Effect of Moderate Electropulsing on Nb Multiterminal Transport Bridges

We investigate targeted and localized material modifications produced by electropulsing of Al-capped Nb microbridges with a multiterminal configuration. The affected regions of the Nb/Al bilayer termi-nals are revealed by an in-lens secondary-electron detector in a scanning electron microscope and by Kelvin-probe force microscopy, both suggesting a decrease in the work function in the modified areas. In contrast, the affected areas are neither apparent through an Everhart-Thornley secondary-electron detector nor through atomic force microscopy, which indicates little morphological change in the microstructure. In addition, we demonstrate that the extent of the electroannealed regions is strongly influenced by the terminal geometry. These results are captured by complementary finite-element modeling, which permits us to estimate that a threshold temperature of 435 +/- 35 K is needed to induce material modifications. These findings provide further insights into the subtle modifications produced by gentle electroannealing of Nb/Al microstructures and represent a step forward towards mastering this emerging nanofabrication technique.