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Home / Academics / Division of Math & Science / Faculty / Christopher Jones / Dissertation / Chapter 2-Section 2.7

2.7 Surface Morphology

A Nanoscope III atomic force microscope (AFM) was used for morphological studies of the surface of the thin films. The surfaces of the thin films and bulk pellets have differing morphologies. The a-axis thin films [Illustration 2.8(a)] have sharp outgrowths scattered on the surface with the smoother areas having a “basket-weave” arrangement of the grains. The sharp outgrowths are believed to arise from initial nucleation points on the substrate followed by fast growth within the a and b directions. The c-axis films [Illustration 2.8(b)] in this case are rougher, but have a more regular morphology. At a greater film thickness than presented here, a-axis thin films deposited by pulsed laser deposition are much rougher than the films used in this experiment due to the faster growth rates42 in the a and b directions. Bulk pellets, of course, are quite rough and have large grain sizes as shown in Illustration 2.7. The resurfacing process also leads to greater roughness for the encapsulated ceramic electrode with pellets having the largest surface area compared to their geometric surface.

Scanning electron micrograph (SEM) of the surface of YBa2Cu3O7-x before sanding

Illustration 2.7: Scanning electron micrograph of the surface of YBa2Cu3O7-x before sanding.

AFM images of a) a-axis thin film on LaAlO3 and b) c-axis film on MgO of YBa2Cu3O7 x, both at thickness of 1500Å.

Illustration 2.8: AFM images of a) a-axis thin film on LaAlO3 and b) c-axis film on MgO of YBa2Cu3O7‑x, both at thickness of 1500.

CV background scans for a) c-axis film b) a-axis film and c) ceramic pellet of YBa2Cu3O7

Figure 2.2: Background scans for a) c-axis film b) a-axis film and c) ceramic pellet of YBa2Cu3O7-x.

The response of background scans in Figure 2.2 reveal a decreasing double layer capacitance for ceramic pellet, a-axis, and c-axis electrodes, respectively. While there may be an anisotropic capacitance of the YBa2Cu3O7‑x thin films, similar to that of basal plane graphite, where both the c-axis YBa2Cu3O7‑x film and the basal plane graphite electrode have smaller capacitance effects than their counterparts, surface roughness and active surface area are likely to be responsible for the differences. As for bulk YBa2Cu3O7‑x electrodes, they have access to a-axis orientations available at the electrode surface, and electrodes have a considerable number of surface defects that can serve as active sites for electrochemical activity. The electrochemical polymerization of polypyrrole (Chapter 3) is one method that can be employed in the study electrochemical activity of a superconductor’s surface. Polymer nucleation has been used to decorate a superconductor’s surface, which was then evaluated by atomic force microscopy.

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Updated on: April 15, 2010 8:26 PM