New functional probes in scanning probe microscopy (SPM) are powerful tools for understanding nanoscale phenomena. The purpose of this study is to develop new measurement methods for SPM and to realize tunnel junctions with a high-temperature superconductor (HTS) probe. Currently, various materials such as tungsten and silicon are used for SPM probes, but no measurements have been made with YBa2Cu3O7-δ (YBCO) probes, which lead to an SPM measurement method using the multiple Andreev reflections [1,2]. Furthermore, controllable formation of the tunnel junction is expected by bringing the sharped probe and sample close to each other.
In the fabrication of the probe, one end of the YBCO rod was sharpened by fine cutter machine and focused ion beam, where c-axis orientation and crystallinity of the YBCO bulk were confirmed by X-ray diffraction measurements [3]. As a result of the condition optimization, a sharp shape with 88.5 nm radius of curvature.
In the evaluation of the probe, the resistance-temperature characteristics of the YBCO were evaluated, and the transition temperature was confirmed to be 88.6 K. The Ga distribution around the probe tip was measured before and after milling, and a decrease in Ga concentration was observed after 10 minutes of milling. Furthermore, current-voltage curves of the fabricated YBCO probes were acquired in liquid nitrogen-cooled SPM systems. In this paper, we will report detailed results including electrical properties of the YBCO probe tip and show the possibility of HTS tunnel junctions using the probes.
[1] E. N. Bratus et al., Phys. Rev. Lett., Vol 74, pp. 2110-2113, 1995.
[2] R. Hiraoka, et al., Phys. Rev. B., Vol .90, p. 241405, 2014.
[3] S. Ariyoshi, A. Ebata, B. Ohnishi, et al., IEEE Trans. Appl. Supercond., Vol. 33, No.5, p.7200104, 2023.
Keywords: Scanning probe microscopy, YBa2Cu3O7-δ (YBCO), Tunnel junction