Double-tip STM for Surface Analysis
  We explore the possibility of using a double-tip STM to probe the single electron Green function of a sample surface, and describe a few important applications: (1) Probing constant energy surfaces in $\k$-space by ballistic transport; (2) Measuring scattering phase shifts of defects; (3) Observing the transition from ballistic to diffusive transport to localization; and (4) Measuring inelastic mean free paths. 
Q.Niu, M.C.Chang, and C.K.Shih