Fig. 2: Structural and chemical characterization of transmon qubit.
From: Systematic improvements in transmon qubit coherence enabled by niobium surface encapsulation
a–d Chemical phase maps generated through STEM energy dispersive spectroscopy of the Nb films capped with Ta, Al, TiN, and Au, respectively. The Ta, Al, and Au capping layers are roughly 10 nm thick and the TiN layer is roughly 5 nm thick. e Plot depicting Nb2O5 counts captured with ToF-SIMS. Each of the capping strategies is effective in mitigating Nb2O5 formation. The Ta capping is particularly effective as a 1000× decrease in Nb2O5− counts is observed with this strategy. f ADF-STEM image of the metal/substrate interface. Minimal intermixing is observed between Nb and the underlying c-plane sapphire substrate. Scale bars in (a)–(d) represent 10 nm. Scale bar in (f) represents 2 nm.
