Effect of Moderate Electropulsing on Nb Multiterminal Transport Bridges

Abstract

We investigate targeted and localized material modifications produced by electropulsing of $\mathrm{Al}$-capped $\mathrm{Nb}$ microbridges with a multiterminal configuration. The affected regions of the $\mathrm{Nb}$/$\mathrm{Al}$ bilayer terminals 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 $435\ifmmode\pm\else\textpm\fi{}35$ K is needed to induce material modifications. These findings provide further insights into the subtle modifications produced by gentle electroannealing of $\mathrm{Nb}$/$\mathrm{Al}$ microstructures and represent a step forward towards mastering this emerging nanofabrication technique.