Use of Ultrasonic Force Microscopy to Image the Interior Nanoparticles in YBa2Cu3O7−x Films

Nanoparticles present in the interior of YBa₂Cu₃O_7-x (YBCO) films were successfully imaged for the first time by using an ultrasonic force microscope (UFM), which can also operate as a conventional atomic force microscope (AFM). Nanoparticles of Y₂BaCuO₅ and BaSnO₃ were introduced into YBCO films using pulsed laser ablation to improve critical current density via enhanced flux pinning. The scanning speed and ultrasonic frequencies in the range of 300-500 kHz were optimized for each sample such that the nanometer sized particles on the surface as well as from the film interior can be imaged with good contrast and resolution. UFM and AFM scans taken of the same locations were compared to show the advantages of using UFM over AFM. We demonstrate that UFM can be used nondestructively to both characterize the interior nanoparticles introduced in YBCO films and provide high resolution images of the screw dislocation induced terraces present in the films.