Etched track pit on mica (height value inverted). Image was taken
with Digital Instruments' NanoScope III operating in Tapping Mode.
Muscovite mica was
etched in HF (52%) for 4 hours. Steps on the pit is 1nm heigh! The pit
is believed to be the result of an alpha-recoil track
enlarged by a preferential etching process. The shape of the pit is related
to the crystal structure of muscovite mica. Step heigh is the c-axis spacing.
For a reference paper on the subject, see Phys. Rev. Lett.