AFM's path to atomic resolution
  We review the progress in the spatial resolution of atomic force microscopy (AFM) in vacuum. After an introduction of the basic principle and a conceptual comparison to scanning tunneling microscopy, the main challenges of AFM and the solutions that have evolved in the first twenty years of its existence are outlined. Some crucial steps along the AFM's path towards higher resolution are discussed, followed by an outlook on current and future applications. 
Franz J. Giessibl