Abstract
The structural changes in carbon nanotubes under electron emission
conditions were investigated in situ in a transmission electron microscope
(TEM). The measurements were performed on individually mounted
free-standing multi-walled carbon nanotubes (CNTs). It was found that the
structure of the carbon nanotubes did not change gradually, as is the case
with field emission electron sources made of sharp metal tips. Instead,
changes occurred only above a current level of a few microamperes, which
was different for each nanotube. Above the threshold current, carbon
nanotubes underwent either structural damage, such as shortening and
splitting of the apex of the nanotube, or closing of their open cap. The results
are discussed on the basis of several models for degradation mechanisms.