  A standard route for fabrication of nanoscopic tunnel junctions is via
electromigration of lithographically prepared gold nanowires. In the
lithography process, a thin adhesion layer, typically titanium, is used to
promote the adhesion of the gold nanowires to the substrate. Here, we
demonstrate that such an adhesion layer plays a vital role in the electrical
transport behavior of electromigrated tunnel junctions. We show that junctions
fabricated from gold deposited on top of a titanium adhesion layer are
electrically stable at ambient conditions, in contrast to gold junctions
without a titanium adhesion layer. We furthermore find that electromigrated
junctions fabricated from pure titanium are electrically exceptionally stable.
Based on our transport data, we provide evidence that the barrier in
gold-on-titanium tunnel devices is formed by the native oxide of titanium.
