  Total electron yield (TEY) imaging is an established scanning transmission
X-ray microscopy (STXM) technique that gives varying contrast based on a
sample's geometry, elemental composition, and electrical conductivity. However,
the TEY-STXM signal is determined solely by the electrons that the beam ejects
from the sample. A related technique, X-ray beam-induced current (XBIC)
imaging, is sensitive to electrons and holes independently, but requires
electric fields in the sample. Here we report that multi-electrode devices can
be wired to produce differential electron yield (DEY) contrast, which is also
independently sensitive to electrons and holes, but does not require an
electric field. Depending on whether the region illuminated by the focused STXM
beam is better connected to one electrode or another, the DEY-STXM contrast
changes sign. DEY-STXM images thus provide a vivid map of a device's
connectivity landscape, which can be key to understanding device function and
failure. To demonstrate an application in the area of failure analysis, we
image a 100~nm, lithographically-defined aluminum nanowire that has failed
after being stressed with a large current density.
