Images from scans of aluminum lines on a silicon substrate.  The metal lines
are imaged in the vdW signals, indicating that they are physically present
on the substrate.  In the first EPD image, only one of the lines is detected,
an indication that the metal lines are contaminated or covered by oxide.
Higher resolution scans at the ends of the metal lines indicate that some
vias are missing, and show gaps in the lines.  These have been attributed
to the effects of electromigration.