The analysis of superconducting thin films modified by AFM lithography with a spectroscopic imaging technique

A practical application of nanolithography using atomic force microscopy (AFM) was accomplished in fabricating superconducting flux flow transistors (SFFTs). It was found that it is essential to oxidize a superconducting thin film, grown on LaAlO3 substrates by a thermal CVD process, by an applied bias voltage between a conducting AFM tip and the films, since I/V characteristics of the device were mainly controlled by the modified gate area in the SFFT. After AFM lithography, the critical current of an YBCO thin film was found to be degraded. Raman lines in the modified YBCO film were observed at 340, 502, and 632 cm−1 in Ar the laser system and 142, 225, and 585 cm−1 in the He-Ne laser system. Raman fluorescence images were also produced by mapping the Raman peaks. A strain image of the peak at 142 cm−1 was most clear, which means that a surface of the YBCO thin film was changed into the YBa2Cu3O6 insulator. AFM nanolithography enables us to fabricate a channel between a source and a drain in SFFT in order to get I/V characteristics.