DEVELOPMENT OF SCANNING PHONON TRANSMISSION MICROSCOPE (SPTM)

高频声子是由SNS隧道结产生的。在扫描声子透射显微镜（SPTM）中，SNS的一个电极被一个超导尖端取代，该尖端在样品上移动，与样品上的N-S覆盖层保持接触。通过这种方式，SPTM扫描样品上的高频声子源，从而研究高频声子通过样品的局部传输。本研究的目的是开发该SPTM，并在SPTM.1的一些技术方面获得了以下结果。超导尖端的制造：由于软超导金属在电抛光方面的困难，它们很少被制造成尖端。采用两段电抛光技术，成功地制备了Nb、Pb、V、Ta、Sn、In和Re的尖端，这些尖端的半径都小于500 nm。2.本工作首次制作出铅和铅尖端。惯性运动系统的发展：低温惯性运动系统是SPTM中不可缺少的，以使尖端接近N-S覆盖层。惯性运动系统的性能在很大程度上取决于压电驱动信号的波形。在这项工作中，测试了各种波形，包括锯齿波、摆线波和抛物线波。发现锯齿波不能进行垂直平移。利用摆线波形，在液氦温度下实现了90 nm/步的惯性运动。超导覆盖层的均匀性：利用扫描霍尔探头（SHP）可以研究超导覆盖层的均匀性。为了测试SHP的性能，在Bi2223磁带上对其残余状态进行了成像实验。发现SHP显微镜清晰地显示了样品内部的缺陷和非超导区域。

High-frequency (HF) phonons are generated from SNS tunnel junctions. In the scanning phonon transmission microscope (SPTM), one electrode of SNS is replaced by a superconducting tip which moves over the sample keeping in contact with the N-S overlayr on the sample. In this manner, SPTM scans the HF phonon source over the sample and thus studies the local transmission of HF phonons through the sample. The purpose of this research is to develop this SPTM,and following results have been obtained on some technical aspects of SPTM.1. Fabrication of superconducting tips : Soft superconducting metals have been rarely fabricated into tips because of their difficulty in electropolishing. By employing a two-stage electropolishing, tip fabrication has been successfully made for Nb, Pb, V,Ta, Sn, In, and Re. All these tips have a tip radius of less than 500 nm. Pb and In tips have been made for the first time in this work.2. Development of the inertia motion system : A low-temperature inertia motion system is indispensable in SPTM for making tip approach to the N-S overlayr. The performance of inertia motion system critically depends on the waveform of the piezo-driving signal. In this work, various waveforms have been tested, includig sawtooth, cycloid, and parabolic waveforms. It is found that the sawtooth waveform cannot make verical translation. Using the cycloid waveform, inertia movement of 90 nm/step has been achieved at liquid helium temperature.3. Uniformity of the superconducting overlayr : uniformity of the superconducting overlayr can be investigated by Scanning Hall Probe (SHP). TO test the capability of SHP,imaging experiments have been carried out on Bi2223 tapes on their remanent state. It is found that the SHP microscopy clearly images defective and non-superconducting regions embbeded inside the sample.