right)-(7\times 7)$ surfaces have been investigated in real time by scanning tunneling microscopy. The combination of variable temperature scanning with unusual very long periods of imaging time have enabled us to observe that single Pb atoms are highly mobile within each half $(7\times 7)$ unit cell. Individual jumps of single atoms between different half cells have been resolved as well as the formation of atom pairs as a result. An activation energy of $0.64\pm 0.07\mathrm{eV}$ has been measured for the diffusion of single atoms between different half cells.