Towards BSCCO Scanning SQUID-on-tip for Atomic Force Microscopy

This thesis explores the initial steps towards integrating high temperature scanning SQUID-on-tip (SOT) with quartz tuning fork atomic force microscopy (QTF-AFM). By combining these imaging techniques into one sensor, the local magnetic field variations and surface topography of a sample can be mapped simultaneously. This allows the SQUID to scan with ultra-sensitive flux sensitivity and nanometer spatial resolution, while its position on the surface remains identifiable. Specifically, this thesis addresses the low operating temperature of conventional SOT by developing a fabrication method that uses BSCCO, a high temperature superconductor, to create SQUIDs through gallium focused ion beam (FIB) milling. The electrical contacting procedure of BSCCO involves mechanical exfoliation and electron-beam lithography. The results yield contact resistances in the order of 100 ohm, which are sufficiently low to perform current transport experiments. The flakes are then structured into 1...Show moreThis thesis explores the initial steps towards integrating high temperature scanning SQUID-on-tip (SOT) with quartz tuning fork atomic force microscopy (QTF-AFM). By combining these imaging techniques into one sensor, the local magnetic field variations and surface topography of a sample can be mapped simultaneously. This allows the SQUID to scan with ultra-sensitive flux sensitivity and nanometer spatial resolution, while its position on the surface remains identifiable. Specifically, this thesis addresses the low operating temperature of conventional SOT by developing a fabrication method that uses BSCCO, a high temperature superconductor, to create SQUIDs through gallium focused ion beam (FIB) milling. The electrical contacting procedure of BSCCO involves mechanical exfoliation and electron-beam lithography. The results yield contact resistances in the order of 100 ohm, which are sufficiently low to perform current transport experiments. The flakes are then structured into 1 micrometer SQUIDs. The Josephson junctions are created by introducing ion beam induced damage to the crystal lattice of BSCCO to suppress superconductivity. The transport measurements reveal no conclusive evidence of SQUID features. However, it is shown that milling sub-200 nm wide structures does not alter the electronic properties of BSCCO, indicating that this nanostructuring method can potentially be applied in fundamental research into high temperature superconductors. This thesis also focuses on depositing multiple SQUID electrodes along a QTF, while keeping the self-sensing and -actuating capabilities of the force sensor intact. The QTF is insulated with a 100 nm thick SiOx layer. It is then covered with a laser micro-machined hardmask, through which 50 nm of titanium is evaporated in the shape of SQUID electrodes. Through fabrication alterations, certain issues involving alignment and electrode interruption can be solved. However, the evaporation method inexplicably compromises the integrity of the insulating barrier, thereby forming electrical shorts. Overall, the findings indicate that while substantial progress has been made in developing fabrication methods for the different components, significant technical hurdles remain. These need to be addressed to realize the potential of BSCCO scanning SQUID-on-tip for atomic force microscopy.Show less

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Towards BSCCO Scanning SQUID-on-tip for Atomic Force Microscopy