Scanning tunneling microscopy of an ionic crystal: ferritin core.

Ferritin molecules were imaged directly in air by scanning tunneling microscopy (STM). The lateral dimensions were close to the values determined by electron microscopy, and the vertical dimension was much reduced. Several clusters of partially naked ferritin cores displayed a hexagonal structure of lattice constant 4.9 +/- 0.5 A. It is thus shown that the STM can be used to image thin ionic crystals at high resolution.