Fine Probe for an STM-SQUID Probe Microscope

We developed a scanning tunneling microscopy (STM) SQUID probe microscope by the combination of the high-T_c SQUID probe microscope with an STM microscope. Preparation of a probe is an important factor for the development of the STM-SQUID microscope. Therefore, we studied the probe preparation in order to improve the resolution of the STM-SQUID microscope. The probe material is a permalloy wire of 90 μm in diameter. We fabricated the probes by sharpening the probe tip by electrochemical polishing. We can fabricate various shaped probe by changing the voltage applied to the electrochemical polishing. The conical angle of the probe tip and tip radius are the important parameters in probe preparation. The tip radius of the probe was about 20 nm after the probe tip was sharpened with a voltage of 30 V. We then measured magnetic images of typical magnetic materials such as a nickel thin film by the STM-SQUID microscope, incorporating the probe with a tip radius of 20 nm. A magnetic domain structure was clearly observed in the magnetic image of the nickel thin film.