Fabrication and Characterization of sub-100nm Pb SQUIDs for nanoscale SQUID-on-Tip Microscopy

Scanning nanoSQUID-on-tip (nSOT) microscopy is a highly sensitive probe of local magnetic field. Unlike traditional microSQUID microscopy and other nanoscale scanned probes, nSOTs provide noninvasive magnetic imaging at sub-100nm length scales while operating in ambient magnetic fields as large as several Tesla (Vasyukov et al. Nature Nano. 8:639-644). I will describe the process for fabricating high-sensitivity nSOTs on the tip of a pulled quartz pipette, including the construction of a home-built thermal evaporator for self-aligned, three-angle deposition of a superconducting Pb film at cryogenic temperatures. Using this instrument, and an associated 4.2K squid-array amplifier based characterization set-up, we achieve reliable production of nSOTs with effective diameter as small as 40nm and spin-sensitivity of approximately 3μ_B/√Hz that remain functional in magnetic fields over 1T.