Atomic force microscopy (AFM) is used widely to study surfaces with a resolution on the nm scale – vastly inferior to atomic resolution offered by scanning tunneling microscopy (STM). In 1982, about a year after the invention of STM, the enigmatic Si 7x7 surface was resolved, a success that many view as the start of nanotechnology. In 1986, the AFM was introduced and hopes were high that resolving atoms in real space would soon be possible for insulators as well. However, profound problems appeared that originate in the physics of the tip-sample interaction and in the difficulties of measuring small forces. Today, the AFM exceeds the STM in spatial resolution, as shown in the image above that depicts a Fe dimer and a nearby Fe trimer adsorbed on a Cu(111) surface. The talk discusses the steps in increasing resolution that also involved in changing the core of the AFM from a Si cantilever to a stiff, self-sensing piezoelectric cantilever ("qPlus sensor"). This sensor allows an uncompromised combination of STM/AFM, demonstrating atomic and subatomic spatial resolution in vacuum, low temperatures as well as in ambient conditions.
University of Regensburg, Germany