Three Dimensional Observation of Flux Pinning Centers in Dy-doped YBa 2 Cu 3 O 7−x Coated Superconductors by STEM Tomography

Nano-catalysts, Au nano-particles on TiO 2 (anatase), were studied by means of quantitative scanning transmission electron microcopy (Q-STEM) and high-resolution transmission electron microcopy (HRTEM). All the Au nano-catalysts were produced from an Au13 precursor, Au 13 [PPh 3 ] 4 [S(CH 2 ) 11 CH 3 ] 4 , TiO 2 supports, with three treatments: (1) thermal heating in the air at 400°C for 2 hours, (2) exposure to ozone (O 3 ) at room temperature, and (3) exposure to atomic oxygen (AO, or O) with a AO dose of 7.3 ×10 18 atom/cm 2 at room temperature. Both reactive oxygen species O3 and AO produced significantly small sizes of Au particles as compared to those from the heating treatment in the air (2.7 ± 0.6 nm, 324 b 264 atoms). Ozone produced the smallest (1.2 ± 0.5 nm, 40 ± 49 atoms), whereas AO produced smaller (2.1 ± 0.7 nm, 72 ± 98 atoms), with a broad size distribution and a variety of shapes. HRTEM studies on the AO treated Au/TiO 2 samples found that there could exist relationship between the particles size and their shapes which also affected by the interaction with TiO 2 supports. The support effect of TiO 2 to the shapes of Au particles was also studied.