The morphological instability of thin foil edges at elevated temperatu
re is studied by in situ TEM. Quasi-periodic instabilities in the edge
profile are observed to develop with a distinct growth direction perp
endicular to the original foil edge direction. This results in the dev
elopment of relatively thick rods perpendicular to the original edge.
The rods are then observed to undergo spheroidization. The use of in s
itu techniques allows the direct study of the thickness changes associ
ated with the formation and propagation of this instability. Such exam
ination of the details of the thickness changes is critical to a full
understanding and perhaps the control of the phenomenon.