Ultrahigh vacuum atomic force microscopy: True atomic resolution

In this note we report the first observation of salient features of the Si(111)(7 × 7) reconstructed surface across monatomic steps by dynamic atomic force microscopy (AFM) in ultrahigh vacuum (UHV). Simultaneous measurements of the resonance frequency shift Δf of the Si cantilever and of the mean tunneling current Īt from the cleaned Si tip indicate a restricted range for stable imaging with true atomic resolution. The corresponding characteristics vs. distance reveal why feedback control via Δf is problematic, whereas it is as successful as in conventional STM via Īt. Furthermore, local dissipation (energy loss of 10-14 W) through individual atoms is observed and explained by the coupling of the surface atoms to phonons.