“Dual‐Bridging” Molecular Engineering at the Hetero‐Interface: Simultaneous Enhancement of Mechanical and Superconducting Performance in NbTi/Quartz Joints

ABSTRACT The reliable integration of superconducting alloys with dielectric substrates is a challenge in the fabrication of advanced cryogenic devices. In this study, a novel Sn‐Bi‐In‐Ga‐Zn quinary solder doped with amino‐functionalized carbon quantum dots (N‐CQDs) was developed to realize the robust joining of Niobium‐Titanium (NbTi) alloy and fused quartz. The impact of N‐CQDs on the interfacial microstructure, mechanical integrity, and superconducting properties was investigated. Results demonstrate N‐CQDs act as “dual‐functional bridges” at the hetero‐interface. The shear strength of the N‐CQD doped joint reached 51.5 MPa at room temperature, a 51.3% enhancement over the untreated joint. This strengthening is attributed to the formation of a covalent siloxane anchoring network (Si─O─Si) on the quartz side and strong amino‐metal coordination on the metallic side, per XPS and FTIR analyses. Furthermore, the self‐field critical current density (Jc) of the joint at 4.2 K was improved by ∼33.3% to 6.4 × 10 5 A/cm −2 . First‐principles density functional theory calculations reveal that amino functionalization significantly increases the interfacial binding energy and enhances the electronic density of states near the Fermi level. Together with the low‐temperature V – I measurements showing a reduced apparent joint/interface resistance, these results suggest improved interfacial electronic coupling and superconducting transport across the joint.