Mitigation of oxide growth on aluminum thin films: The role of self-assembled monolayers in superconducting quantum circuits

The native oxide layer formed on aluminum (Al) surfaces in superconducting quantum circuits is a significant source of two-level system defects, which couple with electric fields and degrade quantum coherence. Recent research has explored etching, encapsulation, and other surface treatments as potential strategies to mitigate the formation of oxides at air interfaces in these circuits. This study demonstrates a novel approach to passivate the Al-air interface using a molecular self-assembled monolayer (SAM). Freshly prepared Al thin films were passivated with SAMs by immersing the Al-coated silicon substrates in SAM solutions. X-ray photoelectron spectroscopy (XPS) confirms the successful binding of the SAM and the absence of further aluminum oxide growth. Moreover, the passivation remains stable after aging for 15 days in ambient conditions, as evidenced by XPS and contact angle measurements. Scanning electron microscopy analyses further support the binding of the SAM to the Al surface and mitigation of oxide growth. These findings suggest that SAM-based passivation offers a promising method for reducing microwave loss and improving the performance of Al-based superconducting quantum circuits.