Theoretical and experimental evidence for "true" atomic resolution under non-vacuum conditions

Abstract

Imaging of atomic scale features (Angstrom resolution) such as individual atoms using an atomic force microscope (AFM) remains highly controversial. Arguments that such resolution is not achievable revolve around two points: (1) that atomic scale defects are not observed and (2) often the experimental images are not reproduced theoretically. Here we show that the AFM is capable of imaging atomic features by presenting images of atomic scale defects at ∼1 Å resolution. Dislocation defects and monatomic growth steps on the {001} surface of the mineral anhydrite (CaSO4) are observed in unfiltered AFM images. Furthermore, the atomic features observed in the experimental AFM images are reproduced by numerical simulation; conclusively addressing the two points above. The combination of experimental images and theoretical simulations enables the comprehensive interpretation of the images. The images of the {001} surface indicate that the AFM observes both the calcium and oxygen atoms at the cleavage plane. In addition, two configurations of the oxygen atoms are observed; a dumbbell shaped feature due to two oxygens (from two different SO4 tetrahedra) sitting just below the cleavage plane and a doughnut shaped feature composed of oxygens from four different SO4 tetrahedra (the two above and two standing above the cleavage plane). The latter are partly due to tip deformation of the surface and are the most common features in experimental images. © 1999 American Institute of Physics.