  For nanoscale electrical characterization and device fabrication it is often
desirable to fabricate planar metal electrodes separated by large aspect ratio
gaps with interelectrode distances well below 100 nm. We demonstrate a
self-aligned process to accomplish this goal using a thin Cr film as a
sacrificial etch layer. The resulting gaps can be as small as 10 nm and have
aspect ratios exceeding 1000, with excellent interelectrode isolation. Such
Ti/Au electrodes are demonstrated on Si substrates and are used to examine a
voltage-driven transition in magnetite nanostructures. This shows the utility
of this fabrication approach even with relatively reactive substrates.
