Defects smaller than 10 nm, with number densities below 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 noncrystalline intrusions into the silicon bulk which show up best in the TEM under conditions of strong edge or bend contrast. If ambient air exposure is <10 min, defect nucleation and growth can be monitored in situ. Possible mechanisms of formation are discussed. (C) 2002 The Electrochemical Society.