  Defects ~10 nm in size, with number densities ~10^{10} cm^{-2}, form
spontaneously beneath ion-milled, etched, or HF-dipped silicon surfaces
examined in our Ti-ion getter-pumped transmission electron microscope (TEM)
after exposure to air. They appear as weakly-strained non-crystalline
intrusions into silicon bulk, that show up best in the TEM under conditions of
strong edge or bend contrast. If ambient air exposure is <10 minutes, defect
nucleation and growth can be monitored {\em in situ}. Possible mechanisms of
formation are discussed.
